Microorganisms

BackgroundThe composition and function of the gut microbiome have been shown to contribute to both health and disease. One of the most powerful modulators of microbial composition and function is diet. Materials & MethodsUsing the E{micro}-TCL1 murine model of B-cell chronic lymphocytic leukemia (CLL), we assigned male and female mice to a high-fat, high-carbohydrate Western diet (HF) or standard chow (CH) diet. ResultsMice consuming a HF diet had significantly shorter survival than those consuming a CH diet, irrespective of sex, with female mice exhibiting particularly poor outcomes. We also observed a significant increase in splenic involvement by CLL in the HF diet-fed mice at time of sacrifice. Mice receiving the HF diet demonstrated immediate and profound effects on the gut microbiome, marked by reduced alpha diversity and significantly different community composition as measured by beta diversity. Notably, there was a sustained increase in Akkermansia muciniphila and Bacteroidetes thetaiotaomicron in HF diet-fed mice, coupled with a corresponding increase in microbiome functional pathways related to arginine and histidine biosynthesis, chitin degradation, and nucleotide biosynthesis. DiscussionCollectively our data provides evidence of the profound and sustained impact of a high-fat Western diet upon the gut microbiome community and CLL pathogenesis in the E{micro}-TCL1 murine model of CLL.

The growth of cultures and formation of mucilage blooms in reaction to salt stress of cyanobacterial cultures are investigated with a focus on the influence of pH. In non-buffered medium, cultures show their pH increasing from 6.5 just after inoculation, up to 11 during the exponential phase. We record the time-evolution of concentration and pH, with different initial OD0. In a second set of experiments, we extract the doubling time of the unbuffered cultures in comparison with those inoculated in pH-buffered BG11 media at four different pH from 6.3 to 10.5 : in the most acid media, all cultures die or grow very slowly. At pH = 10.5, we obtain the fastest growth for all four strains, allowing to qualify these cyanobacteria as being alkaliphiles, though for all strains with comparable initial OD0, the doubling time is shorter for unbuffered cultures. Following a previous study [31]), we finally investigate the influence of pH on mucilage formation and biomass uplift induced by salt stress, involving EPS floculation by cations. Our results show that operating in buffered media significantly influences the mucilage formation, though the observed regimes cannot be simply correlated to the pH value.

BackgroundTuberculosis (TB) is the second-leading cause of deaths from infectious agents and remains a global health threat. Ethionamide (ETH) is a prodrug used in regimens for multidrug-resistant TB, and, partly due to side effects that can lead to low treatment adhesion, resistance arises. Changes in EthA, the monooxygenase that activates ETH, are the main mechanism of resistance. Yet, of hundreds of EthA substitutions found in resistant isolates, only a handful have been annotated as resistance determinants. ResultsAn in silico analysis was carried out on a previously described panel of Mycobacterium tuberculosis clinical isolates for which genomes and ETH susceptibility testing results were available. EthA substitutions were mapped, revealing the existence of hotspots in its sequence. Visualization of the hotspots in the EthA structural model shows that they cluster in three regions, including ligand binding pockets. Models were built of twenty-three variants found in resistant isolates and changes in local configuration was mapped to identify investigate impact on ETH activation. Information from these models contributed to establishing five criteria for scoring whether substitutions are most likely to lead to resistance. Using these criteria, EthA D58G was selected and its expression is shown to increase growth in high ETH concentrations. ConclusionFunctionally relevant regions of EthA are revealed and point out priority substitutions for functional studies, enhancing identification and detection of substitutions not been previously associated with resistance.

Toxoplasma gondii is a globally prevalent zoonotic parasite with multiple life stages and transmission routes, including ingestion and transplacental transmission. It is a major cause of abortion in sheep, goats and pigs, among other production animals, worldwide. While Type II strains are common in livestock in North America and Europe, non-archetypal, non-clonal genotypes are highly prevalent in South America. This study aimed to determine the molecular epidemiology of T. gondii strains causing sheep abortion in Uruguay. Phylogenomic analyses confirmed significant divergence among typed strains and revealed similarities with genotypes previously detected in the human population. Two novel strains, were isolated and characterized, uncovering the connection between their genetic makeup and phenotypes. Differences in virulence could be correlated to differences in gene copy number of the pseudo kinase ROP5 - further highlighting this virulence factor as relevant in wild strains. Whole-genome sequencing further confirmed the divergence among Uruguayan isolates, uncovering at least three distinct evolutionary origins. Overall, our findings highlight the circulation of virulent non-clonal lineages with links to human infections and underscore the importance of furthering genomic surveillance in South America to better understand Toxoplasmas transmission dynamics, pathogenic potential, and zoonotic risk.

