Li Qing, Gänzle Michael G
Department of Agricultural, Food and Nutritional Science, University of Alberta, 4-10 Ag/For Centre, Edmonton, AB, T6G 2P5, Canada.
Appl Microbiol Biotechnol. 2020 Dec;104(23):10091-10103. doi: 10.1007/s00253-020-10979-0. Epub 2020 Oct 29.
Extracellular glycosyl hydrolases are uncommon in lactobacilli and include amylases and fructosidases mediating starch and fructan utilization, respectively. Extracellular arabinanases have not been described in lactobacilli. This study is aimed at identifying the function of an arabinan utilization operon in Lactobacillus crispatus DSM29598 and at characterizing two putative extracellular arabinanases that are located on that operon. The arabinan utilization operon of L. crispatus DSM29598 encodes enzymes for degradation of arabinan, α-galactosidases, β-galactosidases, and enzymes and for utilization of arabinose including phosphoketolase. The two putative extracellular arabinanases, AbnA and AbnB, are homologous to family GH43 endo-arabinanases. In Lactobacillaceae, homologs of these enzymes were identified exclusively in vertebrate-adapted species of the genus Lactobacillus. L. crispatus grew with arabinan from sugar beet pectin as sole carbon source, indicating extracellular arabinanase activity, and produced lactate and acetate, indicating metabolism via the phosphoketolase pathway. The two arabinanases AbnA and AbnB were heterologously expressed and purified by affinity chromatography. AbnA hydrolyzed linear and branched arabinan, while AbnB hydrolyzed only linear arabinan. The optimum pH for AbnA and AbnB was 6 and 7.5, respectively; 40 °C was the optimum temperature for both enzymes. The application of arabinan degrading L. crispatus as probiotic or as synbiotic with pectins may improve the production of short-chain fatty acids from pectin to benefit host health. KEY POINTS: • An arabinan utilization operon in L. crispatus encodes two extracellular arabinanases. • The same operon also encodes metabolic genes for arabinose conversion. • In Lactobacillaceae, extracellular arabinanases are exclusive to Lactobacillus species.
胞外糖基水解酶在乳酸杆菌中并不常见，包括分别介导淀粉和果聚糖利用的淀粉酶和果糖苷酶。乳酸杆菌中尚未有胞外阿拉伯聚糖酶的相关报道。本研究旨在确定卷曲乳杆菌DSM29598中阿拉伯聚糖利用操纵子的功能，并对位于该操纵子上的两种假定的胞外阿拉伯聚糖酶进行表征。卷曲乳杆菌DSM29598的阿拉伯聚糖利用操纵子编码用于降解阿拉伯聚糖的酶、α-半乳糖苷酶、β-半乳糖苷酶以及包括磷酸酮醇酶在内的用于利用阿拉伯糖的酶。两种假定的胞外阿拉伯聚糖酶AbnA和AbnB与GH43家族内切阿拉伯聚糖酶同源。在乳杆菌科中，这些酶的同源物仅在适应脊椎动物的乳酸杆菌属物种中被鉴定到。卷曲乳杆菌能够以甜菜果胶中的阿拉伯聚糖作为唯一碳源生长，表明具有胞外阿拉伯聚糖酶活性，并产生乳酸和乙酸，表明通过磷酸酮醇酶途径进行代谢。两种阿拉伯聚糖酶AbnA和AbnB通过亲和层析进行异源表达和纯化。AbnA能水解线性和分支状阿拉伯聚糖，而AbnB仅能水解线性阿拉伯聚糖。AbnA和AbnB的最适pH分别为6和7.5；两种酶的最适温度均为40℃。将降解阿拉伯聚糖的卷曲乳杆菌用作益生菌或与果胶形成合生元，可能会提高果胶产生短链脂肪酸的量，从而有益于宿主健康。要点：•卷曲乳杆菌中的阿拉伯聚糖利用操纵子编码两种胞外阿拉伯聚糖酶。•同一操纵子还编码阿拉伯糖转化的代谢基因。•在乳杆菌科中，胞外阿拉伯聚糖酶仅存在于乳酸杆菌属物种中。
