Environmental microbiology最新文献

Bacterial degradation of ubiquitous and persistent steroids such as steroid hormones is important for their removal from the environment. Initial studies of steroid degradation in anaerobic bacteria suggested that ring-cleaving hydrolases are involved in oxygen-independent sterane skeleton degradation. However, the enzymes involved in ring A cleavage of the common intermediate androsta-1,4-diene-3,17-dione have remained unknown. Here, we enriched a ring A hydrolase from cholesterol/nitrate grown Sterolibacterium denitrificans and from Escherichia coli after heterologous expression of its gene. This enzyme specifically cleaves the cyclic 1,3-diketone of the central degradation intermediate, androsta-1,3,17-trione to 1,17-dioxo-2,3-seco-androstan-3-oate (DSAO), a hallmark reaction of anaerobic steroid degradation. The highly conserved ring A hydrolase was identified in all known and many previously unknown steroid-degrading proteobacteria. Using enriched enzymes, we enzymatically produced DSAO from the chemically synthesised androsta-1-en-3,17-dione precursor, allowing the identification of subsequent metabolites involved in ring A degradation. The results obtained suggest the involvement of an additional hydrolase, an aldolase, and a β-oxidation-like cascade for complete ring A degradation to form the three-ring 5,10-seco-1,2,3,4-tetranorandrosta-5,17-dione. The results identified a key enzyme of anaerobic steroid degradation that may serve as a functional marker for monitoring steroid contaminant degradation at anoxic environmental sites.

Active geothermal systems are relatively rare in Antarctica and represent metaphorical islands ideal to study microbial dispersal. In this study, we tested the macro-ecological concept that high dispersal rates result in communities being dominated by either habitat generalists or specialists by investigating the microbial communities on four geographically separated geothermal sites on three Antarctic volcanoes (Mts. Erebus, Melbourne, and Rittman). We found that the microbial communities at higher temperature (max 65°C) sites (Tramway Ridge on Erebus and Rittmann) were unique from each other and were dominated by a variety of novel Archaea from class Nitrososphaeria, while lower temperature (max 50°C) sites (Western Crater on Erebus and Melbourne) had characteristically mesophilic communities (Planctomycetes, Acidobacteriota, etc.) that were highly similar. We found that 97% of the detected microbial taxa were regional habitat specialists, with no generalists, with community assembly driven by high dispersal rates and drift (25% and 30% of community assembly, respectively), not environmental selection. Our results indicate that for microbial communities experiencing high dispersal rates between isolated communities, habitat specialists may tend to out-compete habitat generalists.

Rhizobia and legumes form a symbiotic relationship resulting in the formation of root structures known as nodules, where bacteria fix nitrogen. Legumes release flavonoids that are detected by the rhizobial nodulation (Nod) protein NodD, initiating the transcriptional activation of nod genes and subsequent synthesis of Nod Factors (NFs). NFs then induce various legume responses essential for this symbiosis. Although evidence suggests differential regulation of nodD expression and NF biosynthesis during symbiosis, the necessity of this regulation for the formation of nitrogen-fixing nodules remains uncertain. Here, we demonstrate that deletion of the Rlv3841 NodD regulatory domain results in a constitutively active protein (NodD_FI) capable of activating NF biosynthesis gene expression without the presence of flavonoids. Optimised constitutive expression of nodD_FI or nodD3 in nodD null mutants led to wild-type levels of nodulation and nitrogen fixation in pea and M. truncatula, respectively, indicating that flavonoid-regulated nodD expression is not essential for supporting symbiosis. These findings illustrate that transcriptional control of flavonoid-independent NodD regulators can be employed to drive NF biosynthesis, which holds potential for engineering symbiosis between rhizobia and cereals equipped with reconstituted NF receptors.

Symbiotic cnidarians, such as sea anemones and corals, rely on their mutualistic microalgal partners (Symbiodiniaceae) for survival. Marine heatwaves can disrupt this partnership, and it has been proposed that introducing experimentally evolved, heat-tolerant algal symbionts could enhance host thermotolerance. To test this hypothesis, the sea anemone Exaiptasia diaphana (a coral model) was inoculated with either the heterologous wild type or heat-evolved algal symbiont, Cladocopium proliferum, and homologous wild-type Breviolum minutum. The novel symbioses persisted for 1.5 years and determined holobiont thermotolerance during a simulated summer heatwave. Anemones hosting SS8, one of the six heat-evolved strains tested, exhibited the highest thermotolerance. Notably, anemones hosting the wild-type C. proliferum (WT10) were the second most thermally tolerant group, whereas anemones hosting the heat-evolved SS5 or SS9 strains were among the most thermosensitive. Elevated temperatures led to an increase in the levels of many amino acids and a decrease in tricarboxylic acid (TCA) metabolites in all anemone hosts, potentially indicating an increase in autophagy and a reduction in energy and storage production. Some consistent differences were observed in changes in metabolite levels between anemone groups in response to elevated temperature, suggesting that the algal symbiont influenced host metabolome and nutritional budget.

Plant detritus is abundant in grasslands but decomposes slowly and is relatively nutrient-poor, whereas animal carcasses are labile and nutrient-rich. Recent studies have demonstrated that labile nutrients from carcasses can significantly alter the long-term soil microbial function at an ecosystem scale. However, there is a paucity of knowledge on the functional and structural response and temporal scale of soil microbiomes beneath large herbivore carcasses. This study compared microbiome functions and structures of soil beneath Connochaetes taurinus (hereafter ‘wildebeest’) carcasses at various postmortem intervals of decomposition to matched control samples over 18 months. Microbial functions were compared by their community-level physiological profiles determined by sole-carbon substrate utilisation and structures by metagenomic sequences using 16S rRNA gene markers. Overall metabolism and metabolic diversity remained increased and functionally dissimilar to control soils throughout the experimental period, with successive sole-carbon substrate utilisation observed. Conversely, diversity was initially reduced and structurally dissimilar from the control soil but recovered within the experimental period. The study contributes to the knowledge of carcass decomposition by investigating the long-term soil microbiome dynamics resulting from large herbivore carcasses decomposing in a mesic grassland. Microbial functional succession and ecologically relevant bacterial biomarkers of soil beneath the decomposing carcasses were identified for various postmortem intervals.