D.M. Saxena

Degradation of alpha, beta, gamma and delta-hexachlorocyclohexanes by Sphingomonas paucimobilis

Sphingomonas paucimobilis degrades aerobically α, β, γ and δ-hexachlorocyclohexane. With α-HCH, complete degradation occurred after 3 days but with β and γ, and with δ-HCH, 98 and 56 % degradation occurred after 12 and 8 days of incubation, respectively. Pentachlorocyclohexene was formed as the primary metabolite during the degradation of all the HCH isomers.

Cytological and biochemical effects of pesticides on microorganisms

Insecticides are known to alter the growth and activities of microorganisms. These alterations are mediated through cytological and biochemical changes at cellular level. Although an enormous literature is available on the effects of insecticides on the growth and activities of microorganisms, little has been done to understand the effects of insecticides at cellular level. Some microorganisms, being unicellular and having many other attributes in experimental biology, are used as models to understand the mode of action of xenobiotic compounds. Thus information on the cytological and biochemical effects on such organisms may also present a picture of cytological and biochemical effects of insecticides in higher organisms.

Enhanced degradation of hexachlorocyclohexane isomers by Sphingomonas paucimobilis

Hexachlorocyclohexane (HCH) has been banned for use in technologically advanced countries; however, it is still in use in tropical countries like India. Earlier we reported the degradation of HCH isomers by Sphingomonas paucimobilis within 12 days of incubation. Here we report the role of different factors that could enhance the degradation rate of HCH isomers. We found that an increase in the cell number from 102 to 108 cells/ml resulted in an increased degradation rate of HCH isomers viz. α, β, γ, and δ-HCH. While α-HCH and γ-HCH disappeared completely from the medium within 3 days of incubation, a maximum of only 90% and 85% degradation was observed for β and δ-HCH, respectively. We have also observed that adapted cultures degraded HCH isomers more efficiently than did the normal cultures.

Bioconcentration and metabolism of DDT, fenitrothion and chlorpyrifos by the blue-green algae Anabaena sp. and Aulosira fertilissima.

Anabaena and Aulosira fertilissima showed a marked ability to accumulate DDT, fenitrothion and chlorpyrifos. Although the maximum accumulation of DDT was almost the same in both organisms, there were significant differences in their abilities to accumulate fenitrothion and chlorpyrifos. Patterns of uptake of DDT under different treatments were also similar in both Anabaena and Aulosira, but there were significant differences in the patterns of accumulation of fenitrothion between these two organisms. In Aulosira the maximum accumulation of fenitrothion was observed on the second day, whereas, in Anabaena, maximum accumulation was noticed on the first day. A completely different pattern of accumulation of chlorpyrifos was observed in Aulosira, which continued to accumulate chlorpyrifos throughout the experimental period. Bioconcentration of DDT in Anabaena and Aulosira ranged from 3 to 1568 ppm (microg g(-1)) and 6 to 1429 ppm, respectively. Bioconcentration of fenitrothion and chlorpyrifos in Anabaena varied from 53 to 3467 ppm and 7 to 6779 ppm, respectively. In Aulosira the bioconcentration varied from 100 to 6651 ppm and 53 to 3971 ppm for fenitrothion and chlorpyrifos, respectively. Anabaena and Aulosira metabolised DDT to DDD and DDE. Amounts of these DDT metabolites detected in the organisms were dependent on the concentration of treatment. DDD was the major, and DDE the minor, metabolite. These organisms were not able to metabolise the organophosphorus insecticides, fenitrothion and chlorpyrifos.

Effects of DDT, fenitrothion and chlorpyrifos on growth, photosynthesis and nitrogen fixation in Anabaena (Arm 310) and Aulosira fertilissima

Abstract The response of blue-green algae to DDT, fenitrothion and chlorpyrifos revealed that algae are quite sensitive to insecticides and the effects depend on the type and nature of the insecticide, the organisms and the experimental conditions. DDT inhibited the growth of Anabaena whereas it was stimulatory to Aulosira . Fenitrothion and chlorpyrifos were, however, quite toxic even at concentrations of 100 times less than DDT. Organisms recovered from the toxic effect if the treatment continued for 35 days. DDT at all concentrations inhibited photosynthesis in Anabaena and Aulosira . Fenitrothion was extremely toxic to both these organisms as it inhibited photosynthesis by more than 75% at the highest concentration. Chlorpyrifos was comparatively less toxic to Aulosira than Anabaena as it inhibited 14 CO 2 -uptake at 10 ppm by 76.0 and 69.4%, respectively. Nitrogenase activity was stimulated by DDT in Anabaena but inhibited by it in Aulosira , whereas fenitrothion and chlorpyrifos inhibited nitrogenase activity in both the organisms.

