SUMMARY
Chlorococcum oleofaciens is one of the most studied representatives of the Chlorococcum genus, both on the ultrastructural and molecular levels. This alga is very interesting due to its ability to hypersynthetize saturated and unsaturated fatty acids and the possibility of using it as a promising object for biofuel production. This research is devoted to the study of the halotolerant strain of Ch. oleofaciens Ch-1 extracted from the water of the Khara River (Lake Elton Biosphere Reserve, Russia, a UNESCO World Heritage site), mineralization of 14‰. The strain Ch. oleofaciens Ch-1 was studied at the morphological level (light microscopy), as well as using molecular genetics methods (18S rDNA). The objectives of the study included establishing the range of halotolerance of the allocated strain of Ch. oleofaciens as a whole, revealing borders of level of mineralization that are optimum for algae growth, and also tracing features of its morphology and cycle of development in the conditions of various salinity. In the course of the studies performed it was established that the extracted strain of Ch. oleofaciens Ch-1 differed from the typical one by greater variability of some morphological features and had a wide ecological valence: the range of its halotolerance was 0–60‰. The maximum values of quantitative development of Ch. oleofaciens Ch-1 were registered at mineralization of 0–14‰. It is shown that with increasing salinity in the development cycle of the strain, the duration of the adaptation phase increases, the exponential phase decreases, small celled forms are replaced by large celled forms and reproduction features are noted. The obtained results can be used for selection of optimal conditions for cultivation of the halotolerant strain of Ch. oleofaciens for biotechnological purposes.