Bacterial amylolytic activity enhancesβ-glucuronidase expression of amylase-negativeEscherichia coli strain in starch-medium

Abstract

The possibility of associating starch degradation with bacterial beta-glucuronidase expression was examined. We proved that starving, in starch medium, amylase-negative Escherichia coli (M94) which has constitutive beta-glucuronidase greatly reduces (p < 0.01) its background activity, but the addition of both cell-free supernatants or cells of Bacillus subtilis (B10) producing amylase greatly increases (p < 0.01) the E. coli beta-glucuronidase activity. Increases in activity were maximal when amylase in the medium ranged from 0.3 to 0.8 U ml-1 and pH from 6.8 to 6.3, whereas higher amylase activity interacted with E. coli viability and the effect on beta-glucuronidase was less evident. The impact of B. subtilis amylase on E. coli beta-glucuronidase induction, observed when the organisms were co-cultured, indirectly supports the hypothesis that amylolytic activity of hindgut bacteria may be effective on beta-glucuronidase induction of the climax microflora. This last finding is important in the health field, considering the implication between the deconjugating role of this enzyme and consequent activation of toxic and carcinogenic compounds.