Effect of DDT on cell population growth, cell division, and DNA synthesis inStylonychia notophora (stokes)

The effect of DDT on growth and DNA synthesis inStylonychia notophora was investigated. DDT at a concentration of one ppm did not alter the cell population growth and the morphology of the organisms. However, 50 and 100 ppm DDT inhibited growth and cell division. Continuous treatment of the organisms with 100 ppm DDT produced several nuclear abnormalities. Cells treated with 100 ppm DDT in G1 did not enter S-phase while DNA synthesis was blocked in those cells treated in S-phase.

Manipulations of Catabolic Genes for the Degradation and Detoxification of Xenobiotics

Publisher Summary This chapter describes the manipulations of catabolic genes for the degradation and detoxification of xenobiotics. In vitro strain construction requires detailed genetic and biochemical information on the degradation pathways of xenobiotics. The control of catabolic pathways can also be modified by placing key biodegradation enzymes that require inducers, some of which are pollutants themselves, under the control of new regulatory systems. For example, genetic engineering has been used to uncouple the Pseudomonas mendocina toluene monoxygenase from toluene induction to derive Pseudomoms transconjugants that constitutively express the 2,4-D degradation pathway and to derive E. coli recombinant strains to enhance PCBs degradative activity in the presence of exogenous catabolite repressor substance. The cloning of genes for modified enzymes that have useful catabolic properties (such as relaxed substrate specificities or enhanced induction) provides an important repository of genetic diversity for future research.

Effect of DDT on growth of Tetrahymena pyriformis

Summary Effects of DDT on cell population growth and cell dimensions in a ciliate protozoan, Tetrahymena pyriformis have been investigated. DDT at concentrations of 50 and 100 ppm markedly inhibited cell population growth of the organisms and percentage inhibition ranged from 40 – 75. These dosages of DDT also affected the cell dimensions viz., major and minor axes, surface area and volume of the ciliates. By fifth day of treatment ciliates became spherical and cytolysed by tenth day of treatment. When organisms, treated with 100 ppm DDT for 3 days, were transferred to normal culture medium, the inhibition of growth was annulled.

Ultrastructural Studies on a Gymnostome Ciliate Homalozoon vermiculare (Stokes): II. The Endoplasm and Endoplasmic Organelles

Summary The endoplasm of Homalozoon includes macronucleus, micronuclei, mitochondria, parapharyngeal granular mass (PGM), toxicysts, food vacuoles (FVS), water expulsion vesicles (EVS), endoplasmic reticulum, microtubules and lipid droplets. The macronucleus consists of a number of ovoid segments bound by double unit-membranes and contains the “small bodies” — chromatin and two types of the “large bodies” — nucleoli. Micronuclei have cortex of fine fibrils and microtubules, and the central chromatin elements differentiated into two types of bodies. Mitochondria are found in endoplasm specially aggregated near the filamentous layer. The PGM is limited by double unit-membranes and is filled with material of low electron density. Toxicysts are rod shaped tripartite bodies aggregated near the oral rim and scattered in the endoplasm. They consist of a limiting membrane, a capsule and a shaft, and develop from the “pretrichocyst vesicles”. The EVs are limited by a unit membrane and open to surface through a pore. An intervening canal connects the pore to EV. The canal is lined by two sets of microtubules, (i) disposed helically and (ii) running radially. FVs containing paramecium in various stages of digestion and bound by a unit-membrane are present. No cytoproct is present and the undigested myelin-like material is presumably thrown out through EV. Microtubules, packed in bundles of six, run from neck region into the endoplasm. The endoplasmic reticulum is well developed. Membrane bound lipid droplets are present in the endoplasm.

Effect of Organophosphorus Insecticides on the Growth of Tetrahymena pyriformis

Summary The effect of organophosphates viz. Fenthion, Parathion and methyl-Parathion was investigated on the cell population of the ciliate protozoan, Tetrahymena pyriformis (Syngen I). Fenthion and Parathion at the concentration of 1.0 and 5.0 ppm markedly inhibited the cell population growth of the organisms and percentage inhibition ranged from 22.4–77.4% and 38.88–85.57% respectively. A concentration above 5.0 ppm was lethal. With methyl-Parathion, inhibition range was 8-61.22% at concentration range of 0.1-10 ppm. At 10 ppm concentration methyl-Parathion was lethal to the organisms. The order of toxicity was Fenthion > Parathion > methyl-Parathion. These organophosphorus insecticides also affected the cell surface area and volume. In the treated organisms more surface area unit of cell volume was exposed to the environment during the growth cycle as compared to control. The cells recovered on being transferred to toxicant free medium after treatment for 3 d.