Environmental microbiology最新文献

The Hepatincolaceae (Alphaproteobacteria) are a group of bacteria that inhabit the gut of arthropods and other ecdysozoans, associating extracellularly with microvilli. Previous phylogenetic studies, primarily single-gene analyses, suggested their relationship to the Holosporales, which includes intracellular bacteria in protist hosts. However, the genomics of Hepatincolaceae is still in its early stages. In this study, the number of available Hepatincolaceae genomes was increased to examine their evolutionary and functional characteristics. It was found that the previous phylogenetic grouping with Holosporales was incorrect due to sequence compositional biases and that Hepatincolaceae form an independent branch within the Hepatincolaceae. This led to a reinterpretation of their features, proposing a new evolutionary scenario that involves an independent adaptation to host association compared to the Holosporales, with distinct specificities. The Hepatincolaceae exhibit greater nutritional flexibility, utilising various molecules available in the host gut and thriving in anaerobic conditions. However, they have a less complex mechanism for modulating host interactions, which are likely less direct than those of intracellular bacteria. In addition, representatives of Hepatincolaceae show several lineage-specific traits related to differences in host species and life conditions.

Cyanobacterial distributions are shaped by abiotic factors including temperature, light and nutrient availability as well as biotic factors such as grazing and viral infection. In this study, we investigated the abundances of T4-like and T7-like cyanophages and the extent of picocyanobacterial infection in the cold, high-nutrient-low-chlorophyll, sub-Antarctic waters of the southwest Pacific Ocean during austral spring. Synechococcus was the dominant picocyanobacterium, ranging from 4.7 × 10³ to 1.2 × 10⁵ cells∙mL⁻¹, while Prochlorococcus abundances were relatively low overall, ranging from 1.0 × 10³ to 3.9 × 10⁴ cells∙mL⁻¹. Using taxon-specific, single-virus and single-cell polony methods, we found that cyanophages were on average 15-fold, and up to 50-fold, more abundant than cyanobacteria in these waters. T4-like cyanophages (ranging from 1.7 × 10⁵ to 6.5 × 10⁵ phage·mL⁻¹) were 2.7-fold more abundant than T7-like cyanophages (ranging from 3.1 × 10⁴ to 2.8 × 10⁵ phage·mL⁻¹). Picocyanobacteria were primarily infected by T4-like cyanophages with more Synechococcus (4.8%–12.1%) infected than Prochlorococcus (2.5%–6.2%), whereas T7-like cyanophages infected less than 1% of both genera. These infection levels translated to daily mortality in the range of 5.7%–26.2% and 2.9%–14.3% of the standing stock of Synechococcus and Prochlorococcus, respectively. Our findings suggest that T4-like cyanophages are significant agents of cyanobacterial mortality in the cold, low-iron, sub-Antarctic waters of the South Pacific Ocean.

Shotgun and proximity-ligation metagenomic sequencing were used to generate thousands of metagenome assembled genomes (MAGs) from the untreated wastewater, activated sludge bioreactors, and anaerobic digesters from two full-scale municipal wastewater treatment facilities. Analysis of the antibiotic resistance genes (ARGs) in the pool of contigs from the shotgun metagenomic sequences revealed significantly different relative abundances and types of ARGs in the untreated wastewaster compared to the activated sludge bioreactors or the anaerobic digesters (p < 0.05). In contrast, these results were statistically similar when comparing the ARGs in the pool of MAGs, suggesting that proximity-ligation metagenomic sequencing is particularly useful for pairing ARGs with their hosts but less adept at discerning quantitative differences in ARG types and relative abundances. For example, numerous MAGs of the genera Acinetobacter, Enterococcus, Klebsiella and Pseudomonas were identified in the untreated wastewater, many of which harboured plasmid-borne and/or chromosomal-borne ARGs; none of these MAGs, however, were detected in the activated sludge bioreactors or anaerobic digesters. In conclusion, this research demonstrates that the antibiotic resistome undergoes significant transitions in both the relative abundance and the host organisms during the municipal wastewater treatment process.

The leaf surface, known as the phylloplane, presents an oligotrophic and heterogeneous environment due to its topography and uneven distribution of resources. Although it is a challenging environment, leaves support abundant bacterial communities that are spatially structured. However, the factors influencing these spatial distribution patterns are not well understood. To study the changes in population density and spatial distribution of bacteria in synthetic communities, the behaviour of two common bacterial groups in the Arabidopsis thaliana leaf microbiota—Methylobacterium (methylobacteria) and Sphingomonas (sphingomonads)—was examined. Using synthetic communities consisting of two or three species, the hypothesis was tested that the presence of a third species affects the density and spatial interaction of the other two species. Results indicated that methylobacteria exhibit greater sensitivity to changes in population densities and spatial patterns, with higher intra-genus competition and lower densities and aggregation compared to sphingomonads. Pairwise comparisons were insufficient to explain the shifts observed in three-species communities, suggesting that higher-order interactions influence the structuring of complex communities. This emphasises the role of multispecies interactions in determining spatial patterns and community dynamics on the phylloplane.

