FEMS Microbiology Letters

Glutathione (GSH) is a tripeptide that plays essential roles in redox regulation and stress responses across organisms. In Escherichia coli, the GSH-specific {gamma}-glutamyl cyclotransferase (ChaC) has been characterized biochemically, yet its physiological role remains unclear. Moreover, ChaC has been annotated as a regulator of the Na/H antiporter ChaA based on its genomic association, although experimental evidence supporting this function is limited. In this study, we investigated whether chaC and its co-transcribed gene, chaB, are involved in sodium transport or GSH metabolism. Gene expression analyses revealed that chaA, chaB, and chaC are upregulated under salt stress. Functional analyses using deletion mutants showed that loss of chaA reduced salt tolerance, whereas deletion of chaB enhanced tolerance and decreased intracellular sodium levels. In contrast, deletion of chaC had no significant effect on salt tolerance or sodium accumulation. Overexpression of cha genes further indicated that chaA, but not chaB or chaC, contributed to salt tolerance. Importantly, overexpression of chaC significantly reduced intracellular GSH levels, whereas chaB overexpression had no effect. These results indicate that ChaC primarily functions in GSH degradation rather than in cation transport, and that ChaB does not participate in GSH metabolism. Our findings clarify the distinct physiological roles of ChaC and ChaB and provide new insight into bacterial physiology regarding GSH metabolism and ion transport in E. coli.

To investigate the differences in soil nutrients and microbial community structure in the rhizosphere between healthy and diseased Zingiber officinale plants, soil samples were collected from healthy root-zone soil (ZSH), healthy rhizosphere soil (RSH), diseased root-zone soil (ZSD), and diseased rhizosphere soil (RSD). Diseased soils had significantly higher pH values, whereas RSH showed the strongest acidity. Moreover, pH, AN, and AK contents in diseased soils were significantly higher than those in healthy soils, while SOM and AP were significantly lower. The -diversity of microbial communities in diseased soils was significantly reduced, and the community structure was distinctly differentiated from that of healthy soils. In diseased soils, the abundance of potential pathogenic taxa such as Ralstonia solanacearum increased significantly, while beneficial genera such as Bradyrhizobium decreased. Redundancy analysis and correlation analysis indicated that soil pH, AN, SOM, and AP were the major environmental factors driving changes in microbial community structure. The occurrence of soil-borne diseases in Zingiber officinale is closely associated with soil nutrient imbalance and disruption of microbial community structure. The study identified candidate microbial taxa (e.g., beneficial Sphingomonas, Streptomyces) and key soil properties (pH, available nitrogen) that differentiate healthy from diseased ginger soils. Together, these findings provide a theoretical basis for improving diseased soils through microecological regulation strategies, and also serve as a foundation for generating testable hypotheses in future hypothesis-driven research on ginger soil-borne disease suppression.

Rhizosphere microbial communities contribute to the growth and health of their host but may be altered by the incidence of soil-borne pathogens. In avocado, the oomycete Phytophthora cinnamomi, causal agent of Phytophthora root rot (PRR), has been shown to alter rhizosphere bacterial communities, although its effect on fungal communities has seldom been explored. Our objective was thus to determine whether P. cinnamomi induced shifts in diversity, composition and co-occurrence networks of fungal communities in the rhizosphere of avocado trees, and to identify potential antagonists of P. cinnamomi that could be further considered for disease management. Fungal communities associated with the rhizosphere of asymptomatic and PRR-symptomatic avocado trees were studied through ITS metabarcoding. Although -diversity metrics were not significantly different between asymptomatic and PRR-symptomatic trees, differences in {beta}-diversity of rhizosphere fungal communities were detected. Moreover, PRR led to the enrichment of saprotrophic taxa and opportunistic pathogens such as Fusarium, Cladosporium or Plectosphaerella in the avocado rhizosphere, which were possibly attracted by the release of resources from necrosed roots. Co-occurrence network analysis revealed that fungal networks in the rhizosphere of PRR-symptomatic trees were more complex and connected than those from asymptomatic trees, suggesting a response of fungal communities to the disturbance caused by the pathogen. Some connector taxa from the PRR-symptomatic networks (Gibellulopsis, Cladorrhinum or Mycenella) were also identified as members of the P. cinnamomi pathobiome. Their negative correlations with the pathogen indicate they may act as potential antagonists, which calls for further isolation efforts to confirm their biocontrol activity of PRR.

