초록
<P><B>Abstract</B></P><P><I>Lactococcus lactis</I> is a widely used food bacterium mainly known for its fermentation metabolism. An important, and for long time overlooked, trait of this species is its ability to perform respiratory metabolism in the presence of heme and under aerobic conditions. There is no evidence however for the presence of an alternative respiration pathway and AOX activity. In this study, a cDNA fragment encoding the mitochondrial alternative oxidase, the enzyme responsible for alternative respiration, from a citric acid producing <I>Aspergillus niger</I> strain was cloned and expressed in <I>L. lactis</I> as a host strain. Expression of <I>aox1</I> conferred on this organism cyanide-resistant and salicylhydroxamate-sensitive growth. Bioreactor cultures under fully aerobic conditions of the transformed <I>L. lactis</I> showed that the alternative respiratory pathway operates and improves significantly the microorganism's response to oxidizing stress conditions as it enhances biomass production, suppresses lactate formation, and leads to accumulation of large amounts of nisin.</P>