Debaryomyces nepalensis, a halotolerant food-spoiling yeast could grow in complex (YEPD) medium at different pHs ranging between 3.0 and 11.0 in the absence of salt and at pH 3.0-9.0 in the presence of different concentrations of NaCl and KCl. The specific growth rate of D. nepalensis was not affected by the initial pH of the medium in the absence of salts, whereas it was affected in the presence of salts. At 2 M NaCl and KCl, the organism exhibited a synergistic effect on pH and salt stress, which was unique in the Debaryomyces species. Irrespective of the initial pH and salt, the intracellular pH of D. nepalensis was ~7.0. Significant organic acid was produced at neutral and alkaline pH and organic acid production increased with the increase in pH and salt. Very specific organic acids are produced in the presence of NaCl and KCl. Our observation would contribute to a better understanding of the physiological phenomenon of halotolerance in D. nepalensis. © 2008 Springer Science+Business Media, LLC.

Sathyanarayana Naidu Gummadi

Department Of Biotechnology

Sawan Kumar

carboxylic acid

POTASSIUM CHLORIDE

Sodium chloride

Alkalinity

article

cell pH

controlled study

culture medium

DEBARYOMYCES

DEBARYOMYCES NEPALENSIS

FOOD SPOILAGE

fungus growth

GROWTH ACCELERATION

growth rate

GROWTH REGULATION

nonhuman

priority journal

protein expression

SALT STRESS

SALT TOLERANCE

synthesis

Antifungal agents

Carboxylic acids

Culture Media

cytosol

Hydrogen-Ion Concentration

Saccharomycetales

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Current Microbiology

A Xylose reductase (XR) from the halotolerant yeast, Debaryomyces nepalensis NCYC 3413 was purified to apparent homogeneity. The enzyme has a molecular mass of 74. kDa with monomeric subunit of 36.4. kDa (MALDI-TOF/MS) and pI of 6.0. The enzyme exhibited its maximum activity at pH 7.0 and 45°C (21.2. U/mg). In situ gel digestion and peptide mass fingerprinting analysis showed 12-22% sequence homology with XR from other yeasts. Inhibition of the enzyme by DEPC (diethylpyrocarbonate) confirmed the presence of histidine residue in its active site. The enzyme exhibited high preference for pentoses over hexoses with greater catalytic efficiency for arabinose than xylose. The enzyme also showed absolute specificity with NADPH over NADH. The enzyme retained 90% activity with 100. mM of NaCl or KCl and 40% activity with 1. M KCl which suggest that the enzyme is moderately halotolerant and can be utilized for commercial production of xylitol under conditions where salts are present. © 2011 Elsevier Ltd.

Bioresource Technology

Purification and biochemical characterization of a moderately halotolerant NADPH dependent xylose reductase from Debaryomyces nepalensis NCYC 3413

The effect of salt, pH, and temperature stress on the cellular level of antioxidant enzymes, catalase and superoxide dismutase (SOD) and glycerol-3-phosphate dehydrogenase (G3PDH) was studied in Debaryomyces nepalensis NCYC 3413, a halotolerant yeast. The catalase activity increased in different phases, while SOD and G3PDH activities declined in late stationary phase. A significant increase in SOD activity was observed under different stress as compared to control. Salt and temperature stress enhanced the catalase activity where as it was suppressed by pH stress. G3PDH level increased with salt stress, however, no significant change was observed under pH and temperature stress. The observations recorded in this investigation suggested that D. nepalensis has an efficient protective mechanism of antioxidant enzymes and G3PDH against salt, pH, and temperature stresses. © 2010 Springer Science+Business Media, LLC.

Differential response of the catalase, superoxide dismutase and glycerol-3-phosphate dehydrogenase to different environmental stresses in Debaryomyces nepalensis NCYC 3413

