Pakistan Research Repository


Ali, Rashid (2000) MECHANISM OF SALT TOLERANCE IN MICROORGANISMS EXPOSED TO SALINE STRESS. PhD thesis, University of the Punjab, Lahore.



A novel strain of Candida tropicalis has been isolated from saline agricultural land of Pakistan. The organism can tolerate high Levels of salt (15% Nacl) and osmotic stress (50% glucose). One of the interesting features is that it requires salt/osmotic stress for growth induction in minimal medium with glycerol as a carbon source and undergoes morphogenic transition from yeast to filamentous form in the same medium without stress. It retains high level of K+ and allows less Na+ to enter inside the cell, thus maintaining high Na+/K+ ratio, which is in contrast to what has been observed in case of S. cerevisiae. A possible role of Na+ H+ antiportcr and H+-ATPasc in maintaining this high Na+/K+ ratio has been suggested. This high Na+/K+ ratio contributes to a larger extent in protecting Na+ sensitive enzyme like PAP-phosphatase to function normally even under high salt stress (Na+,Li+). Unlike, S. cerevisia, C. tropocalis regulates the synthesis of glycerol (major osmolyte) more efficiently thus Preventing disproportional deviation of carbon and energy into production of cellular osmolytes. It appears that in C, tropicalis physiological changes in the plasma membrane and an active glycerol transporter play important role in osmoregulation, which maintains glycerol concentration ratio (intra/extra cellular) greater than 570 fold. The phospholipase C mediated signal transduction is probably involvcd in the glycerol dependent morphogenic transition, osmotic strcss dependent growth induction and increase in respiration rate in minimal medium with glycerol as carbon source in C, tropicalis. Indicating a possible inter-dependence of stress response, metabolism and morphogenesis. In view of the complex and multigenic nature of the stress response, a functional approach has been adopted to identify critical processes for salt tolerance. As a result of this a Putative transcriptional regulator with strong homology to S. cerevisiae SFL1 gene (encoding a general transcriptional repressor) has been isolated which by over expression in multi copy plasmid YEp351 in S. cerevisiae strain RS 16 improves tolerance to Na+ and Li+.

Item Type:Thesis (PhD)
Uncontrolled Keywords:Salt Tolerance, Microorganisms, Saline Stress, Candida Tropicalis, Halotolerant Yeast, Osmoregulation, Polyol Metabolism,
Subjects:Biological & Medical Sciences (c) > Biological Sciences(c1) > Paleo-botany(c1.9)
ID Code:346
Deposited By:Mr Ghulam Murtaza
Deposited On:27 Jun 2006
Last Modified:04 Oct 2007 21:00

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