Catabolism of sialic acids in an environmental microbial community

In vitro effects of structurally diverse low molecular weight chondroitin sulfates on gut microbiota and metabolome

In this study, low molecular weight chondroitin sulfates (LMCSs) with different structures, named LMCSO, LMCSD, and LMCSH, were prepared by oxidative degradation, deamidation cleavage, and hydrothermal depolymerization, respectively. In vitro fermentation modeling was used to study the effects of CS and LMCSs on gut microbiota and metabolite composition. The degree of carbohydrate metabolism was in the order of CS > LMCSH > LMCSO > LMCSD. Significantly, GlcA in chondroitin-6-sulfate (CSC) was more readily utilized by gut microbiota during fermentation, and this trend was more pronounced in LMCSs. The LMCSs group notably increased microbial richness and evenness, especially in the LMCSD group. Bacteroides fragilis was identified as a potential primary degrader of CS and LMCSs through species-level analysis. The abundance of Escherichia-Shigella was reduced by LMCSs, and short-chain fatty acids production was enhanced, particularly by LMCSO, while the production of beneficial metabolites such as N-acetyl-D-Glucosamine 6-Phosphate (GlcNAc-6P), lactate, and progesterone was stimulated. Among these, the metabolism of the key metabolite GlcNAc-6P was significantly and positively correlated with the abundance of Bacteroides, Clostridium_sensu_stricto_1, and Parabacteroides. Exploring the mechanisms by which gut microbiota metabolize LMCSs with different structures can provide theoretical support for the targeted preparation of LMCSs that modulate the gut microbiota.

Metagenomic survey reveals global distribution and evolution of microbial sialic acid catabolism

Sialic acids comprise a varied group of nine-carbon amino sugars found mostly in humans and other higher metazoans, playing major roles in cell interactions with external environments as well as other cells. Microbial sialic acid catabolism (SAC) has long been considered a virulence determinant, and appears to be mainly the purview of pathogenic and commensal bacterial species associated with eukaryotic hosts. Here, we used 2,521 (pre-)assembled metagenomes to evaluate the distribution of SAC in microbial communities from diverse ecosystems and human body parts. Our results demonstrated that microorganisms possessing SAC globally existed in non-host associated environments, although much less frequently than in mammal hosts. We also showed that the ecological significance and taxonomic diversity of microbial SAC have so far been largely underestimated. Phylogenetic analysis revealed a strong signal of horizontal gene transfer among distinct taxa and habitats, and also suggested a specific ecological pressure and a relatively independent evolution history in environmental communities. Our study expanded the known diversity of microbial SAC, and has provided the backbone for further studies on its ecological roles and potential pathogenesis.

Turnover of the extracellular polymeric matrix of granules performing biological phosphate removal

Polyphosphate accumulating organisms (PAOs) are responsible for enhanced biological phosphate removal (EBPR) from wastewater, where they grow embedded in a matrix of extracellular polymeric substances (EPS). EPSs comprise a mixture of biopolymers like polysaccharides or (glyco)proteins. Despite previous studies, little is known about the dynamics of EPS in mixed cultures, and their production by PAOs and potential consumption by flanking microbes. EPSs are biodegradable and have been suggested to be a substrate for other organisms in the community. Studying EPS turnover can help elucidate their biosynthesis and biodegradation cycles. We analyzed the turnover of proteins and polysaccharides in the EPS of an enrichment culture of PAOs relative to the turnover of internal proteins. An anaerobic-aerobic sequencing batch reactor (SBR) simulating EBPR conditions was operated to enrich for PAOs. After achieving a stable culture, carbon source was switched to uniformly ¹³C-labeled acetate. Samples were collected at the end of each aerobic phase. EPSs were extracted by alkaline treatment. ¹³C enrichment in proteins and sugars (after hydrolysis of polysaccharides) in the extracted EPS were measured by mass spectrometry. The average turnover rate of sugars and proteins (0.167 and 0.192 d^-1 respectively) was higher than the expected value based on the solid removal rate (0.132 d^-1), and no significant difference was observed between intracellular and extracellular proteins. This indicates that EPS from the PAO enriched community is not selectively degraded by flanking populations under stable EBPR process conditions. Instead, we observed general decay of biomass, which corresponds to a value of 0.048 d^-1. KEY POINTS: • Proteins showed a higher turnover rate than carbohydrates. • Turnover of EPS was similar to the turnover of intracellular proteins. • EPS is not preferentially consumed by flanking populations.