RRC ID 50778
Author Keung HY, Li TK, Sham LT, Cheung MK, Cheung PCK, Kwan HS.
Title Mechanistic Study of Utilization of Water-Insoluble Saccharomyces cerevisiae Glucans by Bifidobacterium breve Strain JCM1192.
Journal Appl Environ Microbiol
Abstract Bifidobacteria exert beneficial effects on hosts and are extensively used as probiotics. However, due to the genetic inaccessibility of these bacteria, little is known about their mechanisms of carbohydrate utilization and regulation. Bifidobacterium breve strain JCM1192 can grow on water-insoluble yeast (Saccharomyces cerevisiae) cell wall glucans (YCWG), which were recently considered as potential prebiotics. According to the results of 1H nuclear magnetic resonance (NMR) spectrometry, the YCWG were composed of highly branched (1→3,1→6)-β-glucans and (1→4,1→6)-α-glucans. Although the YCWG were composed of 78.3% β-glucans and 21.7% α-glucans, only α-glucans were consumed by the B. breve strain. The ABC transporter (malEFG1) and pullulanase (aapA) genes were transcriptionally upregulated in the metabolism of insoluble yeast glucans, suggesting their potential involvement in the process. A nonsense mutation identified in the gene encoding an ABC transporter ATP-binding protein (MalK) led to growth failure of an ethyl methanesulfonate-generated mutant with yeast glucans. Coculture of the wild-type strain and the mutant showed that this protein was responsible for the import of yeast glucans or their breakdown products, rather than the export of α-glucan-catabolizing enzymes. Further characterization of the carbohydrate utilization of the mutant and three of its revertants indicated that this mutation was pleiotropic: the mutant could not grow with maltose, glycogen, dextrin, raffinose, cellobiose, melibiose, or turanose. We propose that insoluble yeast α-glucans are hydrolyzed by extracellular pullulanase into maltose and/or maltooligosaccharides, which are then transported into the cell by the ABC transport system composed of MalEFG1 and MalK. The mechanism elucidated here will facilitate the development of B. breve and water-insoluble yeast glucans as novel synbiotics.IMPORTANCE In general, Bifidobacterium strains are genetically intractable. Coupling classic forward genetics with next-generation sequencing, here we identified an ABC transporter ATP-binding protein (MalK) responsible for the import of insoluble yeast glucan breakdown products by B. breve JCM1192. We demonstrated the pleiotropic effects of the ABC transporter ATP-binding protein in maltose/maltooligosaccharide, raffinose, cellobiose, melibiose, and turanose transport. With the addition of transcriptional analysis, we propose that insoluble yeast glucans are broken down by extracellular pullulanase into maltose and/or maltooligosaccharides, which are then transported into the cell by the ABC transport system composed of MalEFG1 and MalK. The mechanism elucidated here will facilitate the development of B. breve and water-insoluble yeast glucans as novel synbiotics.
Volume 83(7)
Published 2017-4-1
DOI 10.1128/AEM.03442-16
PII AEM.03442-16
PMID 28115383
PMC PMC5359474
MeSH ATP-Binding Cassette Transporters / genetics ATP-Binding Cassette Transporters / metabolism Bacterial Proteins / genetics Bacterial Proteins / metabolism Bifidobacterium breve / drug effects Bifidobacterium breve / genetics Bifidobacterium breve / growth & development Bifidobacterium breve / metabolism* Cell Wall / chemistry Cell Wall / metabolism Dextrins / pharmacology Glucans / metabolism* Glycogen / pharmacology Glycoside Hydrolases / genetics Glycoside Hydrolases / metabolism Hydrolysis Maltose / metabolism Maltose / pharmacology Mutation Saccharomyces cerevisiae / chemistry* Solubility Synbiotics Water beta-Glucans / metabolism
IF 4.016
Times Cited 1
Resource
General Microbes JCM 1192