Lipoteichoic acid (LTA) is a Gram-positive bacterial cell surface polymer that participates in host-microbe interactions. It was previously reported that the major human pathogen Streptococcus pneumoniae and the closely related oral commensals S. mitis and S. oralis produce type IV LTAs. Herein, using liquid chromatography/mass spectrometry-based lipidomic analysis, we found that in addition to type IV LTA biosynthetic precursors, S. mitis, S. oralis, and S. pneumoniae also produce glycerophosphate (Gro-P)-linked dihexosyl (DH)-diacylglycerol (DAG), which is a biosynthetic precursor of type I LTA. cdsA and pgsA mutants produce DHDAG but lack (Gro-P)-DHDAG, indicating that the Gro-P moiety is derived from phosphatidylglycerol (PG), whose biosynthesis requires these genes. S. mitis, but not S. pneumoniae or S. oralis, encodes an ortholog of the PG-dependent type I LTA synthase, ltaS. By heterologous expression analyses, we confirmed that S. mitis ltaS confers poly(Gro-P) synthesis in both Escherichia coli and Staphylococcus aureus and that S. mitis ltaS can rescue the growth defect of an S. aureus ltaS mutant. However, we do not detect a poly(Gro-P) polymer in S. mitis using an anti-type I LTA antibody. Moreover, Gro-P-linked DHDAG is still synthesized by an S. mitis ltaS mutant, demonstrating that S. mitis LtaS does not catalyze Gro-P transfer to DHDAG. Finally, an S. mitis ltaS mutant has increased sensitivity to human serum, demonstrating that ltaS confers a beneficial but currently undefined function in S. mitis. Overall, our results demonstrate that S. mitis, S. pneumoniae, and S. oralis produce a Gro-P-linked glycolipid via a PG-dependent, ltaS-independent mechanism.

中文翻译：

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肺炎链球菌、缓和链球菌和口腔链球菌产生依赖于磷脂酰甘油、不依赖于 ltaS 的甘油磷酸连接糖脂

脂磷壁酸 (LTA) 是一种参与宿主-微生物相互作用的革兰氏阳性细菌细胞表面聚合物。据报道，此前，主要的人类病原体肺炎链球菌和密切相关的口腔共生缓症链球菌和口腔链球菌产生IV型长期协议。在本文中，采用液-基于质谱色谱法/质谱分析脂质组，我们发现，除了IV型LTA生物合成前体，缓症链球菌，口腔链球菌和肺炎链球菌也产生甘油（GRO-P） -连接dihexosyl（DH )-二酰基甘油 (DAG)，它是 I 型 LTA 的生物合成前体。cdsA和pgsA突变体产生 DHDAG 但缺乏 (Gro-P)-DHDAG，表明 Gro-P 部分源自磷脂酰甘油 (PG)，其生物合成需要这些基因。缓症链球菌，但不是肺炎链球菌或口腔链球菌，编码PG依赖性I型LTA合酶，的同源物LTAS。通过异源表达分析，我们证实S. mitis ltaS在大肠杆菌和金黄色葡萄球菌中都具有 poly(Gro-P) 合成，并且S. mitis ltaS可以挽救S. aureus ltaS突变体的生长缺陷。然而，我们没有检测到聚（Gro-P）聚合物S. mitis使用抗 I 型 LTA 抗体。此外，Gro-P 连接的 DHDAG 仍由S. mitis ltaS突变体合成，表明S. mitis LtaS 不会催化 Gro-P 转移到 DHDAG。最后，缓症链球菌 LTAS突变体增加了人血清的敏感性，表明LTAS赋予在一个有益的，但是当前未定义功能缓症链球菌。总的来说，我们的结果表明，缓症链球菌，肺炎链球菌和口腔链球菌通过依赖PG，产生GRO-P-联糖脂长期协议不依赖机制。