The arbZ gene from Lactobacillus delbrueckii subsp. lactis confers to Escherichia coli the ability to utilize the beta-glucoside arbutin.

Abstract

From a genomic library of the industrially used strain Lactobacillus delbrueckii subsp. lactis DSM7290, a gene designated arbZ (869bp; encoding a 33.5kDa protein) was isolated by screening E. coli transformants for the ability to utilize the beta-glucoside arbutin. Out of 9000 transformants nine were able to ferment arbutin, whereas no utilization of the beta-glucosides salicin, esculin or cellobiose could be detected. Overexpression of arbZ using the T7-polymerase-T7-promoter-system resulted in the formation of insoluble, catalytically inactive protein aggregates (inclusion bodies). Accordingly, overexpression was not accompanied by an increase in ArbZ activity. Induction of arbZ controlled by the lac promoter under conditions that reduce protein aggregation resulted in a 12-fold increase in arbutin hydrolyzing activity of intact cells and a 13-fold increase in phospho-beta-glycosidase activity in cell-free extracts of the respective transformants. Nucleotide sequence analysis revealed a second gene upstream of arbZ that was designated arbX (830bp). ArbX (32.6kDa) shared similarity with several glycosyltransferases involved in the biosynthesis of lipopolysaccharides in Gram-negative bacteria. In Lb. delbrueckii subsp. lactis DSM7290 two transcripts, one covering arbX together with arbZ and one covering arbZ alone were detected by Northern blot analysis.