Dataset Information

Enterococcus faecalis Maltodextrin Gene Regulation by Combined Action of Maltose Gene Regulator MalR and Pleiotropic Regulator CcpA.

ABSTRACT: 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 ^- ?ccpA 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.IMPORTANCE Enterococcus 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.

SUBMITTER: Grand M

PROVIDER: S-EPMC7480380 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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Enterococcus faecalis Maltodextrin Gene Regulation by Combined Action of Maltose Gene Regulator MalR and Pleiotropic Regulator CcpA.

Grand Maxime M Riboulet-Bisson Eliette E Deutscher Josef J Hartke Axel A Sauvageot Nicolas N

Applied and environmental microbiology 20200901 18

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-m ...[more]

PMID: 32680872

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Project description:Maltose and maltodextrins are formed during the degradation of starch or glycogen. Maltodextrins are composed of a mixture of maltooligosaccharides formed by α-1,4- but also some α-1,6-linked glucosyl residues. The α-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 α-1,4-linked maltooligosaccharides. The purified enzyme converts even-numbered α-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 α-1,6-glucosidase, because it converts the maltotriose isomer isopanose into maltose and glucose. In addition, E. faecalis contains a glucose-producing α-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 α-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 α-1,4- and α-1,6-linked maltooligosaccharides. We found that one of them functions as a maltose-producing α-glucosidase with relaxed linkage specificity (α-1,4 and α-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.

Project description:Maltodextrin is a mixture of maltooligosaccharides, which are produced by the degradation of starch or glycogen. They are mostly composed of ?-1,4- and some ?-1,6-linked glucose residues. Genes presumed to code for the Enterococcus faecalis maltodextrin transporter were induced during enterococcal infection. We therefore carried out a detailed study of maltodextrin transport in this organism. Depending on their length (3 to 7 glucose residues), E. faecalis takes up maltodextrins either via MalT, a maltose-specific permease of the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS), or the ATP binding cassette (ABC) transporter MdxEFG-MsmX. Maltotriose, the smallest maltodextrin, is primarily transported by the PTS permease. A malT mutant therefore exhibits significantly reduced growth on maltose and maltotriose. The residual uptake of the trisaccharide is catalyzed by the ABC transporter, because a malT mdxF double mutant no longer grows on maltotriose. The trisaccharide arrives as maltotriose-6?-P in the cell. MapP, which dephosphorylates maltose-6'-P, also releases Pi from maltotriose-6?-P. Maltotetraose and longer maltodextrins are mainly (or exclusively) taken up via the ABC transporter, because inactivation of the membrane protein MdxF prevents growth on maltotetraose and longer maltodextrins up to at least maltoheptaose. E. faecalis also utilizes panose and isopanose, and we show for the first time, to our knowledge, that in contrast to maltotriose, its two isomers are primarily transported via the ABC transporter. We confirm that maltodextrin utilization via MdxEFG-MsmX affects the colonization capacity of E. faecalis, because inactivation of mdxF significantly reduced enterococcal colonization and/or survival in kidneys and liver of mice after intraperitoneal infection.IMPORTANCE Infections by enterococci, which are major health care-associated pathogens, are difficult to treat due to their increasing resistance to clinically relevant antibiotics, and new strategies are urgently needed. A largely unexplored aspect is how these pathogens proliferate and which substrates they use in order to grow inside infected hosts. The use of maltodextrins as a source of carbon and energy was studied in Enterococcus faecalis and linked to its virulence. Our results demonstrate that E. faecalis can efficiently use glycogen degradation products. We show here that depending on the length of the maltodextrins, one of two different transporters is used: the maltose-PTS transporter MalT, or the MdxEFG-MsmX ABC transporter. MdxEFG-MsmX takes up longer maltodextrins as well as complex molecules, such as panose and isopanose.

Dataset Information

Enterococcus faecalis Maltodextrin Gene Regulation by Combined Action of Maltose Gene Regulator MalR and Pleiotropic Regulator CcpA.

Publications

Enterococcus faecalis Maltodextrin Gene Regulation by Combined Action of Maltose Gene Regulator MalR and Pleiotropic Regulator CcpA.

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