CodY-regulated aminotransferases AraT and BcaT play a major role in the growth of Lactococcus lactis in milk by regulating the intracellular pool of amino acids
CodY-regulated aminotransferases AraT and BcaT play a major role in the growth of Lactococcus lactis in milk by regulating the intracellular pool of amino acids
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DOI：
10.1128/aem.69.6.3061-3068.2003
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发表时间：
2003-06-01
影响因子：
4.4
通讯作者：
Yvon, M
中科院分区：
文献类型：
--
作者：
Chambellon, E;Yvon, M
氨基转移酶催化大多数氨基酸的生物合成的最后一步和它们的催化剂的第一步，可能参与乳中乳酸乳球菌的生长。以前，我们从L.乳酸、AraT和BcaT，它们负责芳香族氨基酸、支链氨基酸和甲硫氨酸的转氨作用。在这项研究中，我们证明了AraT和BcaT的双重失活强烈地降低了L.牛奶中的lactis补充牛奶中的氨基酸和酮酸，这两种氨基转移酶的底物并没有改善双突变体的生长。相反，补充异亮氨酸或含有异亮氨酸的二肽的牛奶几乎完全抑制了双突变体的生长，而它不影响或仅轻微影响野生型菌株的生长。这些结果表明，AraT和BcaT在L.通过降解细胞内过量的异亮氨酸，这是负责生长抑制乳中的乳酸。异亮氨酸的生长抑制可能是由于CodY抑制蛋白水解系统，这是必要的最大增长的L。乳中的乳酸，因为CodY突变体的生长不受添加异亮氨酸到乳中的影响。此外，我们证明了AraT和BcaT是CodY调节子的一部分，因此受营养因素如碳水化合物和氮源的调节。
Aminotransferases, which catalyze the last step of biosynthesis of most amino acids and the first step of their catabolism, may be involved in the growth of Lactococcus lactis in milk. Previously, we isolated two aminotransferases from L. lactis, AraT and BcaT, which are responsible for the transamination of aromatic amino acids, branched-chain amino acids, and methionine. In this study, we demonstrated that double inactivation of AraT and BcaT strongly reduced the growth of L. lactis in milk. Supplementation of milk with amino acids and keto acids that are substrates of both aminotransferases did not improve the growth of the double mutant. On the contrary, supplementation of milk with isoleucine or a dipeptide containing isoleucine almost totally inhibited the growth of the double mutant, while it did not affect or only slightly affected the growth of the wild-type strain. These results suggest that AraT and BcaT play a major role in the growth of L. lactis in milk by degrading the intracellular excess isoleucine, which is responsible for the growth inhibition. The growth inhibition by isoleucine is likely to be due to CodY repression of the proteolytic system, which is necessary for maximal growth of L. lactis in milk, since the growth of the CodY mutant was not affected by addition of isoleucine to milk. Moreover, we demonstrated that AraT and BcaT are part of the CodY regulon and therefore are regulated by nutritional factors, such as the carbohydrate and nitrogen sources.