Showing papers by "Sathyanarayana N. Gummadi published in 2009"

Osmotic adaptation in halotolerant yeast, Debaryomyces nepalensis NCYC 3413: role of osmolytes and cation transport

Abstract: Debaryomyces nepalensis NCYC 3413, a food spoiling yeast isolated from rotten apple, has been previously demonstrated as halotolerant yeast. In the present study, we assessed its growth, change in cell size, and measured the intracellular polyol and cations (Na+ or K+) accumulated during growth in the absence and presence of different concentrations of salts (NaCl and KCl). Cells could tolerate 2 M NaCl and KCl in defined medium. Scanning electron microscopic results showed linear decrease in mean cell diameter with increase in medium salinity. Cells accumulated high amounts of K+ during growth at high concentrations of KCl. However, it accumulated low amounts of Na+ and high amounts of K+ when grown in the presence of NaCl. Cells grown in the absence of salt showed rapid influx of Na+/K+ on incubation with high salt. On incubation with 2 M KCl, cells grown at 2 M NaCl showed an immediate efflux of Na+ and rapid uptake of K+ and vice versa. To withstand the salt stress, osmotic adjustment of intracellular cation was accompanied by intracellular accumulation of polyol (glycerol, arabitol, and sorbitol). Based on our result, we hypothesize that there exists a balanced efflux and synthesis of osmolytes when D. nepalensis was exposed to hypoosmotic and hyperosmotic stress conditions, respectively. Our findings suggest that D. nepalensis is an Na+ excluder yeast and it has an efficient transport system for sodium extrusion.

Optimization of production of caffeine demethylase by Pseudomonas sp. in a bioreactor

Abstract: The effect of pH, aeration rate, and agitation rate on specific productivity of caffeine demethylase from Pseudomonas sp. was studied in a bioreactor. Maximum specific productivity of caffeine demethylase of 2,214 U g cell dry weight−1 h−1 was obtained at 0.27 vvm, 700 rpm, and pH 7.0. Under these conditions, volumetric oxygen transfer coefficient was 74.2 h−1, indicating that caffeine demethylase production by Pseudomonas sp. was highly oxygen-dependent. Different metabolite formation at different agitation and aeration rates can be used as a strategy for recovery of pharmaceutically important metabolites from caffeine by manipulation of conditions in a bacterial culture. This is the first report on production of high levels of caffeine demethylase in bioreactors.

GroES and GroEL are essential chaperones for refolding of recombinant human phospholipid scramblase 1 in E. coli

Abstract: Human phospholipid scramblase 1(hPLSCR1), when expressed in E. coli (BL-21 DE3), forms inclusion bodies that are functionally inactive. We studied the effects of various stress inducing agents and chaperones on soluble expression of hPLSCR1 in E. coli (BL-21 DE3). Addition of 3% (v/v) ethanol before induction and decreasing the post-induction temperature to 15°C increased the solubility of hPLSCR1 to ~10 and ~15% respectively. Presence of groES-groEL complex solubilized the hPLSCR1 to ~30% of the total hPLSCR1. Absence of groES-groEL did not improve the solubility of hPLSCR1 suggesting that groES and groEL are the essential chaperones for the correct folding of hPLSCR1 when over-expressed in E. coli.