Expression of the phospho-beta-glycosidase ArbZ from Lactobacillus delbrueckii subsp lactis in Lactobacillus helveticus: substrate induction and catabolite repression

ArbZ from Lactobacillus delbrueckii subsp. lactis was previously shown to e nable utilization of the beta-glucoside arbutin by Escherichia coli. The ar bZ gene was cloned and expressed in the industrially used beta-glucoside-ne gative strain Lactobacillus helveticus 3036(62). The transformants were abl e to ferment not only arbutin, but also cellobiose, salicin and methyl-beta -glucoside (M beta Glc). Cleavage of beta-glucosides by the transformants d epended on the integrity of the cytoplasmic membrane, whereas in cell-free extracts only C-6-phosphorylated substrates were hydrolysed, This suggested that ArbZ is a phospho-beta-glycosidase. ArbZ activity in transformants of Lb. helveticus was subject to substrate induction mediated by the beta-glu cosides arbutin, salicin and M beta Glc, whereas cellobiose or the beta-gal actoside lactose had no inducing effect. Northern blot analysis proved that induction by M beta Glc was due to enhanced transcription of arbZ. Catabol ite repression of arbZ induction was observed with glucose, mannose, fructo se and galactose. The induction kinetics observed in the presence of these sugars indicated that at least two different mechanisms are operative in ca tabolite repression of arbZ in Lb. helveticus.