Sulphide Ameliorates Thermal Induced Oxidative Stress in a Mesophilic Cyanobacterium Westiellopsis prolifica

Aims: Thermophilic cyanobacteria generally grow in sulphur containing thermal springs. Mesophilic cyanobacteria have optimal temperature in the range of 28°C to 37°C. The aim of the study was to see whether mesophilic cyanobacteria can grow at elevated temperature in the presence of sulphide? If yes, what is the role of sulphide in combating thermal stress in the mesophilic cyanobacteria?

Study Design: Growth of mesophilic cyanobacterium Westiellopsis prolifica was studied at its optimum growth temperature and in presence and absence of sulphide under thermal stress. Simultaneously, level of enzymatic and non-enzymatic antioxidants was studied under above conditions.

Place and Duration of Study: Department of Botany, Punjabi University, Patiala-147002, India, from November 2014 to December, 2015.

Methodology: Out of nine mesophilic cyanobacterial organisms screened, only Westiellopsis prolifica exhibited growth at 42°C, though less than at 28°C. The tolerance level of this organism to sulphide was determined by growing it in graded concentrations (0.5 to 5 mM) of sodium sulphide. Supplementation of 2.5 mM sulphide in the cultures at 42°C negated the negative effect of thermal stress. Enzymatic (SOD, POD, and CAT) and non-enzymatic (glutathione, proline, and ascorbic acid) antioxidants in the test organism grown under thermal stress and in the presence of sulphide were determined. Results: It was observed that level of enzymatic and non-enzymatic antioxidants (glutathione) increased while the content of ascorbic acid decreased in the presence of sulphide.

Conclusion: The organism exhibited less growth with a simultaneous increase of antioxidants such as SOD,POD, and CAT. This is the first report on the role of sulphide in ameliorating thermal stress in mesophilic cyanobacterium Westiellopsis prolifica by triggering enzymatic and non-enzymatic antioxidant defense system. This indicated that under thermal stress reactive oxygen species were produced which were scavenged by these antioxidants. Whether this is true for mesophilic cyanobacteria, in general, can be tested by studying some more strains.