Open AccessBranched-Chain Amino Acid Biosynthesis Is Essential for Optimal Growth of Streptococcus thermophilus in Milk
Author(s) -
Peggy Garault,
Catherine Letort,
Vincent Juillard,
Véronique Monnet
Publication year - 2000
Publication title -
applied and environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.552
H-Index - 324
eISSN - 1070-6291
pISSN - 0099-2240
DOI - 10.1128/aem.66.12.5128-5133.2000
Subject(s) - streptococcus thermophilus , biosynthesis , biochemistry , biology , bacteria , metabolic pathway , gene , structural gene , amino acid , mutant , genetics , lactic acid
Lactic acid bacteria are nutritionally demanding bacteria which need, among other things, amino acids for optimal growth. We identified the branched-chain amino acid (BCAA) biosynthesis pathway as an essential pathway for optimal growth ofStreptococcus thermophilus in milk. Through random insertional mutagenesis, we isolated and characterized two mutants for which growth in milk is affected as a consequence ofilvB andilvC gene interruptions. This situation demonstrates that the BCAA biosynthesis pathway is active inS. thermophilus . BCAA biosynthesis is necessary but not sufficient for optimal growth ofS. thermophilus and is subject to retro-inhibition processes. The specificity of the BCAA biosynthesis pathway inS. thermophilus lies in the independent transcription of theilvC gene encoding a keto acid reductoisomerase acting on acetolactate at the junction of the BCAA and acetoin biosynthesis pathways. The possible advantages forS. thermophilus of keeping this biosynthesis pathway active could be linked either to adaptation of the organism to milk, which is different than that of other dairy bacteria, or to the role of the pathway in maintaining the internal pH.