FEMS Microbiology Letters

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.

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.

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.

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.

Plant roots are broadly colonized by endophytic fungi with saprotrophic capabilities, but our understanding of whether they function in ways that are beneficial or detrimental to the host remains limited to model organisms. We hypothesized that endophytic fungi broadly affect plant access to soil nutrients, particularly organic forms that are typically not directly available to the plant. To address this, we paired 41 fungal endophytes with switchgrass (Panicum virgatum L.) and provided either inorganic or organic forms of nitrogen (N) and phosphorus (P). We evaluated how the fungi affected plant tissue N and P as well as plant growth. We also examined if these outcomes could be predicted from fungal phylogenetic relationships, in vitro traits of the fungi, or characteristics of the habitat from which fungi were isolated. There was substantial variation in both plant N (0.05-0.63%) and P (0.02-0.10%) acquisition that depended on the interaction of fungus and nutrient treatment. More fungi were beneficial for plant N than for P and shoot nutrients generally increased more than root nutrients from fungal associations. However, fungal effects on plant nutrients were not predicted by fungal traits, habitat traits, or fungal phylogenetic relationships. This unpredictability highlights a key challenge for incorporating endophytes into nutrient management strategies. Improving our ability to predict endophyte impacts on host nutrient acquisition will require identifying the mechanisms underlying observed beneficial effects and scaling up to realistic, diverse root microbial communities.

IntroductionLomentospora prolificans is a pathogenic filamentous fungus that causes disease primarily in people with severely compromised immune systems. It is pan-resistant to antifungal drugs, but the mechanism of its resistance to amphotericin B (AMB) is unknown. ObjectivesWe aimed to investigate the mechanism of resistance to AMB of L. prolificans. MethodsThe AMB susceptibility of L. prolificans protoplasts was measured using broth microdilution. L. prolificans, either intact, homogenized or fractionated was incubated with AMB in broth. The same activity was carried out with Aspergillus fumigatus as a control. This broth was then used to prepare microdilution plates with Saccharomyces cerevisiae to determine the activity of the conditioned AMB. ResultsAMB was 16-fold more effective in inhibiting the growth of L. prolificans protoplasts than conidia, but only two-fold more effective against A. fumigatus protoplasts than conidia. Incubation of L. prolificans hyphae with AMB in media diminished drug activity to a much greater extent than A. fumigatus, with 8-fold greater fungal mass of the latter required to achieve the effect of the former. Homogenization and fractionization of L. prolificans revealed that the factor inhibiting AMB activity was soluble with a mass >100 kda. DNase, trypsin, proteinase K, amyloglucosidase, SDS and 0.22 m had no effect on the AMB resistance factor, while treatment with urea, acetonitrile inactivated it. ConclusionWe report a different mechanism for AMB resistance based on the existence of a substance residing in the L. prolificans cell wall that can eliminate the antifungal activity of AMB.

Crop species may shape soil chemical properties and root-associated microbiota, but direct comparisons between contrasting crops remain limited. We compared soils and root-associated bacterial communities of Welsh onion (Allium fistulosum) and sweet potato (Ipomoea batatas) under the same field context. Sweet potato soil showed significantly lower electrical conductivity, inorganic nitrogen, and Mg saturation than control soil. Root-associated communities differed between crops, whereas alpha diversity did not. Proteobacteria-related taxa were more represented in Welsh onion roots, whereas Actinomycetia-related taxa were more represented in sweet potato roots, providing a basis for future studies on crop-specific soil microbial management.

