M. Sathishkumar

Bioreduction of trivalent aurum to nano-crystalline gold particles by active and inactive cells and cell-free extract of Aspergillus oryzae var. viridis.

Bioreduction efficacy of both active (AB) and inactive (IB) cells/biomass of Aspergillus oryzae var. viridis and their respective cell-free extracts (ACE and ICE) to convert trivalent aurum to gold nanoparticles were tested in the present study. Strong plasmon resonance of gold nanoparticles was observed between 540 and 560 nm in the samples obtained from AB, IB, ACE and ICE. Transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were performed to examine the formation of gold nanoparticles. Comparing all four forms of A. oryzae var. viridis, ICE showed high gold nanoparticle productivity. The nanoparticles formed were quite uniform in shape and ranged in size from 10 to 60 nm. In addition some triangle, pentagon and hexagon-shaped nanoplates with size range of 30-400 nm were also synthesized especially at lower pH. Organics from the inactive cells are believed to be responsible for reduction of trivalent aurum to nano-sized gold particles. Organic content of the ICE was found to be double the amount of ACE. High productivity of gold nanoparticles by metabolic-independent process opens up an interesting area of nanoparticle synthesis using waste fungal biomass from industries.

Removal of microcystin-LR and microcystin-RR by graphene oxide: Adsorption and kinetic experiments

Graphene oxide (GO) was employed in the present study for removal of two commonly occurring algal toxins, microcystin-LR (MC-LR) and microcystin-RR (MC-RR), from water. The adsorption performance of GO was compared to that of commercially available activated carbon. Further, adsorption experiments were conducted in the presence of other environmental pollutants to understand the matrix effects of contaminated water on the selective adsorption of MC-LR and MC-RR onto GO. The environmental pollutants addressed in this study included different anions (nitrate NO3-, nitrite NO2-, sulphate SO4(2-), chloride (Cl(-)), phosphate PO4(3-) and fluoride (F(-))) and cations (sodium (Na(+)), potassium (K(+)), magnesium (Mg(2+)) and calcium (Ca(2+))). GO showed very a high adsorption capacity of 1700 μg/g for removal of MC-LR and 1878 μg/g for MC-RR while the maximum adsorption capacity obtained with the commercial activated carbon was 1481.7 μg/g and 1034.1 μg/g for MC-LR and MC-RR, respectively. The sorption kinetic experiments revealed that more than 90% removal of both MC-LR/RR was achieved within 5 min for all the doses studied (500, 700 and 900 μg/L). GO could be reused as an adsorbent following ten cycles of adsorption/desorption with no significant loss in its adsorption capacity.

Biocrystallization of silver and gold ions by inactive cell filtrate of Rhizopus stolonifer

Microbes and their cell filtrates are known to synthesize metal nanoparticles. But maintenance of aseptic conditions and irregularly shaped and sized nanoparticles are major drawbacks of the system. In this study cell filtrate from inactive biomass of Rhizopus stolonifer was used for the first time to produce near uniformly sized and shaped Ag and Au nanoparticles at room temperature. The size of Ag and Au nanoparticles were found in the range of 25-30 nm and 1-5 nm, respectively. UV-vis spectrum, TEM and XRD measurements confirmed the formation of Ag and Au nanoparticles.

Sequestration of Reactive Blue 4 by free and immobilized Bacillus subtilis cells and its extracellular polysaccharides

Bacillus subtilis a gram positive bacteria and its extracellular polysaccharide were used in free form as well as immobilized form as biosorbent for sequestration of an anionic dye, Reactive Blue 4 (RB) in aqueous phase. The dye uptake enhanced with decrease in pH. Extracellular polymeric substances (EPS) and free cells were found to be better adsorbents when compared to alginate immobilized cells (IC) and EPS (IEPS). The presence of functional groups in free cells and EPS was confirmed by FT-IR analysis. Immobilization resulted in poor adsorption performance due to increase in mass transfer resistance by the polymeric matrix. High Q(max) and b values were noted in the case of free cells and free EPS in contrast to IC and IEPS. From the kinetic experiments, the adsorption system was found to be a pseudo-first-order reaction at low dye concentration. Desorption of RB was found to be 100% in 1N NaOH. However, the alginate beads were found to be unstable under high alkaline conditions of NaOH.

Experimental studies on removal of microcystin-LR by peat

Cyanotoxins have caused worldwide concerns for their eclectic occurrence and toxic effects, which led to an intensive search of cost-effective techniques for their removal from contaminated waters. A range of biomaterials was tested for their efficacy to adsorb a potent cyanotoxin, microcystin-LR (MCLR). Among these sorbents, peat showed the maximum efficacy to sequester MCLR. The BET (Brunauer-Emmett-Teller) surface area of peat was found to be 12.134 m(2)/g. The pH of the reaction media played a significant role in removal of MCLR; maximum adsorption occurred at pH 3. Kinetic studies showed that the adsorption of MCLR onto peat was a rapid process. The adsorption capacity (Q(max)) from the Langmuir model was found to be 255.7 μg/g at pH 3. Among various desorption media studied, strong alkali (2N NaOH) showed highest desorption (94%).

