RESUMEN
The degradation of glycosaminoglycans (GAGs) by intestinal bacteria is critical for their colonization in the human gut and the health of the host. Both colonic Bacteroides and Firmicutes have been reported to degrade GAGs; however, the enzymatic details of the latter remain largely unknown. Our bioinformatic analyses of fecal Firmicutes revealed that their genomes, especially Hungatella hathewayi strains, are an abundant source of putative GAG-specific catabolic enzymes. Subsequently, we isolated a Firmicutes strain, H. hathewayi N2-326, that can catabolize various GAGs. While H. hathewayi N2-326 was as efficient in utilizing chondroitin sulfate A (CSA) and dermatan sulfate as Bacteroides thetaiotaomicron, a well-characterized GAG degrader, it outperformed B. thetaiotaomicron in assimilating hyaluronic acid. Unlike B. thetaiotaomicron, H. hathewayi N2-326 could not utilize heparin. The chondroitin lyase activity of H. hathewayi N2-326 was found to be present predominantly in the culture supernatant. Genome sequence analysis revealed three putative GAG lyases, but only the HH-chondroitin ABC lyase was upregulated in the presence of CSA. In addition, five CAZyme gene clusters containing GAG metabolism genes were significantly upregulated when grown on CSA. Further characterization of the recombinant HH-chondroitin ABC lyase revealed that it cleaves GAGs predominantly in an exo-mode to produce unsaturated disaccharides as the primary hydrolytic product while exhibiting a higher specific activity than reported chondroitin ABC lyases. HH-chondroitin ABC lyase represents the first characterized chondroitin lyase from intestinal Firmicutes and offers a viable commercial option for the production of chondroitin, dermatan, and hyaluronan oligosaccharides and also for potential medical applications. IMPORTANCE An increased understanding of GAG metabolism by intestinal bacteria is critical in identifying the driving factors for the composition, modulation, and homeostasis of the human gut microbiota. In addition, GAG-depolymerizing polysaccharide lyases are highly desired enzymes for the production of GAG oligosaccharides and as therapeutics. At present, the dissection of the enzymatic machinery for GAG degradation is highly skewed toward Bacteroides. In this study, we have isolated an efficient GAG-degrading Firmicutes bacterium from human feces and characterized the first chondroitin ABC lyase from a Firmicutes, which complements the fundamental knowledge of GAG utilization in the human colon. The genomic and transcriptomic analysis of the bacterium shows that Firmicutes might use a distinct approach to catabolize GAGs from that used by Bacteroides. The high specific activity of the characterized chondroitin ABC lyase aids future attempts to develop a commercial chondroitinase for industrial and medicinal applications.
Asunto(s)
Condroitina ABC Liasa , Glicosaminoglicanos , Humanos , Bacteroides/genética , Bacteroides/metabolismo , Condroitina ABC Liasa/química , Condroitina ABC Liasa/genética , Condroitina ABC Liasa/metabolismo , Sulfatos de Condroitina/química , Sulfatos de Condroitina/metabolismo , Firmicutes/metabolismo , Glicosaminoglicanos/química , Glicosaminoglicanos/metabolismo , Oligosacáridos/química , Especificidad por Sustrato , Intestinos/metabolismoRESUMEN
Glycosaminoglycans (GAGs) are consistently present in the human colon in free forms and as part of proteoglycans. Their utilization is critical for the colonization and proliferation of gut bacteria and also the health of hosts. Hence, it is essential to determine the GAG-degrading members of the gut bacteria and their enzymatic machinery for GAG depolymerization. In this review, we have summarized the reported GAG utilizers from Bacteroides and presented their polysaccharide utilization loci (PUL) and related enzymatic machineries for the degradation of chondroitin and heparin/heparan sulfate. Although similar comprehensive knowledge of GAG degradation is not available for other gut phyla, we have specified recently isolated GAG degraders from gut Firmicutes and Proteobacteria, and analyzed their genomes for the presence of putative GAG PULs. Deciphering the precise GAG utilization mechanism for various phyla will augment our understanding of their effects on human health.
Asunto(s)
Microbioma Gastrointestinal , Bacterias/genética , Bacterias/metabolismo , Bacteroides/metabolismo , Glicosaminoglicanos/metabolismo , Humanos , Polisacáridos/metabolismoRESUMEN
Phytoestrogens are a class of plant produced polyphenolic compounds with diphenolic structure, which is similar to 17ß-estradiol. These phytoestrogens preferentially bind to estrogen receptors, however, with weak affinity. Recently, many studies have found that these phytoestrogens can be transformed by gut microbiota through novel enzymatic reactions into metabolites with altered bioactivity. Recent studies have also implied that these metabolites could possibly modulate the host gut ecosystem, gene expression, metabolism and the immune system. Thus, isolating gut microbes capable of biotransforming phytoestrogens and characterizing the novel enzymatic reactions involved are principal to understand the mechanisms of beneficial effects brought by gut microbiota and their metabolism on phytoestrogens, and to provide the theoretical knowledge for the development of functional probiotics. In the present review, we summarized works on gut microbial biotransformation of phytoestrogens, including daidzin (isoflavone), phenylnaringenin (prenylflavonoid), lignans, resveratrol (stilbene) and ellagitannins. We mainly focus on gut bacterial isolation, metabolic pathway characterization, and the bidirectional interaction of phytoestrogens with gut microbes to illustrate the novel metabolic capability of gut microbiota and the methods used in these studies.