Influence of effluent irrigation on community composition and function of ammonia-oxidizing bacteria in soil

The effect of effluent irrigation on community composition and function of ammonia-oxidizing bacteria (AOB) in soil was evaluated, using techniques of molecular biology and analytical soil chemistry. Analyses were conducted o n soil sampled from lysimeters and from a grapefruit orchard which had been irrigated with wastewater effluent or fertilizer-amended water (FAW). Spec ifically, comparisons of AOB community composition were conducted using den aturing gradient gel electrophoresis (DGGE) of PCR-amplified fragments of t he gene encoding the alpha -subunit of the ammonia monooxygenase gene (amoA ) recovered from soil samples and subsequent sequencing of relevant bands. A significant and consistent shift in the population composition of AOB was detected in soil irrigated with effluent. This shift was absent in soils i rrigated with FAW, despite the fact that the ammonium concentration in the FAW was similar. At the end of the irrigation period, Nitrosospira-like pop ulations were dominant in soils irrigated with FAW, while Nitrosomonas-like populations were dominant in effluent-irrigated soils. Furthermore, DGGE a nalysis of the amoA gene proved to be a powerful toot in evaluating the soi l AOB community population and population shifts therein.