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LpxK is essential for growth of Acinetobacter baumannii ATCC 19606: relationship to toxic accumulation of lipid A pathway intermediates

Wei, Jun-Rong and Richie, Daryl and Mostafavi, Mina and Metzger Iv, Louis and Rath, Christopher and Sawyer, William and Takeoka, Ken and Dean, Charles (2017) LpxK is essential for growth of Acinetobacter baumannii ATCC 19606: relationship to toxic accumulation of lipid A pathway intermediates. mSphere, 2 (4).

Abstract

Acinetobacter baumannii ATCC 19606 can grow without lipooligosaccharide (LOS). Lipid A, the major component of LOS, is therefore not essential in this species. Despite this, we previously reported that depletion of LpxH (the fourth enzyme in the lipid A biosynthetic pathway), prevented growth of this strain of A. baumannii due to the toxic accumulation of lipid A pathway intermediates. Here, we explored whether a similar phenomenon can occur with depletion of LpxK, a kinase that phosphorylates disaccharide 1-monophosphate (DSMP) at the 4'- position to yield lipid IVA. An A. baumannii ATCC 19606 derivative with LpxK expression under control of an isopropyl β-D-1-thiogalactopyranoside (IPTG) regulated expression system failed to grow without induction, indicating that LpxK is essential for growth. Light and electron microscopy of cells depleted of LpxK revealed morphological changes relating to the cell envelope, consistent with the notion of toxic accumulation of lipid A pathway intermediates disrupting cell membranes. Using a liquid chromatography-mass spectrometry (LCMS) approach, cellular accumulation of the detergent-like pathway intermediates DSMP and lipid X was shown. Toxic accumulation was further supported by restoration of growth upon chemical inhibition of LpxC (upstream of LpxK and the first committed step of lipid A biosynthesis) using CHIR-090. Interestingly, cerulenin, an inhibitor of fatty acid biosynthesis, and an acetyl-CoA carboxylase inhibitor, could also abrogate the requirement for LpxK expression. Intriguingly, growth rescue with these inhibitors was possible on cation-adjusted Mueller-Hinton agar, but not MacConkey agar. The latter contains outer membrane impermeable bile salts, suggesting that despite growth restoration, the cell membrane permeability barrier was not restored. Overall this indicates that LpxK is essential for growth of A. baumannii, since loss of LpxK causes accumulation of detergent-like pathway intermediates that inhibit cell growth.

Item Type: Article
Keywords: LpxK, Acinetobacter baumannii, toxic accumulation, lipid A
Date Deposited: 22 Aug 2017 00:45
Last Modified: 22 Aug 2017 00:45
URI: https://oak.novartis.com/id/eprint/33386

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