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PUL0327 |
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28455338, Appl Environ Microbiol. 2017 Jun 16;83(13):e00038-17. doi: 10.1128/AEM.00038-17. Print 2017 Jul 1. |
| | Enzymes Required for Maltodextrin Catabolism in Enterococcus faecalis Exhibit Novel Activities. |
| | Joyet P, Mokhtari A, Riboulet-Bisson E, Blancato VS, Espariz M, Magni C, Hartke A, Deutscher J, Sauvageot N |
| | Maltose and maltodextrins are formed during the degradation of starch or glycogen. Maltodextrins are composed of a mixture of maltooligosaccharides formed by alpha-1,4- but also some alpha-1,6-linked glucosyl residues. The alpha-1,6-linked glucosyl residues are derived from branching points in the polysaccharides. In Enterococcus faecalis, maltotriose is mainly transported and phosphorylated by a phosphoenolpyruvate:carbohydrate phosphotransferase system. The formed maltotriose-6''-phosphate is intracellularly dephosphorylated by a specific phosphatase, MapP. In contrast, maltotetraose and longer maltooligosaccharides up to maltoheptaose are taken up without phosphorylation via the ATP binding cassette transporter MdxEFG-MsmX. We show that the maltose-producing maltodextrin hydrolase MmdH (GenBank accession no. EFT41964) in strain JH2-2 catalyzes the first catabolic step of alpha-1,4-linked maltooligosaccharides. The purified enzyme converts even-numbered alpha-1,4-linked maltooligosaccharides (maltotetraose, etc.) into maltose and odd-numbered (maltotriose, etc.) into maltose and glucose. Inactivation of mmdH therefore prevents the growth of E. faecalis on maltooligosaccharides ranging from maltotriose to maltoheptaose. Surprisingly, MmdH also functions as a maltogenic alpha-1,6-glucosidase, because it converts the maltotriose isomer isopanose into maltose and glucose. In addition, E. faecalis contains a glucose-producing alpha-1,6-specific maltodextrin hydrolase (GenBank accession no. EFT41963, renamed GmdH). This enzyme converts panose, another maltotriose isomer, into glucose and maltose. A gmdH mutant had therefore lost the capacity to grow on panose. The genes mmdH and gmdH are organized in an operon together with GenBank accession no. EFT41962 (renamed mmgT). Purified MmgT transfers glucosyl residues from one alpha-1,4-linked maltooligosaccharide molecule to another. For example, it catalyzes the disproportionation of maltotriose by transferring a glucosyl residue to another maltotriose molecule, thereby forming maltotetraose and maltose together with a small amount of maltopentaose.IMPORTANCE The utilization of maltodextrins by Enterococcus faecalis has been shown to increase the virulence of this nosocomial pathogen. However, little is known about how this organism catabolizes maltodextrins. We identified two enzymes involved in the metabolism of various alpha-1,4- and alpha-1,6-linked maltooligosaccharides. We found that one of them functions as a maltose-producing alpha-glucosidase with relaxed linkage specificity (alpha-1,4 and alpha-1,6) and exo- and endoglucosidase activities. A third enzyme, which resembles amylomaltase, exclusively transfers glucosyl residues from one maltooligosaccharide molecule to another. Similar enzymes are present in numerous other Firmicutes, such as streptococci and lactobacilli, suggesting that these organisms follow the same maltose degradation pathway as E. faecalis. |
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32680872, Appl Environ Microbiol. 2020 Sep 1;86(18):e01147-20. doi: 10.1128/AEM.01147-20. Print 2020 Sep 1. |
| | Enterococcus faecalis Maltodextrin Gene Regulation by Combined Action of Maltose Gene Regulator MalR and Pleiotropic Regulator CcpA. |
| | Grand M, Riboulet-Bisson E, Deutscher J, Hartke A, Sauvageot N |
| | Enterococci are Gram-positive bacteria present in the healthy human microbiota, but they are also a leading cause of nosocomial infections. Maltodextrin utilization by Enterococcus faecalis has been identified as an important factor for colonization of mammalians hosts. Here, we show that the LacI/GalR transcriptional regulator MalR, the maltose gene regulator, is also the main regulator of the operons encoding an ABC transporter (mdxEFG) and three metabolic enzymes (mmdH-gmdH-mmgT) required for the uptake and catabolism of maltotetraose and longer maltodextrins. The utilization of maltose and maltodextrins is consequently coordinated and induced by the disaccharide maltose, which binds to MalR. Carbon catabolite repression of the mdxEFG and mmdH-gmdH-mmgT operons is mediated by both P-Ser-HPr/MalR and P-Ser-HPr/CcpA. The latter complex exerts only moderate catabolite repression, which became visible when comparing maltodextrin operon expression levels of a malR(-) mutant (with a mutant allele for the malR gene) and a malR(-) DeltaccpA double mutant grown in the presence of maltose, which is transported via a phosphotransferase system and, thus, favors the formation of P-Ser-HPr. Moreover, maltodextrin transport via MdxEFG slows rapidly when glucose is added, suggesting an additional regulation via inducer exclusion. This complex regulation of metabolic operons likely allows E. faecalis to fine-tune gene expression in response to changing environmental conditions.IMPORTANCEEnterococcus faecalis represents a leading cause of hospital-acquired infections worldwide. Several studies highlighted the importance of carbohydrate metabolism in the infection process of this bacterium. The genes required for maltodextrin metabolism are particularly induced during mouse infection and, therefore, should play an important role for pathogenesis. Since no data were hitherto available concerning the regulation of expression of the maltodextrin operons, we have conducted experiments to study the underlying mechanisms. |
