DETECTION AND CHARACTERIZATION OF CYANOBACTERIAL NIFH GENES

The DNA sequence of a 359-bp fragment of nifH was determined for the h eterocystous strains Anabaena sp. strain CA (ATCC 33037), Nostoc musco rum UTEX 1933, a Nostac sp., Gloeothece sp. strain ATCC 27152, Lyngbya lagerheimii UTEX 1930, and Plectonema boryanum IU 594. Results confir med that the DNA sequence of the 359-bp segment is sufficiently variab le to distinguish cyanobacterial nifH genes from other eubacterial and archaeobacterial nifH genes, as well as to distinguish heterocystous from nonheterocystous nifH genes. Nonheterocystous cyanobacterial nifH sequences were greater than 70 and 82% identical on the DNA and amino acid levels, respectively, whereas corresponding values for heterocys tous cyanobacterial nifH sequences were 84 and 91%. The amplified nifH fragments can be used as DNA probes to differentiate between species, although there was substantial cross-reactivity between the nifH ampl ification products of some strains. However, an oligonucleotide design ed from a sequence conserved within the heterocystous cyanobacteria hy bridized primarily with the amplification product from heterocystous s trains. The use of oligonucleotides designed from amplified nifH seque nces shows great promise for characterizing assemblages of diazotrophs .