Environmental microbiology最新文献

Bacterial membrane lipids are typically characterised by fatty acid bilayers linked through ester bonds, whereas those of Archaea are characterised by ether-linked isoprenoids forming bilayers or monolayers of membrane-spanning lipids known as isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs). However, this understanding has been reconsidered with the identification of branched GDGTs (brGDGTs), which are membrane-spanning ether-bound branched alkyl fatty acids of bacterial origin, though their producers are often unidentified. The limited availability of microbial cultures constrains the understanding of the biological sources of these membrane lipids, thus limiting their use as biomarkers. To address this issue, we identified membrane lipids in the Black Sea using high-resolution accurate mass/mass spectrometry and inferred their potential producers by targeting lipid biosynthetic pathways encoded on the metagenome, in metagenome-assembled genomes and unbinned scaffolds. We also identified brGDGTs and highly branched GDGTs in the suboxic and euxinic waters, potentially attributed to Planctomycetota, Cloacimonadota, Desulfobacterota, Chloroflexota, Actinobacteria and Myxococcota—based on their lipid biosynthetic genomic potential. These findings introduce new possibilities for using specific brGDGTs as biomarkers of anoxic conditions in marine environments and highlight the role of these membrane lipids in microbial adaptation.

Seasonality is an important natural feature that drives cyclic environmental changes. Seaweed holobionts, inhabiting shallow waters such as rocky shores and mud flats, are subject to seasonal changes in particular, but little is known about the influence of seasonality on their microbial communities. In this study, we conducted a three-year time series, sampling at two-month intervals, to assess the seasonality of microbial epibiota in the seaweed holobiont Gracilaria vermiculophylla. Our results reveal pronounced seasonal shifts that are both taxonomic and functional, oscillating between late winter and early summer across consecutive years. While epibiota varied taxonomically between populations, they were functionally similar, indicating that seasonal variability drives functional changes, while spatial variability is more redundant. We also identified seasonal core microbiota that consistently (re)associated with the host at specific times, alongside a permanent core that is present year-round, independent of season or geography. These findings highlight the dynamic yet resilient nature of seaweed holobionts and demonstrate that their epibiota undergo predictable changes. Therewith, this research offers important insights into the temporal dynamics of seaweed-associated microbiota and demonstrates that the relationship between seaweed host and its epibiota is not static but naturally subject to an ongoing seasonal succession process.

Nodules harbour microbial communities composed of rhizobia and other lower-abundance bacteria. These non-rhizobial bacteria can promote plant growth. However, their genomic diversity and how this relates to their plant growth-promoting traits remain poorly investigated. Here, we isolated 14 Pseudomonas strains from the nodules of Lotus plants, sequenced their genomes, analysed their genomic and phylogenetic diversity, and assessed their ability to promote plant growth. We identified five distinct species, including a novel species named Pseudomonas monachiensis sp. nov., with strain PLb12A^T, as the type strain. Genome analysis of these nodule-isolated Pseudomonas revealed an abundance of genes associated to plant growth-promoting traits, especially auxin-related genes, compared to closely related type strains. In accordance, most nodule-isolated Pseudomonas strains enhanced shoot growth of Lotus burttii, while only some promoted root growth or early onset of root hair proliferation. However, none of the strains significantly affected the ability to form nodules. Overall, our findings highlight the genotypic diversity and the plant growth-promoting potential of nodule-isolated Pseudomonas and underscore their possible applications in mixed inocula with rhizobia.

Microbes grown in heterogeneous laboratory environments can rapidly diversify into multiple, coexisting variants. While the genetic and evolutionary mechanisms of laboratory adaptive radiations are well studied, how the presence of other species alters the outcomes of diversification is less well understood. To test the effect of co-culture growth on the Pseudomonas fluorescens SBW25 adaptive radiation, Escherichia coli and P. fluorescens were cultured in monoculture and co-culture for 8 weeks. In P. fluorescens monoculture, Wrinkly and Smooth Spreader types rapidly evolved and were maintained over 8 weeks, while E. coli monocultures evolved two colony types, a big and a small colony variant. In contrast, we found that in co-culture, E. coli did not evolve small colony variants. Whole genome sequencing revealed the genetic basis of possible co-culture specific adaptations in both E. coli and P. fluorescens. Altogether, our data support that the presence of multiple species changed the outcome of adaptive radiation.

