Transient Dynamics of Archaea and Bacteria in Sediments and Brine Across a Salinity Gradient in a Solar Saltern of Goa, India

The microbial fluctuations along an increasing salinity gradient during two different salt production phases - initial salt harvesting (ISH) phase and peak salt harvesting (PSH) phase of Siridao solar salterns in Goa, India were examined through high-throughput sequencing of 16S rRNA genes on Illumina MiSeq platform. Elemental analysis of the brine samples showed high concentration of sodium (Na+) and chloride (Cl-) ions thereby indicating its thalassohaline nature. Comparison of relative abundance of sequences revealed that Archaea transited from sediment to brine while Bacteria transited from brine to sediment with increasing salinity. Frequency of Archaea was found to be significantly enriched even in low and moderate salinity sediments with their relative sequence abundance reaching as high as 85%.Euryarchaeotawas found to be the dominant archaeal phylum containing 19 and 17 genera in sediments and brine, respectively. Phylotypes belonging toHalorubrum,Haloarcula,Halorhabdus, andHaloplanuswere common in both sediments and brine. Occurence ofHalobacteriumandNatronomonaswere exclusive to sediments whileHalonotiuswas exclusive to brine. Among sediments, relative sequence frequency ofHalorubrum, andHalorhabdusdecreased whileHaloarcula,Haloplanus, andNatronomonasincreased with increasing salinity. Similarly, the relative abundance ofHaloarculaandHalorubrumincreased with increasing salinity in brine. Sediments and brine samples harbored about 20 and 17 bacterial phyla, respectively.Bacteroidetes,Proteobacteria, andChloroflexiwere the common bacterial phyla in both sediments and brine whileFirmicuteswere dominant albeit in sediments alone. Further,Gammaproteobacteria,Alphaproteobacteria, andDeltaproteobacteriawere observed to be the abundant class within theProteobacteria. Among the bacterial genera, phylotypes belonging toRubricoccusandHalomonaswere widely detected in both brine and sediment whileThioalkalispira,Desulfovermiculus, andMarinobacterwere selectively present in sediments. This study suggests that Bacteria are more susceptible to salinity fluctuations than Archaea, with many bacterial genera being compartment and phase-specific. Our study further indicated that Archaea rather than Bacteria could withstand the wide salinity fluctuation and attain a stable community structure within a short time-frame.