BackgroundPeriodontitis (Perio) is a progressive oral disease characterized by inflammation and degradation of the periodontal apparatus and is associated with local and systemic morbidity including loss of teeth, cardiovascular disease, and diabetes mellitus, among others. Perio is highly prevalent in domestic canines and exhibits certain parallels in pathogenesis and pathophysiology to Perio in humans, although standard treatments are less effective. In both species, a complex interplay between oral microbiota and host immune response is implicated in the etiology of Perio but is not fully understood. ResultsUsing shotgun metagenomics and RNA-seq on oral samples from companion dogs, we identify features of the oral microbiome and host transcriptional profile that are associated with Perio and its progression. We observe differences in microbiota composition between Perio and non-Perio animals that are largely consistent with what has been described in humans but also identify several species that are distinctly associated with canine Perio. We observe an abrupt shift in host gene expression related to immune response and tissue structure that is associated with disease severity, specifically the progression from mild periodontal disease (PD) to more severe Perio and the initiation of clinical attachment loss. The gingival plaque microbiota exhibits a parallel dynamic, with distinct compositional profiles in mild, moderate, and severe PD. We then examine several of the known mechanistic components of the keystone pathogen hypothesis of PD, identifying specific commonalities between canine and human pathologies, including the involvement of Porphyromonas species and related virulence factors. Additionally, we show infiltration of gingival tissue by Porphyromonas and Tannerella spp. via fluorescence microscopy. Finally, we assess correlations between host gene expression and microbial metabolic pathways which suggest additional potential virulence factors. ConclusionsThis work elucidates the metagenomic and transcriptomic signatures of Perio in companion dogs with the goals of informing veterinary medicine, evaluating the potential of canines as a model organism for the study of Perio, and clarifying the relationship between Perio development and progression, the oral microbiota, and the localized host response. Our findings provide insight into the etiopathogenesis of canine Perio and its relationship to human Perio and suggest novel targets of potential translational interest.

BACKGROUNDEndophytic fungi are naturally inhabiting plant organs without causing disease symptoms. They can also contribute to their hosts pest and disease resistance by displaying entomopathogenic and/or antifungal traits. In this study, we evaluated the ability of 11 strains of avocado fungal endophytes to antagonize three important avocado plant pathogens: Colletotrichum gloeosporioides, Fusarium solani, and Phytophthora cinnamomi, and two insect pests: Sitophilus zeamais and Xyleborus bispinatus. RESULTSThe results show that Trichoderma spp. strains were the most effective against the evaluated plant pathogens in terms of growth inhibition, in direct contact assays or through metabolite production. Other fungi, such as Purpureocillium sp. and Pochonia sp., only exhibited pathogen inhibition through diffusible metabolites but displayed strong insecticidal capacity against the evaluated pests, hence being identified as promising multi-target biocontrol agents in the integrative analysis. CONCLUSIONOur findings evidence the potential of avocado fungal endophytes and their metabolites as multi-target biocontrol agents of crop pests and pathogens.

Yarrowia lipolytica is a yeast of industrial interest exhibiting remarkable lipolytic and proteolytic capacities, with a high potential for white biotechnology applications. This yeast can be isolated from a wide range of natural, polluted or anthropogenic environments, including various food products. The present study aims to increase the data on Y. lipolytica phenotypic diversity by evaluating the growth parameters and secreted enzymatic activities of 28 wild-type Y lipolytica (and Yarrowia sp.) strains isolated from various environments across 10 countries. These data could facilitate the selection of appropriate strains for specific research purposes, particularly when wild-type strains are prioritized over genetically engineered ones, like for food-related applications. Notably, strain SWJ-1b exhibited an outstanding combination of favourable characteristics, with optimum (or near) performances for both growth and enzymatic parameters.

