California State University, San Luis Obispo, California, USA
California State University, San Luis Obispo, California, USA.
Appl Environ Microbiol. 2021 Jan 15;87(3). doi: 10.1128/AEM.02109-20.
-Acetylmuramoyl-l-alanine amidases are periplasmic hydrolases that cleave the amide bond between -acetylmuramic acid and alanine in peptidoglycan (PG). Unlike many Gram-negative bacteria that encode redundant periplasmic amidases, appears to encode a single protein that is homologous to AmiB of We screened a transposon mutant library for strains altered in biofilm production and discovered a biofilm-overproducing strain with an insertion in (). Further characterization of biofilm enhancement suggested that this phenotype was due to the overproduction of cellulose, and it was dependent on the cellulose synthase. Additionally, the mutant was nonmotile, perhaps due to defects in its ability to septate during division. The amidase mutant was unable to compete with the wild type for the colonization of 's symbiotic host, the squid In single-strain inoculations, host squid inoculated with the mutant eventually became colonized but with a much lower efficiency than in squid inoculated with the wild type. This observation was consistent with the pleiotropic effects of the mutation and led us to speculate that motile suppressors of the mutant were responsible for the partially restored colonization. In culture, motile suppressor mutants carried point mutations in a single gene (), resulting in a partial restoration of wild-type motility. In addition, these point mutations reversed the effect of the mutation on cellulosic biofilm production. These data are consistent with AmiB possessing amidase activity; they also suggest that AmiB suppresses cellulosic biofilm formation but promotes successful host colonization. Peptidoglycan (PG) is a critical microbe-associated molecular pattern (MAMP) that is sloughed by cells of during symbiotic colonization of squid. Specifically, this process induces significant remodeling of a specialized symbiotic light organ within the squid mantle cavity. This phenomenon is reminiscent of the loss of ciliated epithelium in patients with whooping cough due to the production of PG monomers by Furthermore, PG processing machinery can influence susceptibility to antimicrobials. In this study, we report roles for the PG amidase AmiB, including the beneficial colonization of squid, underscoring the urgency to more deeply understand PG processing machinery and the downstream consequences of their activities.
乙酰胞壁酰-L-丙氨酸酰胺酶是一种周质内水解酶，可裂解肽聚糖（PG）中乙酰胞壁酸和丙氨酸之间的酰胺键。与许多编码冗余周质内酰胺酶的革兰氏阴性细菌不同， 似乎编码一种与 的 AmiB 同源的单一蛋白质。我们筛选了转座子突变体文库，以寻找生物膜生成改变的菌株，并在 中发现了一个插入突变体（）。对生物膜增强的进一步特征表明，这种表型是由于纤维素的过度产生，并且依赖于 纤维素合酶。此外， 突变体是非运动的，可能是由于其在分裂过程中不能进行分隔的能力缺陷。酰胺酶突变体无法与野生型竞争对共生宿主 的定植，共生宿主是鱿鱼 在单菌株接种中，用突变体接种的宿主鱿鱼最终被定植，但效率远低于用野生型接种的鱿鱼。这一观察结果与 突变的多效性效应一致，并促使我们推测 突变体的运动性抑制剂负责部分恢复定植。在培养中，运动性抑制剂突变体在单个基因（）中携带点突变，导致野生型运动性部分恢复。此外，这些点突变逆转了 突变对纤维素生物膜生成的影响。这些数据与 AmiB 具有酰胺酶活性一致；它们还表明 AmiB 抑制纤维素生物膜形成，但促进成功的宿主定植。肽聚糖（PG）是一种关键的微生物相关分子模式（MAMP），在鱿鱼共生定植期间， 细胞会将其剥落。具体而言，这个过程导致鱿鱼套膜腔中的专门共生光器官发生显著重塑。这种现象让人联想到由于 产生 PG 单体，百日咳患者的纤毛上皮丧失。此外，PG 加工机制会影响对抗微生物剂的敏感性。在这项研究中，我们报告了 PG 酰胺酶 AmiB 的作用，包括对鱿鱼的有益定植，这凸显了更深入了解 PG 加工机制及其活动的下游后果的紧迫性。
