Lysozyme is an important component of the innate immune system. It functions by hydrolyzing the peptidoglycan (PG) layer of bacteria. The human pathogen Listeria monocytogenes is intrinsically lysozyme resistant. The peptidoglycan N-deacetylase PgdA and O-acetyltransferase OatA are two known factors contributing to its lysozyme resistance. Furthermore, it was shown that the absence of components of an ABC transporter, referred to here as EslABC, leads to reduced lysozyme resistance. How its activity is linked to lysozyme resistance is still unknown. To investigate this further, a strain with a deletion in eslB, coding for a membrane component of the ABC transporter, was constructed in L. monocytogenes strain 10403S. The eslB mutant showed a 40-fold reduction in the MIC to lysozyme. Analysis of the PG structure revealed that the eslB mutant produced PG with reduced levels of O-acetylation. Using growth and autolysis assays, we showed that the absence of EslB manifests in a growth defect in media containing high concentrations of sugars and increased endogenous cell lysis. A thinner PG layer produced by the eslB mutant under these growth conditions might explain these phenotypes. Furthermore, the eslB mutant had a noticeable cell division defect and formed elongated cells. Microscopy analysis revealed that an early cell division protein still localized in the eslB mutant, indicating that a downstream process is perturbed. Based on our results, we hypothesize that EslB affects the biosynthesis and modification of the cell wall in L. monocytogenes and is thus important for the maintenance of cell wall integrity.

中文翻译：

---

EslB 是单核细胞增生李斯特菌细胞壁生物合成和修饰所必需的

溶菌酶是先天免疫系统的重要组成部分。它通过水解细菌的肽聚糖 (PG) 层发挥作用。人类病原体单核细胞增生李斯特菌本质上是抗溶菌酶的。肽聚糖N-脱乙酰酶PgdA 和O-乙酰转移酶 OatA 是导致其溶菌酶抗性的两个已知因素。此外，显示缺少 ABC 转运蛋白成分（此处称为 EslABC）会导致溶菌酶抗性降低。它的活性如何与溶菌酶抗性相关仍然未知。为了进一步研究这一点，在单核细胞增生李斯特菌中构建了一个eslB缺失的菌株，编码 ABC 转运蛋白的膜成分菌株 10403S。eslB突变体显示溶菌酶的 MIC降低了 40 倍。PG 结构分析表明，eslB突变体产生的PG 具有降低的O-乙酰化水平。使用生长和自溶测定，我们发现 EslB 的缺失表明含有高浓度糖的培养基中的生长缺陷和内源性细胞裂解增加。在这些生长条件下由eslB突变体产生的较薄的 PG 层可以解释这些表型。此外，eslB突变体具有明显的细胞分裂缺陷并形成细长的细胞。显微镜分析显示早期细胞分裂蛋白仍位于eslB突变，表明下游过程受到干扰。根据我们的结果，我们假设 EslB 影响单核细胞增生李斯特菌细胞壁的生物合成和修饰，因此对于维持细胞壁完整性很重要。