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Abstract

Many early studies reported that yeasts caused spoilage of various high-sugar foods and high salted foods such as honey, raw sugar cane, jams. The dominant yeasts isolated from these foods belongs to the genus Zygosaccharomyces, the majorly of which are Z. rouxii, Z. bailii and Z. bisporus. The yeast Zygosaccharomyces bisporous is commercially known for its osmotolerance and moderately halotolerance. When exposed to NaCl, the cells experience both osmotic stress and ion toxicity. Specifically, this research work is focused on the evaluation of NaCl-induced stress responses of a food spoilage yeast Zygosaccharomyces bisporous, particularly with regard to yeast cell growth, viability and various biochemical mechanisms. Experiments were designed by pretreating cells with different sodium chloride concentrations (NaCl; 0.0 M, 0.5 M, 0.75 M, 1.0 M) growing in defined YEPD media and it was clearly observed that growth of cells was reduced with increased concentration of stress agent from 0.0 M to 1.0 M NaCl. Further, we assessed and compared the growth, percent viability and measured the intracellular polyols (mainly glycerol), osmolytes (like trehalose, glutathione) and cations (Na+ or K+) accumulated during growth leading to �osmotic adjustment� as a major element in accomplishing tolerance in the absence and presence of 1.0 M NaCl concentration. It was observed that salt stress is accompanied by an increase in intracellular level of trehalose, glutathione, glycerol and decreasing intracellular Na+/K+, thus reducing sodium toxicity that maintains intracellular redox balance compared to control cells. Moreover, elevated levels of protein carbonyl and lipid peroxidation product especially MDA as oxidation markers was determined and is known to be involved in the disrupting cell membranes. The study of the physiological and molecular mechanisms underlying yeast osmo-regulation and long term osmo-adaptation relate to the importance of these aspects in biotechnology and in agriculture but yet poorly understood. For instance, improving crop resistance to soil salinity stresses is a long-standing goal of agricultural biotechnology. Thus, the understanding of ion homeostasis mechanisms and the creation of salt tolerant yeasts and plants by metabolic engineering is a very important goal of salt stress research. The information hidden in yeast genes may be successfully transferred to other microorganisms, plants and other higher eukaryotes, resulting in the improvement of resistance capabilities. Thus, heterologous expression of genes associated with salt stress resistance remains one of the most important goals in salt stress research. Also, there is almost no substantial knowledge on basic areas of physiology, biochemistry and even genetics related with salt stress in these and other yeasts suggesting the study of more halotolerant yeasts, since they represent potentially good models to unveil some of the physiological and molecular mechanisms underlying yeast long-term extreme tolerance to salt which cannot be approached in less tolerant yeasts such as S. cerevisiae.

Biography

Akshya Sharma is currently pursuing her PhD from the Department of Biochemistry, Panjab University under the guidance of Professor Sukesh Chander Sharma. She has completed her MSc and BSc in Biochemistry from Panjab University. She also holds a certificate of Computer Applications in 2010.

Email: akshya.msdn@gmail.com