Phenotypic and Transcriptomic Characterization of Bacillus subtilis Mutants with Grossly Altered Membrane Composition

The Bacillus subtilis membrane contains diacylglycerol-based lipids with at least five distinct headgroups that together help to define the physical and chemical properties of the lipid bilayer. Here, we describe the phenotypic characterization of mutant strains lacking one or more of the following lipids: glycolipids (ugtP mutants), phosphatidylethanolamine (pssA and psd mutants), lysylphosphatidylglycerol (mprF), and cardiolipin (ywnE and ywjE). Alterations of membrane lipid headgroup composition are generally well-tolerated by the cell, and even severe alterations lead to only modest effects on growth proficiency. Mutants with decreased levels of positively charged lipids display an increased sensitivity to cationic antimicrobial compounds, and cells lacking glycolipids are more sensitive to the peptide antibiotic sublancin and are defective in swarming motility. A quadruple mutant strain (ugtP pssA mprF ywnE), with a membrane comprised predominantly of phosphatidylglycerol, is viable and grows at near-wild-type rates, although it forms long, coiled filaments. Transcriptome comparisons identified numerous regulons with altered expression in cells of the ugtP mutant, the pssA mprF ywnE triple mutant, and the ugtP pssA mprF ywnE quadruple mutant. These effects included a general decrease in expression of the SigD and FapR regulons and increased expression of cell envelope stress responses mediated by sigma(M) and the YvrGHb two-component system.