The microbial cell wall is essential for cell shape maintenance and resistance to external stressors¹. The primary structural component of the cell wall is peptidoglycan (PG), a glycopolymer with peptide crosslinks located outside of the cell membrane¹. PG biosynthesis and structure are responsive to shifting environmental conditions such as pH and salinity^2–6, but mechanisms underlying such adaptations are incompletely understood. Precursors of PG and other cell surface glycopolymers are synthesized in the cytoplasm and then delivered across the cell membrane bound to the recyclable lipid carrier undecaprenyl phosphate (C55-P)⁷. The transporter protein(s) that return C55-P to the cytoplasmic face of the cell membrane have been elusive. Here, we identify the DUF368-containing and DedA transmembrane protein families as candidate C55-P translocases, filling a critical gap in knowledge of the proteins required for the biogenesis of microbial cell surface polymers. Gram-negative and -positive bacteria lacking their cognate DUF368-containing protein exhibited alkaline-dependent cell wall and viability defects, along with increased cell surface C55-P levels. pH-dependent synthetic genetic interactions between DUF368-containing proteins and DedA family members suggest that C55-P transporter usage is dynamic and modulated by environmental inputs. C55-P transporter activity was required by the cholera pathogen for growth and cell shape maintenance in the intestine. We propose that conditional transporter reliance provides resilience in lipid carrier recycling, bolstering microbial fitness within and outside of the host.

微生物细胞壁对于细胞形状的维持和对外部压力源的抵抗力至关重要¹。细胞壁的主要结构成分是肽聚糖 (PG)，这是一种位于细胞膜¹外部的具有肽交联的糖聚合物。PG 的生物合成和结构对不断变化的环境条件（如 pH 值和盐度^2–6）有反应，但这种适应的潜在机制尚不完全清楚。PG 的前体和其他细胞表面糖聚合物在细胞质中合成，然后通过细胞膜传递，与可回收的脂质载体磷酸十一碳烯酯 (C55-P) ^7结合. 将 C55-P 返回细胞膜细胞质面的转运蛋白一直难以捉摸。在这里，我们将含 DUF368 和 DedA 跨膜蛋白家族鉴定为候选 C55-P 转位酶，填补了微生物细胞表面聚合物生物发生所需蛋白质知识的关键空白。缺乏同源含 DUF368 蛋白的革兰氏阴性和阳性细菌表现出依赖碱性的细胞壁和活力缺陷，以及细胞表面 C55-P 水平升高。含 DUF368 的蛋白质与 DedA 家族成员之间的 pH 依赖性合成遗传相互作用表明，C55-P 转运蛋白的使用是动态的，并受环境输入的调节。霍乱病原体需要 C55-P 转运蛋白活性才能在肠道中生长和维持细胞形状。