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

Universität Kaiserslautern, Fachbereich Biologie, Abteilung Mikrobiologie, PO Box 3049, D-67653 Kaiserslautern, Germany¹

Author for correspondence: Bernhard Henrich. Tel: +49 631 2052347. Fax: +49 631 2053799. e-mail: henrich{at}rhrk.uni-kl.de

ArbZ from Lactobacillus delbrueckii subsp. lactis was previously shown to enable utilization of the ß-glucoside arbutin by Escherichia coli. The arbZ gene was cloned and expressed in the industrially used ß-glucoside-negative strain Lactobacillus helveticus 3036(62). The transformants were able to ferment not only arbutin, but also cellobiose, salicin and methyl-ß-glucoside (MßGlc). Cleavage of ß-glucosides by the transformants depended on the integrity of the cytoplasmic membrane, whereas in cell-free extracts only C₆-phosphorylated substrates were hydrolysed. This suggested that ArbZ is a phospho-ß-glycosidase. ArbZ activity in transformants of Lb. helveticus was subject to substrate induction mediated by the ß-glucosides arbutin, salicin and MßGlc, whereas cellobiose or the ß-galactoside lactose had no inducing effect. Northern blot analysis proved that induction by MßGlc was due to enhanced transcription of arbZ. Catabolite repression of arbZ induction was observed with glucose, mannose, fructose and galactose. The induction kinetics observed in the presence of these sugars indicated that at least two different mechanisms are operative in catabolite repression of arbZ in Lb. helveticus.

Keywords: Lactobacillus delbrueckii, ArbZ phospho-ß-glycosidase, substrate induction, catabolite repression

Abbreviations: MßGlc, methyl-ß-glucoside; oNPGal, o-nitrophenyl ß-D-galactopyranoside; oNPGalP, oNPGal 6-phosphate; pNPGlc, p-nitrophenyl ß-D-glucopyranoside; PTS, phosphotransferase system