Nitrification and autotrophic nitrifying bacteria in a hydrocarbon-polluted soil

In vitro ammonia-oxidizing bacteria are capable of oxidizing :hydrocarbons: incompletely,This transformation is accompanied by competitive inhibition of ammonia monooxygenase, the first key enzyme in nitrification. The effect of hydrocarbon pollution on soil nitrification was examined in situ, In a microcosm study, adding diesel fuel hydrocarbon to an uncontaminated soil ( agricultural unfertilized soil) treated with ammonium sulfate dramatically reduced the amount of KCl-extractable nitrate but stimulated ammonium consu mption. In a soil with long history of pollution that was treated with ammo nium sulfate, 90% of the ammonium was transformed into nitrate after 3 week s of incubation. Nitrate production was twofold higher in the contaminated soil than in the agricultural soil to which hydrocarbon was not added. To a ssess if ammonia-oxidizing bacteria acquired resistance to inhibition by hy drocarbon, the contaminated soil was reexposed to diesel fuel. Ammonium con sumption was not affected, but nitrate production was 30% lower than nitrat e production in the absence of hydrocarbon. The apparent reduction in nitri fication resulted from immobilization of ammonium by hydrocarbon-stimulated microbial activity. These results indicated that the hydrocarbon inhibited nitrification in the noncontaminated soil (agricultural soil) and that amm onia-oxidizing bacteria in the polluted soil acquired resistance to inhibit ion by the hydrocarbon, possibly by increasing the affinity of nitrifying b acteria for ammonium in the soil.