Biosynthesis of gold nanoparticles and related cytotoxicity evaluation using A549 cells.

Biosynthesis of gold nanoparticles (AuNPs) has become an attractive area of research as it is environmentally benign. The toxicity of AuNPs synthesized by chemical routes has been widely studied. However, little is known about the toxicity associated with the biological synthesis of AuNPs. The present study was carried out to synthesize AuNPs using star anise (Illicium verum; a commercially available spice in abundance)and evaluate its toxicity using human epithelial lung cells (A549) in comparison with AuNPs synthesized by the traditional chemical methods (using sodium citrate and sodium borohydride). Apart from cell viability, markers of oxidative stress (reduced glutathione) and cell death (caspases) were also evaluated to understand the mechanisms of toxicity. Cell viability was observed to be 65.7 percent and 72.3 percent in cells exposed to chemically synthesized AuNPs at the highest dose (200nM) as compared to 80.2 percent for biologically synthesized AuNPs. Protective coating/capping of AuNPs by various polyphenolic compounds present in star anise extract appears to be a major contributor to lower toxicity observed in biologically synthesized AuNPs.

Isolation, identification, Pb(II) biosorption isotherms and kinetics of a lead adsorbing Penicillium sp. MRF-1 from South Korean mine soil

A heavy metal contaminated soil sample collected from a mine in Chonnam Province of South Korea was found to be a source of heavy metal adsorbing biosorbents. Chemical analyses showed high contents of lead (Pb) at 357 mg/kg and cyanide (CN) at 14.6 mg/kg in the soil. The experimental results showed that Penicillium sp. MRF-1 was the best lead resistant fungus among the four individual metal tolerant fungal species isolated from the soil. Molecular characterization of Penicillium sp. MRF-1 was determined using ITS regions sequences. Effects of pH, temperature and contact time on adsorption of Pb(II) by Penicillium sp. MRF-1 were studied. Favorable conditions for maximum biosportion were found at pH 4 with 3 hr contact time. Biosorption of Pb(II) gradually increased with increasing temperature. Efficient performance of the biosorbent was described using Langmuir and Freundlich isotherms. Adsorption kinetics was studied using pseudo first-order and pseudo second-order models. Biosorbent Penicillium sp. MRF-1 showed the maximum desorption in alkali conditions. Consistent adsorption/desorption potential of the biosorbent in repetitive cycles validated the efficacy of it in large scale. SEM studies given notes on surface modification of fungal biomass under metal stress and FT-IR results showed the presence of amino groups in the surface structure of the biosorbent. In conclusion, the new biosorbent Penicillium sp. MRF-1 may potentially be used as an inexpensive, easily cultivatable material for the removal of lead from aqueous solution.

Immobilization of flavin adenine dinucleotide (FAD) onto carbon cloth and its application as working electrode in an electroenzymatic bioreactor.

A high porosity carbon cloth with immobilized FAD was employed as working electrode in electrochemical NADH-regeneration procedure. Carbon cloth was oxidized with hot acids to create surface carboxyl group and then coupled by adenine amino group of FAD with carbodiimide in the presence of N-hydroxysulfosuccinimide. The bioelectrocatalytic NADH-regeneration was coupled to the conversion of achiral substrate pyruvate into chiral product l-lactate by l-lactate dehydrogenase (l-LDH) within the same reactor. The conversion was completed at 96h in bioreactor with FAD-modified carbon cloth, resulting in about 6mM of l-lactate from 10mM of pyruvate. While with bare carbon cloth, the yield at 120h was around 5mM. Immobilized FAD on the surface of carbon cloth electrode facilitated it to carry electrons from electrode to electron transfer enzymes; thereby NADH-regeneration was accelerated to drive the enzymatic reaction efficiently.

Removal of a potent cyanobacterial hepatotoxin by peat

Microcystins (cyclic heptapeptides), produced by a number of freshwater cyanobacteria, are of health concern in potable water supplies. In this article, the adsorptive removal of microcystin-RR (MCRR) from the aqueous solution by a low-cost adsorbent, peat, was investigated. The BET surface area of peat was found to be 12.134 m2/g. The adsorption process was pH dependent, with maximum adsorption occurring at pH 3. Kinetic studies revealed that the adsorption of MCRR onto peat was a rapid process. The adsorption capacity (Qmax ) as revealed by the Langmuir model was found to be 286 μg/g at pH 3. Among various desorption media studied, strong alkali solutions (2 N NaOH) showed the highest desorption (97%). Thus, peat has potential to be used as an adsorbent for the removal of the cyanotoxin, MCRR, from drinking water.