Abstract
Although the agmatine deiminase system (AgDI) has been investigated in Enterococcus faecalis, little information is available with respect to its gene regulation. In this study we demonstrate that the presence of exogenous agmatine induces the expression of agu genes in this bacterium. In contrast to the homologous and extensively characterized AgDI system of S. mutants, the aguBDAC operon in E. faecalis is not induced in response to low pH. In spite of this, agmatine catabolism in this bacterium contributes by neutralizing the external medium while enhancing bacterial growth. Our results indicate that carbon catabolic repression (CCR) operates on the AgDI system via a mechanism that involves interaction of CcpA and P-Ser-HPr with a cre site found in an unusual position considering the aguB promoter (55 nt upstream the +1 position). In addition, we found that components of the mannose phosphotransferase (PTSMan) system also contributed to CCR in E. faecalis since a complete relief of the PTS-sugars repressive effect was observed only in a PTSMan and CcpA double defective strain. Our gene context analysis revealed that aguR is present in oral and gastrointestinal microorganisms. Thus, regulation of the aguBDAC operon in E. faecalis seems to have evolved to obtain energy and resist low pH conditions in order to persist and colonize gastrointestinal niches.
Highlights
Polyamines (PAs) are bioactive compounds present in all living cells
Growth curves of the wild type E. faecalis JH2-2 strain containing the empty vector pBM02 (JH2-2/pBM02) [28], aguR mutant and aguR2-complemented strains in Luria-Bertani medium (LB) Gal and LBA Gal (LB Gal supplemented with 10 mM agmatine) were compared
These findings indicate that AguR is required for the agmatine deiminase pathway in E. faecalis and that this metabolism contributes to increase culture biomass while maintaining growth medium near neutrality
Summary
Polyamines (PAs) (agmatine, putrescine, spermidine and spermine) are bioactive compounds present in all living cells. They have been described in association with a wide variety of biological reactions, including cellular growth, proliferation, stress response, allergy and inflammatory regulation [1,2]. Enterococcus faecalis is a homofermentative lactic acid bacterium, which can be isolated from the commensal microbiota of mammals. It is associated with food production and could be employed as a probiotic microorganism [4,5,6]. E. faecalis is frequently isolated from diverse types of commercial and traditional food products and is part of the normal human diet around the world [4,5]
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