University of Alberta, Dept. of Agricultural, Food and Nutritional Science, Edmonton, Alberta, Canada.
University of Alberta, Dept. of Agricultural, Food and Nutritional Science, Edmonton, Alberta, Canada; Hubei University of Technology, College of Bioengineering and Food Science, Wuhan, Hubei, PR China.
Food Microbiol. 2020 Apr;86:103343. doi: 10.1016/j.fm.2019.103343. Epub 2019 Sep 30.
The bacterial conversion of glutamine to glutamate is catalyzed by glutamine-amidotransferases or glutaminases. Glutamine deamination contributes to the formation of the bioactive metabolites glutamate, γ-aminobutyrate (GABA) and γ-glutamyl peptides, and to acid resistance. This study aimed to investigate the distribution of glutaminase(s) in lactobacilli, and to evaluate their contribution in L. reuteri to amino acid metabolism and acid resistance. Phylogenetic analysis of the glutaminases gls1, gls2 and gls3 in the genus Lactobacillus demonstrated that glutaminase is exclusively present in host-adapted species of lactobacilli. The disruption gls1, gls2 and gls3 in L. reuteri 100-23 had only a limited effect on the conversion of glutamine to glutamate, GABA, or γ-glutamyl peptides in sourdough. The disruption of all glutaminases in L. reuteri 100-23Δgls1Δgls2Δgls3 but not disruption of gls2 and gls3 eliminated the protective effect of glutamine on the survival of the strain at pH 2.5. Glutamine also enhanced acid resistance of L. reuteri 100-23ΔgadB and L. taiwanensis 107q, strains without glutamate decarboxylase activity. Taken together, the study demonstrates that glutaminases of lactobacilli do not contribute substantially to glutamine metabolism but enhance acid resistance. Their exclusive presence in host-adapted lactobacilli provides an additional link between the adaptation of lactobacilli to specific habitats and their functionality when used as probiotics and starter cultures.
谷氨酰胺到谷氨酸的细菌转化由谷氨酰胺酰胺转移酶或谷氨酰胺酶催化。谷氨酰胺脱氨有助于生物活性代谢物谷氨酸、γ-氨基丁酸 (GABA) 和 γ-谷氨酰肽的形成，并有助于耐酸。本研究旨在调查谷氨酸酶在乳杆菌中的分布，并评估其在乳杆菌属中对氨基酸代谢和耐酸的贡献。乳杆菌属中谷氨酰胺酶 gls1、gls2 和 gls3 的系统发育分析表明，谷氨酸酶仅存在于宿主适应的乳杆菌种中。L. reuteri 100-23 中 gls1、gls2 和 gls3 的缺失对酸面团中谷氨酰胺转化为谷氨酸、GABA 或 γ-谷氨酰肽的影响有限。L. reuteri 100-23Δgls1Δgls2Δgls3 中所有谷氨酸酶的缺失，但 gls2 和 gls3 的缺失消除了谷氨酰胺对菌株在 pH 2.5 下存活的保护作用。谷氨酰胺还增强了缺乏谷氨酸脱羧酶活性的 L. reuteri 100-23ΔgadB 和 L. taiwanensis 107q 的耐酸性。总之，该研究表明，乳杆菌的谷氨酸酶对谷氨酰胺代谢没有实质性贡献，但增强了耐酸性。它们仅存在于宿主适应的乳杆菌中，为乳杆菌适应特定栖息地与其作为益生菌和发酵剂的功能之间提供了另一个联系。
