Astrobiology Workshop, Macquarie University July 12-13 2001

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A molecular phylogeny of culturable and non-culturable prokaryotes from Hamelin Pool, Shark Bay

Brett A Neilan (School of Microbiology and Immunology, The University of New South Wales)

Modern stromatolites represent a significant resource for studying microbial ecology and evolution. To better understand stromatolite morphogenesis, we employed specific genetic probes to characterise the cyanobacteria responsible for stromatolite construction in a range of environments. Isolates of cyanobacteria were collected from stromatolites in thermal springs, hypersaline lakes, and oceanic fringes on two continents. Strains included both unicellular and filamentous types. A PCR specific for cyanobacterial 16S rDNA was developed, and the resulting products of the DNA amplification reaction were sequenced and the data used to infer relatedness between the isolates studied and other members of the cyanobacterial radiation. Complete sequence was generated for the region from position 27 to 408 for 13 strains of cyanobacteria associated with stromatolites. All stromatolite-derived sequences were most closely related to cyanobacteria, as indicated by local sequence alignment. It was possible to correlate genetic identity with morphological nomenclatures and to expand the phylogeny of benthic cyanobacteria, and isolate designations were correlated with geographical origin and the morphology of the associated stromatolite. These inferences were also expanded to temporal variation in the dominant resident cyanobacterial species based on sampling of surface and core scinter laminations. Under the methods employed, only one cyanobacterial strain was detected in each sample, indicating the dominance of a specific clonal population of cyanobacteria at any one time in the stromatolite's biota. The data indicate that internal core samples of a stromatolite up to 10 years old can be successfully analysed to identify preserved cyanobacteria.