Characterization of cyanobacterial glnA gene diversity and gene expression in marine environments

PCR primers were designed and used to amplify glnA, the gene that encodes glutamine synthetase, from pure cultures of cyanobacteria and four samples from different marine environments. The glnA phylogeny was similar to that of the 16S rRNA gene, indicating that glnA gene sequences can be used to identify cyanobacteria expressing the glnA gene. Diverse unicellular cyanobacteria glnA genes were recovered from the North Pacific Subtropical Gyre, Monterey Bay, Chesapeake Bay and waters off the New Jersey coast. The majority of sequences were closely related to sequences from Synechococcus strains (78-88% identical DNA sequences). A few sequences that clustered with Prochlorococcus glnA genes were recovered from Monterey Bay and the North Pacific Subtropical Gyre. The expression of glnA was assayed by reverse transcriptase PCR to determine if there was a daily pattern in gene expression of samples collected from New Jersey's Longterm Environmental Observatory site (LEO-15). glnA expression varied over the day, with different glnA sequence types exhibiting different daily cycles. Results showed that the glnA gene can be used to characterize the diversity of natural populations of cyanobacteria, and to characterize gene expression patterns of individual species or strains.