Long-term compositional changes after transplant in a microbial mat cyanobacterial community revealed using a polyphasic approach

Using a polyphasic approach that included microscopy, cultivation and 16S rRNA-based cultivation-independent molecular fingerprinting, we compared the cyanobacterial composition of Solar Lake microbial mats and samples thereof transplanted and maintained in new settings for extended periods of time. Significant changes in community composition, with clear replacement of the dominant cyanobacterium, Microcoleus chthonoplastes, were detected in all cases. The most dramatic shifts occurred in a sample kept in the laboratory for 3 years, which resulted in dominance by an Oscillatoria-like cyanobacterium whose 16S rRNA closely matched that of a morphologically similar isolate from mats in Mexico. Transfer of Solar Lake mat to an artificial experimental pond with incubation under seminatural conditions resulted in an increase in cyanobacterial diversity. Judging from the molecular signatures, two novel, previously unrecognized and phylogenetically well-delimited cyanobacterial populations became dominant. Through cultivation, one population was shown to correspond to a filamentous, non-heterocystous group of Cyanobacteria with very narrow trichomes (≅0.75-1.5 μm). The most dominant novel molecular signature, however, could not be identified by cultivation efforts or correlation with microscopy and, upon phylogenetic analyses, its 16S rRNA genes showed no particular close association to known cyanobacterial groups.