Nidhi Gupta

Modulating electron transfer properties of gold nanoparticles for efficient biosensing.

Present study concerns modulating the electron transfer properties of gold nanoparticles through amino acid induced coupling among them. In addition to conductivity, the amino functionalization of the nanoparticles results in enhanced activity and operational stability of the biosensor fabricated using the same. Nanoparticles synthesized using amino acid as reducing agent (average diameter-20 nm), incorporate the natural coupling property of amino acids and are seen to align in a chain-like arrangement. The coupling of the individual nanoparticles to form chain like structure was confirmed by both absorption spectroscopy as well as transmission electron microscopy. The glucose biosensor developed by adsorption of glucose oxidase (GOx) enzyme onto these coupled gold nanoparticles showed enhanced efficiency as compared to the one with glucose oxidase immobilized onto gold nanoparticles synthesized using the conventional method (trisodium citrate as reducing agent). The fabricated biosensor demonstrated a wide linear concentration range from 1 μM-5mM and a high sensitivity of 47.2 μA mM(-1) cm(-2). Also, an enhanced selectivity to glucose was observed with negligible interference in the physiological range, from easily oxidizable biospecies, e.g. uric acid and ascorbic acid. Furthermore, the electrochemical biosensor has excellent long term stability- retaining greater than 85% of the biosensor activity up to 60 days.

Biodegradation of Carbazole by Newly Isolated Acinetobacter spp.

In this study, two bacterial isolates designated Alp6 and Alp7 were isolated from soil collected from dye industries and screened for their ability to degrade carbazole. Growing cells of the isolates Alp6 and Alp7 could degrade 99.9% and 98.5% of carbazole, respectively in 216xa0h. The specific activity for degradation by the resting cells of Alp6 was found to be 7.96xa0μmol/min/g dry cell weight, while for Alp7 it was 5.82xa0μmol/min/g dry cell weight. Phylogenetic analysis based on 16S rDNA gene sequences showed that isolates Alp6 and Alp7 belonged to the genus Acinetobacter. To the best of our knowledge, this is the first report on the Acinetobacter spp. showing utilization of carbazole as carbon and nitrogen source.

Biodegradation of Carbazole and Dibenzothiophene by Bacteria Isolated from Petroleum-Contaminated Sites

ABSTRACT This study reports the isolation of bacterial cultures, capable of selective removal of nitrogen and sulfur from carbazole and dibenzothiophene, respectively. The isolates utilizing carbazole were found to be suitable for biorefining. These were designated as P10 and P11, and were identified as Pseudomonas sp. Growing cells of P10 and P11 could utilize 77% carbazole in 250 and 120 h, respectively. Isolates showing utilization of dibenzothiophene were not suitable for biorefining industry. Results suggest these Pseudomonas isolates may be useful in petroleum biorefining for the selective removal of organically bound nitrogen from petroleum.

Degradation of carbazole, dibenzothiophene and polyaromatic hydrocarbons by recombinant Rhodococcus sp.

ObjectivesWith the view of designing a single biocatalyst for biorefining, carbazole dioxygenase was cloned from Pseudomonas sp. and expressed in Rhodococcus sp.ResultsThe recombinant, IGTS8, degraded both carbazole and dibenzothiophene at 400xa0mg/l in 24xa0h. Maximum carbazole degradation was in 1:1 (v/v) hexadecane/aqueous phase. Anthracene, phenanthrene, pyrene, fluoranthene and fluorine were also degraded without affecting the aliphatic component.ConclusionsRecombinant Rhodococcus sp. IGTS8 can function as a single biocatalyst for removing major contaminants of fossil fuels viz. dibenzothiophene, carbazole and polyaromatic compounds.

High-level expression, purification and characterization of carbazole dioxygenase, a three components dioxygenase, of Pseudomonas GBS.5

ObjectiveTo investigate the conversion of carbazole into 2′-aminobiphenyl-2,3-diol using carbazole dioxygenase (CARDO) that is a multicomponent enzyme consisting of homotrimeric terminal oxygenases (CarAa), a ferredoxin (CarAc) and a ferredoxin reductase (CarAd) unit, encoded by the carAa, carAc and carAd genes, respectively.ResultsThe enzyme subunits containing a GST tag were expressed independently in E. coli. The expressed proteins were purified by one-step immobilized affinity chromatography and three purified proteins could reconstitute the CARDO activity in vitro and showed activity against carbazole as well as against wide range of polyaromatic compounds.ConclusionThis method provides an efficient way to obtain an active carbazole dioxygenase with high yield, high purity and with activity against a wide range of polyaromatic compounds.

Dearomatization of diesel oil using Pseudomonas sp.

ObjectivesTo improve the quality of diesel fuel via removal of aromatic compounds using Pseudomonas sp.ResultsIn the present study Pseudomonas sp. was able to remove 94% of fluorene, 59% of phenanthrene, 49% of anthracene, 52% of fluoranthene, 45% of pyrene and 75% carbazole present in diesel oil. Additionally, it also does not affect the aliphatic content of fuel thus maintaining the carbon backbone of the fuel.ConclusionsPseudomonas sp. is a potential biocatalyst that can be used in the refining industry.