First report of microorganisms of Caucasus glaciers (Georgia)

Glaciers constitute freshwater reservoirs. They are the main contributors to sea level rise, play an important role in global carbon cycle and are the source of water for people. Despite extreme conditions, they are also a habitat for a number of cryophilic organisms. To fill the gap in the knowledge on the biota on glaciers in Caucasus, the aim of the study was to: (i) isolate and enumerate culturable heterotrophs; (ii) determine the number of coliforms and enterococci bacteria; and (iii) analyze total microbial 16S rRNA gene in cryoconite sediments, ice and gravel. The material was collected from two glaciers in Caucasus (Georgia, Svaneti region). Bacteria Aeromonas sp. and Pseudomonas sp. were found. The total number of culturable heterotrophic bacteria ranged from 0.2 × 101 colony forming units per mL in ice and gravel of the Chalaadi Glacier to 3.9 × 103 colony forming units per mL in a cryoconite sediments of the Adishi Glacier. The average number of 16S rRNA gene copies ranged from 5.3 × 105/g to 5.3 × 106/g in ice and gravel from Chalaadi Glacier and from 3.1 × 105/g to 1.5 × 107/g in a cryoconite of the Adishi Glacier. The 16S rRNA gene of five Pseudomonas sp. isolates was sequenced. Moreover, in the analyzed cryoconite material, a rare collembolan Gnathisotoma sp. was found, which constitutes the first record of springtails in cryoconite holes in the Northern hemisphere.