A Cardiolipin-Deficient Mutant of Rhodobacter Sphaeroides has an Altered Cell Shape and is Impaired in Biofilm Formation

Abstract

Cell shape has been suggested to play an important role in regulating bacterial attachment to surfaces and the formation of communities associated with surfaces. We found that a cardiolipin synthase deletion mutant of the rod-shaped bacterium Rhodobacter sphaeroides—in which synthesis of the anionic, highly curved phospholipid cardiolipin (CL) is reduced by 90%—produces ellipsoidal-shaped cells that are impaired in forming biofilms. Reducing the concentration of CL did not cause significant defects in R. sphaeroides cell growth, swimming motility, lipopolysaccharide and exopolysaccharide production, surface adhesion protein expression, and membrane permeability. Complementation of the CL-deficient mutant by ectopically expressing CL synthase restored cells to their rod shape and increased biofilm formation. Treating R. sphaeroidescells with a low concentration (10 μg/mL) of the small molecule MreB inhibitor, S-(3,4-dichlorobenzyl) isothiourea (A22), produced ellipsoid-shaped cells that had no obvious growth defect, yet reduced R. sphaeroides biofilm formation. This study demonstrates that CL plays a role in R. sphaeroides cell shape determination, biofilm formation, and the ability of this bacterium to adapt to its environment.