Antiserum to Nitrogenase Generated from an Amplified DNA Fragment from Natural Populations of Trichodesmium spp

A fragment of the nifH gene was amplified from natural populations of Trichodesmium spp. and cloned into a maltose-binding protein (MBP) expression vector. The peptide product of the amplified 359-bp fragment of nifH was cleaved from the fusion protein, purified, and used to generate a specific antibody to the Fe protein of nitrogenase. The antiserum recognized the MBP-nitrogenase fusion protein and the cleaved nif peptide product but not MBP. The antibody cross-reacted with nitrogenase from natural populations of Trichodesmium spp. from the Caribbean Sea and with a cultured isolate from the Kuroshio waters (Trichodesmium sp. strain NIBB1067). The same nifH fragment was amplified, cloned, and sequenced from Trichodesmium sp. strain NIBB1067 and was found to be 98% identical at both the protein and DNA levels to nifH from the Caribbean populations. Three of the six nucleotide differences between the Trichodesmium sp. strain NIBB1067 and the Trichodesmium spp. nifH sequence had also been found in a second sequence from the natural populations, indicating either that there is more than one strain of Trichodesmium sp. in natural assemblages or that there are multiple copies of nifH in the genome. This DNA fragment, which is easily amplified with the polymerase chain reaction, may provide a good indicator of species relatedness without requiring extensive cloning or sequencing. Furthermore, the use of the polymerase chain reaction in combination with a MBP protein fusion vector provides a rapid method for production of highly specific sera, starting with a small amount of DNA.