AMPLIFICATION OF THE AMOA GENE FROM DIVERSE SPECIES OF AMMONIUM-OXIDIZING BACTERIA AND FROM AN INDIGENOUS BACTERIAL POPULATION FROM SEAWATER

Because the chemolithotrophic ammonium-oxidizing bacteria are an integ ral component of nitrogen biogeochemistry, a sensitive and accurate me thod to detect this ecologically important group of microorganisms is needed. The amoA gene of these organisms encodes the active site of am monia monooxygenase, an enzyme unique to this group of nitrifying bact eria. We report here the use of the PCR technique to detect the amoA g ene from pure cultures of chemolithotrophic ammonium-oxidizing bacteri a, ammonium oxidizers introduced into filtered seawater, and the natur al bacterial population of an unfiltered seawater sample. Oligonucleot ide primers, based on the published amoA sequence from Nitrosomonas eu ropaea, were used to amplify DNA from pure cultures of Nitrosomonas eu ropaea, Nitrosomonas cryotolerans, and Nitrosococcus oceanus and from bacteria in seawater collected offshore near the Florida Keys. Partial sequencing of the amplification products verified that they were amoA . These primers, used in conjunction with a radiolabeled amoA gene pro be from Nitrosomonas europaea, could detect Nitrosococcus oceanus inoc ulated into filter-sterilized seawater at 10(4) cells liter(-1). Nativ e marine bacteria containing amoA could also be detected at their natu rally occurring titer in oligotrophic seawater. Amplification of the g ene for ammonia monooxygenase may provide a method to estimate the dis tribution and relative abundance of chemolithotrophic ammonium-oxidizi ng bacteria in the environment.