Régulations métaboliques de Lactococcus lactis en culture pure ou mixte dans le lait

Abstract

Metabolic regulation of Laetoeoeeus Jactis grown in pure or co-culture in milk. The cell responds to environmental changes by triggering or repressing the expression of its genes in order to adapt its metabolism to the new conditions. The measure of promoter activities could thus allow an indirect assessment of the extemal signais that the cell has integrated and the modification of its metabolic potential. We have developed a method using this idea to evaluate the bacterial metabolism independently of its extemalized products. Promoter activity is measured by following the expression of luciferases as reporter genes. Two different luciferase genes were used, luxAB from the bacteria Vibrio harveyi and lue from the eucaryote Photinus pyralis. The activity of the procaryotic and the eucaryotic enzymes is detectable by on-Iine measure- ment with whole cells when the cells provide the cofactors FMNH and ATP, respectively. This method is very sensitive, aIlowing the detection of weak promoter activity, or moderate transcription at low cell density. To demonstrate that this method is efficient, we studied promoter activities modulated by the presence of available amino acids with bacterial culture in milk. This allows us to see when the cells are starving, either in pure cultures or in mixed cultures with competing bac- teria. As the two luciferases can be detected independently in the same culture, this method should allow the study of the interaction between strains in coculture at the molecular level. © InralElsevier, Paris. metabolism Iluciferase 1 metabolic probe 1 mixte culture 1 Laetoeoeeus laetis/ milk