Abstract
Cyanobacterial biodiversity represents a significant reservoir for the potential discovery of new promising microorganism species. The purpose of this research is to explore the diversity of cyanobacteria and identify thermotolerant species found in the Zharkent geothermal spring situated in the Zhetysu region. At the time of water sampling from the spring, the temperature reached 75-80 °C. Cyanobacterial mats in the form of microbial agglomerations were identified on the stream periphery. Nine cyanobacterial species were found in these cyanobacterial mats, including Synechococcus, Phormidium, Gloeocapsa, Oscillatoria, Fischerella, and Nostoc. Among the cyanobacteria inhabiting the hot spring, 44% were non-heterocystous forms, while the rest exhibited heterocystous characteristics or were present as single-celled organisms. The order Oscillatoriales was the most predominant, including four species, followed by the order Chroococcales with three species. Pure cultures of cyanobacteria, such as Oscillatoria formasa, Nostoc commune, Anabaena cylindrica, and Fischerella thermalis, were isolated from the geothermal spring. These cultures were subjected to thermotolext56rance assessment at different temperatures. All examined strains exhibited a high growth rate at 45-50°C, with a slowdown at 55 and 60°C. The optimal growth temperature was 45-50°C, except for the Fischerella thermalis strain, which showed active growth at 60°C. The obtained results emphasize the potential application of the isolated strains in biotechnology.