嗜热链球菌在生长过程中产生的胞外多糖能够改善发酵乳制品质地,还具有多种生理生化功能。为探究组氨酸、异亮氨酸和谷氨酸对嗜热链球菌937胞外多糖的调控机制,该研究通过全基因组测序,分析了菌株胞外多糖合成途径,随后探究了3种氨基酸浓度提升对菌株生长、胞外多糖产量和性质以及epsABCD转录水平的影响。结果发现,该菌具有转运葡萄糖、蔗糖等特异性PTS转运系统和乳糖渗透酶;具有合成UDP-葡萄糖、UDP-半乳糖和dTDP-鼠李糖的潜力;染色体上存在由18个编码基因组成的eps基因簇。当3种氨基酸浓度提升至15 mmol/L时,菌株胞外多糖产量提升1.5倍、分子质量提升1.2倍、单糖组成摩尔比发生变化并且epsABCD转录水平均显著上调(P＜0.05)。3种氨基酸通过调控epsABCD的表达,提升了胞外多糖产量并调节了化学性质,该研究结果在基因水平上为嗜热链球菌胞外多糖生物合成提供了更好的解释。
The exopolysaccharides produced by Streptococcus thermophilus during its growth can improve the texture of fermented dairy products and have various physiological and biochemical functions.To explore the regulatory mechanism of histidine, isoleucine, and glutamate on the exopolysaccharide of S.thermophilus 937, this study analyzed the exopolysaccharide synthesis pathway of the strain through whole genome sequencing.It then explored the effects of the concentration of 3 amino acids on the strain growth, the production and properties of exopolysaccharides, and the transcription level of epsABCD of the strain.Results showed that the strain had a specific PTS for glucose and sucrose transport system and lactose osmotic enzyme.It had the potential to synthesize UDP-glucose, UDP-galactose, and dTDP-rhamnose.There was the eps gene cluster composed of 18 coding genes on the chromosome.When the concentration of 3 amino acids was increased to 15 mmol/L, the exopolysaccharide production of the strain increased by 1.5 times, the molecular weight increased by 1.2 times, the molar ratio of monosaccharide composition changed, and the epsABCD transcription level was significantly upregulated (P<0.05).The 3 amino acids enhanced the production of exopolysaccharides and regulated the properties by regulating the expression of epsABCD.The results of this study provided a better understanding of the exopolysaccharide biosynthesis of Streptococcus thermophilus at the gene level.
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