Implications of alpha-amylase production and beta-glucuronidase expression in Escherichia coli strains.

Two Escherichia coli strains in which alpha-amylase production differed were used to study in depth some characteristics related to beta-glucuronidase induction by starch. The beta-glucuronidase background activity in Luria broth medium was comparable for the two isolates, but only amylase positive S1 was able to grow on starch molecules supplied as the sole carbon source. In this case growth resulted at higher beta-glucuronidase levels (p < 0.01) with respect to basal activity and the induced expression was maximal (6.1-fold) when cultures reached the stationary phase. Growth in the presence of a protein synthesis inhibitor (chloramphenicol) was associated with a marked reduction of activity. The beta-glucuronidase activity of amylase negative M94 remained unchanged during starvation on starch medium, but an induced response was observed with methylumbelliferyl-glucuronide. These results further support the hypothesis that starch metabolism is involved in the complex beta-glucuronidase regulation of E. coli strains. This is relevant not only for basic research but also to investigating gut microbial enzymology.