FEMS microbiology ecology最新文献

Iron cycling including phototrophic Fe(II) oxidation has been observed in multiple permanently stratified meromictic lakes, yet less focus has been on dimictic lakes which seasonally overturn and are vastly more common. Here we investigated iron cycling in a dimictic lake, Großes Heiliges Meer in northwest Germany, using 16S rRNA amplicon sequencing, as well as in-situ and lab-based experiments. Bacterial community composition in the lake follows geochemical gradients and differs markedly between oxic and anoxic conditions. Potential iron-metabolizing bacteria were found mostly in anoxic conditions at 7 and 8 m depth and were comprised of taxa from the genera Chlorobium, Thiodictyon, Sideroxydans, Geobacter and Rhodoferrax. We were able to recreate active iron cycling 1) with an ex-situ microbial community from 8 m depth and 2) with a successful microbial enrichment culture from 7 m depth. Varying the light and organic carbon availability in lab-based experiments showed that Fe(III) reduction overshadows Fe(II) oxidation leading to a cryptic iron cycle. Overall we could demonstrate that microbial iron cycling can be a key biogeochemical process in dimictic lakes despite regular disturbance, and that complex environmental factors like organic substrates control the balance between Fe(II) oxidation and Fe(III) reduction.

Environmental factors like diet and antibiotics modulate the gut microbiota in early life. During weaning, gut microbiota progressively diversifies through exposure to non-digestible carbohydrates (NDCs) from diet, while antibiotic perturbations might disrupt this process. Supplementing an infant's diet with prebiotic NDCs may mitigate the adverse effects of antibiotics on gut microbiota development. This study evaluated the influence of supplementation with 2-fucosyllactose (2'-FL), galacto-oligosaccharides (GOS), or isomalto/malto-polysaccharides containing 87% of α(1→6) linkages (IMMP-87), on the recovery of antibiotic-perturbed microbiota. The TIM-2 in vitro colon model inoculated with fecal microbiota of nine-month-old infants was used to simulate the colon of weaning infants exposed to the antibiotics amoxicillin/clavulanate or azithromycin. Both antibiotics induced changes in microbiota composition, with no signs of recovery in azithromycin-treated microbiota within 72 h. Moreover, antibiotic exposure affected microbiota activity, indicated by a low valerate production, and azithromycin treatment was associated with increased succinate production. The IMMP-87 supplementation promoted the compositional recovery of amoxicillin/clavulanate-perturbed microbiota, associated with the recovery of Ruminococcus, Ruminococcus gauvreauii group, and Holdemanella. NDC supplementation did not influence compositional recovery of azithromycin-treated microbiota. Irrespective of antibiotic exposure, supplementation with 2'-FL, GOS, or IMMP-87 enhanced microbiota activity by increasing short-chain fatty acids production (acetate, propionate, and butyrate).

Lytic bacteriophages ('phages') can limit bacterial densities and shape community structure, either directly through lysis or indirectly through costs to resistance. However, phages have also been reported to have no, and in some cases even positive, effects on host densities. Here, we investigate the mechanisms behind an increase in host density in Variovorax sp. populations following a fixation of resistance that was maintained after phage extinction. Our results demonstrate that the density increase was a genetic trait coinciding with resistance emergence. Growth curves showed that phage resistance shifted population growth curves such that density was higher in the death-phase. This density-increasing effect of resistance had important implications for community structure with phage resistant Variovorax decreasing the density of a conspecific. That resistance to lytic phage can increase host densities has implications for wider ecology and phage therapy where lytic phages are presumed to have negative effects on their hosts.

Unlike in eusocial bees where the identity, acquisition, and function of symbiotic microbes are well understood, little is known about the relationships formed between solitary bees and bacteria. Assessing the potential role of microbes in solitary bee health is important, especially in the face of global bee declines. Early evidence suggests solitary bee microbiomes differ between bee species and development stages, but the reported bacteria are often indistinguishable from environmental taxa. Here, we use metabarcoding of the 16S rRNA gene to characterize the bacterial communities associated with solitary resin bee Megachile tosticauda. We describe the microbiome at different life cycle stages, and within pollen provisions, and investigate indirect inheritance from nesting substrate upon eclosion. The microbiome of adult M. tosticauda was consistent between samples, and the bacterial composition of larval pollen supplies changed with progressing larval development. In wild adults and pollen provisions, the genus Acinetobacter-a common nectar associate-dominated the communities. In prepupae and frass, Tyzzerella dominated, a genus that has been found in a number of other immature bee systems. Intriguingly, while wild adults did not harbour Tyzzerella, all bees that had newly emerged from the nest did. The combined observations show that M. tosticauda acquire their bacterial community from the environment, and Tyzzerella may represent a beneficial symbiont for mature brood.

