DETERMINATION OF N2 FIXATION POTENTIAL IN THE MARINE-ENVIRONMENT - APPLICATION OF THE POLYMERASE CHAIN-REACTION

Since determinations of aquatic N2 fixation potentials have been hampe red by the inability to quantitatively culture diazotrophs, we evaluat ed the polymerase chain reaction (PCR) for the detection of N2-fixing microorganisms in marine samples. We used previously described degener ate oligonucleotide primers which are universal for the nifH gene to d etermine the levels of detection for N2-fixing genes in seawater sampl es. A marine isolate of Klebsiella sp. was used as an internal standar d in DNA samples obtained from natural marine microbial assemblages to establish a limit of detection. We obtained a limit of detection equi valent to 10 cells ml-1. This approach is useful for determining the p otential for nitrogen fixation in the marine environment, regardless o f whether or not N2 fixation is occurring at the time of sampling.