One of the effects of the intensified agricultural activities involves environmental pollution by pesticides, which are bound to get into the soil and ultimately into the water sources through leaching. The recurrent exposure of soil microbiota to these poisonous substances facilitates the process of adaptive resistance and catabolic functions. In the current research, bacterial cultures taken in Karuppur and Salem pesticide-contaminated agricultural soils were filtered on their capability to decompose organophosphate pesticides. Two strong isolates, which were referred to as Bacillus sp. and Micrococcus sp. had a great level of tolerance and degradation capacity. Significant biomolecular changes in these isolates were observed after long-term exposure (three months) to organophosphate pesticides. A protein estimation showed a strong rise in the overall total protein content indicating the activation of stress-related and degradative enzymes. Genomic DNA damage was identified by DNA ladder assay, which is a genotoxic stress caused by pesticides. Thus, plasmid profiling also revealed a rise of copy number and change of the size of plasmids, implying potential adaption through plasmids and greater degradation potential. This evidence indicates that long-term exposure to pesticides leads to microbial adaptation in terms of physiological and genetic changes to allow survival in adverse environments. The isolates identified have great potential to be used in bioremediation strategies that will be used in detoxifying the soils that have been contaminated with organophosphate.

Pathogenic aquatic oomycetes Aphanomyces astaci and Saprolegnia parasitica represent a major threat to biodiversity and aquaculture production, but their interactions with host-associated microbes remain poorly understood. From a collection of bacterial isolates (n = 336) obtained from fish and crayfish hosts, we focused on Pseudomonas spp. (n = 70) and confirmed their previously reported strong inhibitory potential against A. astaci and S. parasitica. However, our results also revealed substantial inter- and intra-species variation in antagonism. To capture this variation, we selected eight isolates belonging to different Pseudomonas species groups (P. fluorescens, P. putida, and P. syringae) and displaying contrasting levels of anti-oomycete activity for further phenotypic assays and comparative genomic analysis. Across these isolates, mycelial inhibition was markedly stronger against A. astaci than against S. parasitica, indicating species-specific differences in susceptibility. Comparative genomic analysis revealed substantial variation in biosynthetic gene cluster (BGC) repertoires among the analysed strains. Strongly inhibitory isolates carried candidate BGCs with similarity to characterised bioactive pathways, including pyoluteorin, rhizoxin, pyrrolnitrin, DAPG, and orfamide, alongside with multiple uncharacterised clusters that were either shared among inhibitory isolates or restricted to individual strains. All analysed genomes also contained clusters related to siderophore and HCN biosynthesis. However, in vitro assays showed that siderophore production was not clearly associated with inhibitory activity and that inhibition was mediated mainly by diffusible rather than volatile compounds. Altogether, our results suggest that Pseudomonas anti-oomycete activity is species- and strain-dependent and likely reflects different combinations of multiple, predominantly diffusible metabolites rather than a single conserved mechanism. In conclusion, this study provides a foundation for future work aimed at resolving mechanisms underlying microbial antagonism toward aquatic oomycete pathogens.

