High affinity p-nitrophenol oxidation by Bacillus sphaericus JS905

Abstract

Bacillus sphaericus JS905, isolated from an agricultural soil by selective enrichment, transforms p-nitrophenol (PNP) releasing only nitrite in stoichiometric amounts. The kinetics of PNP oxidation by this strain were successfully measured using an extant respirometric assay. Washed PNP-grown cells displayed very high substrate affinity ( K s) values of 0.003 and 0.023 mg PNP l −1, and low specific growth rate ( μ max) values of 0.021 and 0.019 h −1 at 30 and 37°C, respectively, at initial substrate concentration of 0.70 and 1.40 mg PNP l −1. Substrate inhibition was only evident at substrate concentration of 2.80 mg PNP l −1; the measured kinetic parameters were 0.055 and 0.043 h −1. Temperature had a small impact on the measured values for μ max and K s. Surprisingly, values for the endogenous decay coefficient (0.015 and 0.020 h −1 at 30 and 37°C, respectively) were of the same size as the specific growth rate. This indicates that net growth of B. sphaericus JS905 on PNP when used as a sole substrate is very small. As a result, the advantage of the high affinity PNP removal by this strain must probably depend on its growth on other primary substrates. The O 2/PNP stoichiometry indicates the consumption of 3 mol of molecular oxygen for the oxidation of each mol of PNP.