Prokaryotic Community Diversity Along an Increasing Salt Gradient in a Soda Ash Concentration Pond

The effect of salinity on prokaryotic community diversity in Abijata-Shalla Soda Ash Concentration Pond system was investigated by using high-throughput 16S rRNA gene 454 pyrosequencing. Surface water and brine samples from five sites spanning a salinity range of 3.4 % (Lake Abijata) to 32 % (SP230F, crystallizer pond) were analyzed. Overall, 33 prokaryotic phyla were detected, and the dominant prokaryotic phyla accounted for more than 95 % of the reads consisting of Planctomycetes, Bacteroidetes, candidate division TM7, Deinococcus-Thermus, Firmicutes, Actinobacteria, Proteobacteria, and Euryarchaeota. Diversity indices indicated that operational taxonomic unit (OTU) richness decreases drastically with increasing salinity in the pond system. A total of 471 OTUs were found at 3.4 % salinity whereas 49 OTUs were detected in pond SP211 (25 % salinity), and only 19 OTUs in the crystallization pond at 32 % salinity (SP230F). Along the salinity gradient, archaeal community gradually replaced bacterial community. Thus, archaeal community accounted for 0.4 % in Lake Abijata while 99.0 % in pond SP230F. This study demonstrates that salinity appears to be the key environmental parameter in structuring the prokaryotic communities of haloalkaline environments. Further, it confirmed that the prokaryotic diversity in Lake Abijata is high and it harbors taxa with low or no phylogenetic similarities to existing prokaryotic taxa and thus represents novel microorganisms.