Background: Human activities such as mining generally lead to increased heavy metal concentrations in the environment. While traditional remediation techniques are often costly, the use of fungi as bioremediators, known as mycoremediation, is increasingly gaining attention as a sustainable approach for removal of heavy metals. Here, we evaluated heavy metal levels inside the Kiirunavaara iron ore mine in Northern Sweden and analysed fungal responses to various metal concentrations by comparing growth and metal uptake in mine-derived isolates and closely related control isolates. Results: Sediments inside the mine were enriched in heavy metals compared to those from the outlet of the mine to natural lakes. Six Fusarium isolates were recovered from contaminated mining environments: five isolates from inside the mine were identified as Fusarium oxysporum, and one isolate from the outlet was identified as Fusarium tricinctum. Isolates from the mine and outlet showed overall higher survival and biomass production in presence of copper, iron, and zinc across a range of concentrations (up to 1000 mg/L) compared to control isolates. At the same time, these isolates often exhibited reduced relative metal uptake. As a result, mycoremediation potential, assessed as total uptake in the grown mycelium, was isolate-dependent. Conclusions: Based on these results, we conclude that Fusarium isolates from the Kiirunavaara mine show increased growth in media enriched with heavy metals compared to closely related control isolates. We additionally show that mycoremediation potential is not necessarily associated with environmental origin. Instead, mycoremediation potential should be evaluated on a case-by-case basis for each isolate and based on specific needs for mycoremediation.

IntroductionErgosterol-targeting azoles are widely used in the treatment of Candida albicans infection. In addition to direct antifungal activity, azoles are known to enhance neutrophil-mediated killing of C. albicans, but the underlying mechanisms remain unclear, particularly whether ergosterol depletion directly modulates host immune responses. Gap StatementIt remains unknown whether reduced ergosterol levels alone, independent of broader disruption to sterol biosynthesis and fungal morphogenesis, influence neutrophil antifungal activity. AimThis study aimed to determine how genetic disruption of late-stage ergosterol biosynthesis affects neutrophil-mediated responses to C. albicans. MethodologyDoxycycline-repressible GRACE mutants targeting late-stage ergosterol biosynthesis genes (ERG4, ERG5, ERG3 and ERG28) were co-incubated with primary human neutrophils. Fungal survival, oxidative burst, phagocytosis, neutrophil extracellular trap (NET) formation and cell wall composition were assessed. ResultsAll ergosterol-deficient strains induced elevated neutrophil reactive oxygen species (ROS) production; however, only ERG4 depletion was associated with enhanced fungal clearance. This phenotype correlated with increased phagocytosis and reduced NET formation. Cell wall analysis revealed no changes in total chitin or mannan content but demonstrated significantly increased surface exposure of {beta}-1,3-glucan in ERG4-depleted cells. ConclusionThese findings indicate that disruption of late-stage ergosterol biosynthesis, particularly via ERG4, enhances neutrophil antifungal responses and is associated with increased {beta}-glucan exposure. This study highlights a potential role for ergosterol in immune evasion and suggests that targeting terminal steps of the pathway may improve host-mediated clearance of C. albicans.

Plant growth promoting microbes enhance developmental progression of the host by influencing its nutrient availability or by deploying secondary metabolites responsible for manipulating the hormonal crosstalk. Microbacterium bengalense sp. nov. GB16_1_BI (Accession number: SRX9280401), a newly identified ammonium releasing Actinomycetota, could enhance plant growth by manipulating rhizosphere bacteria. Amplicon sequencing of the 16S rRNA V3-V4 region from the rhizosphere of the black rice (Chakhao Poireiton) showed that GB16_1_BI could inhibit most bacteria. However, GB16_1_BI inoculation encouraged the growth of rare bacteria specific to waterlogged rice rhizosphere. Analysis of the OTUs using PICRUSt2 (Phylogenetic investigation of communities by reconstruction of unobserved states) showed increased abundance in the marker genes for nitrogen cycling (nifH, nrfA and nrt) but not for nifD or nifK which was also reflected in the ANOSIM analysis in the OTUs of the N-fixing bacteria. Marker genes for methane metabolism (comA, comB, cofG and cofH) were also more abundant in the inoculated plants than the control; however, ANOSIM studies did not support this observation in the OTUs of methane cycling bacteria. Both Methylosinus and Methylocystis, the two most abundant methanotrophic OTUs, are also known to be nitrogen fixers. Hence, GB16_1_BI could influence plant growth predominantly by manipulating nitrogen cycling microbes. The genome sequence as well as untargeted metabolome analyses of GB16_1_BI showed abundance of secondary metabolites with probable antimicrobial activity. GB16_1_BI could utilize varied carbohydrates and amino acid as energy source and form persister-like cells may help it to survive in the soil in absence of the host plant.