Abstract Introduction: Streptococcus is the second genus involved in bone and joint infections (BJIs) after Staphylococcus. Streptococcus agalactiae is the predominant Streptococcus species implicated in BJIs. However, unlike Staphylococcus-related BJIs, data on S. agalactiae infections remain scarce. Methods: We conducted a retrospective cohort study from the West Region cohort of the CRIOAc registry among six university hospitals including all microbiologically confirmed streptococcal BJI in adults between 2014 and 2023. Results: 1454 patients were included, with a median age of 67 years and 65% male. S. agalactiae was the predominant streptococcal species involved 423/1454(29%). The most prevalent comorbidities identified were obesity (378/1454;26%) and diabetes mellitus (343/1454;24%). Prosthetic joint infections (PJIs) were the most common (653/1454;45%), although diabetic foot osteitis was less prevalent overall, it was significantly more associated with S. agalactiae infections (48/423;11% versus 70/1031;7%, p=0.05). S. agalactiae BJIs were more frequently lower-limb infections and chronic infections (240/423;57% versus 502/1031;49%, p=0.04). Half of the cohort had a polymicrobial infection and were slightly more frequent with S. agalactiae BJIs (235/423;56% versus 498/1031;48%, p=0.1). These results were consistent with a sensitivity analysis excluding diabetic foot related osteitis. Logistic regression analysis identified arteriopathy (OR: 4.16; IC95:1.64-11.24, p=0.003), and obesity (OR: 2.57; IC95: 1.41-4.78, p=0.002) as specific risk factors for S. agalactiae BJIs. Conclusion: S. agalactiae emerges as a prominent and distinct pathogen in complex streptococcal BJIs, with specific risk factors such as arteriopathy, obesity and diabetes mellitus, and more chronic infections.

Red Mark Syndrome (RMS) is a widespread skin disease affecting rainbow trout (Onchorhynchus mykiss). It provokes substantial economic losses in aquaculture, and is putatively caused by a Rickettsiales bacterium named Midichloria-like organism (RMS-MLO), which is strongly associated with RMS lesions. However, RMS-MLO ecology and epidemiology in aquaculture systems remain poorly understood. In this study, we analysed environmental DNA to monitor the presence of RMS-MLO and its putative vector Ichthyophthirius multifiliis in a trout farm in Northern Italy over one year. Water and sediment samples were monthly collected from multiple water tanks. RMS-MLO was consistently detected by PCR throughout the study in all trout-containing tanks, both in water and sediment samples, but never in the trout-free inflow tank. We did not observe an increase in RMS-MLO abundance during the single RMS outbreak recorded nor in relation with the co-occurrence of I. multifiliis. Our findings indicate a long-term persistence of RMS-MLO in the aquaculture, possibly as a consequence of infections with low prevalence or abundance, rather than its entry from the external environment at the time of RMS outbreaks. Additionally, hints were recorded for a potential role of free-living aquatic microeukaryotes as additional occasional reservoirs. In contrast, I. multifiliis was negatively related with RMS-MLO, while it significantly increased in abundance during the RMS outbreak, particularly in the inflow tank. This supports that, rather than a stable reservoir, I. multifiliis may act as a facilitator of RMS outbreaks, which might indeed be triggered by the entry of this parasite in trout farms.

The Bacillus genus comprises physiologically versatile, endospore-forming bacteria widely distributed in natural environments. In this study, we report the isolation and genomic characterization of strain Bva_UNVM-123, recovered from agricultural soil in Pergamino, Argentina. Whole-genome sequencing using Illumina technology yielded a 5.1 Mbp draft genome assembled in 67 contigs with a GC content of 36%. Comparative genomic analyses using the TYGS server and digital DNADNA hybridization (dDDH) values supported its classification as a potentially novel species within the Bacillus sensu lato (s.l.) group. Genome annotation revealed 4,866 protein-coding genes, including multiple determinants conferring resistance to antibiotics (e.g., fosfomycin, tetracycline, beta-lactams) and toxic heavy metals (e.g., arsenic, cadmium, mercury), supporting its potential application in bioremediation. Additionally, PathogenFinder predicted a low probability of human pathogenicity (0.207), reinforcing its safety for environmental use. Functional classification based on Swiss-Prot further supported a metabolically versatile profile and revealed the presence of resistance-related categories associated with environmental adaptation. This study adds to the growing knowledge of environmental Bacillus species and their biotechnological potential

