Suparna Mukherji

Strain specificity in antimicrobial activity of silver and copper nanoparticles.

The antimicrobial properties of silver and copper nanoparticles were investigated using Escherichia coli (four strains), Bacillus subtilis and Staphylococcus aureus (three strains). The average sizes of the silver and copper nanoparticles were 3 nm and 9 nm, respectively, as determined through transmission electron microscopy. Energy-dispersive X-ray spectra of silver and copper nanoparticles revealed that while silver was in its pure form, an oxide layer existed on the copper nanoparticles. The bactericidal effect of silver and copper nanoparticles were compared based on diameter of inhibition zone in disk diffusion tests and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of nanoparticles dispersed in batch cultures. Bacterial sensitivity to nanoparticles was found to vary depending on the microbial species. Disk diffusion studies with E. coli and S. aureus revealed greater effectiveness of the silver nanoparticles compared to the copper nanoparticles. B. subtilis depicted the highest sensitivity to nanoparticles compared to the other strains and was more adversely affected by the copper nanoparticles. Good correlation was observed between MIC and MBC (r2=0.98) measured in liquid cultures. For copper nanoparticles a good negative correlation was observed between the inhibition zone observed in disk diffusion test and MIC/MBC determined based on liquid cultures with the various strains (r2=-0.75). Although strain-specific variation in MIC/MBC was negligible for S. aureus, some strain-specific variation was observed for E. coli.

Size-controlled silver nanoparticles synthesized over the range 5–100 nm using the same protocol and their antibacterial efficacy

A systematic and detailed study for size-specific antibacterial efficacy of silver nanoparticles (AgNPs) synthesized using a co-reduction approach is presented here. Nucleation and growth kinetics during the synthesis process was precisely controlled and AgNPs of average size 5, 7, 10, 15, 20, 30, 50, 63, 85, and 100 nm were synthesized with good yield and monodispersity. We found the bacteriostatic/bactericidal effect of AgNPs to be size and dose-dependent as determined by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of silver nanoparticles against four bacterial strains. Out of the tested strains, Escherichia coli MTCC 443 and Staphylococcus aureus NCIM 5201 were found to be the most and least sensitive strains regardless of AgNP size. For AgNPs with less than 10 nm size, the antibacterial efficacy was significantly enhanced as revealed through delayed bacterial growth kinetics, corresponding MIC/MBC values and disk diffusion tests. AgNPs of the smallest size, i.e., 5 nm demonstrated the best results and mediated the fastest bactericidal activity against all the tested strains compared to AgNPs having 7 nm and 10 nm sizes at similar bacterial concentrations. TEM analysis of AgNP treated bacterial cells showed the presence of AgNPs on the cell membrane, and AgNPs internalized within the cells.

Surface hydrophobicity of petroleum hydrocarbon degrading Burkholderia strains and their interactions with NAPLs and surfaces

Bacterial cell surface hydrophobicity (CSH) is an important factor governing the growth and adhesion behavior of microorganisms on non-aqueous phase liquids (NAPLs). In this work CSH and surface charge was quantified for three oil degrading Burkholderia cultures: aliphatic degrader Burkholderia cepacia (ES1) and two strains of aromatic degrading Burkholderia multivorans (NG1 and HN1) based on contact angle and zeta potential measurement. Model non-aqueous phase liquids (NAPLs) were formulated using n-hexadecane, naphthalene, phenanthrene and pyrene in varying concentration. Adhesion on to glass surfaces of varying hydrophobicity and adherence to n-hexadecane was quantified and correlated with hydrophobicity of the surface; variation in CSH of the culture in response to model NAPL used as growth substrate; and variation in zeta potential as a result of variation in growth substrate, ionic strength and pH of resuspension solution. B. cepacia (ES1) and B. multivorans (HN1) depicted comparable CSH which was higher than that of B. multivorans (NG1). For each culture, CSH was found to vary with the model NAPL used as growth substrate. Adhesion to glass increased with increase in CSH of the bacterial culture and with increase in hydrophobicity of the glass surface. B. cepacia (ES1) with lower negative zeta potential consistently depicted greater adhesion compared to B. multivorans (HN1). Adherence to n-hexadecane was significantly affected by various other factors, such as, growth substrate, pH, resuspension solution and their interactions as revealed through statistical analysis. These factors affected both the zeta potential and adherence to n-hexadecane to varying degree for the three Burkholderia cultures.

