Abstract
Lactobacillus paracasei is common in the non-starter lactic acid bacteria (LAB) community of raw milk cheeses. This species can significantly contribute to flavor formation through amino acid metabolism. In this study, the DNA and RNA of L. paracasei FAM18149 were sequenced using next-generation sequencing technologies to reconstruct the metabolism of the sulfur-containing amino acids cysteine and methionine. Twenty-three genes were found to be involved in cysteine biosynthesis, the conversion of cysteine to methionine and vice versa, the S-adenosylmethionine recycling pathway, and the transport of sulfur-containing amino acids. Additionally, six methionine-specific T-boxes and one cysteine-specific T-box were found. Five of these were located upstream of genes encoding transporter functions. RNA-seq analysis and reverse-transcription quantitative polymerase reaction assays showed that expression of genes located downstream of these T-boxes was affected by the absence of either cysteine or methionine. Remarkably, the cysK2-ctl1-cysE2 operon, which is associated with te methionine-to-cysteine conversion and is upregulated in the absence of cysteine, showed high read coverage in the 5′-untranslated region and an antisense-RNA in the 3′-untranslated region. This indicates that this operon is regulated by the combination of cis- and antisense-mediated regulation mechanisms. The results of this study may help in the selection of L. paracasei strains to control sulfuric flavor formation in cheese.
Highlights
Lactic acid bacteria (LAB), which can ferment diverse materials such as milk, meat, and plants, are widely used in food fermentation
The present study extends to the overall response of L. paracasei FAM18149 to cysteine and methionine using next-generation sequencing technologies, bioinformatic analysis, and PCR-based methods
The assembly of the PacBio reads obtained from the sequencing of Genomic DNA (gDNA) from L. paracasei FAM18149 resulted in six circular scaffolds (Supplementary Table S1)
Summary
Lactic acid bacteria (LAB), which can ferment diverse materials such as milk, meat, and plants, are widely used in food fermentation. Lactobacillus paracasei is of particular interest as it is found in a variety of habitats, including the human body, and fermented food. It is often found in cheese at the end of ripening, and the use of this species in adjunct cultures can improve ripening and flavor development (Beresford and Williams, 2004). The production of VSCs is probably associated with side activities of enzymes involved in cysteine and methionine biosynthesis. This hypothesis is supported by the observation that the recombinant
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