Abstract
Photosynthetic prokaryotes known as cyanobacteria produce an extensive range of primary and secondary metabolites that serve multiple biotechnological and biomedical purposes. The non-model filamentous Phormidium species capture researchers’ attention through their biotechnological potentials from diverse metabolites and their ability to thrive in tough environments while producing bioactive compounds. In this study, a thermotolerant strain of Phormidium ambiguum was isolated from the Chundzha thermal springs in southeastern Kazakhstan and characterized morphologically, physiologically, and biochemically. This cyanobacterium demonstrated fast growth in its culture media along with significant accumulation of proteins (44.8% DM), carbohydrates (45% DM), and photosynthetic pigments like chlorophyll a and valuable carotenoids, including b-carotene, myxoxantophyll and zeaxanthin. The LC-ESI-MS/MS analysis of cyanobacterial non-polar extract identified 150 potential metabolites which include fatty acid derivatives, terpenoids and carotenoid-related compounds known for their antioxidant and antimicrobial properties, as well as immune system stimulation. Biological assays confirmed a weak antioxidant capacity in the DPPH test, while in immunological assays, the extract of P. ambiguum stimulated T lymphocyte proliferation and activation, as well as NK cell proliferation in vitro. It also exhibited moderate antibacterial activity towards tested Gram-negative and Gram-positive bacterial strains. While additional studies are required to address environmental robustness, biosynthetic regulation, and practical scalability, the present findings indicate that P. ambiguum represents a valuable non-model cyanobacterium for exploratory bioprospecting. Its metabolite profile and observed bioactivities support further investigation of this thermotolerant strain as a potential source of immunomodulatory, antioxidant, and antimicrobial compounds under controlled conditions.