Biodegradation of pyrene by a Pseudomonas aeruginosa strain RS1 isolated from refinery sludge

High molecular weight (HMW) polynuclear aromatic hydrocarbons (PAHs) with more than three rings are inherently difficult to degrade. Degradation of HMW PAHs is primarily reported for actinomycetes, such as, Rhodococcus and Mycobacterium. This study reports pyrene degradation by a Pseudomonas aeruginosa strain isolated from tank bottom sludge in a refinery. High cell surface hydrophobicity induced during growth on pyrene facilitated its utilization as sole carbon source. Specific growth rate (μ) in the range of 0.03-0.085 h(-1) could be achieved over the concentration range 25-500 mg/L. The specific growth rate and specific pyrene utilization rate increased linearly with increase in total pyrene concentration. Although various degradation intermediates were identified in the aqueous phase, accumulation of total organic carbon (TOC) in the aqueous phase was only a small fraction of TOC equivalents of pyrene lost from the cultures. The degradation pathway appears to be similar to that reported for Mycobacterium sp. PYR-I.

Surfactant aided biodegradation of NAPLs by Burkholderia multivorans: Comparison between Triton X-100 and rhamnolipid JBR-515

Both chemical surfactants and biosurfactants have been effectively used for the degradation of petroleum hydrocarbons. Chemical surfactants are known to enhance biodegradation effectively while activity of biosurfactants is also comparable and they have the additional advantage of being biodegradable. However, the mode of action of chemical surfactants and biosurfactants may vary. This work was conducted to determine the mode of action of Triton X-100 and rhamnolipid JBR-515 by exploring the factors affecting the process of surfactant aided biodegradation of model non aqueous phase liquids (NAPLs) by a naphthalene degrader, Burkholderia multivorans (NG1). Emulsification studies, growth rate and degradation rate studies were conducted and correlated with alteration in cell surface properties including surface hydrophobicity, cell surface charge and cell surface functional groups. Triton X-100 and JBR-515 demonstrated distinct mode of uptake of NAPLs. Triton X-100 enhanced bioavailability by emulsification and supported direct interfacial uptake of model NAPLs by B. multivorans (NG1). Conversely, the biosurfactant rhamnolipid JBR-515 did not demonstrate emulsification of NAPLs and enhanced bioavailability through micellar solubilization. NAPL composition influenced the alteration in the cell surface properties. For both the surfactants, increase in surfactant concentration increased the rate of utilization of aliphatic hydrocarbons from the NAPLs.

Degradation of phenolics, nitrogen-heterocyclics and polynuclear aromatic hydrocarbons in a rotating biological contactor

The degradation of phenolics, heterocyclics and polynuclear aromatic hydrocarbons (PAHs) in a synthetic biomass gasifier wastewater with average COD of 1388 mg/L was studied in a three stage rotating biological contactor (RBC) using the pyrene degrader, Exiguobacterium aurantiacum and activated sludge consortia (1:3 v/v). As the organic loading rate (OLR) was varied from 3.3 to 14 g/m(2)/d, the COD removal ranged from 63.3% to 92.6%. Complete removal of all the constituents was observed at the lowest OLR of 3.3g/m(2)/d. At 24h hydraulic retention time (HRT) and OLR of 6.6g/m(2)/d complete removal of pyridine, quinoline and benzene and 85-96% removal of phenol, naphthalene, phenanthrene, fluoranthene and pyrene was observed. E. aurantiacum was found to be the dominant bacteria in the biofilm. Clarks model provided good fits to data for all the three stages of the RBC.

Characterization of oily sludge from a refinery and biodegradability assessment using various hydrocarbon degrading strains and reconstituted consortia.

Oily sludge obtained from a refinery in India contained 10-11% oil associated with fine particulates. Along with Fe, Ca and Mg various toxic elements were associated with the sludge solids (Pb, Mn, Cu, Zn, As, Bi, Cd, Cr, Co, Ni and V). The oil contained 41-56% asphaltenes and the maltenes comprised of 49 ± 4%, 42 ± 2% and 4 ± 2%, aliphatic, aromatic and polar fractions, respectively. Biodegradation studies with the maltene fraction of oil provided as sole substrate revealed higher degradation by various 3-5 membered reconstituted consortia compared to pure bacterial strains and up to 42 ± 8% degradation could be achieved over 30 days. In contrast, over the same period up to 71.5 ± 2% oil degradation could be achieved using dried oily sludge (15% w/v) as sole substrate. Significant biodegradation observed in the un-inoculated controls indicated the presence of indigenous microorganisms in oily sludge. However, large variability in oil degradation was observed in the un-inoculated controls. Greater biodegradation of the maltene fraction led to significant enrichment of asphaltenes in residual oil associated with the sludge.

