Abstract
Enterococcus faecium is a gut commensal of humans and animals. In the intestinal tract, E. faecium will have access to a wide variety of carbohydrates, including maltodextrins and maltose, which are the sugars that result from the enzymatic digestion of starch by host-derived and microbial amylases. In this study, we identified the genetic determinants for maltodextrin utilization of E. faecium E1162. We generated a deletion mutant of the mdxABCD-pulA gene cluster that is homologous to maltodextrin uptake genes in other Gram-positive bacteria, and a deletion mutant of the mdxR gene, which is predicted to encode a LacI family regulator of mdxABCD-pulA. Both mutations impaired growth on maltodextrins but had no effect on the growth on maltose and glucose. Comparative transcriptome analysis showed that eight genes (including mdxABCD-pulA) were expressed at significantly lower levels in the isogenic ΔmdxR mutant strain compared to the parental strain when grown on maltose. Quantitative real-time RT-PCR confirmed the results of transcriptome analysis and showed that the transcription of a putative maltose utilization gene cluster is induced in a semi-defined medium supplemented with maltose but is not regulated by MdxR. Understanding the maltodextrin metabolism of E. faecium could yield novel insights into the underlying mechanisms that contribute to the gut commensal lifestyle of E. faecium.
Highlights
Enterococci are facultative anaerobic Gram-positive bacteria commonly found in the gastrointestinal tracts of humans and animals [1]
A search of the E1162 genome for the orthologs of the L. monocytogenes and B. subtilis maltodextrin utilization proteins led to the identification of a gene cluster, that is predicted to encode maltose/maltodextrin ATP-binding cassette (ABC) transporter proteins and a neopullulanase which is predicted to hydrolyze the α-1,4 linkages in starch
We have identified the genetic determinants of E. faecium that contribute to its ability to metabolize maltodextrin which is present as a breakdown product of starch in the digestive tract of humans and animals
Summary
Enterococci are facultative anaerobic Gram-positive bacteria commonly found in the gastrointestinal tracts of humans and animals [1]. In the last twenty years, E. faecium has emerged as a clinical pathogen of major importance. This development has been linked to its ability to efficiently acquire antibiotic resistance genes and genetic elements that may contribute to virulence [2,3]. The ability of both commensal and clinical E. faecium strains to effectively colonize the intestinal tract determines the ecological success of this species. The metabolism of carbohydrates in the complicated food webs of the mammalian intestinal tract is crucially important for gut colonization of commensals and opportunistic pathogens [4,5,6,7,8]. Carbohydrate utilization of E. faecium remains poorly understood despite its potential importance in colonization and adaptation to healthy individuals [9] and hospitalized patients [10]
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