Microbial Ecology最新文献

Nitrogen availability limits primary production in the Arctic Ocean, making it vital to understand its sources and sinks to predict future productivity. Although nitrogen fixation has been reported in the Arctic Ocean, data remain scarce, especially in the Atlantic sector. Here, we measured nitrogen fixation rates and examined diazotroph community composition across the Fram Strait, targeting Polar waters in the East Greenland Current, Atlantic waters in the West Spitsbergen Current, and their frontal zone. Nitrogen fixation was mainly low (< 1 nmol N L^-1 d^-1) in Polar waters, however, elevated at the one station in the Atlantic water sector (up to 10.15 nmol N L^-1 d^-1). Rates were only detectable in the epipelagic layer (0-100 m) across the strait and positively correlated with temperature, primary production, and chlorophyll-a fluorescence, and negatively correlated with coloured dissolved organic matter and silicate. The diazotrophs were dominated by non-cyanobacterial diazotrophs (NCDs; 77% of nifH amplicon reads), with an Arctic Betaproteobacterial group (order Rhodocyclales) accounting for 11% of sequence reads. This group was quantifiable (up to 6700 nifH gene copies L^-1) within the West Spitsbergen Current and the frontal zone, where the highest nitrogen fixation and primary production occurred, and its prevalence was positively correlated with temperature. We propose that temperature and freshly produced dissolved organic matter influence the NCD-dominated nitrogen fixation in Fram Strait. Our study suggests that NCDs are key diazotrophs in Fram Strait, and that nitrogen fixation rates and their potential importance for primary production vary across the contrasting water masses entering and exiting the Arctic Ocean. We encourage future studies to quantify these nitrogen fluxes and evaluate their importance for productivity in the Arctic Ocean.

The olive tree (Olea europaea L.) hosts diverse endophytic microbial communities that contribute to its resilience, productivity, and adaptation to environmental stressors. Since the temperature increases caused by global climate change primarily affects the aerial part of the plant, this review synthesizes current knowledge on the diversity, composition, and ecological drivers of olive phyllosphere endophytes, with a focus on bacterial and fungal communities. We highlight the role of host-related factors-including plant genotype, organ specificity, age, and phenological stage-in shaping microbiota structure across spatial and temporal scales. Genotype consistently emerges as a major determinant of microbial composition, while leaves and twigs harbor distinct yet overlapping communities. Geographic location, environmental variables, and seasonal shifts significantly influence microbial assemblages, with closer sites often supporting more similar communities. We also discuss the impact of agricultural practices and biotic and abiotic stressors on microbiota stability and function. Notably, several cultivable taxa-including Bacillus, Paenibacillus, Pantoea, Aureobasidium, and Penicillium-exhibit antagonistic activity against key olive pathogens, underscoring their potential as biological control agents. We conclude by emphasizing the need for functional studies to elucidate the roles of keystone endophytes and to inform microbiome-based strategies for sustainable olive cultivation.

Although phages shape bacterial evolution and physiology, the specificity of host transcriptomic responses to phage infection remains incompletely understood. Here, we performed global transcriptomic profiling of Escherichia coli exposed to two lytic phages, ΦX174 and T4, and the temperate phage λ, to explore both conserved and phage-specific host responses. All infections induced stress-related genes, including SOS and general stress pathways, along with repression of anabolic processes such as purine and amino acid biosynthesis, suggesting a metabolic shift to conserve resources. Notably, ΦX174 strongly activated the phage shock protein operon, while both ΦX174 and λ selectively induced soxS, a regulator of oxidative stress. Despite infecting the same host, each phage triggered distinct transcriptional signatures. These findings highlight the complexity of bacterial responses and the value of transcriptomics in decoding host-phage interactions, offering insights into resistance, survival, and co-evolution.

Warming is altering the functioning of desert ecosystems in global drylands. Microbial communities are crucial for maintaining these ecosystems, yet how their co-occurrence networks and assembly mechanisms respond to warming remains unclear. Using 16 S and ITS rRNA amplicon sequencing, we examined bacterial and fungal community composition and structure. Further, we investigated cross-trophic bacterial-fungal interactions via inter-domain ecological network analysis. Warming significantly altered the diversity, composition, and structure of both bacterial and fungal communities. It increased bacterial network complexity but simplified the fungal network. Notably, warming enhanced cross-trophic interactions between bacteria and fungi, facilitating the maintenance of microbial hierarchical interactions, particularly bacterial network complexity. However, microbial keystone taxa declined dramatically under warming, 41.18% of these belonged to Ascomycota. Neutral community models and normalized stochastic ratio-based analyses revealed that deterministic processes dominated community assembly, with warming increasing their relative importance by 8-46%. This suggests a potential deterministic environmental filtering induced by warming. Collectively, these findings advance our understanding of the ecological mechanisms and microbial interactions underpinning rhizospheric communities in drylands under future climate change.

