Abstract
Elucidating the amino acid (AA) metabolism patterns of Streptococcus thermophilus has important effects on the precise design of nitrogen sources for high-cell-density culture. Transcriptomics and metabolomics were combined to reveal the cysteine, methionine, glutamate, glutamine, arginine, aspartate, asparagine and alanine metabolic pathways in S. thermophilus MN-ZLW-002, including glutathione. The changes in the synthesis, consumption and concentration of AAs and their metabolites, as well as regulatory genes with time were revealed. The metabolism of L-cysteine, L-glutamate, L-aspartate and L-alanine generated some potential functional metabolites. The metabolism of methionine and glutamate generated potential harmful metabolites. S. thermophilus MN-ZLW-002 can synthesize glutathione. Some potential functional metabolites have similar biological functions, indicating that S. thermophilus can resist environmental stresses through multiple mechanisms. The expression of some key genes in synthesis pathway of AA indicated that cysteine, methionine, asparagine, aspartate, arginine and lysine were insufficient or imbalance between nutrient components. The accumulation of large amounts of AA metabolites might be the primary cause of the overconsumption of AAs and influence the growth of S. thermophilus. The present study revealed the metabolic profiles of abovementioned AAs as well as those of regulatory genes and metabolites. These results were beneficial to the precise design of nitrogen sources and regulation of functional metabolites for the high-cell-density culture of S. thermophilus.
Highlights
Streptococcus thermophilus is widely used as a starter in the manufacturing of fermented dairy products
Based on our results and those of previous studies, we proposed the following series of questions: (i) How are these amino acid (AA) metabolized in S. thermophilus? (ii) What are the key genes involved in the regulation of the metabolism of these AAs? (iii) Which metabolites are generated? (IV) What pathway is responsible for the overconsumption of AAs? the metabolic pathways of various AAs in S. thermophilus during pH-controlled batch fermentations with a simulated high-density-culture environment have not systematically studied
Shortages of cysteine and methionine would completely prevent the growth of S. thermophilus[13]
Summary
Streptococcus thermophilus is widely used as a starter in the manufacturing of fermented dairy products. The reasons for the functions of the abovementioned AAs and their metabolic pathways in S. thermophilus have not been fully studied. Based on our results and those of previous studies, we proposed the following series of questions: (i) How are these AAs metabolized in S. thermophilus? The metabolic pathways of various AAs in S. thermophilus during pH-controlled batch fermentations with a simulated high-density-culture environment have not systematically studied. To answer the abovementioned questions, transcriptomics and metabolomics were combined to investigate the metabolic profiles of these AAs in S. thermophilus. Clarification of these questions will aid the understanding of the mechanistic action of AAs on the growth of S. thermophilus and the design of cultivation media
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