ABSTRACT

Amino acid (acyl carrier protein) ligases (AALs) are a relatively new family of bacterial amino acid adenylating enzymes with unknown function(s). Here, genomic enzymology tools that employ sequence similarity networks and genome context analyses were used to hypothesize the metabolic function(s) of AALs. In over 50% of species, aal and its cognate acyl carrier protein (acp) genes, along with three more genes, formed a highly conserved AAL cassette. AAL cassettes were strongly associated with surface polysaccharide gene clusters in Proteobacteria and Actinobacteria, yet were prevalent among soil and rhizosphere-associated α- and β-Proteobacteria, including symbiotic α- and β-rhizobia and some Mycolata. Based on these associations, AAL cassettes were proposed to encode a noncanonical Acp-dependent polysaccharide modification route. Genomic-inferred predictions were substantiated by published experimental evidence, revealing a role for AAL cassettes in biosynthesis of biofilm-forming exopolysaccharide in pathogenic Burkholderia and expression of aal and acp genes in nitrogen-fixing Rhizobium bacteroids. Aal and acp genes were associated with dltBD-like homologs that modify cell wall teichoic acids with d-alanine, including in Paenibacillus and certain other bacteria. Characterization of pathways that involve AAL and Acp may lead to developing new plant and human disease-controlling agents as well as strains with improved nitrogen fixation capacity.

中文翻译：

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基因组和分子证据揭示了与细菌细胞表面多糖相关的新途径

摘要

氨基酸（酰基载体蛋白）连接酶 (AAL) 是一个相对较新的细菌氨基酸腺苷酸化酶家族，其功能未知。在这里，采用序列相似性网络和基因组背景分析的基因组酶学工具被用来假设 AAL 的代谢功能。在超过 50% 的物种中，aal及其同源酰基载体蛋白 ( acp ) 基因以及另外三个基因形成了高度保守的 AAL 盒。AAL 盒与变形菌和放线菌的表面多糖基因簇密切相关，但在土壤和根际相关的α-和β-变形菌中普遍存在，包括共生的α-和β-根瘤菌和一些Mycolata。基于这些关联，提出了 AAL 盒来编码非规范的 Acp 依赖性多糖修饰途径。已发表的实验证据证实了基因组推断的预测，揭示了 AAL 盒在致病性伯克霍尔德菌中形成生物膜的胞外多糖的生物合成以及固氮根瘤菌中aal和acp基因的表达中的作用。Aal和acp基因与用d-丙氨酸修饰细胞壁磷壁酸的dltBD样同源物相关，包括在类芽孢杆菌中和某些其他细菌。对涉及 AAL 和 Acp 的途径的表征可能会导致开发新的植物和人类疾病控制剂以及具有改善固氮能力的菌株。