Abstract
The bacterial lipid membrane, consisting both of fatty acid (acyl) tails and polar head groups, responds to changing conditions through alteration of either the acyl tails and/or head groups. This plasticity is critical for cell survival as it allows maintenance of both the protective nature of the membrane as well as functioning membrane protein complexes. Bacteria that live in fatty-acid rich environments, such as those found in the human host, can exploit host fatty acids to synthesize their own membranes, in turn, altering their physiology. Enterococcus faecalis is such an organism: it is a commensal of the mammalian intestine where it is exposed to fatty-acid rich bile, as well as a major cause of hospital infections during which it is exposed to fatty acid containing-serum. Within, we employed an untargeted approach to detect the most common phospholipid species of E. faecalis OG1RF via ultra-high performance liquid chromatography high-resolution mass spectrometry (UHPLC-HRMS). We examined not only how the composition responds upon exposure to host fatty acids but also how deletion of genes predicted to synthesize major polar head groups impact lipid composition. Regardless of genetic background and differing basal lipid composition, all strains were able to alter their lipid composition upon exposure to individual host fatty acids. Specific gene deletion strains, however, had altered survival to membrane damaging agents. Combined, the enterococcal lipidome is highly resilient in response to both genetic and environmental perturbation, likely contributing to stress survival.
Highlights
The bacterial cellular envelope, consisting of the cell wall and membrane, is the first line of defense from environmental stresses (Silhavy et al, 2010)
Previous research utilizing fatty acid methyl ester (FAME) analysis has shown that E. faecalis OG1RF can incorporate exogenous fatty acids including oleic acid and linoleic acid from host fluids, altering its membrane fatty acid content and sensitivity to membrane damaging agents (Saito et al, 2014, 2018; Harp et al, 2016; Brewer et al, 2020)
We examined the plasticity of the enterococcal lipid composition in response to both environmental perturbations and genetic alterations
Summary
The bacterial cellular envelope, consisting of the cell wall and membrane, is the first line of defense from environmental stresses (Silhavy et al, 2010). The cellular membrane that is composed primarily of lipids, is critical as it blocks the accumulation of toxins, senses changing conditions, houses protein signaling systems that are critical for stimulating gene expression changes, and provides a location for the major energetic complexes (Strahl and Errington, 2017). The majority of these lipids are phospholipids that consist of a polar head group and fatty acid (acyl). Depletion of cardiolipin in Escherichia coli leads to pleiotropic effects on its physiology (Rowlett et al, 2017)
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