PHENOTYPIC AND GENOTYPIC COMPARISON OF SYMBIOTIC AND FREE-LIVING CYANOBACTERIA FROM A SINGLE FIELD SITE

PCR amplification techniques were used to compare cyanobacterial symbi onts from a cyanobacterium; bryophyte symbiosis and free-living cyanob acteria from the same field site. Thirty-one symbiotic cyanobacteria w ere isolated from the hornwort Phaeoceros sp. at several closely space d locations, and 40 free-living cyanobacteria were isolated from the i mmediate vicinity of the same plants. One of the symbiotic isolates wa s a species of Calothrix, a genus not previously known to form bryophy te symbioses, and the remainder were Nostoc spp. Of the free-living st rains, two were Calothrix spp., three were Chlorogloeopsis spp, and th e rest were Nostoc spp. All of the symbiotic and all hut one of the fr ee-living strains were able to reconstitute the symbiosis with axenic cultures of both Phaeoceros and:the liverwort Blasia sp. Axenic cyanob acterial strains were compared by DNA amplification using PCR with eit her short arbitrary primers or primers specific for the regions flanki ng the 16S-23S rRNA internal transcribed spacer. With one exception, t he two techniques produced complementary results and confirmed fbr the first time that a diversity of symbiotic cyanobacteria infect Phaeoce ros in the field. Symbionts from adjacent colonies were different as o ften as they were the same, showing that the same thallus could be inf ected with many different cyanobacterial strains. Strains found to be identical by the techniques employed here were often found as symbiont s in different thalli at the same locale but were never found free-liv ing. Only one of the free-living strains, and none of the symbiotic st rains, was found at more than one sample site, implying a highly local ized distribution of strains.