Project description:Members of the bacterial phylum Spirochaetes are primarily studied for their commensal and pathogenic roles in animal hosts. However, Spirochaetes are also frequently detected in anoxic hydrocarbon-contaminated environments but their ecological role in such ecosystems has so far remained unclear. Here we provide a functional trait to these frequently detected organisms with an example of a sulfate-reducing, naphthalene-degrading enrichment culture consisting of a sulfate-reducing deltaproteobacterium Desulfobacterium naphthalenivorans and a novel spirochete Rectinema cohabitans. Using a combination of genomic, proteomic, and physiological studies we show that R. cohabitans grows by fermentation of organic compounds derived from biomass from dead cells (necromass). It recycles the derived electrons in the form of H2 to the sulfate-reducing D. naphthalenivorans, thereby supporting naphthalene degradation and forming a simple microbial loop. We provide metagenomic evidence that equivalent associations between Spirochaetes and hydrocarbon-degrading microorganisms are of general importance in hydrocarbon- and organohalide-contaminated ecosystems. We propose that environmental Spirochaetes form a critical component of a microbial loop central to nutrient cycling in subsurface environments. This emphasizes the importance of necromass and H2-cycling in highly toxic contaminated subsurface habitats such as hydrocarbon-polluted aquifers.
Project description:Freshwater ecosystems can be largely affected by neighboring agriculture fields where potential fertilizer nitrate run-off may leach into surrounding water bodies. To counteract this eutrophic driver, farmers often utilize denitrifying woodchip bioreactors (WBRs) in which a consortium of microorganisms convert the nitrate into nitrogen-gases in anoxia, fueled by the degradation of lignocellulose. Polysaccharide-degrading strategies have been well-described for various aerobic and anaerobic systems, including the use of carbohydrate-active enzymes, utilization of lytic polysaccharide monooxygenases (LPMOs) and other redox enzymes, as well as the use of cellulosomes and polysaccharide utilization loci. However, for denitrifying microorganisms, the lignocellulose-degrading strategies remain largely unknown. Here, we have applied a combination of enrichment techniques, gas measurements, multi-omics approaches, and amplicon sequencing of fungal ITS and procaryotic 16S rRNA genes to highlight microbial drivers for lignocellulose transformation in woodchip bioreactors with the aim to provide an in-depth characterization of the indigenous microorganisms and their active enzymes. Our findings highlight a microbial community enriched for lignocellulose-degrading denitrifiers with key players from Giesbergeria, Cellulomonas, Azonexus, and UBA5070, including polysaccharide utilization loci from Bacteroidetes. A wide substrate specificity is observed among the many expressed carbohydrate active enzymes (CAZymes), evidencing a swift degradation of lignocellulose, including even enzymes with auxiliary activities whose functionality is still puzzling under strict anaerobic conditions.