A magnesium transporter CorA of Mycobacterium smegmatis enhances the tolerance of structurally unrelated antibiotics in the host cells

Abstract

Ion transporters or channels are involved in maintaining metal homeostasis in bacterial cells by aiding the movement of metal ions across the cell, which might also facilitate the export of antimicrobials. Ubiquitous magnesium transporter, CorA of Mycobacterium smegmatis is well known for its role in maintaining magnesium homeostasis. However, little is known about its involvement in exerting antimicrobial resistance. Here, with the help of molecular genetics, in vivo and in silico studies we tried to envisage the role of CorA of M. smegmatis in antimicrobial resistance of M. smegmatis and E. coli. Expression of corA in M. smegmatis and E. coli increased the tolerance of the host cells towards various structurally unrelated antibiotics and anti-tubercular drugs. In addition, a significantly lower accumulation of norfloxacin and ofloxacin by the host cells expressing corA further indicated its role in enhancing the efflux pump activity. Moreover, the presence of a sub-inhibitory concentration of Mg2+ resulted in increased low-level tolerance towards the tested drugs. Furthermore, CorA enhanced the biofilm-forming ability of cells expressing it. Overall, we speculate that magnesium transporter CorA facilitates multi-drug efflux activity of the host cells where Mg2+ might act as a facilitator in the process. IMPORTANCEMagnesium acts as a co-factor for various biochemical and physiological reactions, such as protein synthesis, cell membrane integrity, nucleic acid synthesis, etc. Metal transporters maintain metal homeostasis by regulating the uptake, efflux, or transportation of metals in certain necessary cellular compartments. In bacteria, magnesium ion (Mg2+) is mainly supplied by the CorA protein which is a ubiquitous family of transport proteins and extensively studied in E. coli and Salmonella sp. However, little is known about the functional relationship of metal transporters of Mycobacterium sp with extrusion of antibiotics, and their involvement in stress tolerance. Here, we report CorA (MSMEG_5056), a magnesium transporter of Mycobacterium smegmatis in influencing the extrusion of multiple structurally unrelated classes of drugs and enhancing the biofilm formation of E. coli and Mycobacterium smegmatis. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=74 SRC="FIGDIR/small/602764v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@11a5f5corg.highwire.dtl.DTLVardef@6ac8f9org.highwire.dtl.DTLVardef@b083dcorg.highwire.dtl.DTLVardef@a0fb8a_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical Abstract:C_FLOATNO Hypothetical model of Antibiotic export by CorA. Antibiotics bind to the closed state of the protein (left). During the transition to the open state (right), the to-and-fro motion between multiple open states drives the efflux of the antibiotic while facilitating the import of Mg2+. The colors of the models correspond to the chain ID. The bottom views of both the closed and open states are shown in the rectangular box, with the color indicated by their respective chain IDs. C_FIG