The AAA+ ATPase RavA-ViaA complex sensitizes Escherichia coli to aminoglycosides under anaerobic low energy conservation conditions

Abstract

Aminoglycosides have been used against Gram-negative bacteria for decades. Yet, uncertainties remain about various aspects of their uptake mechanism. Moreover their killing efficiency is well known to vary as a function of growth conditions and types of metabolism used by the targeted bacterium. Here we show that RavA, an AAA+ ATPase from the MoxR subfamily, associated with its VWA-containing partner, ViaA sensitize E. coli to lethal concentrations of AG, including gentamycin (Gm) and tobramycin, but not of antibiotics of other classes. We show this sensitizing effect to be due to enhanced Gm uptake in a proton motive force dependent manner. We evaluated the influence of RavA ViaA throughout a series of growth conditions, including aerobiosis and anaerobiosis. This led us to observe that the sensitizing effect of RavA ViaA varies with the respiratory chain used, i.e. RavA ViaA influence was prominent in the absence of exogenous electron acceptor or with fumarate, i.e. in poor energy conservation conditions, and dispensable in the presence of nitrate or oxygen, i.e. in high level of energy conservation. We propose RavA ViaA to be able to sense energetic state of the cell and to be used under low energy conditions for facilitating uptake of chemicals across the membrane, including Gm. Author SummaryAntibiotic resistance is a major public health, social and economic problem. Aminoglycosides are known for their high efficiency against Gram-negative bacteria but their use is restricted to life threatening infections because of their nephrotoxicity and ototoxicity at therapeutic dose. Elucidation of AG sensitization mechanisms in bacteria will allow the use of a decreased effective dose of AGs. Here we identified new molecular actors, RavA and ViaA, which sensitize E. coli to AG under anaerobiosis. RavA belongs to the AAA+ ATPase family while ViaA bears a VWA motif. Moreover we show here that the influence of RavA ViaA on AG sensitivity varies with growth conditions and respiratory metabolism used by E. coli. This is a significant step forward as anaerobiosis is well known to reduce antibacterial activity of AG. This study emphasizes the crucial importance of the relationships between culture conditions, metabolism and antibiotic resistance.