The pathogenic fungus Trichosporon asahii causes severe mycoses in immunocompromised hosts, such as neutropenic patients. In Cryptococcus neoformans, the unfolded protein response (UPR) sensor Ire1 induces hxl1 mRNA splicing and contributes to stress responses and virulence. The function of Ire1-triggered hxl1 mRNA splicing in stress tolerance and virulence of T. asahii, however, remains unclear. Here, we demonstrated that ire1- and hxl1 gene-deficient T. asahii mutants are sensitive to dithiothreitol (DTT), an inducer of endoplasmic reticulum stress, and exhibit reduced virulence in a silkworm infection model. DTT treatment induced hxl1 mRNA splicing in the wild-type strain, whereas ire1 gene-deficient mutants did not undergo hxl1 mRNA splicing. The ire1 gene-deficient mutants were more sensitive than the parent strain to DTT, H2O2, Congo red, and SDS, and showed reduced virulence in silkworms. Similarly, hxl1 gene-deficient mutants exhibited increased sensitivity to these stressors and reduced virulence. Both the ire1 gene-deficient and hxl1 gene-deficient mutants showed decreased expression of reactive oxygen species-detoxifying related genes CAT2, SOD1, and SOD2, compared with the parent strain. Together, these findings suggest that Ire1-triggered hxl1 mRNA splicing contributes to stress resistance and virulence in T. asahii.

Biological membranes are laterally heterogeneous and contain specialized microdomains called lipid rafts. Lipid rafts serve as organizational platforms that cluster signaling molecules or modulate membrane protein conformation through their unique lipid environment. There are specific lipid raft marker proteins whose functions remain obscure. One of these proteins is flotillin which has been linked to endocytosis. Here, we investigated the regulation and function of FloA, the sole flotillin homolog in the model fungus Aspergillus nidulans. FloA expression is specifically upregulated in response to calcium stress, which is a regulatory pattern also conserved in Aspergillus fumigatus. Whereas in A. fumigatus floA is regulated by the calcium regulatory protein CrzA, this is not the case in A. nidulans. BioID proximity labeling revealed that A. nidulans FloA physically interacts with proteins in the endocytic pathway as well as another lipid raft marker, the plasma membrane H+-ATPase PmaA. Under calcium stress, PmaA undergoes internalization from the cytoplasmic membrane. However, when floA is deleted, PmaA internalization is prevented, resulting in cell death. Together, we demonstrate that FloA is essential for the internalization of PmaA during calcium stress, a process that prevents intracellular calcium overload and promotes cell viability. Our results also provide further evidence for flotillin-assisted endocytosis. Author abstractLipids and proteins in a cell membrane can cluster together in small regions often called "lipid rafts", which help the cell interact with its surroundings. Lipid rafts can bring receptors together or influence how membrane proteins behave. Flotillin is a protein which is often found within lipid rafts, but its exact role is not well understood. Instead of using complex mammalian systems, we studied flotillins in the fungus Aspergillus nidulans, which is a simpler model organism that allows for a better understanding of cellular processes. We found that more flotillins are produced when the fungus is exposed to calcium stress. When flotillins were missing, the cells were unable to remove the protein PmaA from the cell membrane during calcium stress. As a result, the fungus could not cope with the calcium stress and eventually died. Therefore, we propose that flotillins are important for the fungus to reorganize its membranes and coping with calcium stress.

Bordetella produce a wide array of virulence factors. These factors are involved in bacterial colonization and evasion of immune defenses. Our recent studies revealed that the bacteria produce an exoglycan, Bordetella oligosaccharide (BOS). B. petrii is the evolutionary early divergent species of the genus Bordetella. This study has focused on the investigation of two B. petrii type strains: clinical and environmental. We employed nuclear magnetic resonance (NMR) analyses to elucidate the structural differences between their lipopolysaccharides. Our findings revealed that the LPS of clinical B. petrii strain comprises a hexasaccharide unit, that was structurally identical to the BOS. This form of LPS is only a minor population in the bacterial outer membrane of the environmental strain. In addition to the cell-bound BOS, its secreted glycoform was also found in growth media of B. petrii. Anti-BOS neoglycoconjugate antibodies cross-reacted with B. petrii LPS. This suggest that the newly identified BOS associated with B. petrii PS would be a potential vaccine element against Bordetella.

