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首页> 外文期刊>Journal of bacteriology >Gene inactivation in Lactococcus lactis: histidine biosynthesis.
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Gene inactivation in Lactococcus lactis: histidine biosynthesis.

机译：乳酸乳球菌中的基因失活：组氨​​酸的生物合成。

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Lactococcus lactis strains from dairy and nondairy sources were tested for the ability to grow in the absence of histidine. Among 60 dairy strains tested, 56 required histidine, whereas only 1 of 11 nondairy strains had this requirement. Moreover, 10 of the 56 auxotrophic strains were able to grow in the presence of histidinol (Hol+), the immediate histidine precursor. This indicates that adaptation to milk often results in histidine auxotrophy. The histidine operon was detected by Southern hybridization in eight dairy auxotrophic strains tested. A large part of the histidine operon (8 kb, containing seven histidine biosynthetic genes and three unrelated open reading frames [ORFs]) was cloned from an auxotroph, which had an inactive hisD gene, as judged by its inability to grow on histidinol. Complementation analysis of three genes, hisA, hisB, and hisG, in Escherichia coli showed that they also were inactive. Sequence analysis of the cloned histidine region, which revealed 98.6% overall homology with that of the previously analyzed prototrophic strain, showed the presence of frameshift mutations in three his genes, hisC, hisG, and hisH, and two genes unrelated to histidine biosynthesis, ORF3 and ORF6. In addition, several mutations were detected in the promoter region of the operon. Northern (RNA) hybridization analysis showed a much lower amount of the his transcript in the auxotrophic strain than in the prototrophic strain. The mutations detected account for the histidine auxotrophy of the analyzed strain. Certain other dairy auxotrophic strains carry a lower number of mutations, since they were able to revert either to a Hol+ phenotype or to histidine prototrophy.
机译：测试了来自乳品和非乳品来源的乳酸乳球菌菌株在没有组氨酸的情况下生长的能力。在测试的60个乳品菌株中，有56个需要组氨酸，而11个非乳品菌株中只有1个具有此要求。此外，这56个营养缺陷型菌株中有10个能够在组氨酸的直接前体组氨酸（Hol +）存在下生长。这表明适应牛奶通常会导致组氨酸营养缺陷。通过Southern杂交在测试的八种乳品营养缺陷型菌株中检测到组氨酸操纵子。从营养缺陷型中克隆了大部分的组氨酸操纵子（8 kb，包含七个组氨酸生物合成基因和三个不相关的开放阅读框[ORF]），根据其不能在组蛋白醇上生长来判断，该营养缺陷型具有hisD基因失活。对大肠杆菌中的三个基因hisA，hisB和hisG的互补分析表明它们也没有活性。克隆的组氨酸区域的序列分析显示与先前分析的原养菌株的整体同源性为98.6％，显示在他的三个基因hisC，hisG和hisH以及两个与组氨酸生物合成无关的基因ORF3中存在移码突变和ORF6。另外，在操纵子的启动子区域中检测到一些突变。 Northern（RNA）杂交分析显示，营养缺陷型菌株中his转录物的数量远低于营养缺陷型菌株中his转录物的数量。检测到的突变解释了所分析菌株的组氨酸营养缺陷型。某些其他乳品营养缺陷型菌株携带较少数量的突变，因为它们能够还原为Hol +表型或组氨酸原养型。

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