The microbiota and microbiome associated with zooplankton remains rather understudied compared to other animal groups and/or taxa. The present study aimed at investigating the whole-body bacterial microbiota of Daphnia spp. in two contrasting Greek lakes, the shallow and hypertrophic Lake Koronia vs. the deep and mesotrophic Lake Vegoritida, including both egg-bearing and non-egg-bearing individuals. In both lakes, 2,060 bacterial operational taxonomic units (OTUs) were found, with 223 of them being conditionally rare (crOTUs) with low contribution even for the dominant phyla, with L. Vegoritida having more crOTUs than L. Koronia. The individuals microbiota had inconsiderable overlap with the surrounding water microbiota in both lakes. The two lakes showed significant differences in their Daphnia -associated microbiota. L. Koronia had richer OTUs and rather homogeneous bacterial communities, with higher occupancy. Overall, no significant differences in between the microbiota of egg-bearing and non-egg-bearing Daphnia individuals in both lakes. However, regarding the most important OTUs (miOTUs), the L. Koronia miOTUs were highly overlapped between the individuals with and without eggs, with only one missing from the individuals without eggs. In L. Vegoritida the individuals without eggs had only six miOTUs and while egg-bearing individuals had nine different ones; the two lakes had no shared miOTUs., considerable differences occurred.. A total of 27 miOTUs, was found and belonged to the Pseudomonadota, unclassified Bacteria, Cyanobacteria, Bacteroidota, Bacillota and Actinomycetota. Those miOTUs, where assignment to the genus level was possible, they were related to Cyanobium, Mucilaginibacter, Flavobacterium and Staphylococcus. This study showed that lake morphotype and ecological status can exert some impact on Daphnia-associated bacterial microbiota, with more pronounced effects on egg-bearing and non-egg-bearing individuals.

Tropical coral reef ecosystems worldwide are being impacted by combined pressures of climate change and human activities that introduce large quantities of nutrients and sediments into coastal areas. In this context, phytoplankton represent a critical link between dissolved inorganic nutrients and coral reef food webs, yet their role in these ecosystems remains understudied. We investigated ecological responses of the summer phytoplankton community of Shiraho Reef (Ishigaki Island, Okinawa, Japan) to nutrient enrichment using field-based microcosm experiments under natural light and temperature conditions in September 2022 and 2023. Treatments included single and combined additions of nitrogen, phosphorus, and silicon. Chlorophyll a (Chl a) concentrations increased after three days under combined nutrient conditions, whereas single-nutrient additions produced limited responses, indicating a strong co-limitation by nitrogen and phosphorus in the reef. Analysis of size-fractionated Chl a revealed shifts from picophytoplankton that typically dominate tropical oligotrophic ecosystems toward larger groups supported by enhanced nutrient availability. Our results show short-term impacts of nutrient enrichment events on phytoplankton size structure and biogeochemical cycling in coral reefs, and highlight the importance of pelagic processes in coral reef carbon dynamics under nutrient-enrichment.

Toxoplasma gondii is a widespread human pathogen that has multiple, clinically relevant stages in its complex life cycle, including fast-replicating tachyzoites and latent bradyzoites. Bradyzoite differentiation is triggered by stress responses that lead to changes in transcription, translation, and metabolism. Two aspects of this process are addressed in this report: first, whether proteins that play roles in bradyzoite differentiation are specific to T. gondii and other bradyzoite-forming parasites of the Sarcocystidae family, and second, whether new bradyzoite differentiation proteins can be identified in T. gondii. To answer these questions, a phylogenetic approach was used, comparing proteomes of select members of the Sarcocystidae family that form morphologically different bradyzoite cysts and members of the Eimeriidae family that do not form cysts. This approach resulted in 8 distinct clusters of T. gondii proteins that reflected different conservation patterns; for example, one cluster showed conservation among all organisms, while another showed conservation in bradyzoite cyst-forming organisms. Known T. gondii proteins involved in bradyzoite differentiation were found in all clusters, indicating that this process uses both highly conserved pathways as well as bradyzoite-specific pathways. Importantly, the cluster containing proteins that are conserved in bradyzoite-forming organisms contained several known regulators of bradyzoites, and will be a source for identifying novel T. gondii proteins that are involved in bradyzoite differentiation.

