OXYGEN-DEPENDENT REGULATION OF THE EXPRESSION OF THE CATALASE GENE KATA OF LACTOBACILLUS SAKEI LTH677

The catalase gene katA of Lactobacillus sakei LTH677 was cloned and ex pressed in Escherichia coli UM2, Lactobacillus casei LK1, and Lactobac illus curvatus LTH1432, The last host is a catalase deficient plasmid- cured derivative of a starter organism used in meat fermentation, The regulation of katA expression was found to be the same in L, sakei LTH 677 and the recombinant strains, The addition of H2O2 to anaerobic cul tures, as well as a switch to aerobic conditions, resulted in a strong increase in KatA activity. The expression was investigated in more de tail with L, sakei LTH677 and L, curvatus LTH4002, The recombinant str ain LTH4002 did not accumulate H2O2 under glucose-limited aerobic cond itions and remained viable in the stationary phase, Under inductive co nditions, the katA-specific mRNA and the apoenzyme were synthesized de novo, Deletion derivatives of the katA promoter were produced, and th e regulatory response was investigated by fusion to the beta-glucuroni dase reporter gene gusA and expression in L. sakei LTH677. The fact th at gene expression was subject to induction was confirmed at the level of transcription and protein synthesis, A small putative regulatory s equence of at least 25 bp was identified located upstream of the -35 s ite. Competition experiments performed with L. sakei LTH677 harboring the fusion constructs consisting of the katA promoter and gusA reveale d that an activator protein is involved in the transcriptional inducti on of katA.