On the pull: periplasmic trapping of sugars before transport.

Bacteria have evolved many routes for taking up nutrients, demonstrating great versatility in the types and mechanism of uptake used in different physiological conditions. The discovery of a single transporter in the bacterium Advenella mimigardefordensis for the uptake of five different sugars, including L-glucose and D-xylose, is described in this issue (Meinert et al., ), providing yet another example of the surprising adaptability of bacterial transport strategies. The transporter identified is a tripartite ATP-independent (TRAP) transporter, not previously associated with sugar transport, and in fact does not transport the sugars directly at all, rather requiring them to be converted in the periplasm to their respective sugar acid forms before transport through what appears to be a novel general sugar acid transporter. In this commentary, I describe how this process is consistent with the known mechanisms of TRAP transporters and consider how the role of sugar oxidation, or oxidative fermentation, operates with multiple hexose and pentose sugars. Finally I suggest that the periplasmic conversion of nutrients acquired across the outer membrane, before transport across the inner membrane, could have potentially useful biological functions in Gram negative bacteria.