Enterococcus faecalis Uses a Phosphotransferase System Permease and a Host Colonization-Related ABC Transporter for Maltodextrin Uptake

Abstract

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-6Љ-P in the cell. MapP, which dephosphorylates maltose-6=-P, also releases P i from maltotriose-6Љ-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

Enzymes Required for Maltodextrin Catabolism in Enterococcus faecalis Exhibit Novel Activities

“…The higher energetic transport costs can be compensated in bacteria which use a phosphorylase for the catabolism of maltose and maltodextrins. The same kind of "energy saving" also applies for the special case of enterococci and streptococci, which in the first catabolic step dephosphorylate maltose-6=-P and maltotriose-6Љ-P produced during PTS-catalyzed uptake (8,9). Maltose formed directly from maltose-6=-P by MapP or from maltotriose-6Љ-P by the combined action of MapP and MmdH is subsequently phosphorolyzed to glucose and glucose-1-P (Fig.…”

“…EFT41964 of E. faecalis JH2-2 are located upstream from an operon which encodes an ABC transporter catalyzing the uptake of maltotetraose and longer maltooligosaccharides ( Fig. 1) (9). Genes with sequences nearly identical to those of mmgT to EFT41964 are found in all E. faecalis strains for which the genome has been sequenced, and they are usually annotated as ␣-amylase genes.…”

“…In contrast to maltotetraose, but similar to maltose (8), maltotriose is taken up and phosphorylated by the PTS permease MalT. Intracellular maltotriose-6Љ-P is subsequently dephosphorylated to maltotriose by the phosphatase MapP (9), thus making it a substrate for EFT41964. Complementation of the mutant strain with the EFT41964 wild-type allele expressed from the agmatine-inducible aguB promoter restored growth on maltotriose and maltotetraose, confirming that EFT41964 is essential for their catabolism (Fig.…”

“…5). In contrast to maltotriose, which is mainly taken up by the PTS permease MalT, isopanose is transported by E. faecalis via the MdxEFG-MsmX ABC transporter (9), and the wild-type strain grows on the triose. Interestingly, deletion of mmdH prevented growth on isopanose (Fig.…”

“…5). Panose is taken up by the maltodextrin ABC transporter (9). In contrast to the wild-type strain, a mutant deleted for GenBank accession no.…”