关键词: 植物乳杆菌；细菌素；氨基酸；基因表达；实时聚合酶链式反应

Abstract: The main purpose of this study is to explore the effects of amino acids on the growth and bacteriocin synthesis of Lactobacillus plantarum. L. plantarum KLDS1.0391 was cultured in chemically?defined?medium with predetermined concentrations of amino acids. The content of lactic acid in the culture supernatant was determined by high performance liquid chromatography (HPLC). The expression of the genes associated with bacteriocin and amino acid synthesis was analyzed by real-time polymerase chain reaction (real-time PCR). The results showed that the deficiency of Asp, His, Ile, Leu, Pro, Thr, Tyr, Asn, and Gln significantly reduced the growth capacity and bacteriocin production of the strain (P < 0.05). The deficiency of Glu, Gly, Ala, Cys, Arg, Phe, Ser, Trp and Val affected only the growth of the bacterium, but had no obvious effect on the synthesis of bacteriocin. Lys stress (deficiency or excess) had little effect on the growth of the strain, but significantly affected the synthesis of bacteriocin by it. The chromatographic results showed that single deficiency of Lys, Tyr, Ile, Leu, Met, Asp, Asn, Pro or Thr increased the lactic acid content. Real-time-PCR showed that the genes related to bacteriocin synthesis plnEF, plnD and plNC8HK were significantly down-regulated in the absence of Lys (P < 0.05), while they were up-regulated more significantly with increasing exogenous Lys up to 2.0 g/L. The key genes involved in amino acid synthesis dapG and yclM were significantly up-regulated in the absence of Lys, but down-regulated in the presence of 2.0 g/L Lys (P < 0.05). Therefore, it can be speculated that in the absence of Lys, the expression of genes such as dapG and yclM is up-regulated to synthesize a variety of proteins essential to the growth and metabolism of bacteria. Lysine can positively induce bacteriocin synthesis, which may play an important role as a substrate for bacteriocin synthesis.

Key words: Lactobacillus plantarum; bacteriocin; amino acid; gene expression; real-time polymerase chain reaction