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首页> 外文期刊>Applied Microbiology >Sequencing and Transcriptional Analysis of the Streptococcus thermophilus Histamine Biosynthesis Gene Cluster: Factors That Affect Differential hdcA Expression
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Sequencing and Transcriptional Analysis of the Streptococcus thermophilus Histamine Biosynthesis Gene Cluster: Factors That Affect Differential hdcA Expression

机译：嗜热链球菌组胺生物合成基因簇的测序和转录分析：影响差异hdcA表达的因素。

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Histamine, a toxic compound that is formed by the decarboxylation of histidine through the action of microbial decarboxylases, can accumulate in fermented food products. From a total of 69 Streptococcus thermophilus strains screened, two strains, CHCC1524 and CHCC6483, showed the capacity to produce histamine. The hdc clusters of S. thermophilus CHCC1524 and CHCC6483 were sequenced, and the factors that affect histamine biosynthesis and histidine-decarboxylating gene ( hdcA ) expression were studied. The hdc cluster began with the hdcA gene, was followed by a transporter ( hdcP ), and ended with the hdcB gene, which is of unknown function. The three genes were orientated in the same direction. The genetic organization of the hdc cluster showed a unique organization among the lactic acid bacterial group and resembled those of Staphylococcus and Clostridium species, thus indicating possible acquisition through a horizontal transfer mechanism. Transcriptional analysis of the hdc cluster revealed the existence of a polycistronic mRNA covering the three genes. The histidine-decarboxylating gene ( hdcA ) of S. thermophilus demonstrated maximum expression during the stationary growth phase, with high expression levels correlated with high histamine levels. Limited expression was evident during the lag and exponential growth phases. Low-temperature (4°C) incubation of milk inoculated with a histamine-producing strain showed lower levels of histamine than did inoculated milk kept at 42°C. This reduction was attributed to a reduction in the activity of the HdcA enzyme itself rather than a reduction in gene expression or the presence of a lower cell number.
机译：组胺是一种通过微生物脱羧酶的作用使组氨酸脱羧而形成的有毒化合物，可在发酵食品中积累。从总共筛选的69株嗜热链球菌菌株中，两个菌株CHCC1524和CHCC6483显示出产生组胺的能力。对嗜热链球菌CHCC1524和CHCC6483的hdc簇进行测序，研究了影响组胺生物合成和组氨酸脱羧基因（hdcA）表达的因素。 hdc簇以hdcA基因开始，然后是转运蛋白（hdcP），最后以功能未知的hdcB基因结束。这三个基因的方向相同。 hdc簇的遗传组织在乳酸菌群中表现出独特的组织，类似于葡萄球菌和梭状芽孢杆菌，因此表明可能通过水平转移机制获得。对hdc簇的转录分析显示存在覆盖这三个基因的多顺反子mRNA。嗜热链球菌的组氨酸脱羧基因（hdcA）在固定生长期表现出最大表达，高表达水平与高组胺水平相关。在滞后和指数生长期，表达有限。与保持在42°C的接种牛奶相比，用产生组胺的菌株接种的牛奶进行低温（4°C）孵育显示组胺水平较低。这种减少归因于HdcA酶本身活性的减少，而不是基因表达的减少或较低细胞数的存在。

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