Leela Iyengar

Bacterial Decolorization and Degradation of Azo Dyes

Color has always been a part of human life since long. All colorants, until the middle of nineteenth century, were of natural origin. Manufacturing of synthetic dyes started in 1856 and the first compound to be synthesized was aniline purple. By the beginning of the twenteeth century, synthetic dyes almost completely replaced natural compounds. Synthetic dyes represent an important class of industrial chemicals, which are used extensively in textile, leather tanning, paper production, food technology, agriculture, light harvesting array, coloring and pharmaceuticals

Mechanism of disinfection: Effect of chlorine on cell membrane functions

Abstract To elucidate the mechanism of disinfection by chlorine, its effects on some vital properties associated with cell membrane of Escherchia coli were studied. There was no significant change in Zeta potential at bactericidal doses of chlorine. Treatment with chlorine induced the leakage of macromolecules from the cells indicating the permeability changes of the membrane. Proteins and RNA were detected in the supernatant when the cells were treated with chlorine dose of 1.5 mg 1−1 (100 μg Cl mg−1 N). The presence of DNA was observed only at high chlorine doses. The studies on oxidative phosphorylation of cell free extract indicated the complete cessation of phosphate uptake at a dose of 0.4 mg 1−1 (30 μg Cl mg−1 N). There was about 70% decrease in the oxygen uptake corresponding to chlorine dose of 0.8 mg 1−1.

Isolation, identification and application of novel bacterial consortium TJ-1 for the decolourization of structurally different azo dyes

A novel bacterial consortium (TJ-1), which could decolorize Acid Orange 7 (AO7) and manyother azo dyes, was developed. In TJ-1 three bacterial strains were identified as Aeromonas caviae, Proteus mirabilis and Rhodococcus globerulus by 16S rRNA gene sequence analysis. AO7 decolorization was significantly higher with the use of consortium as compared to the use of individual strains, indicating complementary interactions among these strains. AO7 decolorization was observed under microaerophilic condition in the presence of organic carbon source. Either yeast extract (YE) alone or a combination of YE and glucose resulted in much higher decolorization of AO7 as compared to glucose alone, peptone or starch. Kinetic studies with different initial AO7 concentrations showed that more than 90% decolorization could be achieved even at 200mg/l within 16h. Fed-batch studies showed that AO7 decolorization required 10h during the first cycle and 5h in the second and third cycles, showing that bacterial cells could be used for multiple cycles. The consortium also decolorized fifteen other azo dyes individually as well as a simulated wastewater containing a mixture of all the sixteen azo dyes, thus, conferring the possibility of application of TJ-1 for the treatment of industrial wastewaters.

ORIGINAL PAPERS Biosorption of U, La, Pr, Nd, Eu and Dy by Pseudomonas aeruginosa

Kinetic studies with Pseudomonas aeruginosa using actinides and lanthanides indicated a two-phase metal uptake. Equilibrium uptake data of all the metals studied could be fitted to Langmuir as well as Freundlich models. The Scatchard plots showed that there were mainly two types of receptor sites on the cell walls of P. aeruginosa having different affinities for the metal ions. EDAX studies revealed replacement of calcium and magnesium ions from biomass by sorbed metal. Around 85% of the adsorbed metal could be released using citrate buffer (pH 4.0, 0.2 M). Metal desorption was as high as 95% with HCl. Continuous flow studies using P. aeruginosa immobilized on activated alumina gave 80% enhancement of lanthanum removal efficiency compared to the control column. Regeneration of the column resulted in 80% of its initial capacity in succeeding cycles. Journal of Industrial Microbiology & Biotechnology (2000) 25, 1–7.

Degradation of phenol and phenolic compounds by a defined denitrifying bacterial culture

Phenol, a major pollutant in several industrial waste waters is often used as a model compound for studies on biodegradation. This study investigated the anoxic degradation of phenol and other phenolic compounds by a defined mixed culture of Alcaligenes faecalis and Enterobacter species. The culture was capable of degrading high concentrations of phenol (up to 600 mg/l) under anoxic conditions in a simple minimal mineral medium at an initial cell mass of 8 mg/l. However, the lag phase in growth and phenol removal increased with increase in phenol concentration. Dissolved CO2 was an absolute requirement for phenol degradation. In addition to nitrate, nitrite and oxygen could be used as electron acceptors. The kinetic constants, maximum specific growth rate μmax; inhibition constant, Ki and saturation constant, Ks were determined to be 0.206 h−1, 113 and 15 mg phenol/l respectively. p-Hydroxybenzoic acid was identified as an intermediate during phenol degradation. Apart from phenol, the culture utilized few other monocyclic aromatic compounds as growth substrates. The defined culture has remained stable with consistent phenol-degrading ability for more than 3 years and thus shows promise for its application in anoxic treatment of industrial waste waters containing phenolic compounds.