Particle-attached bacterial (PAB) communities play pivotal roles in water organic matter decomposition, nutrient cycling, and the natural self-purification processes. However, we know little about their responses to seasonal environmental fluctuations, under eutrophication in reservoir ecosystems. In this study, we studied the shifts of PAB communities to seasonal environmental fluctuations in tropical China. Trophic state index (TSI) indicated that the studied reservoirs ranged from mesotrophic to eutrophic state with a gradual increase in TSI from 31 to 58. In eutrophic reservoirs, Cyanobacteria, especially Raphidiopsis raciborskii, significantly increased in its relative abundance from the wet to dry season, but Synechococcales and Microcystaceae decreased. In contrast, the relative abundance of Clostridia, Bacilli, Coriobacteriia, Enterobacteriales, and Vibrionales were more susceptible to seasonal environmental fluctuations in mesotrophic than eutrophic reservoirs. PAB co-occurrence relationships in mesotrophic reservoirs varied more greatly in response to seasonal environmental fluctuations, compared with eutrophic reservoirs, in terms of topological properties of connectedness, average degree, robustness, and vulnerability. Our results further demonstrated that the seasonal stability of PAB co-occurrence relationships was strongly correlative with TSI through mediating key bacterial taxa and community biodiversity. We proposed that eutrophication dramatically reduced the seasonal variation of PAB community compositions and co-occurring relationships in reservoir ecosystems.

This study aimed to identify factors influencing bacterial diversity in the Meuse River watershed by analyzing 42 locations sampled in spring and summer 2019, combined with biweekly sampling of one mid-stream location for a year. Bacterial community composition (BCC) was assessed in the small (SF; <5 µm) and large fractions (LF; ≥5 µm,), alongside physico-chemical parameters. LF consistently exhibited greater alpha diversity than SF. During the spatial campaigns, alpha diversity increased downstream in spring with high discharge, and BCC differed significantly between headwaters and the main river. Along this axis, several genera, Flavobacterium, Limnohabitans, and Aquirufa stood out as indicators of good water quality. Rhodoferax, another taxon indicative of good water quality, prevailed in the headwaters and during winter. In contrast, two cyanobacteria genera indicators of poor river quality, Microcystis PCC 7914 and Cyanobium PCC 6307, peaked in summer. BCC in spring and summer temporal samples aligned with spatial ones, while winter and autumn samples had distinct BCC. Finally, season, temperature, and distance from river mouth were the main driving parameters of beta diversity, outweighing the effect of fraction size on the BCC. These findings reinforce the notion that local conditions exert significant influence on bacterial communities in rivers.

Bacillus subtilis a Gram-positive soil-dwelling bacterium known for its wide range of bioactive secondary metabolites. The lipopeptide plipastatin produced by most B. subtilis isolates have been shown to exhibit potent antifungal activity against plant pathogenic fungi. While the effect of these antifungal compounds are well studied in the context of biocontrol, much less is known of their role in the environment, which also harbor nonproducing strains of these compounds. Fusarium species produce multiple antibacterial compounds resulting in dysbiosis of the plant-associated microbiome and inhibition of plant beneficial bacteria like B. subtilis. While plipastatin is expected to be important for survival of B. subtilis, not all isolates carry the biosynthetic gene cluster for plipastatin suggesting that the protective effect of plipastatin might be shared. In this study, we investigated the protective effect of plipastatin against Fusarium oxysporum in a coculture using a producer and a nonproducer isolate of plipastatin. We tested the survival of single and cocultured strains under Fusarium challenge in liquid media and solid agar plates to dissect the influence of spatial structure. Our results highlights that plipastatin protects the nonproducer strain in a density-dependent manner.

