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2006 - 200912010 - 20111
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Subject: Microbiology × Author: Chawla, Niti × Start date: 1995 × Type: Thesis ×
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    ThesisItemOpen Access
    Microbial remediation of chlorpyriphos contaminated soil
    (CCSHAU, 2011) Chawla, Niti; Suneja, Sunita
    Twenty six bacterial isolates were obtained from chlorpyriphos contaminated soil samples by enrichment culture technique. Eight bacterial isolates showed growth upto 30,000-40,000 ppm chlorpyriphos amended in Mineral salt medium (MSM) containing glucose (0.2%). Out of eight, four isolates produced yellow coloured colonies on MSM agar plates containing chlorpyriphos (50 ppm) and bromo thymol blue (BTB) indicator and also showed the reduction of 2,3,5-triphenyltetrazolium chloride (TTC) in MSM that confirmed their chlorpyriphos degrading capability. These four isolates were selected for different carbon and nitrogen source utilization pattern on MSM agar plates. With all the isolates, good growth was observed in presence of five carbon and five nitrogen sources. Therefore, these carbon and nitrogen sources were selected for chlorpyriphos utilization in MSM. More bacterial count and protein content was observed in the medium amended with glucose as carbon source and ammonium chloride as nitrogen source as compared to medium amended with other carbon and nitrogen sources with all the four isolates. To study the utilization of chlorpyriphos in liquid medium (containing glucose and ammonium chloride), medium was amended with 100 ppm chlorpyriphos. After 7 days of growth, residual chlorpyriphos was determined in the medium. Maximum utilization of chlorpyriphos was found with the isolate SB1 (80.1 %) followed by HIC2 (76.2 %), SGB2 (65.2%) and HIIGA2 (58.1%) respectively. Growth of four selected isolates was studied in sterilized as well as unsterilized soil amended with chlorpyriphos (100 ppm) for a period of two months under laboratory conditions. Viable count was higher in chlorpyriphos amended soil as compared to unamended soil with all the isolates. Chlorpyriphos level decreased in all the treatments. Percent utilization of chlorpyriphos was found more in unsterilized soil as compared to sterilized soil. Maximum utilization of chlorpyriphos was found with the isolate SB1 (66.0 %) followed by HIC2 (58.0 %), SGB2 (48.0%) and HIIGA2 (36.4 %) in sterilized soil. Similar trend was observed in unsterilized soil i.e. maximum utilization of chlorpyriphos with the isolate SB1 (79.2%) followed by HIC2 (74.5%), SGB2 (60.8%) and HIIGA2 (43.3 %) respectively. A pot experiment was conducted to evaluate the potential of the two chlorpyriphos utilizing isolates in the presence of cotton plants under natural conditions. Germination of seeds was not observed in the treatments amended with 200 ppm chlorpyriphos. Shoot and root growth was found to be significantly higher in the inoculated treatments amended with 50-100 ppm chlorpyriphos as compared to their respective uninoculated treatments. Significant decrease in chlorpyriphos content was observed in soil as well as cotton seeds on inoculation with bacterial isolates. In naturally contaminated soil (0.15 ppm chlorpyriphos), residues were not detected in soil and cotton seeds of both inoculated and uninoculated treatments On the basis of various standard morphological and biochemical tests as described in Bergey’s Manual of Determinative Bacteriology, the isolate SB1 belonged to the genus Pseudomonas and the isolate HIC2 to Xanthomonas.
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    ThesisItemOpen Access
    Colonisation behaviour of gluconacetobacter diazotrophicus in cotton plant
    (CCSHAU, 2006) Chawla, Niti; Bansal, R.K.
    Studies on the colonisation behaviour of Gluconacetobacter diazotrophicus 35-47 introduced as seed treatment was undertaken in root-knot nematode (Meloidogyne incognita) infected and healthy cotton (Gossypium hirsutum) cv. H-1098 plants grown in sterilized and natural field soil in green house. G. diazotrophicus 35-47 inoculation significantly reduced root-knot disease intensity and also enhanced plant growth parameters of both nematode infected and healthy cotton plants in sterilized as well as natural field soil. Studies on colonisation behaviour of the bacterium has indicated that it colonised root surface and not the internal tissues of the cotton plant, suggesting that it is a ‘root-surface coloniser’ and not the ‘endophyte’ of cotton. From the results, it is also evident that bacterium could grow upto last day of observation (90 DAS) of plant growth in natural field soil in healthy plants, however, nematode infection reduced bacterial multiplication. Optimisation study on the cotton root surface sterilisation showed that exposure in 10% sodium hypochlorite (containing 4% free chlorine) solution for 15 minutes followed by 5-6 times rinsing in sterile distilled water is sufficient to achieve complete surface sterility.