Introduction: Bacterial meningitis (BM) is a common bacterial infection of the central nervous system, and its incidence in children varies by age, with the highest rates observed in infants younger than two months old. Objective: To describe the etiology, epidemiology, and clinical presentation of children under 5 years of age with BM at HOMI between 2016 to 2023. Materials and methods: Descriptive study of children under 5 years of age with suspected BM. Probable cases were those with CSF results consistent with BM. Confirmed cases had a positive CSF culture or blood culture for a bacterial pathogen or a positive molecular test for a bacterium in the CSF. Demographic variables, incidence of BM per year, mortality, and sequelae among survivors were analyzed. Results: A total of 527 suspected cases of BM were evaluated. Of these, 22.8% (120/527) were classified as probable cases and 13.1% (69/527) as confirmed cases. Children under 2 years of age accounted for 37.2% of probable cases and 78.2% of confirmed cases. Among confirmed cases, the most frequent symptoms were fever (98.3%), altered consciousness (39.1%), seizures (36.2%), and lethargy (27.5%). The mortality rate was 11.6% (8/69), and the mean hospital stay among patients with BM was 24.5 days. Streptococcus pneumoniae was identified in 26.1% of confirmed cases, with most isolates belonging to serotypes not included in PCV10. Haemophilus influenzae accounted for 17.4% of cases, of which 77.7% were serotype b. Neisseria meningitidis represented 10.1% of cases, and 60% of these were serogroup C. Other pathogens were identified in 49.1% of patients. Conclusion: Sentinel surveillance makes it possible to measure the impact of public health interventions and evaluate the impact of vaccines already used.

The Mediterranean Sea harbors a rich diversity of macroalgae with pharmacological potential. In this study, metabolite composition, antioxidant and antifungal activities of methanol and ethyl acetate extracts from Rugulopteryx okamurae, Dictyota fasciola, Batophora sp., Codium fragile, and Palisada tenerrima from the southeastern coast of Spain were evaluated. R. okamurae, Batophora sp. and C. fragile are non-native. All extracts exhibited antioxidant activity, particularly those obtained with methanol. R. okamurae and Batophora sp. showed the highest activity, inhibiting the DPPH{middle dot}radical by more than 40% at 1 mg/ml. All extracts contained phenolics and flavonoids, which may contribute to the observed antioxidant activity. Moreover, the methanolic extracts of R. okamurae and P. tenerrima exhibited in vitro fungistatic activity against the wilt pathogen Fusarium oxysporum f. sp. cubense tropical race 4. R. okamurae extracts showed the strongest antifungal activity against F. oxysporum f. sp. cubense TR4, with inhibition values of 23.3% and 30.5% at doses of 10 and 20 mg/well, respectively. The methanolic P. tenerrima also showed notable activity (19.8% and 20.7% inhibition), whereas other extracts displayed lower effect. LC-MS/MS analysis of R. okamurae extract revealed a diverse metabolite profile including oxylipin-type metabolites, terpenoid-like compounds and carotenoids. Our findings highlight coastal macroalgae from SE Spain as sources of bioactive compounds and support the valorization of biomass from invaders such as R. okamurae.

Short Interrupted Repeats Cassettes (SIRC) are recently discovered eukaryotic DNA elements possessing many traits of satellite DNA and mobile genetic elements, and consisted of short direct repeats interspersed with diverse spacer sequences. The SIRC ensemble of individual species is highly heterogenous and cannot be studied using alignment methods. It was found that number of similar SIRC sequences in a given pair of species is in general correlated with their taxonomic distance, and, at the same time, closely related species can possess very diverged SIRC ensembles, which makes SIRC evolutionary pattern closer to mobile genetic element type. The SIRC sequences make up clusters with comparable sequence patterns, that are likely to demonstrate doublet evolutionary model which strongly supports that the SIRC structure is supported by the evolutionary selection. Several SIRC sequences of Arabidopsis were found to be of ancient origin with traceable evolution history as far as to the moss clade. We carried out unbiased detection of SIRC ensembles in 10 plant genomes and found that, despite very high intraspecies heterogeneity, SIRC sets possess strong interspecies phylogenetic signal. Key messageShort Interrupted Repeats Cassettes are elements of ancient origin, and could potentially be used to trace organism history, and to facilitate syntheny and Hi-C analysis.