The secreted phospholipase C/sphingomyelinase, PlcH, is the heat-labile hemolysin of Pseudomonas aeruginosa and one of its important secreted virulence factors. While there are known and suspected genes that impact PlcH production in P. aeruginosa, we sought to identify additional genes by screening the PA14 transposon mutant library to measure extracellular PlcH enzyme activity induced by choline. The library as a whole had a log2-normal distribution of NPPC activity with notable tails that included the genes of interest. These outlier genes included nearly all of those known to be important for PlcH production in response to choline, including those required for choline metabolism, glycine betaine sensing, and secretion through the outer membrane. Interestingly, higher PlcH production was also seen in mutants of the protease associated genes lon, mucD, and clpA, as well as other genes. Additionally, we identified genes impacting baseline levels of PlcH production, which include genes in the dimethylglycine metabolism locus involved in choline metabolism. The high hit rate of known and suspected genes supports the power of this screen and our verification of these genes by clean deletion in strain PA14 confirm the broad importance of these systems across P. aeruginosa, as previous work was confined to strain PAO1. There were many genes identified in this screen that were not individually examined and the complete screen results reported here should allow others to identify intersection of their genes of interest with PlcH production. ImportancePseudomonas aeruginosa is an important opportunistic pathogen that employs multiple independent virulence factors to cause infection, one of which is the hemolytic phospholipase C/sphingomyelinase PlcH. Using a whole genome screen, we identified both known and previously unknown genes contributing to P. aeruginosa PlcH production. Our findings provide insight into the integration of various cellular processes with PlcH production and identify potential genes that may impact the PlcH expression heterogeneity seen in P. aeruginosa clinical isolates.

The persistence of specialised survival spores produced by microbial pathogens represents a primary bottleneck in the management of plant diseases. In oomycetes, these spores (known as oospores) are largely impervious to chemical control, allowing them to persist in soil and initiate new infection cycles over many years. A prominent example is the soil-borne pathogen Phytophthora agathidicida, the causal agent of kauri dieback disease, where long-lived oospores hinder conservation efforts in native forests. The resilience of oospores is attributed to their thick wall composed of complex {beta}-glucan layers that render the oospores impermeable to most conventional biocides. Here we have investigated an enzyme-based approach for weakening the oospore cell wall. We searched enzyme databases to select {beta}-glucanases targeting a variety of linkages found in Phytophthora oospore walls. Eight of these {beta}-glucanases were successfully purified and tested for their digestive activity against intact oospores in vitro using a phenol-sulfuric acid assay. We showed that combining these enzymes was crucial to achieve significant digestion through synergies and additive effects. The optimal combination, comprising 1,3-, 1,6-, and 1,3(4)-{beta}-glucanases, was evaluated for its ability to permeabilise oospores to five biocides typically effective only on other, more sensitive lifecycle stages of the pathogen. Using a live/dead fluorescence assay, we observed that the effects of the membrane-targeting biocides were potentiated in oospores that were pre-treated with the {beta}-glucanase mixture. Our results highlight enzymatic cell wall permeabilisation as a promising strategy toward improved management of oospore persistence in kauri forest soils and against broader oomycete threats. KeypointsO_LIOur phenol-sulfuric acid assay can be used to screen for oospore-degrading enzymes. C_LIO_LISynergistic enzyme combinations are essential for effective oospore wall digestion. C_LIO_LIEnzyme pre-treatment sensitises oospores to membrane-targeting biocides. C_LI

