N-Acetylmuramoyl-l-alanine amidases are periplasmic hydrolases that cleave the amide bond between N-acetylmuramic acid and alanine in peptidoglycan (PG). Unlike many Gram-negative bacteria that encode redundant periplasmic amidases, Vibrio fischeri appears to encode a single protein that is homologous to AmiB of Vibrio cholerae. We screened a V. fischeri transposon mutant library for strains altered in biofilm production and discovered a biofilm-overproducing strain with an insertion in amiB (VF_2326). Further characterization of biofilm enhancement suggested that this phenotype was due to the overproduction of cellulose, and it was dependent on the bcsA cellulose synthase. Additionally, the amiB 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 V. fischeri’s symbiotic host, the squid Euprymna scolopes. 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 amiB mutation and led us to speculate that motile suppressors of the amiB mutant were responsible for the partially restored colonization. In culture, motile suppressor mutants carried point mutations in a single gene (VF_1477), resulting in a partial restoration of wild-type motility. In addition, these point mutations reversed the effect of the amiB mutation on cellulosic biofilm production. These data are consistent with V. fischeri AmiB possessing amidase activity; they also suggest that AmiB suppresses cellulosic biofilm formation but promotes successful host colonization.

中文翻译：

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正常细胞分裂，运动性和共生能力需要费氏弧菌酰胺酶活性

N-乙酰基村酰胺基-1-丙氨酸酰胺酶是周质水解酶，其裂解肽聚糖（PG）中N-乙酰基村酰胺酸和丙氨酸之间的酰胺键。与许多编码多余的周质酰胺酶的革兰氏阴性细菌不同，费氏弧菌似乎编码与霍乱弧菌AmiB同源的单个蛋白质。我们筛选了费氏弧菌转座子突变体文库，寻找在生物膜生产中发生改变的菌株，并发现了在amiB（VF_2326中插入）。生物膜增强的进一步表征表明，该表型是由于纤维素的过量生产所致，并且它依赖于bcsA纤维素合酶。另外，amiB突变体是不运动的，可能是由于其在分裂过程中分离的能力存在缺陷。酰胺酶突变体不能与野生型进行的殖民竞争V.鲵的共生主机，鱿鱼Euprymna scolopes。在单株接种中，用突变体接种的宿主鱿鱼最终被定殖，但效率远低于用野生型接种的鱿鱼。该观察结果与amiB的多效性作用相一致突变并导致我们推测amiB突变体的运动抑制因子是部分恢复定殖的原因。在文化中，能动性抑制突变体在单个基因（VF_1477）中携带点突变，导致野生型运动性的部分恢复。此外，这些点突变逆转了amiB突变对纤维素生物膜生产的影响。这些数据与一致的五鲵非洲驻布隆迪特派团拥有酰胺酶的活性; 他们还建议AmiB抑制纤维素生物膜形成，但促进成功的宿主定植。