Application studies of biosorption for monazite processing industry effluents

While studies on the potential of many biosorbents for heavy metal uptake have been reported, the results on scale-up are relatively scanty. Even in those papers where there is a report of reactor performance, more emphasis is given to the metal uptake part and the critical issue of headloss development in columns is not touched upon. This paper presents the results of a scale-up study conducted with an established biosorbent. Ganoderma lucidum, for uptake of rare earth elements. The uptake as well as the reactor characteristics are discussed.

Evaluation of two commercial field test kits used for screening of groundwater for arsenic in Northern India

In this study two relatively new arsenic field kits, namely Wagtech Digital Arsenator (WFTK) and Chem-In Corp field test kit (CFTK) for arsenic were evaluated. The response of the two field test kits to known standards (Both As(III) and As(V)) is detailed. In addition around 157 arsenic-contaminated field samples obtained from various locations of Ballia and Kanpur districts, U.P., India were tested using the two kits and the results were compared with the laboratory-based colorimetric method (silver diethyldithiocarbamate method, SDDC). The concentration of arsenic in the 157 samples ranged from 0 to 468 microg l(-1). WFTK is seen to be suitable for measuring arsenic concentration <5-100 microg l(-1) using the digital meter. CFTK was not able to detect As(V) and its usage is cautioned in Uttar Pradesh where As(V) is seen to occur in appreciable concentrations. The Pearsons correlation between the silver diethyldithiocarbamate method and WFTK was found to be 0.87 and for the corresponding correlation with CFTK was 0.41 in the concentration range used in this study. Spearmans rank correlation coefficients comparing the WFTK and CFTK to laboratory measurements in the concentration range of 0-100 microg l(-1) were 0.95 (p<0.001) and 0.64 (p<0.001) respectively.

Mechanism of disinfection

Abstract Certain biochemical aspects of mechanism of disinfection are discussed in the paper. The total dehydrogenase activity of intact E. coli cells is affected by chlorine dose and this correlates with per cent survivals. The succinic dehydrogenase activity in the crude extract of E. coli is affected by chlorine within the bactericidal concentrations. The dose required for inhibition of above enzyme is less than that for intact cells. To deliniate the mechanism of inhibition of succinic dehydrogenase, the effect of chlorine on thiol groups present in crude extract is studied. After chlorine exposure there is a reduction in thiol groups indicating the thiol groups to be vulnerable to the oxidising influence of chlorine. The inhibition of succinic dehydrogenase induced due to lower doses of chlorine can significantly be reversed with reduced glutathione. The ATP-ase which is localised in cytoplasmic membrane of cell, like succinic dehydrogenase, is not affected to any degree by chlorine in bactericidal concentrations. The catalase activity of E. coli is not affected.

Mineralization of 4-aminobenzenesulfonate (4-ABS) by Agrobacterium sp . strain PNS-1

A bacterial strain, PNS-1, isolated from activated sludge, could utilize sulphanilic acid (4-ABS) as the sole organic carbon and energy source under aerobic conditions. Determination and comparison of 16S r DNA sequences showed that the strain PNS-1 is closely related to the species of Agrobacterium genus. Growth on 4-ABS was accompanied with ammonia and sulfate release. TOC results showed complete mineralization of sulphanilic acid. This strain was highly specific for 4-ABS as none of the sulphonated aromatics used in the present study including other ABS isomers were utilized. Strain PNS-1 could, however, utilize all the tested monocyclic aromatic compounds devoid of a sulfonate group. No intermediates could be detected either in the growth phase or with dense cell suspensions. Presence of chloramphenicol completely inhibited 4-ABS degradation by cells pregrown on succinate, indicating that degradation enzymes are inducible. No plasmid could be detected in the Agrobacterium sp. Strain PNS-1 suggesting that 4-ABS degradative genes may be chromosomal encoded.

Site of interaction of copper on Bacillus polymyxa.

Copper uptake potential of different bacterial strains isolatedfrom contaminated soil was compared. The bacterial strainidentified as Bacillus polymyxa showed maximum copperuptake capacity. An attempt was made to elucidate the site ofinteraction of Cu(II) with B. polymyxa using electronparamagnetic resonance (EPR) studies. The EPR spectra showedthat accumulated copper formed complexes with oxygen andnitrogen which may be the carboxyl groups of cell-wallpeptidoglycan and nitrogen atoms of aminosugars or structuralproteins. The absence of super hyperfine splitting in theg ⊥ region of EPR spectra of treated B. polymyxa cellsafter Cu(II) uptake indicated that copper could be coordinatedwith the oxygen atoms from carboxyl groups of peptidoglycan inthe cell walls.