Toxicity assessment of organic pollutants: Reliability of bioluminescence inhibition assay and univariate QSAR models using freshly prepared Vibrio fischeri

The toxicity of 14 industrially relevant organic chemicals was determined using freshly grown Vibrio fischeri bioluminescence inhibition assay. The results were compared to lyophilized V. fischeri, 96h fish, 48h Daphnia magna and 95h green algae bioassays. Reliability of octanol-water partition coefficient (K(ow)), and first order simple and valence molecular connectivity index ((1)chi, (1)chi(v)) based regression models for predicting toxicity to V. fischeri was studied. Correlations were obtained between freshly grown V. fischeri data (Log(EC50)) and Log(K(ow)), molecular connectivity indices ((1)chi, (1)chi(v)), energy of the highest occupied (E(HOMO)) and lowest unoccupied (E(LUMO)) molecular orbitals, and their difference (E(LUMO)-E(HOMO)). A good match was observed between V. fischeri assay conducted with freshly grown and lyophilized culture (r2=0.90). Good correlations (r2>0.95) were obtained with all the other bioassays after excluding compounds with Log(K(ow)) less than 2.0. Available regression models based on Log(K(ow)) and (1)chi(v) yielded lower toxicity values. V. fischeri bioassay showed fairly good correlation with Log(K(ow)), (1)chi and (1)chi(v) (r2>0.75) but poor correlation with E(HOMO), E(LUMO) and (E(LUMO)-E(HOMO)) in presence of polar compounds. E(HOMO) and E(LUMO) values are affected by polarity and can be used along with Log(K(ow)) and (1)chi(v) for generating better predictive models.

Nature and prevalence of non-additive toxic effects in industrially relevant mixtures of organic chemicals.

The concentration addition (CA) and the independent action (IA) models are widely used for predicting mixture toxicity based on its composition and individual component dose-response profiles. However, the prediction based on these models may be inaccurate due to interaction among mixture components. In this work, the nature and prevalence of non-additive effects were explored for binary, ternary and quaternary mixtures composed of hydrophobic organic compounds (HOCs). The toxicity of each individual component and mixture was determined using the Vibrio fischeri bioluminescence inhibition assay. For each combination of chemicals specified by the 2(n) factorial design, the percent deviation of the predicted toxic effect from the measured value was used to characterize mixtures as synergistic (positive deviation) and antagonistic (negative deviation). An arbitrary classification scheme was proposed based on the magnitude of deviation (d) as: additive (< or =10%, class-I) and moderately (10< d < or =30 %, class-II), highly (30< d < or =50%, class-III) and very highly (>50%, class-IV) antagonistic/synergistic. Naphthalene, n-butanol, o-xylene, catechol and p-cresol led to synergism in mixtures while 1, 2, 4-trimethylbenzene and 1, 3-dimethylnaphthalene contributed to antagonism. Most of the mixtures depicted additive or antagonistic effect. Synergism was prominent in some of the mixtures, such as, pulp and paper, textile dyes, and a mixture composed of polynuclear aromatic hydrocarbons. The organic chemical industry mixture depicted the highest abundance of antagonism and least synergism. Mixture toxicity was found to depend on partition coefficient, molecular connectivity index and relative concentration of the components.

Comparative mutagenicity assessment of aerosols in emissions from biofuel combustion

Abstract This study was designed to determine the mutagenicity in extracts of aerosols generated from biofuel combustion in household cooking devices commonly used in India. Wood, dung cake and biofuel briquette were used as fuel in various stoves, including both traditional and improved stoves made of mud, fired clay and metal. The combustion aerosols of particle diameter less than 2.5 μm (PM2.5) were collected, and their organic extracts were tested for mutagenicity using the Ames Assay test with TA98 and TA100 strains of Salmonella typhimurium and studies were performed both with and without metabolic activation to account for direct and indirect acting mutagens. The measured mutagenicity emission factors, i.e., number of revertants per kg of fuel burnt, indicate that wood demonstrates significantly lower mutagenicity compared to dung cake and briquette. No significant stove effect was observed across all the fuels studied. The contribution of direct-acting mutagens was found to be greater than 70% in all cases. Such a high relative contribution of direct-acting mutagenicity has not been previously reported for biomass combustion aerosols.