Ruchi Gaur

University at Buffalo, The State University of New York, Buffalo, New York, United States

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Publications (11)26.89 Total impact

  • R. Gaur · S. K. Khare
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    ABSTRACT: Abstract Lipases (triacylglycerol acylhydrolases, EC are ubiquitous biocatalysts known to catalyze the hydrolysis of water insoluble triglycerides in aqueous medium and carry out the reverse reaction (synthesis) under organic solvent rich medium. Microbial lipases have received a great deal of attention in the field of food technology, pharmaceutical sciences, chemical and detergent industries due to their stability, selectivity, mild operation conditions and broad substrate specificity. Despite these advantages, low activity and stability displayed in organic medium has restricted their commercial application in organic synthesis. Researchers have explored alternative ways to modify the enzymes making them suitable for use in non-conventional media. In this context, harvesting lipases from “Solvent Tolerant Microbes” has recently become an attractive approach. These microbes are able to grow in the presence of high concentrations of organic solvents, generally known to have detrimental effect on microorganisms. Such microbes survive through novel adaptation mechanisms and secretion of solvent stable enzymes having efficient functionality in solvent-rich media. These enzymes could be useful for bioconversion in non-conventional media. In the current review, this approach is described with an emphasis on characteristics, applications and genetic aspect of lipases from the genus Pseudomonas.
    No preview · Article · Sep 2011 · Biocatalysis and Biotransformation
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    ABSTRACT: Saccharomyces cerevisiae expresses two proteins that together support high-affinity Fe-uptake. These are a multicopper oxidase, Fet3p, with specificity towards Fe²⁺ and a ferric iron permease, Ftr1p, which supports Fe-accumulation. Homologues of the genes encoding these two proteins are found in all fungal genomes including those for the pathogens, Candida albicans and Cryptococcus neoformans. At least one of these loci represents a virulence factor for each pathogen suggesting that this complex would be an appropriate pharmacologic target. However, the mechanism by which this protein pair supports Fe-uptake in any fungal pathogen has not been elucidated. Taking advantage of the robust molecular genetics available in S. cerevisiae, we identify the two of five candidate ferroxidases likely involved in high-affinity Fe-uptake in C. albicans, Fet31 and Fet34. Both localize to the yeast plasma membrane and both support Fe-uptake along with an Ftr1 protein, either from C. albicans or from S. cerevisiae. We express and characterize Fet34, demonstrating that it is functionally homologous to ScFet3p. Using S. cerevisiae as host for the functional expression of the C. albicans Fe-uptake proteins, we demonstrate that they support a mechanism of Fe-trafficking that involves channelling of the CaFet34-generated Fe³⁺ directly to CaFtr1 for transport into the cytoplasm.
    Full-text · Article · Jun 2011 · Molecular Microbiology
  • Ruchi Gaur · Sunil Kumar Khare
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    ABSTRACT: Continuous hydrolysis of palm oil by Pseudomonas aeruginosa PseA lipase has been investigated in isooctane-aqueous biphasic system using statistical approach. PseA lipase could hydrolyze all the oils tested, palm oil being best hydrolyzed. Factors influencing palm oil hydrolysis were screened by Plackett–Burman screening and their optimal values were determined by response surface methodology (RSM). Under optimized conditions, 89% palm oil hydrolysis was achieved within 2 h at 30 °C. Due to its broad substrate specificity, the present lipase may find potential applications in bioconversion and bioremediation of oil rich industrial waste. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
