Abstract
Fatty acids play a major role in determining membrane biophysical properties. Staphylococcus aureus produces branched-chain fatty acids (BCFAs) and straight-chain saturated fatty acids (SCSFAs), and can directly incorporate exogenous SCSFAs and straight-chain unsaturated fatty acids (SCUFAs). Many S. aureus strains produce the triterpenoid pigment staphyloxanthin, and the balance of BCFAs, SCSFAs and staphyloxanthin determines membrane fluidity. Here, we investigated the relationship of fatty acid and carotenoid production in S. aureus using a pigmented strain (Pig1), its carotenoid-deficient mutant (Pig1ΔcrtM) and the naturally non-pigmented Staphylococcus argenteus that lacks carotenoid biosynthesis genes and is closely related to S. aureus. Fatty acid compositions in all strains were similar under a given culture condition indicating that staphyloxanthin does not influence fatty acid composition. Strain Pig1 had decreased membrane fluidity as measured by fluorescence anisotropy compared to the other strains under all conditions indicating that staphyloxanthin helps maintain membrane rigidity. We could find no evidence for correlation of expression of crtM and fatty acid biosynthesis genes. Supplementation of medium with glucose increased SCSFA production and decreased BCFA and staphyloxanthin production, whereas acetate-supplementation also decreased BCFAs but increased staphyloxanthin production. We believe that staphyloxanthin levels are influenced more through metabolic regulation than responding to fatty acids incorporated into the membrane.
Highlights
It is generally accepted that the fatty acid composition of membrane phospholipids have a major impact on determining membrane biophysical and, thereby, physiological properties [1].Staphylococcus aureus is a Gram-positive bacterial pathogen that shows a significant growth environment-dependent plasticity in its membrane fatty acid composition [2]
S. aureus are generally considered to be a mixture of saturated branched-chain fatty acids (BCFAs) and straight-chain fatty acids (SCSFAs) that are synthesized by fatty acid biosynthesis system II
Mueller-Hinton broth (MHB)-grown cells had 81% BCFAs and the serum-grown cells had a significant proportion of straight-chain unsaturated fatty acids (SCUFAs) (41%) (Table 1)
Summary
It is generally accepted that the fatty acid composition of membrane phospholipids have a major impact on determining membrane biophysical and, thereby, physiological properties [1]. Staphylococcus aureus is a Gram-positive bacterial pathogen that shows a significant growth environment-dependent plasticity in its membrane fatty acid composition [2]. S. aureus are generally considered to be a mixture of saturated branched-chain fatty acids (BCFAs) and straight-chain fatty acids (SCSFAs) that are synthesized by fatty acid biosynthesis system II (FAS II). Some bacteriological media such as Mueller-Hinton broth (MHB) promote a high proportion of BCFAs, whereas others such as Tryptic Soy Broth (TSB) result in decreased BCFAs and increased. S. aureus lacks a fatty acid desaturase enzyme that converts saturated fatty acids into unsaturated products [2,6], and, BCFAs play a critical role
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