Vido Karin, Le Bars Dominique, Mistou Michel-Yves, Anglade Patricia, Gruss Alexandra, Gaudu Philippe
Unité de Recherches Laitières et Génétique Appliquée, Institut National de la Recherche Agronomique, Domaine de Vilvert, 78352 Jouy en Josas, France.
J Bacteriol. 2004 Mar;186(6):1648-57. doi: 10.1128/JB.186.6.1648-1657.2004.
Sugar fermentation was long considered the sole means of energy metabolism available to lactic acid bacteria. We recently showed that metabolism of Lactococcus lactis shifts progressively from fermentation to respiration during growth when oxygen and heme are available. To provide insights into this phenomenon, we compared the proteomic profiles of L. lactis under fermentative and respiratory growth conditions in rich medium. We identified 21 proteins whose levels differed significantly between these conditions. Two major groups of proteins were distinguished, one involved in carbon metabolism and the second in nitrogen metabolism. Unexpectedly, enzymes of the proteolytic system (PepO1 and PepC) which are repressed in rich medium in fermentation growth were induced under respiratory conditions despite the availability of free amino acids. A triple mutant (dtpT dtpP oppA) deficient in oligopeptide transport displayed normal respiration, showing that increased proteolytic activity is not an absolute requirement for respiratory metabolism. Transcriptional analysis confirmed that pepO1 is induced under respiration-permissive conditions. This induction was independent of CodY, the major regulator of proteolytic functions in L. lactis. We also observed that pepO1 induction is redox sensitive. In a codY mutant, pepO1 expression was increased twofold in aeration and eightfold in respiration-permissive conditions compared to static conditions. These observations suggest that new regulators activate proteolysis in L. lactis, which help to maintain the energetic needs of L. lactis during respiration.
长期以来，糖发酵一直被认为是乳酸菌进行能量代谢的唯一方式。我们最近发现，在有氧和血红素存在的情况下，乳酸乳球菌在生长过程中其代谢会逐渐从发酵转变为呼吸作用。为了深入了解这一现象，我们比较了乳酸乳球菌在丰富培养基中发酵生长和呼吸生长条件下的蛋白质组图谱。我们鉴定出21种在这些条件下水平有显著差异的蛋白质。区分出了两大类蛋白质，一类参与碳代谢，另一类参与氮代谢。出乎意料的是，尽管有游离氨基酸存在，但在发酵生长的丰富培养基中受到抑制的蛋白水解系统的酶（PepO1和PepC）在呼吸条件下却被诱导表达。一个缺乏寡肽转运功能的三重突变体（dtpT dtpP oppA）表现出正常的呼吸作用，这表明蛋白水解活性的增加并非呼吸代谢的绝对必要条件。转录分析证实pepO1在允许呼吸的条件下被诱导表达。这种诱导独立于乳酸乳球菌中蛋白水解功能的主要调节因子CodY。我们还观察到pepO1的诱导对氧化还原敏感。在一个codY突变体中，与静态条件相比，pepO1的表达在通气条件下增加了两倍，在允许呼吸的条件下增加了八倍。这些观察结果表明，新的调节因子激活了乳酸乳球菌中的蛋白水解作用，这有助于维持乳酸乳球菌在呼吸过程中的能量需求。