The Canadian province of Alberta contains substantial oilsands reservoirs, consisting of bitumen, clay and sand. Extracting oil involves separating bitumen from inorganic particles using hot water and chemical diluents, resulting in liquid tailings waste with ecotoxicologically significant compounds. Ongoing efforts aim to reclaim tailings-affected areas, with protist colonisation serving as one assessment method of reclamation progress. Oilsands-associated protist communities have mainly been evaluated using amplicon sequencing of the 18S rRNA V4 region; however, this barcode may overlook important protist groups. This study examined how community assessment methods between the V4 and V9 regions differ in representing protist diversity across four oilsands-associated environments. The V9 barcode identified more operational taxonomical units (OTUs) for Discoba, Metamonada and Amoebozoa compared with the V4. A comparative shotgun metagenomics approach revealed few eukaryotic contigs but did recover a complete Paramicrosporidia mitochondrial genome, only the second publicly available from microsporidians. Both V4 and V9 markers were informative for assessing community diversity in oilsands-associated environments and are most effective when combined for a comprehensive taxonomic estimate, particularly in anoxic environments.

The microbiome influences critical aspects of mosquito biology and variations in microbial composition can impact the outcomes of laboratory studies. To investigate how biotic and abiotic conditions in an insectary affect the composition of the mosquito microbiome, a single cohort of Aedes aegypti eggs was divided into three batches and transferred to three different climate-controlled insectaries within the Liverpool School of Tropical Medicine. The bacterial microbiome composition was compared as mosquitoes developed, the microbiome of the mosquitoes' food sources was characterised, environmental conditions over time in each insectary were measured, and mosquito development and survival were recorded. While developmental success was similar across all three insectaries, differences in microbiome composition were observed between mosquitoes from each insectary. Environmental conditions and bacterial input via food sources varied between insectaries, potentially contributing to the observed differences in microbiome composition. At both adult and larval stages, specific members of the mosquito microbiome were associated with particular insectaries; the insectary with less stable and cooler conditions resulted in a slower pupation rate and higher diversity of the larval microbiome. These findings underscore that even minor inconsistencies in rearing conditions can affect the composition of the mosquito microbiome, which may influence experimental outcomes.

Streptofilum capillatum was recently described and immediately caught scientific attention, because it forms a phylogenetically deep branch in the streptophytes and is characterised by a unique cell coverage composed of piliform scales. Its phylogenetic position and taxonomic rank are still controversial discussed. In the present study, we isolated further strains of Streptofilum from biocrusts in sand dunes and Arctic tundra soil. Molecular and morphological characterisation including transmission electron microscopy confirmed that both new strains belong to Streptofilum. The Arctic strain is described as a new species, Streptofilum arcticum sp. nov., based on molecular differences, a specific sarcinoid morphology and unique ultrastructure with massive cell coverage composed of pili-shaped scales. A comprehensive characterisation of the ecophysiological traits of both new Streptofilum isolates and the original one revealed a broad temperature tolerance, a rapid recovery of photosynthetic performance after desiccation, an efficient photosynthesis at low light and a tolerance to high-light conditions. In addition, Streptofilum could cope with UV irradiation, but only S. capillatum grew under UV exposure. All Streptofilum strains are well-adapted to water-deprived terrestrial habitats such as biocrusts. From this study it can be concluded that already early-branching streptophytes were able to tolerate terrestrial conditions.

Cellulolytic flagellates are essential for the symbiotic digestion of lignocellulose in the gut of lower termites. Most species are associated with host-specific consortia of bacterial symbionts from various phyla. 16S rRNA-based diversity studies and taxon-specific fluorescence in situ hybridization revealed a termite-specific clade of Actinomycetales that colonise the cytoplasm of Trichonympha spp. and other gut flagellates, representing the only known case of intracellular Actinomycetota in protists. Comparative analysis of eleven metagenome-assembled genomes from lower termites allowed us to describe them as new genera of Bifidobacteriaceae. Like the previously investigated Candidatus Ancillula trichonymphae, they ferment sugars via the bifidobacterium shunt but, unlike their free-living relatives, experienced significant genome erosion. Additionally, they acquired new functions by horizontal gene transfer from other gut bacteria, including the capacity to produce hydrogen. Members of the genus Ancillula (average genome size 1.56 ± 0.2 Mbp) retained most pathways for the synthesis of amino acids, including a threonine/serine exporter, providing concrete evidence for the basis of the mutualistic relationship with their host. By contrast, Opitulatrix species (1.23 ± 0.1 Mbp) lost most of their biosynthetic capacities, indicating that an originally mutualistic symbiosis is on the decline.