Iron is an essential micronutrient that shapes host-pathogen interactions during infection. However, the contribution of iron to the virulence adaptation of the Enterobacter cloacae complex (ECC) remain poorly characterized. This study profiled the effects of iron on E. roggenkampii and E. asburiae clinical isolates. Growth kinetics were assessed in Luria-Bertani broth supplemented with varying iron concentrations and 5% sheep blood, and EDTA. Recovered strains were used for motility and antibiotic susceptibility assays. Phenotypic virulence trait of iron-naive and iron-recovered strains was determined using biofilm formation assays. Whole-genome sequencing was conducted to identify genetic determinants associated with iron acquisition and metabolism. Presence of iron increased bacterial growth, reduced antibiotic susceptibility, and enhanced biofilm formation. At higher iron concentrations, iron-recovered strains exhibited increased biofilm biomass, while there was a high biofilm formation with iron-naive strains at lower iron levels. Genomic analysis identified genes associated with ferrous and ferric iron transport, heme uptake, siderophore biosynthesis, and virulence-related functions, including adhesion and biofilm formation. These findings demonstrate that iron availability and prior exposure modulate ECC physiology and phenotypic traits associated with virulence, supporting a role for iron in shaping adaptive pathogenic potential. Graphical AbstractThe influence of iron metabolism on virulence adaptation of Enterobacter cloacae complex O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=107 SRC="FIGDIR/small/737523v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@aa351eorg.highwire.dtl.DTLVardef@855345org.highwire.dtl.DTLVardef@11e0da5org.highwire.dtl.DTLVardef@11f851_HPS_FORMAT_FIGEXP M_FIG C_FIG

Bacteriophages are abundant and diverse in soils, playing a major role in regulating bacterial communities and consequently affecting biogeochemical cycles. Such host-phage interactions may be influenced by fluctuations in soil moisture, as observed in wetlands soils which constitute a key feature of the ongoing climate change. Here, we investigated the spatial and temporal dynamics of both bacteria and T4-type bacteriophage community structures and diversities in soil of a freshwater wetland. Soil was sampled in three sites across a proximal soil transect presenting an increase moisture content at seven dates over an 18 months period with contrasted flooding periods. DNA was extracted and we applied amplicon sequencing of the bacterial 16S rRNA gene and viral g23 gene. Bacterial community composition varied across the proximal soil transect, with Methylomirabilia and Gammaproteobacteria being significantly enriched in the wettest site and comprising ASVs affiliated to methanotroph and denitrifying bacteria, respectively. We identified a large diversity of T4-type phages, among which a fraction was novel, while others were similar to phages previously sequenced from various biomes. These findings suggest that T4-type phages are capable of successfully colonizing diverse niches in the biosphere, contributing to their ubiquity and diversity. Viral community was however dominated by few vASVs, which were highly represented in one or two of the three studied sites supporting the Bank model. All together our results indicate that T4-type phages have broad host ranges and more likely follow bacterial population dynamics. The present study provides new insights into the role of phages in soil, highlighting their interactions with bacterial hosts involved in carbon and nitrogen cycles, interactions that are likely regulated by fluctuations in soil moisture, as observed in wetlands. HighlightsO_LIBoth bacterial and T4-type phages were structured across proximal sites C_LIO_LIBacterial 16S rRNA gene copy number was inversely correlated to the soil moisture C_LIO_LI26 viral ASVs did not cluster with reference sequences C_LIO_LIviral ASVs seem to be primarily controlled by host availability C_LIO_LISoil bacteria and phage diversities were significantly lower in the wettest site C_LI

Chronic Rhinosinusitis (CRS) is a common chronic inflammation of the paranasal sinus mucosa. Staphylococcus aureus contributes to its severity through biofilm formation. In this study, we isolated eight sequential methicillin-resistant S. aureus (MRSA) isolates from a patient with severe CRS over a period of 672 days (T1-T8). The isolates were phenotypically and genomically characterised, and the extracellular biofilm proteome analysed. We identified an accumulation of mutations that included the acquisition of an IS21 family insertion sequence inactivating the icaR gene and nucleotide variants in various genes including the transcription repair coupling factor (mfd). The genomic changes were associated with a switch to a mucoid phenotype from T3 onwards (Day 178), with a significant increase in biofilm-forming capacity and the secretion of multiple enterotoxins. Targeted mutagenesis confirmed mfd is a regulator of strain mucoidy with enhanced biofilm and enterotoxin production. These findings support mfd as a target for novel anti-virulence therapies.