Research on microbial biogeography has revealed key patterns like the diversity-area relationship and distance-decay of similarity. However, how habitat size affects bacterial diversity in freshwater environments remains largely unclear. Here, we characterize bacterial communities in the littoral zones of ten mountain lakes in the Sierra Nevada, California, ranging in surface area from 0.92 to 71.72 hectares. Despite significant habitat size effects on community composition, dominant bacterial phyla were shared across lakes. We found no evidence for diversity-area relationships, either in single samples (alpha diversity) or cumulative lake-level samples (within-lake gamma diversity), when accounting for environmental variation. Moreover, within-lake beta diversity showed little spatial structuring, with similar bacterial community composition across samples regardless of geographic distance. Gamma diversity did not reach saturation with our sample size, and lake size had no effect on the predicted sample size necessary to reach gamma diversity saturation. Our findings offer new insights into diversity-area dynamics and spatial structuring by investigating alpha, beta, and gamma diversity in freshwater environments. Notably, individual water samples captured much of the bacterial community, with strong correlations between alpha and gamma diversity. These results advance our understanding of microbial biogeography and inform sampling designs for characterizing bacterial diversity in freshwater ecosystems.

The Betaproteobacterium Thiobacillus denitrificans (ATCC 25259) oxidizes Fe(II) while reducing nitrate, yet its capacity for autotrophic growth as a nitrate-reducing Fe(II)-oxidizer remains uncertain. This study explored this capacity through cultivation experiments across multiple transfers, using growth medium with Fe(II) and nitrate as sole electron donor and acceptor, respectively. This setup necessitated nitrate reduction coupled to Fe(II) oxidation as the primary energy-yielding mechanism and Fe(II) as the exclusive electron donor for CO2 fixation and biomass production. Thiosulfate/nitrate pre-grown T. denitrificans oxidized 42% of 10 mM Fe(II), reduced 54% of 3.5 mM nitrate, and accumulated 1.6 mM nitrite, but showed no cell growth. Subsequent transfers from this Fe(II)/nitrate culture to fresh medium with Fe(II) and nitrate showed no nitrate-reducing Fe(II) oxidation or population growth. While bacterial activity (Fe(II) oxidation, nitrate reduction) occurred in the first transfer from thiosulfate/nitrate to Fe(II)/nitrate, nitrite was produced, further reacting with Fe(II) abiotically (chemodenitrification). A kinetic model assessed enzymatic versus abiotic Fe(II) oxidation, revealing enzymatic oxidation accounted for twice as much (ca. 70%) as abiotic denitrification (ca. 30%) within 22 days. These findings suggest T. denitrificans performs the first step of denitrification with Fe(II) as an electron donor but does not achieve autotrophic growth under these conditions.

Studying bacteria in anaerobic digestion (AD) is crucial for optimising microbial processes. While abundant taxa are often studied, less abundant groups may harbour novel metabolic potential. This study fills the gap by focusing on the Planctomycetota phylum, known to encode diverse carbohydrate-active enzymes (CAZymes). Despite their common presence in diverse aerobic and anaerobic environments, their role in AD is relatively unexplored. We utilised both culture-dependent and culture-independent techniques to investigate the phylogenetic and metabolic diversity of Planctomycetota within AD reactors. Our findings revealed that among the diverse planctomycetotal operational taxonomic units present, only a few are prevalent and abundant community members. Planctomycetota share functional traits with e.g. Verrucomicrobiota exhibiting distinct CAZyme gene repertoires that indicates specialisation in degrading algal polysaccharides and glycoproteins. To explore the planctomycetotal metabolic capabilities, we monitored their presence in algal-fed digesters. Additionally, we isolated a strain from mucin-based medium, revealing its genetic potential for a mixotrophic lifestyle. Based on the genomic analysis, we propose to introduce the Candidatus Luxemburgiella decessa gen. nov. sp. nov., belonging to the Thermoguttaceae family within the Pirellulales order of the Planctomycetia class. This study enhances our understanding of Planctomycetota in AD by highlighting their phylogenetic diversity and metabolic capabilities.