Selective benefit of the sucrose TonB-dependent receptor, SucA, in Caulobacter crescentus

Gram-negative bacteria have outer membrane proteins called TonB-dependent receptors (TBDRs) that facilitate energy-dependent transport of substrates. <i>Caulobacter crescentus</i> is a gram-negative bacterium with a large set of TBDRs, yet the function of many of these TBDRs remains uncharacterized. This study focuses on SucA, a TBDR that transports sucrose. Previous studies showed that <i>sucA</i> expression was induced in the presence of sucrose, yet did not provide a measurable fitness advantage under the conditions tested. This work identifies conditions where <i>sucA</i> does confer a significant growth advantage and provides evidence that SucA activity relies on the proton motive force, a feature of canonical TBDRs.