AUTHOR=Mutaguchi Yuta , Kasuga Kano , Kojima Ikuo 

TITLE=Production of d-Branched-Chain Amino Acids by Lactic Acid Bacteria Carrying Homologs to Isoleucine 2-Epimerase of Lactobacillus buchneri

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01540

DOI=10.3389/fmicb.2018.01540

ISSN=1664-302X

ABSTRACT=<p>Isoleucine 2-epimerase (ILEP) is a novel branched-chain amino acid racemase isolated from <italic>Lactobacillus buchneri</italic>. In this study, we examined production of free <sc>d</sc>-branched-chain amino acids such as <sc>d</sc>-valine, <sc>d</sc>-leucine, and <sc>d</sc>-<italic>allo</italic>-isoleucine, using lactic acid bacteria carrying homologs to ILEP. Twelve selected strains of lactic acid bacteria were grown at optimal growth temperatures and accumulation of <sc>d</sc>-branched-chain amino acids in the medium was monitored in exponential, early stationary, and stationary phases. To analyze the <sc>d</sc>-branched-chain amino acids, enantiomers in the medium were initially converted into diastereomers using pre-column derivatization with <italic>o</italic>-phthaldialdehyde plus <italic>N</italic>-isobutyryl-<sc>l</sc>-cysteine. The resultant fluorescent isoindole derivatives were analyzed on an octadecylsilyl stationary phase using ultra-high performance liquid chromatography. The analyses revealed that the seven following lactic acid bacteria carrying homologs showing 53–60% amino acid sequence identity to the <italic>L. buchneri</italic> ILEP accumulate <sc>d</sc>-branched-chain amino acids: <italic>Lactobacillus fermentum</italic> and <italic>Weissella paramesenteroides</italic> produce <sc>d</sc>-valine, <sc>d</sc>-leucine, and <sc>d</sc>-<italic>allo</italic>-isoleucine; <italic>Lactobacillus reuteri, Leuconostoc mesenteroides</italic> subsp. <italic>mesenteroides</italic>, and <italic>Leuconostoc gelidum</italic> subsp. <italic>gasicomitatum</italic> accumulate <sc>d</sc>-leucine and <sc>d</sc>-<italic>allo</italic>-isoleucine; and <italic>Lactobacillus vaginalis</italic> and <italic>Leuconostoc pseudomesenteroides</italic> produce <sc>d</sc>-<italic>allo</italic>-isoleucine. These results suggest that <sc>d</sc>-branched-chain amino acids are produced by a variety of lactic acid bacteria species, particularly those carrying homologs to the ILEP.</p>