Defective interfering particles (DIPs) derived from the influenza A virus (IAV) are a promising antiviral agent due to their strong antiviral efficacy demonstrated in various animal models. OP7 is an unconventional IAV DIP with multiple point mutations in the viral RNA (vRNA) of genome segment 7, as opposed to the large internal genomic deletions typically found in conventional IAV DIPs. Further, OP7 showed an even higher interfering efficacy than conventional DIPs. However, the inhibitory effect of OP7 on standard virus (STV) replication has primarily been investigated in Madin-Darby Canine Kidney (MDCK) cells, which lack a functional myxovirus resistance (Mx)-mediated antiviral activity against IAV. In this study, we examined the antiviral activity and mechanism of antiviral action of OP7 in an interferon (IFN)-competent human lung carcinoma cell line (Calu-3) in vitro. We performed STV and OP7 co-infection experiments using a variety of infection conditions and measured the time-resolved dynamics in viral titer, vRNA, protein level, and host cell gene expression. We observed that OP7 co-infection results in enhanced type I IFN responses and markedly reduced infectious virus release, even at low doses. Additionally, we found that at a high STV multiplicity of infection (MOI), the replication interference of OP7, suppressing the replication of STV vRNA, appears to be the dominant mechanism of its antiviral action. At a low MOI, however, IFN induction seems to be more important. Furthermore, we examined the efficacious co-infection time window for potential prophylactic and therapeutic antiviral treatment. We observed an antiviral effect exerted by OP7 infection for up to seven days before STV infection and up to 24 hours after STV infection. Together, these findings demonstrate that OP7 is a potent antiviral DIP. Therefore, this work supports the further development of OP7 as a therapeutic and prophylactic antiviral agent.

BackgroundThis study investigated rumen microbiome reconstitution and methane (CH4) emissions following a complete exchange of rumen contents between low- and high-CH4-yielding Norwegian Red dairy cows. Twenty cows were screened for CH4 yield, and two low and two high emitters were selected for rumen cannulation and content swap. Total rumen contents were swapped after complete evacuation and washing of both the rumen and omasum. Rumen samples were collected twice in weeks -1, 1, 3, and 7 for fermentation analysis, metagenomics, and metaproteomics, and at week 8 CH4 production was measured. ResultsPrior to the swap, low and high emitters produced 21.2 {+/-} 0.7 and 26.3 {+/-} 1.4 g CH4/kg dry-matter intake (DMI), respectively. Eight weeks after swap, CH4 yields were 12.7 {+/-} 0.3 and 28.9 {+/-} 0.3 g CH4/kg DMI, respectively, showing that the CH4 phenotype of each cow was maintained. Analysis of metagenome-derived 16S rRNA gene sequences showed that low emitters gradually re-established their original microbial community, whereas high emitters retained donor-like microbiota. Metaproteomic mapping suggested higher expression of Prevotella-associated succinate-propionate pathway enzymes in low emitters at week 7, though these differences were modest. ConclusionThese findings suggest that host factors influence CH4 output and microbial reconstitution, with low emitters restoring their native microbiome while high emitters retained a donor-associated community yet continued to emit high CH4. Results should be interpreted with caution given the small sample size (n = 2 per phenotype) and require confirmation in larger studies. ImportanceReducing enteric methane from cattle requires understanding whether the rumen microbiome or the host animal is the primary driver of methane output. We exchanged the entire rumen contents between low- and high-methane-yielding dairy cows and measured methane production alongside metagenomic and metaproteomic profiling over two months. Despite receiving each others microbiomes, each cows methane phenotype persisted--low emitters stayed low and high emitters stayed high. Microbiome reconstitution was asymmetric: low emitters restored their original microbial community, while high emitters retained the donor microbiota. Methanogen communities did not differ between phenotypes, pointing to host-level rather than microbial-level control of methane yield. These pilot findings suggest that breeding for favorable host traits may be essential for lasting methane reduction, and that microbiome transfer alone is unlikely to shift an animals methane phenotype. Larger studies are needed to confirm these observations.