Aspergillus fumigatus is a thermotolerant saprobe found in soils and plant debris worldwide and an important pathogen of humans causing two million deaths annually. A. fumigatus makes abundant asexual spores (conidia) which are widely distributed by wind and can be inhaled from the environment. In susceptible individuals inhaled conidia break dormancy, germinate and grow in the lung leading to serious disease. Recent work has shown that conidia made at 37{degrees}C and 50{degrees}C have different morphologies and germination kinetics. While the asexual cycle is well-characterized at 37{degrees}C, much less is known about the asexual cycle at 50{degrees}C. Here, we combine flow cytometry and transcriptomics to track morphology and gene expression in the hyphae, conidiophores and conidia of A. fumigatus during asexual development at 37{degrees}C or 50{degrees}C. We show that the temperature during a narrow time window in late-stage conidiophore development dictates resulting conidial morphology, transcriptional program, and germination kinetics. As expected, conidiation at 37{degrees}C resulted in upregulation of brlA, the master regulator of asexual development, and its downstream targets in conidiophores and conidia. Surprisingly, conidiation at 50{degrees}C resulted in upregulation of MAT1-1, the master regulator of sexual development and its downstream targets in conidiophores and conidia. Our findings suggest that temperature during late conidiophore development transcriptionally primes conidia for asexual, parasexual or sexual development enhancing chances of survival for progeny. Our findings are especially relevant for agricultural compost where a wide gradient of temperatures exists, abundant A. fumigatus has been isolated, and resistance to antifungals is thought to evolve. IMPORTANCEThe human pathogen Aspergillus fumigatus has been found in natural and agricultural environments around the world. Disease is acquired when susceptible individuals inhale airborne asexual spores from the environment, which in agriculture generally includes proximity to compost and plant debris piles. This work shows that the environmental temperature when A. fumigatus spores are made determines the transcriptomes of those spores, priming them for future asexual or sexual development. The survival of asexual and sexual spores is very different at different temperatures, so these results are important for understanding how this pathogen survives in varied hostile environments. In addition, there are very few antifungal drugs with which to treat A. fumigatus infections, and resistance is increasing driven in part by agricultural use of fungicides. These results suggest that higher temperatures during asexual spore formation can lead to increased sexual reproduction and greater chances to evolve antifungal resistance.

Pseudomonas aeruginosa is a clinically significant bacterial pathogen that poses a serious threat to aquaculture. However, there are limited information on Massilia isolates against pathogenic P. aeruginosa in aquaculture. In the present study, a facultative predator, M. varians isolate P2-4, was isolated from aquaculture sediment using Chinese mitten crab Eriocheir sinensis-pathogenic P. aeruginosa as the prey bacterium, and its genomic feature, bacteriolysis-related genes, safety, bacteriolytic spectrum, and in vitro and in vivo antibacterial effects against pathogenic P. aeruginosa in E. sinensis were further characterized. Isolate P2-4 consisted of one chromosome and one plasmid (with a total of 75 tRNAs, 7 5S rRNAs, 7 16S rRNAs, 7 23S rRNAs, 34 sRNAs, 5,238 coding genes, 20 genomic islands, 1 prophage, 23 insertion sequences, and 102 repeat sequences), and harbored 19 bacteriolysis-related genes (pilA, pilB, pilC, pilD, pilF, pilG, pilH, pilM, pilO, pilP, pilQ, pilS, pilR, pilT, mltA, mltB, mltC, mltD, and dacB) associated with cellular motility and cell wall lysis. In addition, the isolate carried no virulence genes, was unable to produce haemolysin, hydrogen sulfide, nitrite and ammonia, and avirulent in E. sinensis with a 7-day acute intraperitoneal LD50 value of above 5.0 x 108 CFU/mL. Furthermore, the isolate possessed a wide bacteriolytic spectrum against pathogenic Shewanella algae, Aeromonas caviae, A. hydrophila, and Photobacterium damselae besides P. aeruginosa, exhibited bacteriolysis rates of 99.35% to 99.99% towards the pathogenic P. aeruginosa at 1.0x103 to 1.0x10{square} CFU/mL, and displayed relative percentage survivals of 42.31% to 73.08% against P. aeruginosa infection in E. sinensis at doses of 6.0 x 103 to 6.0 x 105 CFU/g diet. To our knowledge, this study for the first time demonstrates a M. varians strain as a potential biocontrol agent against pathogenic P. aeruginosa in aquaculture.

