ENRICHMENT CULTURE AND MICROSCOPY CONCEAL DIVERSE THERMOPHILIC SYNECHOCOCCUS POPULATIONS IN A SINGLE HOT-SPRING MICROBIAL MAT HABITAT

Recent molecular studies have shown a great disparity between naturall y occurring and cultivated microorganisms. We investigated the basis f or disparity by studying thermophilic unicellular cyanobacteria whose morphologic simplicity suggested that a single cosmopolitan species ex ists in hot spring microbial mats worldwide. We found that partial 16S rRNA sequences for all thermophilic Synechococcus culture collection strains from diverse habitats are identical. Through oligonucleotide p robe analysis and cultivation, we provide evidence that this species i s strongly selected for in laboratory culture to the exclusion of many more-predominant cyanobacterial species coexisting in the Octopus Spr ing mat in Yellowstone National Park The phylogenetic diversity among Octopus Spring cyanobacteria is of similar magnitude to that exhibited by all cyanobacteria so far investigated. We obtained axenic isolates of two predominant cyanobacterial species by diluting inocula prior t o enrichment. One isolate has a 16S rRNA sequence we have not yet dete cted by cloning. The other has a 16S rRNA sequence identical to a new cloned sequence we report herein. This is the first cultivated species whose 16S rRNA sequence has been detected in this mat system by cloni ng. We infer that biodiversity within this community is linked to guil d structure.