O_LISpawning salmon transport marine-derived nutrients (MDN) into riparian forests, influencing soil, plant, and animal communities, yet their effects on fungal communities remain poorly understood. C_LIO_LIWe used DNA metabarcoding to examine fungal responses to three spatial patterns of salmon-derived nitrogen (N) in southwest Alaska: (i) patchy inputs from wildlife-deposited carcasses, (ii) a 21-year carcass relocation experiment, and (iii) natural N gradients with distance from streams. C_LIO_LIDecomposing carcasses increased saprotrophic fungal diversity, identifying taxa responsible for salmon carcass decomposition. Long-term carcass relocation reduced diversity of medium-distance fringe ectomycorrhizal fungi (EMF), whereas recent, patchy carcass inputs increased diversity of both medium-distance fringe and long-distance EMF--guilds often associated with low-nutrient environments. Along natural stream N gradients, EMF responses varied markedly within functional guilds and genera, revealing unexpected variation in N sensitivity among closely related taxa. C_LIO_LIPulsed, spatially heterogeneous nutrient inputs enhanced diversity of typically nitrophobic EMF, likely reflecting their capacity to maintain extensive mycelial networks, exploit nutrient hotspots, and mobilize organic N and phosphorus. The diversity of responses along natural N gradients suggests that mechanisms linking EMF traits to nutrient acquisition and tolerance remain unresolved. Our findings emphasize the importance of linking fungal community composition with functional attributes and nutrient dynamics. C_LI

To establish infection and cause disease, the intracellular pathogen Shigella must successfully navigate a series of host defenses and distinct microenvironments within the human body. One way Shigella navigates these enviroments is by using the secondary messenger c-di-GMP, which regulates many different bacterial behaviours. C-di-GMP is synthesized by diguanylate cyclases (DGCs) and broken down by c-di-GMP specific phosphodiesterases (PDEs). In this study, we investigated how Shigellas c-di-GMP specific PDEs impact c-di-GMP turn-over and subsequently biofilm and virulence phenotypes. We knocked out each of Shigellas six c-di-GMP specific PDEs to determine how these PDEs impact biofilm, virulence and c-di-GMP levels within the bacterial cell. We found that these PDEs negatively regulate c-di-GMP levels while modulating Shigellas virulence and biofilm behaviour. We also noted that altering expression of these Shigella PDEs changes bacterial cell size. Transcriptome analysis revealed that a Shigella {Delta}pdeB strain showed reduced expression of many genes, including the virulence genes ipgD and ipgE, as well as genes associated with lipid metabolism. We confirmed that a Shigella {Delta}pdeB strain had altered levels of stearic acid, and expression of pdeB alters Shigella antibiotic susceptibility. This study highlights the complexities of c-di-GMP signaling in regulating numerous Shigella pathways.

Cyanophages can influence the dynamics of toxic cyanobacterial blooms. However, cyanobacteria can become resistant to viruses through natural selection processes. Here, we investigate the acquisition of virus resistance in a toxic, freshwater, gas-vacuolate, bloom-forming cyanobacterium, Microcystis aeruginosa, under different nutrient concentrations. We find that gas-vacuolate M. aeruginosa subpopulations acquire virus resistance in low nitrogen cultures regardless of their phosphorus concentration, whereas non-vacuolate subpopulations do not. After resequencing susceptible and resistant M. aeruginosa variants, we identify a mutation in the transmembrane domain of a nitrogen-related transporter as the most likely genetic cause of the resistance. Infection experiments further reveal a larger viral burst size and higher phycocyanin content in gas-vacuolate cells compared to non-vacuolate ones. Based on these experimental results, we propose an ecological model in which lower nitrogen concentrations, higher light intensities and increased virus-host contact rates facilitate the evolution of virus resistance in upper lake layers during Microcystis-dominated blooms.

Symbiotic interactions between plants and nitrogen-fixing microorganisms are essential for sustainable agriculture, yet the molecular mechanisms underlying plant-cyanobacterium symbiosis remain poorly understood. In particular, the nature of the signalling mechanisms mediating partner recognition in associations involving Nostoc species is largely unknown. Recent proteomic analyses have identified proteins homologous to rhizobial Nod factors biosynthetic enzymes in Nostoc punctiforme, suggesting the existence of a Nod-like signalling system. However, the functional role of these components has not been experimentally validated. Here, we investigate the contribution of nod-like biosynthetic and regulatory genes to symbiosis by analysing mutants of N. punctiforme affected in genes with homology to nodB and nodD. Phenotypic characterization revealed that disruption of nodB-like genes does not impair free-living growth but affects early stages of plant association and colonization. Specifically, the nodB1 mutant is impaired in plant association and shows a mild defect in colonization, whereas the nodB3 mutant exhibits a severe defect in colonization. In contrast, nodD-like mutants exhibited altered symbiotic phenotypes, with specific regulators differentially affecting interaction and colonization efficiency in rice (Oryza sativa). In particular, mutation of nodD2 and nodD3 reduced plant association and severely compromised colonization in Oryza sativa, with a more pronounced phenotype in nodD3 mutant. Altogether, our results provide genetic evidence supporting the involvement of Nod-like components in cyanobacterial symbiosis and suggest the existence of a regulatory and biosynthetic module contributing to plant colonization. These findings shed new light on the evolution and diversity of symbiotic signalling mechanisms across plant-microbe interactions.