    No preview · Article · Jan 2011 · Asia-Pacific Journal of Chemical Engineering
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    ABSTRACT: Aminopeptidase from a solvent tolerant strain Pseudomonas aeruginosa PseA was purified and studied for its biochemical and molecular characteristics. Ion-exchange chromatography resulted in 11.9-fold purification and 38% recovery of the 56 kDa enzyme. The enzyme was found to be stable over a pH range of 6.0–8.0 and appreciably thermostable up to 70 °C. PseA aminopeptidase exhibited Km of 3.02 mM and Vmax of 6.71 μmol/mg/min towards l-Leu-p-nitroanilide. Remarkable stability in both hydrophilic and hydrophobic solvents makes PseA aminopeptidase unique. Partial N-terminal sequence of enzyme showed exact match with probable aminopeptidase of P. aeruginosa PAO1, coded by gene pepB. Polymerase chain reaction amplified the 1611-bp open reading frame encoding a 57.51 kDa, 536 amino acid PseA PepB polypeptide. The deduced PseA PepB protein sequence contained a 24-residue signal peptide (2.57 kDa) followed by a 1.28 kDa propeptide and a mature product of 500 residues. Search for conserved domain in PseA aminopeptidase explored its place in zinc-metallopeptidase family. Primary sequence analysis showed the hydrophobic inclination of the protein; and the 3D structure modeling elucidated the presence of a high content of hydrophobic residues on its surface probably imparting solvent stability to it. The enzyme might find potential applications in non-aqueous enzymology due to its marked thermostability and striking solvent stability.
    No preview · Article · May 2010 · PROCESS BIOCHEMISTRY
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    R Gaur · S.K. Khare
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    ABSTRACT: Solvent-tolerant bacteria have emerged as a new class of micro-organisms able to grow at high concentrations of toxic solvents. Such bacteria and their solvent-stable enzymes are perceived to be useful for biotransformations in nonaqueous media. In the present study, the solvent-responsive features of a lipase-producing, solvent-tolerant strain Pseudomonas aeruginosa PseA have been investigated to understand the cellular mechanisms followed under solvent-rich conditions. The solvents, cyclohexane and tetradecane with differing log P-values (3.2 and 7.6 respectively), have been used as model systems. Effect of solvents on (i) the cell morphology and structure (ii) surface hydrophobicity and (iii) permeability of cell membrane have been examined using transmission electron microscopy, atomic force microscopy and other biochemical techniques. The results show that (i) less hydrophobic (low log P-value) solvent cyclohexane alters the cell membrane integrity and (ii) cells adapt to organic solvents by changing morphology, size, permeability and surface hydrophobicity. However, no such changes were observed in the cells grown in tetradecane. It may be concluded that P. aeruginosa PseA responds differently to solvents of different hydrophobicities. Bacterial cell membrane is more permeable to less hydrophobic solvents that eventually accumulate in the cytoplasm, while highly hydrophobic solvents have lesser tendency to access the membrane. To the best of our knowledge, these are first time observations that show that way of bacterial solvent adaptability depends on nature of solvent. Difference in cellular responses towards solvents of varying log P-values (hydrophobicity) might prove useful to search for a suitable solvent for carrying out whole-cell biocatalysis.
    Full-text · Article · Oct 2009 · Letters in Applied Microbiology
  • S. Khare · R. Gaur

