Mats of Microcoleus from alkaliphilic and halophilic communities

: A detailed description of the macrostructure, the ultrastructure, and the species diversity of alkaliphilic mat from Lake Khilganta (Buryatiya) is presented. The structure of this mat was found to be similar to that of halophilic mats from hypersaline lagoons of Lake Sivash (Crimea) that we studied earlier. Microcoleus chthonoplastes was the dominant form of cyanobacteria in both mats (in the alkaliphilic mat, Phormidium molle was another dominant form). Both mats had a pronounced laminated structure. However, unlike halophilic mats with calcium carbonate and gypsum laminas, the alkaliphilic mat contained calcium phosphate laminas instead of gypsum ones. The species diversity of microorganisms in the alkaliphilic mat was at least as rich as that in the halophilic mat; however, in the halophilic mat, the distribution of organisms between layers was more clear-cut. In the alkaliphilic mat, the highest species diversity was observed in the upper mat layers at the boundary between zones of oxygenic and anoxygenic photosynthesis. This fact can be explained by the ephemeral nature of soda lakes.