Bacteria in natural environments frequently encounter nutrient limitation leading to growth arrest and must balance the potential benefits of continuing to respond to the environment by making new proteins against the costs of depleting limited resources. We previously showed that the RNA polymerase-binding regulator SutA enhances transcription of hundreds of genes during nutrient limitation in Pseudomonas aeruginosa, suggesting that it might be part of a regulatory network facilitating limited new protein synthesis. Here, we sought to expand our understanding of this network by identifying transcriptional regulators influencing sutA expression. Using northern blotting, western blotting, and reporter assays, we found that the sigma factors FliA and RpoS, and the DNA-binding regulator Lrp, impact expression from a proximal sutA promoter during the transition to stationary phase. This constellation of regulators and the dynamics of SutA expression lead us to propose that SutA is part of a regulatory network that facilitates scavenging. Scavenging includes motility toward possible nutrient sources and uptake mechanisms for these nutrients, activities which require an investment of resources but can yield important benefits during starvation. In vitro transcription experiments, proteomic analysis and reporter assays suggest that SutA directly supports new protein synthesis driven by RpoS and indirectly supports flagellar motility, perhaps by helping maintain protein biosynthetic capacity against the metabolic costs of motility. SutA expression is controlled by multiple regulatory inputs, including negative autoregulation, and the protein appears to be short-lived. These properties are consistent with a role in supporting short, controlled bursts of gene expression during nutrient limitation. Author StatementMany bacteria engage in cycles of colonising a nutrient-rich location, using the available nutrients, and then dispersing in search of a new location to colonise. While searching for new nutrients in a low-resource environment, bacteria will be starved and must coordinate resource-intensive processes such as new protein synthesis, motility, and nutrient uptake so that each crucial activity can be accomplished but none use too much of the limited pool of resources. We previously identified a regulator in Pseudomonas aeruginosa called SutA, which facilitates new protein synthesis under starvation conditions. Here, we have identified regulators of SutA expression. We find that the housekeeping sigma factor RpoD drives expression during growth, but at the entry to stationary phase, where SutA has obvious impacts on cellular physiology, the stress sigma factor RpoS, the flagellar sigma factor FliA, and the amino acid sensing transcription factor Lrp are important. Finally, we find that all cells in a nutrient-limited population express some SutA, but appear to do so in infrequent bursts, and that the protein is likely unstable. Together, these findings suggest that SutA contributes to the coordination of resource use while bacteria scavenge for new nutrients, facilitating limited amounts of new protein synthesis.

The exchange of energy and organisms across habitat boundaries links aquatic and terrestrial ecosystems and sustains ecosystem functioning. Although disturbance may disrupt these linkages, the mechanisms at play remain poorly understood. Here, we investigated the extent to which flow intermittency may disrupt riparian-aquatic ecosystem linkages by altering consumer communities in the recipient ecosystem or by altering resource quality in the donor ecosystem. We ran an experiment in an intermittent river network in California, focusing on a critical forest-to-river subsidy (organic matter in the form of leaf litter), its transformation, and its reciprocal benefit (aquatic insect production). Using three riparian species (willow, cottonwood, and oak) at sites spanning a gradient of flow permanence, we quantified intraspecific plasticity in leaf traits (specific leaf area, nitrogen and phosphorus concentrations, and {delta}13C), measured decomposition rates, and estimated the secondary production of aquatic shredders (Plecoptera). Across all leaf species, decomposition rates were 16-36% lower at intermittent than perennial sites, an effect largely driven by intraspecific leaf trait plasticity rather than changes in consumer abundance. At high flow intermittency, willow experienced water stress (enriched {delta}13C) and reduced specific leaf area, while cottonwood showed primarily stoichiometric responses (reduced leaf nitrogen and phosphorus). Despite these divergent strategies, all species produced lower-quality litter at intermittent sites. Variance partitioning confirmed that initial litter quality uniquely explained 51.5% of variation in decomposition rates, more than double the contribution of invertebrate community metrics; and structural equation modeling revealed that both leaf traits and stonefly (Plecoptera) secondary production significantly predicted decomposition rates, with leaf traits exerting the stronger effect. Notably, stonefly secondary production was 37-98% lower at intermittent sites across leaf species. Because these insects later emerge as terrestrial adults, they provide a significant energy flux to riparian predators, and, thus, impoverished litter quality suppresses the reciprocal transfer of energy back to terrestrial food webs. As drought intensifies globally, the decoupling of terrestrial-aquatic linkages may begin in the riparian canopy.