    No preview · Article · Sep 2009 · New Biotechnology
  • Ruchi Gaur · Anshu Gupta · S. K. Khare
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    ABSTRACT: Lipase from a solvent tolerant strain of Pseudomonas aeruginosa PseA has been purified by gel exclusion chromatography leading to 8.6-fold purification and 51.6% recovery. Mr of purified lipase as determined by SDS–PAGE was estimated to be approximately 60 kDa. The optimum pH and temperature for activity of lipase were found to be 8.0 and 40 °C. The lipase was found to be stable in the pH range 6–8.5 and temperature range 25–50 °C. It was stable in presence of divalent metal ions like Ca2+, Mg2+ whereas Cu2+ and Zn2+ were found to be inhibitory. The enzyme activity was not affected significantly by 1 mM EDTA. β-Mercaptoethanol reduced the enzyme activity to 48% after 1 h whereas glutathione activated the lipase. Serine inhibitor PMSF showed no reduction in enzyme activity. Non-ionic detergents Tween-80 and Brij-35 stimulated the lipase activity. Cationic surfactant CTAB inhibited the enzyme activity whereas anionic surfactants sodium deoxycholate caused only 10% reduction in activity. Lipase preferred longer carbon chain (C16) fatty acid ester substrates over the shorter ones and showed random positional specificity for triolein hydrolysis.
    No preview · Article · Oct 2008 · PROCESS BIOCHEMISTRY
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    Ruchi Gaur · G N Gupta · M Vamsikrishnan · S K Khare
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    ABSTRACT: Highly active Pseudomonas aeruginosa lipase protein-coated microcrystals (PAL PCMC) have been prepared by immobilization of protein onto K2SO4 as excipient solid support carrier and n-propanol as precipitating solvent. Transmission electron micrographs confirmed the formation of PAL PCMC. These PCMC were found to be a catalytically more active and stable preparation for p-nitrophenyl palmitate hydrolysis in n-heptane, compared to free lipase. The V max, K m, and temperature optimum for PAL PCMC increased from 0.49 to 5.66 nmol min−1 mg−1, 589 to 679.8 mmol, and 40°C to 45°C, respectively. These were thermally more stable with 4.65, 2.56, and 1.24-fold improvement in half lives at 45°C, 55°C, and 60°C compared to free P. aeruginosa PseA lipase. Their catalytic efficiency was enhanced by tenfold over that of free enzyme. PAL PCMC offer a simple and effective technique for obtaining stable and efficient lipase preparation for biocatalysis in nonaqueous medium.
    Full-text · Article · Sep 2008 · Applied biochemistry and biotechnology
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    ABSTRACT: Three phase partitioning (TPP), a technique used in protein purification has been evaluated, for extraction of oil from three different plant sources viz: mango kernel, soybean and rice bran. The process consists of simultaneous addition of t-butanol (1:1,v/v) and ammonium sulphate (w/v) to a crude preparation/slurry. Under optimized condition, the protein appears as an interfacial precipitate between upper t-butanol containing oil and lower aqueous phase. Pretreatment of the slurries with a commercial enzyme preparation of proteases, Protizyme, followed by three phase partitioning resulted in 98%, 86% and 79% (w/w) oil yields in case of soybean, rice bran and mango kernel, respectively. The efficiency of the present technique is comparable to solvent extraction with an added advantage of being less time consuming and using t-butanol which is a safer solvent as compared to n-hexane used in conventional oil extraction process.
    No preview · Article · Mar 2007 · Bioresource Technology
  • Ruchi Gaur · Hema Pant · Ruchi Jain · S.K. Khare
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    ABSTRACT: Aspergillus oryzae β-galactosidase was immobilized by three different techniques, namely adsorption on celite, covalent coupling to chitosan and aggregation by cross-linking. These techniques were compared in terms of the yield of immobilized preparation, enzymatic characteristics, stability and efficiency in oligosaccharide synthesis. Immobilization led to increase in Km in each case. Immobilization on chitosan gave maximum enzyme yield and oligosaccharide synthesis. At 60 °C, the chitosan-immobilized enzyme was stabilized (by 1.6-fold) due to protection effect of the matrix. However, at 65 °C, the t1/2 of cross-linked enzyme aggregates (CLEA) of β-galactosidase was 1.07 h as compared to 0.79 h in the case of free enzyme. Both chitosan-immobilized enzyme and CLEA were used for oligosaccharide synthesis. Using 20% (w/v) lactose, the chitosan-immobilized enzyme gave maximum oligosaccharide yield (17.3% of the total sugar) as compared to free enzyme (10.0%) in 2 h at 40 °C. CLEA were instead found effective in lactose hydrolysis yielding 78% monosaccharide in 12 h.
    No preview · Article · Aug 2006 · Food Chemistry
  • Ruchi Gaur · Lata · S. K. Khare
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    ABSTRACT: Xylanase from Scytalidium thermophilum was immobilized on Eudragit L-100, a pH sensitive copolymer of methacrylic acid and methyl methacrylate. The enzyme was non-covalently immobilized and the system expressed 70% xylanase activity. The immobilized preparation had broader optimum temperature of activity between 55 and 65°C as compared to 65°C in case of free enzyme and broader optimum pH between 6.0 and 7.0 as compared to 6.5 in case of free enzyme. Immobilization increased the t1/2 of enzyme at 60°C from 15 to 30min with a stabilization factor of 2. The Km and Vmax values for the immobilized and free xylanase were 0.5% xylan and 0.89μmol/ml/min and 0.35% xylan and 1.01μmol/ml/min respectively. An Arrhenius plot showed an increased value of activation energy for immobilized xylanase (227kcal/mol) as compared to free xylanase (210kcal/mol) confirming the higher temperature stability of the free enzyme. Enzymatic saccharification of xylan was also improved by xylanase immobilization.
    No preview · Article · Oct 2005 · World Journal of Microbiology and Biotechnology

Publication Stats

264 Citations
26.89 Total Impact Points


  • 2011
    • University at Buffalo, The State University of New York
      • Department of Biochemistry
      Buffalo, New York, United States
  • 2005-2011
    • Indian Institute of Technology Delhi
      • Department of Chemistry
      New Dilli, NCT, India
  • 2010
    • Indian Institute of Technology Ropar
      • Department of Chemistry
      Rūpar, Punjab, India