Ramlibacter tataouinensis, the type species of the genus Ramlibacter, is renowned for its ability to thrive in hot, arid and nutrient-poor desert soils. To investigate whether its adaptive properties are shared across all 20 currently described Ramlibacter species found in diverse terrestrial and aquatic habitats worldwide, we conducted a comprehensive analysis of 16S rRNA sequences and genomic information available from the literature. Our study encompassed approximately 40 deposited genomes, allowing us to propose a genomic phylogeny that aligns with the 16S rRNA phylogeny. Our findings reveal several conserved features across the genus Ramlibacter. This includes the presence of light sensors, environmental sensing networks, organic carbon and phosphate acquisition systems and the ability to store carbon and energy in the form of polyhydroxyalkanoate or polyphosphate granules. These shared traits rationalise the widespread distribution of Ramlibacter in oligotrophic terrestrial and aquatic environments. They also explain the genus' ability to withstand desiccation, endure extended periods of starvation, and survive in nutrient-depleted conditions. Notably, certain adaptive features are further enhanced in several species by their pleiomorphism and ability to form cysts. Overall, our study not only highlights the ecological adaptations of Ramlibacter species but also extends our understanding of microbial ecology in oligotrophic environments.

Coastal ecosystems are increasingly exposed to high nutrient loads and salinity intrusions due to rising seawater levels. Microbial communities, key drivers of elemental cycles in these ecosystems, consequently, experience fluctuations. This study investigates how the methane-rich coastal sediment microbiome from the Stockholm Archipelago copes with high and low nitrogen and sulfide loading by simulating coastal conditions in two methane-saturated anoxic brackish bioreactors. Over a year, the bioreactors were subjected to the same ratio of nitrate, ammonium and sulfide (2:1:1) under eutrophic or oligotrophic conditions and monitored using 16S rRNA gene amplicon and metagenomic sequencing. Sulfide was depleted in both conditions. Sulfide-dependent denitrification was the predominant process in eutrophic conditions, whereas dissimilatory nitrate reduction to ammonium dominated under oligotrophic conditions. Methane oxidation was driven by Methylobacter and Methylomonas in eutrophic conditions, whereas a more diverse methane-oxidising microbial community developed under oligotrophic conditions, which likely competed for nitrate with anaerobic methanotrophic archaea and the gammaproteobacterial MBAE14. Novel putative copper-dependent membrane-bound monooxygenases (Cu-MMOs) were identified in MBAE14 and co-enriched Rugosibacter genomes, suggesting the need for further physiological and genetic characterisation. This study highlights the importance of understanding coastal anoxic microbiomes under fluctuating conditions, revealing complex interactions and novel pathways crucial for ecosystem functioning.

Nitrogen compounds often serve as crucial electron donors and acceptors in microbial energy metabolism, playing a key role in biogeochemical cycles. The energetic favorability of nitrogen oxidation–reduction (redox) reactions, driven by the thermodynamic properties of these compounds, may have shaped the evolution of microbial energy metabolism, though the extent of their influence remains unclear. This study quantitatively evaluated the similarity between energetically superior nitrogen reactions, identified from 988 theoretically plausible reactions, and the nitrogen community-level network, reconstructed as a combination of enzymatic reactions representing intracellular to interspecies-level reaction interactions. Our analysis revealed significant link overlap rates between these networks. Notably, composite enzymatic reactions aligned more closely with energetically superior reactions than individual enzymatic reactions. These findings suggest that selective pressure from the energetic favorability of redox reactions can operate primarily at the species or community level, underscoring the critical role of thermodynamics in shaping microbial metabolic networks and ecosystem functioning.

Monooxygenase (MO) enzymes are responsible for the oxidation of hydrocarbons and other compounds in the carbon and nitrogen cycles, are important for the biodegradation of pollutants and can act as biocatalysts for chemical manufacture. The soluble di-iron monooxygenases (SDIMOs) are of interest due to their broad substrate range, high enantioselectivity and ability to oxidise inert substrates such as methane. Here, we re-examine the phylogeny and functions of these enzymes, using recent advances in the field and expansions in sequence diversity in databases to highlight relationships between SDIMOs and revisit their classification. We discuss the impact of horizontal gene transfer on SDIMO phylogeny, the potential of SDIMOs for the biodegradation of pollutants and the importance of heterologous expression as a tool for understanding SDIMO functions and enabling their use as biocatalysts. Our analysis highlights current knowledge gaps, most notably, the unknown substrate ranges and physiological roles of enzymes that have so far only been detected via genome or metagenome sequencing. Enhanced understanding of the diversity and functions of the SDIMO enzymes will enable better prediction and management of biogeochemical processes and also enable new applications of these enzymes for biocatalysis and bioremediation.