Duwat P, Sourice S, Cesselin B, Lamberet G, Vido K, Gaudu P, Le Loir Y, Violet F, Loubière P, Gruss A
Génétique Appliquée-URLGA, Institut National de la Recherche Agronomique, Domaine de Vilvert, 78352 Jouy en Josas, France.
J Bacteriol. 2001 Aug;183(15):4509-16. doi: 10.1128/JB.183.15.4509-4516.2001.
Oxygen is a major determinant of both survival and mortality of aerobic organisms. For the facultative anaerobe Lactococcus lactis, oxygen has negative effects on both growth and survival. We show here that oxygen can be beneficial to L. lactis if heme is present during aerated growth. The growth period is extended and long-term survival is markedly improved compared to results obtained under the usual fermentation conditions. We considered that improved growth and survival could be due to the capacity of L. lactis to undergo respiration. To test this idea, we confirmed that the metabolic behavior of lactococci in the presence of oxygen and hemin is consistent with respiration and is most pronounced late in growth. We then used a genetic approach to show the following. (i) The cydA gene, encoding cytochrome d oxidase, is required for respiration and plays a direct role in oxygen utilization. cydA expression is induced late in growth under respiration conditions. (ii) The hemZ gene, encoding ferrochelatase, which converts protoporphyrin IX to heme, is needed for respiration if the precursor, rather than the final heme product, is present in the medium. Surprisingly, survival improved by respiration is observed in a superoxide dismutase-deficient strain, a result which emphasizes the physiological differences between fermenting and respiring lactococci. These studies confirm respiratory metabolism in L. lactis and suggest that this organism may be better adapted to respiration than to traditional fermentative metabolism.
氧气是需氧生物生存和死亡的主要决定因素。对于兼性厌氧菌乳酸乳球菌来说，氧气对其生长和存活均有负面影响。我们在此表明，如果在通气培养过程中存在血红素，氧气对乳酸乳球菌可能是有益的。与在常规发酵条件下获得的结果相比，生长周期得以延长，长期存活率显著提高。我们认为生长和存活的改善可能归因于乳酸乳球菌进行呼吸作用的能力。为了验证这一想法，我们证实了在氧气和血红素存在的情况下，乳球菌的代谢行为与呼吸作用一致，且在生长后期最为明显。然后我们采用遗传学方法来证明以下几点。（i）编码细胞色素d氧化酶的cydA基因是呼吸作用所必需的，并且在氧气利用中起直接作用。cydA表达在呼吸条件下生长后期被诱导。（ii）如果培养基中存在前体而非最终的血红素产物，编码亚铁螯合酶（将原卟啉IX转化为血红素）的hemZ基因是呼吸作用所必需的。令人惊讶的是，在超氧化物歧化酶缺陷型菌株中观察到呼吸作用改善了存活率，这一结果强调了发酵型和呼吸型乳球菌之间的生理差异。这些研究证实了乳酸乳球菌中的呼吸代谢，并表明该生物体可能更适应呼吸作用而非传统的发酵代谢。
