New Dominant Groups Along A Salinity Gradient

We describe community structure of two hypersaline solar salterns, an intermediate salinity pond (19%) and the other a crystallizer pond (37%) using pyrosequencing. The analyes of these large metagenomes (nearly 784 Mb), in combination with previously available datasets along the salinity gradient confirmed known trends e.g. the vast dominance of the square archaeon Haloquadratum walsbyi, but also revealed novel, dominant and previously unsuspected microbial groups. We describe for the first time, a low GC actinobacterial group abundant in low and intermediate salinity systems. The surprising diversity of the intermediate salinity habitat was also reflected in discovery of microbes that were not known to have halophilic tendencies e.g. Clavibacter, Gramella. Stringent metagenomic assembly revealed the a dominant novel low-GC euryarchaeota and another as yet unidentified gammaproteobacteria. Single cell sequencing of an archaeal genome obtained using multiple displacement amplification yielded a draft genome which indicated a photoheterotrophic, and polysaccharide degrading lifestyle of an abundant low GC euryarchaote, related to Nanohaloarchaea, with the lowest GC content described so far for any euryarchaeote. The assembled metagenomic contigs of the high GC gammaproteobacterium indicated that it is most closely related to the halophilic genus Alkalilimnicola and the non-halophilic genus Nitrococcus and is likely a heterotroph. These unexpected discoveries reveal the utility of an unbiased metagenomic approach to understanding and describing even previously well described microbial community assemblages.