Inositol lipids are ubiquitous in eukaryotes and have finely tuned roles in cellular signalling and membrane homoeostasis. In Bacteria, however, inositol lipid production is relatively rare. Recently, the prominent human gut bacterium Bacteroides thetaiotaomicron (BT) was reported to produce inositol lipids and sphingolipids, but the pathways remain ambiguous and their prevalence unclear. Here, using genomic and biochemical approaches, we investigated the gene cluster for inositol lipid synthesis in BT using a previously undescribed strain with inducible control of sphingolipid synthesis. We characterized the biosynthetic pathway from myo-inositol-phosphate (MIP) synthesis to phosphoinositol dihydroceramide, determined the crystal structure of the recombinant BT MIP synthase enzyme and identified the phosphatase responsible for the conversion of bacterially-derived phosphatidylinositol phosphate (PIP-DAG) to phosphatidylinositol (PI-DAG). In vitro, loss of inositol lipid production altered BT capsule expression and antimicrobial peptide resistance. In vivo, loss of inositol lipids decreased bacterial fitness in a gnotobiotic mouse model. We identified a second putative, previously undescribed pathway for bacterial PI-DAG synthesis without a PIP-DAG intermediate, common in Prevotella. Our results indicate that inositol sphingolipid production is widespread in host-associated Bacteroidetes and has implications for symbiosis.

肌醇脂质在真核生物中无处不在，并且在细胞信号传导和膜稳态中具有微调作用。然而，在细菌中，肌醇脂质的产生相对较少。最近，著名的人类肠道细菌Bacteroides thetaiotaomicron据报道 (BT) 会产生肌醇脂质和鞘脂，但途径仍然不明确，其流行程度也不清楚。在这里，我们使用基因组和生物化学方法，使用以前未描述的具有鞘脂合成诱导控制的菌株研究了 BT 中肌醇脂质合成的基因簇。我们表征了从肌醇磷酸 (MIP) 合成到磷酸肌醇二氢神经酰胺的生物合成途径，确定了重组 BT MIP 合酶的晶体结构，并鉴定了负责将细菌来源的磷脂酰肌醇磷酸 (PIP-DAG) 转化为磷酸肌醇的磷酸酶磷脂酰肌醇 (PI-DAG)。在体外，肌醇脂质生产的丧失改变了 BT 胶囊表达和抗菌肽耐药性。体内，肌醇脂质的损失降低了无菌小鼠模型中的细菌适应性。我们确定了第二个推定的、以前未描述的细菌 PI-DAG 合成途径，没有 PIP-DAG 中间体，常见于普氏菌属。我们的结果表明，肌醇鞘脂的产生广泛存在于宿主相关的拟杆菌中，并且对共生具有影响。