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 r RNA-based cultivation-independent molecular fingerprinting, we compared the cyanobacterial composition of Solar Lake microbial mats and samples thereo f transplanted and maintained in new settings for extended periods of time. Significant changes in community composition, with clear replacement of th e dominant cyanobacterium, Microcoleus chthonoplastes, were detected in all cases. The most dramatic shifts occurred in a sample kept in the laborator y for 3 years, which resulted in dominance by an Oscillatoria-like cyanobac terium whose 16S rRNA closely matched that of a morphologically similar iso late from mats in Mexico. Transfer of Solar Lake mat to an artificial exper imental pond with incubation under seminatural conditions resulted in an in crease in cyanobacterial diversity. Judging from the molecular signatures, two novel, previously unrecognized and phylogenetically well-delimited cyan obacterial populations became dominant. Through cultivation, one population was shown to correspond to a filamentous, non-heterocystous group of Cyano bacteria with very narrow trichomes (approximate to 0.75-1.5 mum). The most dominant novel molecular signature, however, could not be identified by cu ltivation efforts or correlation with microscopy and, upon phylogenetic ana lyses, its 16S rRNA genes showed no particular close association to known c yanobacterial groups.