Marine algal blooms play a vital role in oceanic carbon cycling, yet the ecological consequences of algal organic matter released following their collapse via viral infection are poorly understood. Recent studies have shown that viral infection dramatically alters the hosts intracellular metabolite composition, and the subsequent viral lysate selectively promotes the growth of specific prokaryotic populations. This study aimed to elucidate the effect of organic matter derived from healthy and virus-infected cells of the bloom-forming alga Heterosigma akashiwo on the growth of heterotrophic eukaryotes, specifically Labyrinthulomycetes. These marine protists are primarily saprotrophic or predatory and contribute to dissolved organic matter (DOM) decomposition and nutrient cycling. Our field monitoring in Osaka Bay over 12 months revealed that while the overall Labyrinthulomycetes community showed no clear seasonality, specific populations of the protists co-occurred with Heterosigma akashiwo. To mechanistically investigate the potential trophic linkage suggested by these field observations, a co-culture system comprising H. akashiwo, its specific virus (HaV53), and Aurantiochytrium sp. NBRC102614, used here as a model Labyrinthulomycete, was established. In the co-culture experiments, viral lysis of H. akashiwo led to a significant increase in the cell density of Aurantiochytrium sp., demonstrating that Aurantiochytrium can thrive on substrates derived from the virus-infected alga, such as viral-induced dissolved organic matter (vDOM). These findings highlight that heterotrophic Labyrinthulomycetes are one of key consumers of virus-modified organic matter, playing a pivotal role in carbon cycling following the collapse of harmful algal blooms and influencing carbon transfer in coastal microbial food webs. IMPORTANCEMarine ecosystems are tightly regulated by the interplay between microalgae, viruses, and heterotrophic eukaryotes, yet their roles within this network have long been underestimated. Accordingly, this study aimed to provide an overview of the dynamics of environmental microalgae and heterotrophic eukaryotes, namely Heterosigma species and Labyrinthulomycetes, and to elucidate the impact of virus-infected Heterosigma akashiwo on the growth and proliferation of Aurantiochytrium species within heterotrophic Labyrinthulomycetes. This study revealed the dynamics of several Labyrinthulomycetes species associated with Heterosigma populations in coastal marine environments and demonstrated that Aurantiochytrium species have the capacity to redistribute carbon, such as by utilizing vDOM released during the termination of Heterosigma blooms via viral infection, thereby repositioning Aurantiochytrium from a passive component of Heterosigma viral infection toward an active ecological agent that facilitates energy transfer and contributes to the maintenance of microalgal community dynamics. Overall, this work provides new insights into the fate of virus-infected Heterosigma in coastal marine systems mediated by heterotrophic Labyrinthulomycetes, particularly Aurantiochytrium species, thereby filling an important knowledge gap in microbial ecology.

Phylogenetic group B2 Escherichia coli is associated with urinary tract infections and other pathologies, but the basis for this phylogenetic skew is not understood. One aspect of urinary tract infections is binding to and entering uroepithelial cells. To test whether a phylogenetic skew exists for cell invasion, we examined invasion of 10 E. coli strains from three phylogenetic groups into CRL2169 and HTB-9 cells, which are derived from grade 1 and grade 2 bladder carcinomas, respectively. The top four strains that invaded CRL2169 were from group B2: three of these strains had more flagella gene transcripts than the other seven strains. The seven strains that invaded HTB-9 were from different phylogenetic groups. For the model uropathogenic group B2 strain UTI89, which expresses pili over flagella, loss of flagella or pili impacted invasion into CRL2169 to similar extents, but loss of pili had a greater effect on invasion into HTB-9 and a murine infection model than loss of flagella. A hyperflagellated variant of a group A strain did not invade either cell line better than the parental strain. Reported transcript differences, which were confirmed experimentally, showed that CRL2169 was more differentiated. The endocytosis stimulator tanshinone enhanced invasion into HTB-9, but not into CRL2169, which suggests differences in endocytic pathways and is consistent with differences in differentiation states. If the initial or recurring event in urinary tract infection is invasion into differentiated urothelial cells, as opposed to tight junctions, then the role of flagella may have been underestimated.