Robust Suppression of Lipopolysaccharide Deficiency in Acinetobacter baumannii by Growth in Minimal Medium

Gram-negative bacteria are defined by their asymmetric outer membrane that consists of phospholipids on the inner leaflet and lipopolysaccharide (LPS) in the outer leaflet. LPS is essential in all but a few Gram-negative species; the reason for this differential essentiality is not well understood. One species that can survive without LPS,Acinetobacter baumannii , shows characteristic growth and morphology phenotypes. We show that these phenotypes can be suppressed under conditions of slow growth and describe how LPS loss is connected to the growth defects. In addition to better defining the challengesA. baumannii cells face in the absence of LPS, we provide a new hypothesis that may explain the species-dependent conditional essentiality.