Bam complex associated proteins in Escherichia coli are functionally linked to peptidoglycan biosynthesis, membrane fluidity and DNA replication

Abstract

Biogenesis of the bacterial outer membrane is key to bacterial survival and antibiotic resistance. Central to this is the β-barrel assembly machine (Bam) complex and its associated chaperones, which are responsible for transport, folding and insertion of outer membrane proteins (OMPs). The Escherichia coli Bam complex is composed of two essential subunits, BamA and BamD, and three non-essential accessory lipoproteins, BamB, BamC and BamE. Optimal Bam function is further dependent on the non-essential periplasmic chaperones DegP, Skp and SurA. Despite intensive study, the specific function of these non-essential Bam-associated proteins remains unknown. Here, we analysed Δ bamB , Δ bamC , Δ bamE , Δ surA , Δ skp and Δ degP knockout strains by phenotypic screening, conservation analysis and high-throughput genetics. We reveal that Bam complex activity is impacted by changes in outer membrane lipid composition and that enterobacterial common antigen is essential in the absence of the chaperone SurA. We also show components of peptidoglycan are conditionally essential with Bam accessory lipoproteins and that DNA replication control is perturbed in the absence of specific OMP assembly components. Together, our data indicates potential mechanisms for coordination of OMP biogenesis with other cellular growth processes such as LPS and peptidoglycan biogenesis, and DNA replication control.