African Journal of Biomedical Research

Aim:  This is an established fact that thermophilic cyanobacteria typically thrive in sulfur-rich thermal springs, while mesophilic cyanobacteria have an optimal growth temperature range of 28°C to 37°C. The objective of this study was to investigate whether mesophilic cyanobacteria can grow at elevated temperatures in the presence of sulfide. Additionally, the study aimed to explore the role of sulfide in mitigating thermal stress in mesophilic cyanobacteria.   Research Methodology: Randomly isolated mesophilic cyanobacteria from rice fields of Patiala (India) were tested for their tolerance to thermal stress. Out of those, Geitlerinema acutissimum was able to grow at 42 °C, though the growth was less than at 28°C. Further  the growth of the mesophilic   Geitlerinema acutissimum   was examined both at its optimal growth temperature and under thermal stress, with and without the presence of sulfide. In parallel, the levels of enzymatic   antioxidants were assessed under these conditions. The tolerance of Geitlerinema acutissimum  to sulfide was evaluated by growing the organism in varying concentrations (0.5 to 5 mM) of sodium sulfide. It was found that the addition of 2.5 mM sulfide to cultures at 42°C alleviated the negative effects of thermal stress. The levels of enzymatic (SOD, POD, and CAT) antioxidants were measured in the test organism grown under thermal stress with and without sulfide. The incorporation of 2.5 mM and 0.5 mM sulphide, respectively in culture of mesophilic and thermophilic cyanobacteria enhanced these parameters under thermal stress with more pronounced effect in Geitlerinema acutissimum   . These results indicated the protective role of sulphide on these parameters. The activities of superoxide dismutase, peroxidase and  catalase   levels increased in presence of sulphide under thermal stress.   Result and conclusion: These results indicated the operation of   enzymatic   defense system in Geitlerinema acutissimum   to counter effect of thermal stress. The present study suggested that during thermal stress reactive oxygen species were produced, but  Sulphide appears to be a signal molecule under thermal stress to enhance levels of enzymatic antioxidants. Whether this mechanism applies to other mesophilic cyanobacteria can be further explored by studying additional strains. The organism exhibited reduced growth accompanied by an increase in antioxidants such as SOD, POD, and CAT. This study is the first to report the role of sulfide in mitigating thermal stress in Geitlerinema acutissimum, through activation of enzymatic antioxidant defense mechanisms.