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J Bacteriol. 2019 Oct 21;201(22). pii: e00420-19. doi: 10.1128/JB.00420-19. Print 2019 Nov 15.

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

Author information

1
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA.
2
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA losick@mcb.harvard.edu kahne@chemistry.harvard.edu.
3
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, USA.
4
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.

Abstract

Lipopolysaccharide (LPS) is normally considered to be essential for viability in Gram-negative bacteria but can be removed in Acinetobacter baumannii Mutant cells lacking this component of the outer membrane show growth and morphological defects. Here, we report that growth rates equivalent to the wild type can be achieved simply by propagation in minimal medium. The loss of LPS requires that cells rely on phospholipids for both leaflets of the outer membrane. We show that growth rate in the absence of LPS is not limited by nutrient availability but by the rate of outer membrane biogenesis. We hypothesize that because cells grow more slowly, outer membrane synthesis ceases to be rate limiting in minimal medium.IMPORTANCE 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 challenges A. baumannii cells face in the absence of LPS, we provide a new hypothesis that may explain the species-dependent conditional essentiality.

KEYWORDS:

Acinetobacter baumannii ; lipopolysaccharide loss; suppressors

PMID:
31451545
DOI:
10.1128/JB.00420-19

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