SRA

We recently demonstrated that colistin resistance in Acinetobacter baumannii can result from mutational inactivation of genes essential for lipid A biosynthesis. Consequently, strains harboring these mutations are unable to produce the major Gram negative bacterial surface component, lipopolysaccharide (LPS). To understand how A. baumannii compensates for the lack of LPS, we compared the transcriptional profile of the A. baumannii type strain ATCC19606, to that of an isogenic, LPS-deficient, lpxA mutant strain. Analysis of the expression profiles indicated that the LPS-deficient strain showed increased expression of many genes involved in cell envelope and membrane biogenesis. In particular, up-regulated genes included those involved in the Lol lipoprotein transport system and the Mla-retrograde phospholipid transport system. In addition, genes involved in the synthesis and transport of poly-beta-1,6-N-acetylglucosamine (PNAG) were also up-regulated and a corresponding increase in PNAG production was observed. The LPS-deficient strain also exhibited reduced expression of genes predicted to encode the fimbrial subunit FimA and a type VI secretion system (T6SS). The reduced expression of genes involved in T6SS correlated with the detection of the T6SS-effector protein, AssC, in culture supernatants of the A. baumannii wild-type strain, but not in the LPS-deficient strain. Taken together, these data show that, in response to total LPS loss, A. baumannii alters the expression of critical transport and biosynthesis systems associated with modulating the composition and structure of the bacterial surface. Overall design: Comparison of a gene expression in biological duplicate samples derived from parent bacterial strain to an isogenic mutant strain.