Soil harbours a wide diversity of microbes responsible for essential functions, such as depolymerizing the C and N in organic matter through the production of exoenzymes. Some of these exoenzymes are universal, whereas others are specific to certain microbes. We hypothesized that higher microbial alpha diversity is associated with greater depolymerization capacity, specifically for protein and cellulose depolymerization, which will result in more N being mineralized. We therefore diluted two soil microbial communities, one from a forest soil and one from an agricultural soil, to create a diversity gradient. After nine weeks, we transferred these communities to a synthetic soil in which microbial necromass was the only nitrogen source. Before the transfer and two weeks after, we quantified protease, deaminase and {beta}-glucosidase potential activity, characterized the bacterial and fungal communities, and measured the quantity of nitrogen mineralized. The dilution had very little effect on the processes measured, with no clear trend. For identical alpha diversity values, some communities had high process rates, while other not. It appeared that these communities varied widely, a side effect of the dilution approach, and that this variation was significantly linked to process rates. This shows that community composition (beta diversity) is more strongly related to enzymatic potential and mineralization than species richness (alpha diversity) following necromass addition. In conclusion, the relationship between diversity and depolymerization of microbial necromass is not simply a matter of a linear decrease along with diversity but is rather linked to how reduced diversity results in more stochastic microbial communities. Highlights- Community composition (beta diversity) influence more microbial necromass depolymerization than species richness - Abundance of specific microbes explained ammonification and nitrification processes - Mineralization rates is different between crop and forest soil

Climate-driven increases in sea surface temperature have been associated with the expansion of Vibrio species and a corresponding rise in vibriosis cases in both human populations and aquaculture systems. Coastal waters across the south of England are increasingly becoming suitable for the growth and establishment of both human- and aquaculture-associated Vibrio species, potentially increasing vulnerability to the types of infections and disease outbreaks already reported elsewhere in the world. In this study, we report the presence of a diverse and well-established Vibrio community within the Teign Estuary, (Southwest, UK), including the human-pathogenic species V. parahaemolyticus, V. cholerae (non-O1/non-O139), V. alginolyticus, and V. diabolicus, as well as the important aquaculture pathogens V. jasicida, V. aestuarianus, and V. anguillarum. We identified V. diabolicus, a species that was indistinguishable from V. alginolyticus using conventional biochemical identification methods and could only be accurately resolved by whole-genome sequencing and developed novel PCR targets to differentiate these species in the lab. Using the insect infection model Galleria mellonella, we demonstrate that environmental isolates of V. cholerae (non-O1/non-O139), V. parahaemolyticus, and V. alginolyticus possess virulence potential. We also investigated the effects of sewage effluent on the growth of Vibrio isolates from the Teign Estuary and found that sewage can preferentially promote the growth of Vibrio species. Furthermore, several Vibrio isolates were multidrug resistant and carried antimicrobial resistance genes, highlighting the potential role of environmental Vibrio populations in the Teign Estuary as reservoirs of antimicrobial resistance. Together, these findings demonstrate how rising sea surface temperatures and sewage pollution may influence the emergence, persistence, and public health and aquaculture significance of Vibrio species in UK coastal waters.

There is disagreement on whether secondary endosymbionts are found in the major cereal pest aphid, Rhopalosiphum padi. Some papers report a diversity of secondary bacterial endosymbionts while others have failed to find evidence of these bacteria in this species. Here we revisit this issue by summarizing the relevant literature and through additional sampling of the species in Australia, China and Denmark using a combination of molecular approaches. We find a general absence of secondary endosymbionts beyond the obligate endosymbiont Hamiltonella defensa in R. padi. While the inconsistency in survey results may reflect rapid changes in endosymbiont turnover in populations and/or the impact of ecological factors such as host plant type on endosymbiont diversity, we are concerned that technical issues may be at least partly responsible for inconsistencies in the literature. This leads us to emphasize the importance of multiple sources of evidence required to establish and characterize endosymbiont infections, including PCR and qPCR assays, DNA Sanger sequencing and 16SrRNA gene metabarcoding. We note that several major aphid pests show a low incidence of secondary endosymbionts which raises issues about the importance of these endosymbionts in aphids that constitute pests, even though endosymbionts can in some cases increase host fitness and therefore pest impact.

