Properties of in situ Escherichia coli -D-glucuronidase (GUS): evaluation of chemical interference on the direct enzyme assay for faecal pollution detection in water

Abstract

A study of the activity of Escherichia coli
-D-glucuronidase (GUS) in polluted stagnant and running water samples was performed with an objective of assessing the viability of a direct marker enzyme assay as a suitable alternative to membrane filtration for the indication of faecal pollution in water intended for drinking purposes. The effects of temperature, pH and the presence of different ions on enzyme activity were investigated. GUS exhibited optimal activity at 40oC over a broad pH range (5-9). In general, CO3 2- (as Na2CO3), Cl- (NaCl) and NO3 - (KNO3) increased GUS activity, while ferric chloride (FeCl3), OCl- (as NaOCl) and ferulic acid were inhibitory. However, the enzymatic response to these effectors differed with the source of the sample. Therefore, when these compounds are present in water intended for drinking purposes they can either exaggerate or give false negatives with regards to GUS activity. Environmental GUS properties are different from those of the commercially available (and pure) E. coli GUS. This helps to explain difficulties encountered in applying laboratory methods (developed through seeding of pure water samples with pure enzymes and cultures) to environmental analyses.