Abstract
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%. Euryarchaeota was found to be the dominant archaeal phylum containing 19 and 17 genera in sediments and brine, respectively. Phylotypes belonging to Halorubrum, Haloarcula, Halorhabdus, and Haloplanus were common in both sediments and brine. Occurence of Halobacterium and Natronomonas were exclusive to sediments while Halonotius was exclusive to brine. Among sediments, relative sequence frequency of Halorubrum, and Halorhabdus decreased while Haloarcula, Haloplanus, and Natronomonas increased with increasing salinity. Similarly, the relative abundance of Haloarcula and Halorubrum increased with increasing salinity in brine. Sediments and brine samples harbored about 20 and 17 bacterial phyla, respectively. Bacteroidetes, Proteobacteria, and Chloroflexi were the common bacterial phyla in both sediments and brine while Firmicutes were dominant albeit in sediments alone. Further, Gammaproteobacteria, Alphaproteobacteria, and Deltaproteobacteria were observed to be the abundant class within the Proteobacteria. Among the bacterial genera, phylotypes belonging to Rubricoccus and Halomonas were widely detected in both brine and sediment while Thioalkalispira, Desulfovermiculus, and Marinobacter were 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.
Highlights
Hypersaline environments like salt lakes and solar salterns are characterized by the presence of high content of salt (>3.5% salinity) and the diversity of organisms in these habitats is unique (Oren, 2002; Ventosa, 2006; Paul and Mormile, 2017)
The salinity of brine samples increased from 2.1% to 25.2% and 4% to 28% during initial salt harvesting (ISH) and peak salt harvesting (PSH) respectively (Table 1)
The salinity of sediment samples increased from 1.3% to 22.3% and 2.3% to 24.8% during ISH and PSH, respectively
Summary
Hypersaline environments like salt lakes and solar salterns are characterized by the presence of high content of salt (>3.5% salinity) and the diversity of organisms in these habitats is unique (Oren, 2002; Ventosa, 2006; Paul and Mormile, 2017). Coastal solar salterns, employed primarily for the production of edible sodium chloride, contain a series of pans for concentrating seawater, thereby facilitating the sequential precipitation of calcite (CaCO3), gypsum (CaSO4) followed by halite (NaCl), leaving behind salts of magnesium and potassium (Javor, 2002). These ecosystems make an excellent model for studying the diversity patterns due to the maintenance of constant salinity over a period with minimal external disturbances. Studies on hypersaline environments have gathered interest in the past four decades (Rodriguez-Valera et al, 1981; Ventosa et al, 1982, 1998) due to their importance in understanding the metabolic, physiological and genetic adaptation of organisms in high salinity coupled with their potential biotechnological applications (Oren, 1999, 2010; Siglioccolo et al, 2011; Yin et al, 2015; Gunde-Cimerman et al, 2018)
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