The high-altitude regions of the Tibet Autonomous Region possess abundant cold-water resources, with annual average water temperatures suitable for culturing triploid rainbow trout. However, environmental challenges-including low atmospheric pressure, hypoxic water conditions, and significant diurnal temperature fluctuations-necessitate precise optimization of stocking density. Inadequate densities result in suboptimal resource utilization, whereas excessive densities induce chronic stress, leading to suppressed growth, reduced survival, and intestinal microbiota dysbiosis. Currently, research on appropriate stocking densities under these specific conditions remains limited. This study investigated the effects of stocking density on growth performance, intestinal microbiota, and tissue health of triploid rainbow trout, to identify the optimal density to support sustainable aquaculture in high-altitude plateau areas. Three stocking densities were tested over a 60-day culture period in 0.25 m³ cylindrical tanks (radius 0.45 m, water depth 0.45 m, adjusted for internal volume): Low-Density (LD, 100 fish/barrel), Medium-Density (MD, 200 fish/barrel), and High-Density (HD, 300 fish/barrel). Results demonstrated that the final body weight (Wt) and specific growth rate (SGR) in the LD treatment were significantly higher than those in the HD group (Wt: P ≤ 0.009; SGR: P ≤ 0.019). Survival rate was also significantly greater in the LD treatment compared to HD (P < 0.036), with values of 84.67%, 80.83%, and 72.67% for LD, MD, and HD, respectively. Alpha diversity of both water and gut microbial communities varied with stocking density. Principal component analysis (PCA) revealed differentiated clustering of microbial communities in water and the intestine across density treatments (Water: P = 0.35; intestinal microbiota: P = 0.7). The dominant phyla in aquatic and intestinal microbiomes were Proteobacteria, Firmicutes, and Bacteroidetes. In intestinal samples, the genus Pseudomonas was significantly more abundant in the HD and MD treatments than in the LD treatment. Co-occurrence network analysis revealed a higher average degree in LD and MD treatments, suggesting enhanced stability of microbial ecosystems in both the intestine and water under these conditions. In conclusion, low and medium stocking densities are more suitable for cultivating triploid rainbow trout in high-altitude plateau environments. These findings provide a scientific basis for ecologically sound, efficient, and healthy aquaculture practices for this species in alpine regions.

The distribution of diversity in function of climate has been largely studied in plants and animals, leading to a large body of literature on macroecological rules applied to large geographic scales. However, the applicability of these rules to microbes has almost never been tested at local scales. Arcellinida are a diverse group of protists known to be narrow ecological specialists and constitute therefore an excellent group to test general rules validated on "macrobes", like the water-energy balance that stipulates that biodiversity peaks with humidity and temperature. In order to test that hypothesis, we collected 122 samples from four cedar forests situated along an elevation gradient in Lebanon, spanning different local climates. We evaluated their diversity using an Arcellinida-specific metabarcoding approach based on the cytochrome oxidase subunit I gene. Our study shows that Arcellinida richness and phylogenetic diversity follow a unimodal distribution, peaking at mid-elevations. β-diversity was chiefly the product of turnover, illustrating the high spatial heterogeneity of the forests. Precipitation and actual evapotranspiration were identified as key drivers of diversity, thus supporting the water-energy balance hypothesis. Communities situated at higher or lower elevation were, to a large extent, subsets of more diverse mid-elevation assemblages, which designates the latter as biodiversity sources. These results suggest that, under the increasing aridification of the Middle East due to climate change, Arcellinida communities will lose diversity and will undergo a process of homogenisation, with possible consequences on ecosystem functioning.

Salt marshes, despite their ecological importance (i.e., carbon sequestration) and rapid decline due to climate change and sea-level rise. Salt marsh ecosystems provide essential services such as removal of pollutants, carbon sequestration, and protection of coastal lands from storm surges. These services are strongly influenced by plant productivity, which is closely linked to microbial processes such as biogeochemical cycling of carbon, nitrogen, and sulfur. To retain carbon sequestration and other ecological functions, substantial efforts are currently directed towards coastal marsh restoration. Restoration efforts often lack comprehensive assessments of ecosystem functioning. Here, in an effort to assess ecosystem functions, we compared the microbial and viral community composition, as well as the genetic potential between reference and 10-year-old restored marshes in Galveston Bay, TX, USA. Duplicate bulk surface sediment in stands of Spartina alterniflora were sampled for metagenomic analysis. Metagenome assembled genomes analysis showed that while the microbial community composition was largely similar among sites, the overall metabolic potential was dissimilar. Restored sites displayed a higher abundance of carbon and nitrogen cycling functions compared to reference sites, which mainly consisted of sulfur cycling. Although the restored sites developed sediment microbial communities that approached reference microbial composition, the differences in the metabolic functions suggest that even after 10 years, the restored sites were still in a transitional stage of development. The differences between the reference and restored sites were even more differentiated in the viral community's predicted host composition. Additionally, viruses potentially play a variety of roles within the sediment community, including population control and biogeochemical cycles participation through auxiliary metabolic genes. These results highlight the prolonged timeline of functional development in restored salt marshes and highlight the need to develop approaches to boost the development of soil microbial communities in newly created habitats.