Plant-associated bacteria can promote plant growth under saline conditions, but salinity-dependent changes in bacterial physiological traits remain insufficiently understood. Here, we isolated bacteria from seedlings of quinoa (Chenopodium quinoa Willd.) lines maintained under laboratory propagation for more than 30 years and evaluated their activity under saline conditions. A quinoa-associated Pantoea isolate, strain 6PN, promoted primary root elongation and whole-plant dry weight of Arabidopsis thaliana under salt stress, whereas no significant effect was observed under non-saline conditions. Comparative analyses with reference Pantoea agglomerans strains showed that strain 6PN exhibited salinity-responsive indole-3-acetic acid (IAA) production. Genome analysis identified a putative ipdC gene and additional genes related to stress responses, nutrient acquisition, polysaccharide biosynthesis and export, flagellar biosynthesis, and chemotaxis. Phylogenomic analysis indicated that strain 6PN was genomically distinct from representative Pantoea species examined here. In an Arabidopsis trench-plate assay, GFP-labeled strain 6PN was recovered from spatially separated plant tissues at higher levels than a GFP-labeled reference strain under saline conditions. These results identify strain 6PN as a quinoa-associated Pantoea isolate with salinity-responsive IAA production and plant growth-promoting activity under defined salt-stress conditions.

Future climate change may reshape ecological communities not only by increasing mean temperature, but also by altering the consequences of increasingly frequent heatwaves. Predicting these effects requires understanding how background warming interacts with short heatwaves in natural communities, where responses can arise through direct thermal stress and species interactions. We tested this using 32 outdoor freshwater mesocosms exposed to sustained near-future warming while capturing a documented natural heatwave. Warming raised temperature maxima that exceeded the thermal threshold of the pond snail, a main grazer in the community. Warmed communities showed lower grazer abundance, increased macrophyte and insect herbivore abundance, reduced phytoplankton biomass, and lower zooplankton density. Complementary assays showed that heatwave-level temperatures promoted macrophyte growth and reduced grazer survival, whereas reduced zooplankton performance mainly reflected indirect warming effects via food-web cascades. Thus, near-future warming can amplify natural heatwave impacts by exceeding consumer thermal thresholds and propagating through species interactions.

Nutritional symbionts can be essential for their animal hosts. The bacterial symbiont of the leaffooted bug, Leptoglossus zonatus, Caballeronia, is acquired from the environment each generation in the 2nd instar. The symbiont is critical for L. zonatus: aposymbiotic bugs are unable to reproduce. We hypothesized that symbiotic bugs excrete Caballeronia where juveniles might find and consume them. We inoculated L. zonatus with GFP-labelled Caballeronia and examined feces of each life stage. We found that Caballeronia is excreted almost exclusively in the adult stage. We then asked if 2nd instar nymphs could acquire Caballeronia from feces. Nymphs were provided with a) feces from adults fed GFP-labelled Caballeronia, b) GFP-Caballeronia in culture, or c) water only. We found that feces-fed bugs had similar rates of symbiont acquisition to those fed Caballeronia in culture, indicating that feces can be a source of Caballeronia for L. zonatus. However, compared to culture fed individuals, bugs fed feces had reduced survivorship and required longer to develop, and surviving adults had reduced mass. Bacterial motility assays showed that in contrast to cultured Caballeronia cells, Caballeronia in feces were non-motile. These results show suggest that feces can be a source of Caballeronia, at least in some environments, however transmission mode can influence success of the offspring.