At the Shores of a Vanishing Sea: Microbial Communities of Aral and Southern Aral Sea Region

Since the early 1960s, agricultural development in the irrigated areas of Uzbekistan resulted in a 90% decrease of the Aral Sea area, while the water salinity increased from 1 to 20%. The goal of the present work was to investigate the diversity of microbial communities of the water and sediments of the Western Aral Sea, as well as of the adjacent soils and basins, using high-throughput sequencing of the V4 variable region of the 16S rRNA genes. It was found that Aral Sea water with a salinity of 22% was inhabited by uncultured Archaea of the family Haloferacaceae (22-43%), as well as by bacteria of the genera Spiribacter and Psychroflexus. In the Aral Sea sediments, the share of archaea was much lower (2-17%), and among them uncultured Woesearchaeales predominated. Predominant bacteria of Aral sediments were sulfate reducers of the phylum Desulfobacterota, as well as members of the genera Fusibacter, Halanaerobium, Guyparkeria, Marinobacter, Idiomarina, and Thiomicrospira. In soil samples of the former Aral Sea bed with salinity of 8.2%, a variety of archaea of the phylum Halobacterota were present, as well as uncultured bacteria of the family Nitrosococcaceae. However, in the rhizosphere of Ewresmann's teresken plant (Kraschennininikovia ewresmanniana) growing there, archaea accounted for only 4% and mainly belonged to the family Nitrososphearaceae. In the rhizosphere microbiome, 33% of all prokaryotes were uncultured members of the phylum Actinomycetota. The microbial community of the teresken rhizosphere turned out to be similar to the soil microbial communities of the Ustyurt plateau located 3 km from the Aral Sea shore. The fresh water flowing along the former Aral Sea bed from an artificially drilled well also caused significant changes in the microbial communities: cyanobacterial mats and associated organotrophic bacteria developed along the stream bed with the increasing salinity (0.25-2%). Finally, the greatest prokaryotic diversity was found in the microbial community of the Lake Sudochye sediment with salinity of 1%, which is probably a modern analog of the Aral Sea microbiome before its shallowing.