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The morphological and genetic diversity of cyanobacteria associated with cycads was examined using PCR amplification techniques and 16S rRNA gene sequence analysis. Eighteen symbiotic cyanobacteria were isolated from different cycad species. One of the symbiotic isolates was a species of Calothrix, a genus not previously reported to form symbioses with Cycadaceae family, and the remainder were Nostoc spp. Axenic cyanobacterial strains were compared by DNA amplification using PCR with either short arbitrary primers or primers specific for the repetitive sequences. Based on fingerprint patterns and phenograms, it was revealed that cyanobacterial symbionts exhibit important genetic diversity among host plants, both within and between cycad populations. A phylogenetic analysis based on 16S rRNA gene sequence analysis revealed that most of the symbiotic cyanobacterial isolates fell into well-separated clades.

G r o w t h o f wheat in a nitrogen-free hydroponic co-culture with a mutant strain o f the cyanobacterium Anabaena variabilis (strain SA-1) was e n h a n c e d over plants g r o w n with the parent strain SA-0. This increase was achieved in the dry weight, grain yield, and total nitrogen content o f the plants. Nitrogenase activity o f the mutant strain SA-1 was increased in a co-culture o f the cyanobacterial mutant with wheat plants c o m p a r e d to the activity o f the wild-type strain in association with wheat.

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