Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland.
Int J Food Microbiol. 2011 Jan 31;145(1):186-94. doi: 10.1016/j.ijfoodmicro.2010.12.011. Epub 2010 Dec 22.
Lactose metabolism is one of the most important areas of research on Lactic Acid Bacteria (LAB). In rapidly acidifying industrial Lactococcus lactis strains, lactose is transported by a lactose-specific phosphotransferase system (PTS) encoded by a plasmid. However, an alternative lactose catabolic pathway was evidenced in the plasmid-cured, and thus initially lactose-negative L. lactis IL1403. We showed that in this strain the chromosomally-encoded cellobiose-specific PTS system comprising the celB, ptcB and ptcA genes is also able to transport lactose. By expression studies in the wild type IL1403 strain and IBB550, its ccpA-deficient derivative, we demonstrated that celB, ptcB and ptcA are tightly regulated by the general catabolite repression system, whereas celB additionally requires the presence of cellobiose to be fully induced. The comparison of expression levels of sugar catabolic genes indicated that the efficiency of CcpA-mediated catabolic repression depends on conservation of the cre sequence, and that in the case of perfect matching with the cre consensus, CcpA still drives a strong repression even under non-repressing conditions.
乳糖代谢是乳酸菌（LAB）研究的最重要领域之一。在快速酸化的工业乳球菌 lactis 菌株中，乳糖由质粒编码的乳糖特异性磷酸转移酶系统（PTS）运输。然而，在质粒消除的、最初无乳糖的 L. lactis IL1403 中，已经证明存在替代的乳糖分解代谢途径。我们表明，在该菌株中，由 celB、ptcB 和 ptcA 基因组成的染色体编码的纤维二糖特异性 PTS 系统也能够运输乳糖。通过在野生型 IL1403 菌株和 IBB550（其 ccpA 缺陷型衍生物）中的表达研究，我们证明 celB、ptcB 和 ptcA 受到一般分解代谢物阻遏系统的紧密调控，而 celB 另外需要纤维二糖的存在才能完全诱导。糖分解代谢基因表达水平的比较表明，CcpA 介导的分解代谢阻遏的效率取决于 cre 序列的保守性，并且在与 cre 共识完全匹配的情况下，即使在非阻遏条件下，CcpA 仍能驱动强烈的阻遏。
