The bacterial plasma membrane is an important cellular compartment. In recent years it has become obvious that protein complexes and lipids are not uniformly distributed within membranes. Current hypotheses suggest that flotillin proteins are required for the formation of complexes of membrane proteins including cell-wall synthetic proteins. We show here that bacterial flotillins are important factors for membrane fluidity homeostasis. Loss of flotillins leads to a decrease in membrane fluidity that in turn leads to alterations in MreB dynamics and, as a consequence, in peptidoglycan synthesis. These alterations are reverted when membrane fluidity is restored by a chemical fluidizer. In vitro, the addition of a flotillin increases membrane fluidity of liposomes. Our data support a model in which flotillins are required for direct control of membrane fluidity rather than for the formation of protein complexes via direct protein-protein interactions.

20The bacterial plasma membrane is an important cellular compartment. In recent years 21 it has become obvious that protein complexes and lipids are not uniformly distributed 22 within membranes. Current hypotheses suggest that flotillin proteins are required for the 23 formation of complexes of membrane proteins including cell-wall synthetic proteins. We 24show here that bacterial flotillins are important factors for membrane fluidity 25 homeostasis. Loss of flotillins leads to a decrease in membrane fluidity that in turn leads 26to alterations in MreB dynamics and, as a consequence, in peptidoglycan synthesis. These 27 alterations are reverted when membrane fluidity is restored by a chemical fluidizer. In 28 sufficient to convert spherical cells to a rod shape 8,9 . In Bacillus subtilis, the motion of MreB 54 along the membrane is associated with elongasome activity 10,11 and the velocity of MreB 55 patches is related to growth rate 12 , indicating that MreB motion can be used as a marker for 56 elongasome activity. Interestingly, MreB localizes to and organizes regions of increased 57 membrane fluidity (RIF) 13 , which in turn is linked to the presence of LipidII, which favours a 58 more fluid membrane and promotes local membrane disorder 14,15 . Inhibition of LipidII 59 synthesis by genetic or chemical means results in a dissolution of membrane structures 60 observed with the dye FM 4-64 and release of MreB from the membrane 10,11,16,17 . 61Next to RIFs, membrane regions of decreased fluidity have been identified in bacteria 7,18,19 . 62

No abstract