Recently, our group showed that the dental pathogen Streptococcus mutans is inherently more tolerant to high zinc stress than other streptococci, a phenotype associated with the presence of a P-type ATPase exporter named ZccE, virtually unique to S. mutans. In addition to zccE, a previous transcriptome analysis revealed that S. mutans upregulates genes involved in glutathione uptake during initial exposure to zinc stress. Glutathione, a major supplier of organic sulfur that also plays key roles in antioxidant defense and xenobiotic detoxification, forms coordination complexes with a variety of metals, including zinc, thereby functioning as a buffer that protects cells from metal intoxication. To investigate the contribution of glutathione zinc tolerance in S. mutans, the gshT gene, which encodes the substrate-binding subunit of a glutathione transporter, was deleted in both the parent and {Delta}zccE strains and the ability of these mutants to overcome zinc stress through intracellular glutathione accumulation determined. Targeted metabolomics revealed that S. mutans accumulates glutathione in a GshT-dependent manner following zinc stress, a response that was strikingly amplified in the {Delta}zccE strain. Although glutathione supplementation had a minimal and non-significant impact on growth of either parent or mutant strains in sub-inhibitory zinc concentrations, the {Delta}gshT strain exhibited increased zinc sensitivity in a plate-based assay. However, the {Delta}zccE{Delta}gshT mutant displayed enhanced zinc tolerance compared to the {Delta}zccE single mutant. While glutathione alone did not alter zinc levels in the UA159 or {Delta}zccE strains, the combination of zinc and glutathione nearly doubled intracellular zinc levels in {Delta}zccE compared to cells grown in zinc only. We conclude that while glutathione may play a minor role in S. mutans zinc tolerance, uncontrolled glutathione uptake observed in {Delta}zccE facilitates zinc entry, as glutathione:Zn2+ complexes inadvertently promote zinc intoxication via a Trojan horse mechanism.

Soil microbial communities have a variety of mechanisms to deal with emerging drought stress. One well-documented mechanism is increased microbial production of extracellular polymeric substances (EPS), which can potentially change the soil density and water holding capacity. Yet little is known about how microbial diversity influences the functional capacity of EPS formation and the resulting outcomes in water dynamics. To understand more about communal microbiome EPS production, we set up sterile mesocosms where we examined the effects of microbial diversity (high or low treatments) and nutrient input (supplement or deficient treatments) on these processes. To capture the microhydrology of the mesocosms, we measured water holding (WH), infiltration, evaporation, and soil properties we believe microbes are altering (EPS, soil aggregation). Our hypothesis stated that if diversity was artificially manipulated, then soil-water properties will be altered via production of EPS. We predicted that low diversity systems would have lower functional diversity, leading to less EPS production, moisture storage, and minimal changes from inert soil media. As predicted, we found that the high-diversity systems had a higher water retention and lower rates of water loss over time than low-diversity systems. This trend was magnified in the nutrient-supplemented treatment, suggesting that EPS production and subsequent water-holding traits are emergent features of the microbiome. Unexpectedly, we observed a correlation between the amount of water retained and the quantity of lipid EPS produced. This suggests that EPS composition, rather than quantity, is determinative of a biofilms function. In conclusion, it appears that microbial diversity influences soil properties that are important to moisture retention within these systems. To date, the role that microbes and their diversity play in soil hydrology has been severely understudied, so this work aims to build ecological understandings of these systems. These findings are valuable, for if we learn how microbes manipulate soil moisture, we can apply these functions to advance sustainable agricultural practices and enhance ecosystem resilience to water scarcity in arid regions. Open Research StatementUpon publication data, and code will be made available through Zenodo. Sequencing data will be uploaded to NCBI SRA.