Staphylococcus aureus can incorporate exogenous straight-chain unsaturated and saturated fatty acids (SCUFAs and SCFAs, respectively) to replace some of the normally biosynthesized branched-chain fatty acids and SCFAs. In this study, the impact of human serum on the S. aureus lipidome and cell envelope structure was comprehensively characterized. When S. aureus was grown in the presence of 20% human serum, typical human serum lipids, such as cholesterol, sphingomyelin, phosphatidylethanolamines, and phosphatidylcholines, were present in the total lipid extracts. Mass spectrometry showed that SCUFAs were incorporated into all major S. aureus lipid classes, i.e., phosphatidylglycerols, lysyl-phosphatidylglycerols, cardiolipins, and diglucosyldiacylglycerols. Heat-killed S. aureus retained fewer serum lipids and failed to incorporate SCUFAs, suggesting that association and incorporation of serum lipids with S. aureus require a living or nondenatured cell. Cytoplasmic membranes isolated from lysostaphin-produced protoplasts of serum-grown cells retained serum lipids, but washing cells with Triton X-100 removed most of them. Furthermore, electron microscopy studies showed that serum-grown cells had thicker cell envelopes and associated material on the surface, which was partially removed by Triton X-100 washing. To investigate which serum lipids were preferentially hydrolyzed by S. aureus lipases for incorporation, we incubated individual serum lipid classes with S. aureus and found that cholesteryl esters (CEs) and triglycerides (TGs) are the major donors of the incorporated fatty acids. Further experiments using purified Geh lipase confirmed that CEs and TGs were the substrates of this enzyme. Thus, growth in the presence of serum altered the nature of the cell surface with implications for interactions with the host.

中文翻译：

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人血清中生长的金黄色葡萄球菌细胞包膜的脂质学和超微结构表征。

金黄色葡萄球菌可以掺入外源性直链不饱和脂肪酸和饱和脂肪酸（分别为SCUFA和SCFA）来代替一些通常由生物合成的支链脂肪酸和SCFA。在这项研究中，人类血清对金黄色葡萄球菌脂质组和细胞包膜结构的影响被全面表征。当金黄色葡萄球菌在20％的人类血清中生长时，总脂质提取物中会存在典型的人类血清脂质，例如胆固醇，鞘磷脂，磷脂酰乙醇胺和磷脂酰胆碱。质谱表明，SCUFA已被纳入所有主要的金黄色葡萄球菌脂质类别，即磷脂酰甘油，赖氨酰磷脂酰甘油，心磷脂和二葡糖基二酰基甘油。热灭活的金黄色葡萄球菌保留的血清脂质较少，未能掺入SCUFA，这表明血清脂质与金黄色葡萄球菌的结合和掺入需要活的或未变性的细胞。从溶葡萄球菌素产生的血清生长细胞的原生质体中分离出的细胞质膜保留了血清脂质，但是用Triton X-100洗涤的细胞去除了大部分脂质。此外，电子显微镜研究表明，血清生长的细胞在表面具有较厚的细胞包膜和相关物质，通过Triton X-100洗涤可将其部分除去。调查哪些血清脂质​​被金黄色葡萄球菌优先水解为了掺入脂肪酶，我们将各种血清脂质类别与金黄色葡萄球菌一起孵育，发现胆固醇酯（CEs）和甘油三酸酯（TGs）是掺入脂肪酸的主要供体。使用纯化的盖氏脂肪酶的进一步实验证实，CE和TG是该酶的底物。因此，在血清存在下的生长改变了细胞表面的性质，暗示了与宿主的相互作用。