This paper reports the interaction of salt (NaCl and KCl), initial pH, and temperature and their effects on the specific growth rate and lag phase of food spoiling halotolerant yeast, Debaryomyces nepalensis. The optimization of salt, initial pH, and temperature was carried out using response surface methodology based on central composite design. The mathematical model showed that salt has a significant effect on specific growth rate and lag phase of D. nepalensis. The optimal conditions of salt concentration, pH, and temperature of growth were found to be 0.3 M NaCl, 7.1, 26 °C and 0.6 M KCl, 5.6, 25°C, respectively. Under these conditions, a maximum specific growth rate of 0.41 and 0.5 h -1 was observed in medium containing NaCl and KCl, respectively. Lag phase can be increased most effectively either by increasing salt concentrations or both by decreasing (≤20°C) or increasing the temperature (≥40°C) with moderate (1.5 M) or low salt concentration (0.5 M), respectively. Results show that D. nepalensis need to generate weak acids to maintain the intracellular pH under pH and saline stress conditions. The results obtained in this study will be helpful in using optimal conditions for the maximum growth of the strain for the production of certain metabolites like organic acids and glycerol and designing food preservation procedures. © 2009 Springer Science + Business Media, LLC.

Food and Bioprocess Technology

Use of Response Surface Methodology to Study the Combined Effect of Salt, pH, and Temperature on the Growth of Food-Spoiling Halotolerant Yeast, Debaryomyces nepalensis NCYC 3413

Efficient conversion of hexose and pentose (glucose and xylose) by a single strain is a very important factor for the production of industrially important metabolites using lignocellulose as the substrate. The kinetics of growth and polyol production by Debaryomyces nepalensis NCYC 3413 was studied under single and mixed substrate conditions. In the presence of glucose, the strain produced ethanol (35.8 ± 2.3 g/l), glycerol (9.0 ± 0.2 g/l), and arabitol (6.3 ± 0.2 g/l). In the presence of xylose, the strain produced xylitol (38 ± 1.8 g/l) and glycerol (18 ± 1.0 g/l) as major metabolites. Diauxic growth was observed when the strain was grown with different combinations of glucose/xylose, and glucose was the preferred substrate. The presence of glucose enhanced the conversion of xylose to xylitol. By feeding a mixture of glucose at 100 g/l and xylose at 100 g/l, it was found that the strain produced a maximum of 72 ± 3 g/l of xylitol. A study of important enzymes involved in the synthesis of xylitol (xylose reductase (XR) and xylitol dehydrogenase (XDH)), glycerol (glycerol-3-phosphate dehydrogenase (G3PDH)) and ethanol (alcohol dehydrogenase (ADH)) in cells grown in the presence of glucose and xylose revealed high specific activity of G3PDH and ADH in cells grown in the presence of glucose, whereas high specific activity of XR, XDH, and G3PDH was observed in cells grown in the presence of xylose. To our knowledge, this is the first study to elaborate the glucose and xylose metabolic pathway in this yeast strain. © 2010 Springer-Verlag.

Applied Microbiology and Biotechnology

Metabolism of glucose and xylose as single and mixed feed in Debaryomyces nepalensis NCYC 3413: Production of industrially important metabolites

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.

Extremophiles : life under extreme conditions

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

In this study, Debaryomyces nepalensis NCYC 3413 isolated from rotten apple was studied for its halotolerance and its growth was compared with that of Saccharomyces cerevisiae in high salt medium. The specific growth rate of D. nepalensis was not affected by KCl even up to a concentration of 1 M, whereas NaCl and LiCl affected the growth of D. nepalensis. Among all tested salts, LiCl showed maximum inhibition on growth. At all conditions, halotolerance of D. nepalensis was much higher than that of S. cerevisiae. D. nepalensis showed maximum viability (80-100%) when grown in KCl, which was higher than with NaCl and LiCl. Pectinase production by D. nepalensis was noted at all high salt concentrations, namely, 2 M NaCl, 2 M KCl, and 0.5 M LiCl, and the maximum specific activity was observed when the strain was grown in 2 M NaCl. © 2007 Springer Science+Business Media, LLC.

Effect of salts on growth and pectinase production by halotolerant yeast, Debaryomyces nepalensis NCYC 3413

Methods in Microbiology

26 Characterization of Organic Compatible Solutes of Halotolerant and Halophilic Microorganisms

FEMS Yeast Research

Mechanisms underlying the halotolerant way of

Growth Under Alkaline Conditions of the Salt-Tolerant Yeast Debaryomyces hansenii IFO10939

Yeast

Saccharomyces cerevisiaeandZygosaccharomyces mellisexhibit different hyperosmotic shock responses

Growth of halotolerant food spoiling yeast Debaryomyces nepalensis NCYC 3413 under the influence of pH and salt

Journal	Current Microbiology
ISSN	03438651
Open Access	No