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Biofilms microscopically dominated by cyanobacteria and diatoms of two CO2 degassing karst-water creeks in Germany were investigated for their diversities along a gradient of calcification using SSU rRNA gene cloning and sequencing from environmental samples. The recovered totals of 731/413 cyanobacteria/diatom clones were grouped at 97/98% similarity levels into 28/29 molecular OTUs widely spread over their corresponding sequence phylogenies forming mostly monophyletic subclades. Sequence comparisons with named reference strains from NCBI/GenBank as well as newly determined references from the SAG culture collection left about half of the cyanobacteria OTUs still unidentified. Most of the diatom OTUs could be identified at least at the generic level. To improve identification also cultures of cyanobacteria and diatoms were established that allowed even species identification of some diatoms, but also revealed additional cyanobacteria hard to identify which were not recovered in the clone libraries. A significant correlation of the relative OTU abundances in clone libraries with values of SIcalcite was found and, therefore, redundancy analysis distinguished highly calcified sites far from the spring from those less calcified closer to the spring. The noncalcified spring sites were clearly distinct from all other sites by the presence of four cyanobacteria OTUs exclusively retrieved and that no diatoms could be recovered from there. Four cyanobacteria and three diatom OTUs were recovered whose increasing relative abundance per clone library was correlated with increasing calcification. This may indicate that not only cyanobacteria, but also diatoms are more directly involved in the biogenic impact on tufa formation than assumed previously. [ABSTRACT FROM AUTHOR]

In the hypersaline Lake 21 on the Kiritimati Atoll (Kiribati, Central Pacific) laminated photosynthetic microbial mats have been found that were located above a layer of reticulate microbialites and characterized by large mineral deposits in the suboxic zone of the gelatinous mat matrix. The microbial population inhabiting these mats was studied using cultivation-dependent methods. For the enrichment of strains representing functional groups that are known to predominate in hypersaline microbial mats various cultivation techniques were applied including the use of highly selective defined media as well as more universal complex media. A total of 62 strains were cultured and identified by 16S rRNA gene sequencing. The obtained isolates represented a broad spectrum of metabolic types and could be affiliated to several major phylogenetic lineages of Bacteria and Archaea, including the classes Actinobacteria, Alphaproteobacteria, Bacilli, Bacteroidia, Chlorobia, Clostridia, Cyanobacteria, Deltaproteobacteria, Deferribacteres, Flavobacteriia, Gammaproteobacteria, Halobacteria, Methanomicrobia, Phycisphaerae, Spirochaetia as well as a novel phylogenetic lineage within the Planctomyces-Verrucomicrobia-Chlamydia superphylum, represented by the isolate L21-Fru-AB. Besides photoautotrophic cyanobacteria, most of the aerobic strains cultured could be assigned to a respiratory chemoheterotrophic or mixotrophic type of metabolism. A majority of the anaerobic isolates represented either saccharolytic fermentative bacteria or incompletely-oxidizing sulfate reducers that likely drive the anaerobic decomposition processes in this habitat. The obtained isolates will be useful for the reconstruction of various defined microbial communities in the laboratory in order to test hypotheses about the relevance of certain microbial clades on mineral precipitation in hypersaline mats. [ABSTRACT FROM AUTHOR]