Increasing tolerance to and degradation of high p-nitrophenol concentrations by inoculum size manipulations of Arthrobacter 4Hβ isolated from agricultural soil

Arthrobacter sp. 4Hβ, capable of degrading and utilizing high concentrations of p-nitrophenol (PNP) as sole carbon, nitrogen and energy source, was isolated from agricultural soil by a simple enrichment culture. Bacterial growth was accompanied by PNP disappearance and nitrite accumulation, with optimal degradation conditions of 30 °C and pH 8. The degradation pathway was via hydroquinone production. Prolonged acclimation period, lower tolerance and reduced degradation rate were obtained upon culturing the bacteria in the presence of increasing PNP concentrations. Complete and 17% removal of 400 and 800 mg l−1 initial PNP concentration, respectively, was obtained within 24 h of incubation. This latter inhibition of PNP degradation was overcome by increasing the inoculum size. The data suggest that manipulating inoculum size can increase strain 4Hβ's tolerance to, and degradation of high PNP concentrations, as required in certain bioremediation technologies.