Weathering of sulphur-bearing rocks leads to acid rock drainage (ARD), which decreases water pH, mobilizes heavy metals, and forms coloured coatings of metal precipitates on riverbeds. This study assessed the effects of ARD on microbial biofilm biodiversity and community structure in alpine streams across two Pyrenean regions (Núria and Chistau). Biofilms were sampled from acidic (pH < 5.5) and non-acidic (pH > 6.5) streams, and at their confluence, where metal precipitates occur (white-coated streams). We characterised bacterial and eukaryote communities by molecular tools and specifically analysed the diatom communities by morphology approach. Their respective community composition varied with stream category for both bacteria and eukaryotes, but only bacteria exhibited a loss in diversity in acidic and white-coated streams. Diatom communities and diversity differences were driven mainly by region. In acidic and white-coated streams, bacteria which can use metals and sulphurs in their metabolic processes increased, together with fungi and some photosynthetic groups (Chlorophyta, Streptophyta) among eukaryotes. Amplicon Sequence Variants (ASVs) assigned to acidophilic and psychrotolerant bacteria were highly associated with acidic streams, and Cyanophyceae ASVs were highly associated with white-coated ones. As for eukaryotes, ASVs of Chrysophyceae were associated with both acidic and white-coated streams. Nonetheless, the regional factor remained consistently significant across microbial communities. This study indicates that ARD-affected streams can support microbial communities adapted to their extreme conditions, with the communities in white-coated rivers differing markedly from those in acidic rivers.

The cloud forest harbors the highest amphibian diversity in Mexico, particularly among plethodontid salamanders. However, the expansion of agricultural and cattle ranching activities has significantly impacted this ecosystem and their native species. Beyond direct effects on cloud forest-dwelling species, effects of land-use change on free-living and salamander skin associated bacterial assemblages are underexplored in the cloud forest and in plethodontid salamanders specifically. This study examines how historical land-use changes may influence environmental and salamander skin bacterial communities, focusing on two types of previous land-use and six sympatric plethodontid salamanders from the cloud forest. Furthermore, we explored the presence of the pathogenic fungus Batrachochytrium dendrobatidis (Bd), due to its potential interaction with salamander skin bacterial communities. We found that skin bacterial communities varied with land-use history: in habitats formerly used for agriculture salamanders exhibited higher bacterial diversity, and communities' dispersion varied depending on the previous land-use. We found a very low Bd prevalence throughout the study area. Our findings suggest that bacterial communities associated with the skin of plethodontid salamanders may be influenced by land-use history in cloud forest fragments.

Temporary ponds, characterized by periodic or intermittent hydroperiods, are globally widespread in all the biogeographical regions and host peculiar biotic communities. Here we investigated shifts in diatom community assemblages across two contrasting biogeographical regions in Italy, the Mediterranean and the Alpine. The study focused on 24 temporary ponds, with 12 ponds sampled at Castelporziano (CP) and 12 at Campo Imperatore (GS). Our results highlighted that γ diversity varied significantly between the two study sites, indicating a notably greater species richness in GS compared to CP. In GS, functional richness values were generally higher, whereas no significant differences were detected for functional distance and functional divergence. Species composition differed significantly between CP and GS indicating that the two sites host distinct communities, with species turnover (0.904) which contributed most to total beta diversity (0.926), while nestedness (0.021) was negligible. CP communities were characterized by pronounced functional clustering in specific sites while GS exhibited both clustering and slight overdispersion. However, although GS communities occupy slightly larger trait space, both regions shared most functional strategies, reflecting substantial redundancy in functional traits across the two environments. Overall, diatom communities in the GS were characterized by higher frequencies of small, mobile, low-profile, and mucilaginous-tube taxa, whereas CP ponds displayed relatively higher representation of larger or motile forms. Although our study is a starting point, large-scale analyses of diatom communities are crucial, as climate change may rapidly and irreversibly alter taxonomic and functional diversity, profoundly affecting the ecology of these temporary habitats and surrounding landscapes.