Effects of membrane tension on nanopropeller driven bacterial motion

Our present capabilities to build nanomachines are very limited compared to the elegance and efficiency of bio-nanomachines. The flagellar motor of bacteria is an example of a bionanomachine. It is a structured aggregate of proteins anchored in many bacterial cell membranes (formed mostly from phospholipids). While a large body of work characterizes various functional components of flagellar proteins, limited literature exists on the role of phospholipids of the membranes anchoring the protein. It is assumed that the membranes do not play any active role in the nano-propeller's functioning. However, it is relevant to question this assumption for several reasons. Firstly, the anchor for any machine on any scale is essential in terms of the work-load the machine can deliver. Secondly, it is now clear that localized protein-lipid interactions are essential for functioning of many transmembrane proteins. These interactions result in formation of "nano-domains" of specific lipid constituents around the protein providing the desired functionality. Thus, regardless of whether the bacterial membrane is primarily an anchor for flagellar proteins or specific lipid components of the membrane are actively participating in nano-propeller driven motion of bacteria, it is important to investigate the role of the membrane itself in working of this bionanomachine. Using video microscopy with a 33 ms resolution to monitor bacterial motion, we investigate effects of varying the membrane tension, by providing different osmotic environments, on the performance of the flagellar motor. Our data strongly demonstrate an active role of bacterial membranes in the nano-propeller driven bacterial motion. Our results point towards reconsidering performance of classical bionanomachines like bacterial flagellar motor and F1-F0 ATPase in view of the membranes in which they are packed in, in contrast to just the proteins by themselves.