Rhizosphere soil enzymes as indicators of perturbations caused by enzyme substrate addition and inoculation of a genetically modified strain of Pseudomonas fluorescens on wheat seed

Abstract

Comparative assays for determining chitobiosidase, N-acetyl glucosaminidase, acid phosphatase, alkaline phosphatase, phosphodiesterase, aryl sulfatase and urease activities from small samples of soil were developed. The enzyme assays and ATP biomass assessments were used to monitor perturbations caused by the presence of Pseudomonas fluorescens in the rhizosphere of wheat. Microbial biomass as well as the measured enzyme activities decreased with depth, except for acid phosphatase activity, which was similar at all depths. A combined substrate mix addition of urea, colloidal chitin and glycerophosphate significantly increased N-acetyl glucosaminidase, chitobiosidase, aryl sulfatase and urease activities, but did not cause a significant difference in acid and alkaline phosphatase and phosphodiesterase activities. Inoculation of seeds with P. fluorescens resulted in significant increases in rhizosphere chitobiosidase and urease activities at 5–20-cm depth and a significant decrease in alkaline phosphatase activity. Inoculation with the bacterium in the presence of substrate mix gave opposing effects to those treatments without substrate mix addition: chitobiosidase, aryl sulfatase and urease activities were significantly lower, and alkaline phosphatase was significantly higher at the 5–20-cm depth interval with inoculation of bacteria. Biomass values for the combined bacteria and substrate mix treatment were significantly higher than the substrate mix alone treatment.