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

Since determinations of aquatic N2 fixation potentials have been hampered by the inability to quantitatively culture diazotrophs, we evaluated the polymerase chain reaction (PCR) for the detection of N2-fixing microorganisms in marine samples. We used previously described degenerate oligonucleotide primers which are universal for the nifH gene to determine the levels of detection for N2-fixing genes in seawater samples. A marine isolate of Klebsiella sp. was used as an internal standard in DNA samples obtained from natural marine microbial assemblages to establish a limit of detection. We obtained a limit of detection equivalent to 10 cells ml-1. This approach is useful for determining the potential for nitrogen fixation in the marine environment, regardless of whether or not N2 fixation is occurring at the time of sampling.