Mycobacterium transporter Rv0783c drives drug efflux and biofilm growth

Tuberculosis (TB) remains a leading global health threat, made worse by the rise of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB. Even with many drugs and treatment strategies available, bacteria find ways to survive. One important but underexplored survival tactic is active export of antibiotics from bacterial cells by transporters known as efflux pumps. Mycobacterium species carry many such transporters in their genomes, and some are turned on in clinical isolates or when bacteria are exposed to drugs. To investigate one of these candidates, researchers led by Anindya S. Ghosh focused on Rv0783c, a putative transporter reported to be overexpressed under drug stress. The team tested whether Rv0783c could move antibiotics out of cells and whether it affected bacterial behaviors linked to persistence. Using simpler, well-understood bacterial hosts allowed the investigators to isolate the effect of this single gene and to link its activity to both drug resistance and biofilm formation—two traits that help bacteria survive treatment and persist in the body.

The study examined Rv0783c in heterologous hosts, namely Escherichia coli and Mycobacterium smegmatis, to see whether it changes sensitivity to drugs. Rv0783c conferred resistance to multiple structurally diverse antibiotics, including fluoroquinolones and other anti-TB drugs, and it was shown to help extrude first and second-line anti-TB drugs. Functional tests measured drug accumulation and the active efflux of ethidium bromide (EtBr), confirming that Rv0783c acts as a transporter. That efflux activity depended on the cell’s energy state: it was nullified by the proton-motive force blocker, CCCP. In addition to pumping out drugs, expression of Rv0783c enhanced biofilm formation, a state associated with persistence. The researchers also used site-directed mutagenesis guided by in silico analysis to identify key residues that interact with antibiotics, confirming parts of the protein needed for transport.

Taken together, these findings indicate that Rv0783c is a proton-motive force dependent multidrug efflux transporter that can reduce intracellular drug levels and promote a biofilm-associated, persistence-friendly lifestyle. That dual effect—extruding first and second-line anti-TB drugs and enhancing biofilm formation—helps explain how Mycobacterium species might withstand therapy and contribute to MDR and XDR problems. The proton-motive force dependence and the identification of interacting residues provide starting points for designing inhibitors that could block this pump and restore drug effectiveness. Because the work was done in heterologous hosts, the next steps will need to examine Rv0783c’s role in Mycobacterium tuberculosis clinical strains and in infection models. Still, the study highlights a concrete molecular mechanism linking efflux and persistence that could be targeted to improve TB treatment outcomes.