Sivagnanam Silambarasan

Role of Gordonia sp JAAS1 in biodegradation of chlorpyrifos and its hydrolysing metabolite 3,5,6-trichloro-2-pyridinol.

Paddy field soil with prior exposure to chlorpyrifos was chosen for the biodegradation of the pesticide by employing bacteria with special emphasis given to actinomycetes. Actinomycetes are organisms predominantly known for their bioactive compounds, but there is dearth of work pertaining to their role in bioremediation. So this work was carried out to screen for actinomycetes and assess their potential in degradation of the pesticide. Actinobacterial strains were isolated from paddy field soil, with capabilities to degrade chlorpyrifos and its major metabolite 3,5,6‐trichloro‐2‐pyridinol (TCP). Two strains were successfully isolated among which one strain was efficient and was able to tolerate high concentrations of chlorpyrifos. This strain was selected for further investigation; it was identified as Gordonia sp based on 16S rRNA analysis and designated as Gordonia sp JAAS1. The actinobacterial strain was able to degrade 110 mg l−1 of chlorpyrifos within 24 h incubation, and TCP was found to accumulate in the culture medium. However, after 72 h of incubation, TCP was degraded, and finally, diethylthiophosphoric acid (DETP) was obtained.

Mycoremediation of endosulfan and its metabolites in aqueous medium and soil by Botryosphaeria laricina JAS6 and Aspergillus tamarii JAS9.

Microbial degradation offers an efficient and ecofriendly approach to remove toxicants from the contaminated environments. Botryosphaeria laricina JAS6 and Aspergillus tamarii JAS9 were capable of degrading endosulfan and their metabolites which were isolated through enrichment technique. Both the strains were able to withstand an exposure of 1300 mg/L and showed luxuriant growth at 1000 mg/L of endosulfan. The change in pH in the culture broth was from 6.8 to 3.4 and 3.8 during growth kinetic studies of JAS6 and JAS9 strains, respectively upon biological degradation of endosulfan. The degradation of endosulfan by JAS6 and JAS9 strains were examined by HPLC. The biodegradation rate constant (k) and the initial concentration were reduced by 50% (DT50) which was determined by first and pseudo first order kinetic models. In the present investigation it has been revealed that Botryosphaeria laricina JAS6 and Aspergillus tamarii JAS9 possessing endosulfan degrading capability are being reported for the first time. These findings confirm the degradation of endosulfan by JAS6 and JAS9 strains which were accompanied by significant reduction in the toxicity and could be used as remedial measure in contaminated environments.

Biodegradation of chlorpyrifos and its hydrolysis product 3,5,6-trichloro-2-pyridinol using a novel bacterium Ochrobactrum sp. JAS2: A proposal of its metabolic pathway

Biodegradation of chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol (TCP) were studied with a novel bacterial strain JAS2 isolated from paddy rhizosphere soil. The molecular characterization based on 16S rRNA gene sequence homology confirmed its identity as Ochrobactrum sp. JAS2. The JAS2 strain degraded 300mgl(-1) of chlorpyrifos within 12h of incubation in the aqueous medium and it produced the TCP metabolite. However, after 72h of incubation TCP was also completely degraded by the JAS2 strain. A tentative degradation pathway of chlorpyrifos by Ochrobactrum sp. JAS2 has been proposed on basis of GC-MS analysis. The complete degradation of chlorpyrifos occurred within 24h in the soil spiked with and without addition of nutrients inoculated with Ochrobactrum sp. JAS2. TCP was obtained in both the studies which was degraded completely by 96h in the soil spiked with nutrients and whereas 120h in absence of nutrients in the soil. The mpd gene which is responsible for organophosphorus hydrolase production was identified. The isolates Ochrobactrum sp. JAS2 also exhibited a time dependent increase in the amount of tricalcium phosphate solubilization in Pikovskayas medium. Further screening of the strain JAS2 for auxiliary plant growth promoting activities revealed its remarkable capability of producing the indole acetic acid (IAA), hydrogen cyanide (HCN) and ammonia.

Biomineralization and formulation of endosulfan degrading bacterial and fungal consortiums

Microbial degradation offers an effective approach to remove toxicants and in this study, a microbial consortium consisting of bacterial strains and fungal strains were originally obtained from endosulfan contaminated agricultural soils. Identification of the bacterial isolates by 16S rRNA sequences revealed the isolates to be Halophilic bacterium JAS4, Klebsiella pneumoniae JAS8, Enterobacter asburiae JAS5, and Enterobacter cloacae JAS7, whereas the fungal isolates were identified by 18S rRNA sequences and the isolates were Botryosphaeria laricina JAS6, Aspergillus tamarii JAS9 and Lasiodiplodia sp. JAS12. The biodegradation of endosulfan was monitored by using HPLC and FTIR analysis. The bacterial and fungal consortium could degrade 1000 mg l(-1) of endosulfan efficiently in aqueous medium and in soil. The infrared spectrum of endosulfan degraded samples in the aqueous medium by bacterial and fungal consortium showed bands at 1400 and 950 cm(-1) which are the characteristics of COOH group and acid dimer band respectively. In the present investigation, low cost solid materials such as sawdust, soil, fly ash, molasses and nutrients were used for the formulation of microbial consortium and to achieve greater multiplication and survival of the microbial strains.

Efficacy of Ganoderma sp. JAS4 in bioremediation of chlorpyrifos and its hydrolyzing metabolite TCP from agricultural soil.

A novel fungal strain JAS4 was isolated from agricultural soil and was found to be highly effective in degrading chlorpyrifos and its major degradation product 3,5,6‐trichloro‐2‐pyridinol (TCP). The molecular characterization based on 18S rRNA sequence analysis, revealed strain JAS4 as Ganoderma sp. which could able to degrade chlorpyrifos and its metabolite in an aqueous medium with rate constant of 0.8460 day−1, following first order rate kinetics, and the time in which the initial insecticide concentration was reduced by 50% (DT50) was 0.81 days. Studies on biodegradation in soil with nutrients showed that JAS4 strain exhibited efficient degradation of insecticide with a rate constant of 0.9 day−1, and DT50 was 0.73 day. In contrast, degradation of insecticide in soil without nutrients was characterized by a rate constant of 0.7576 day−1 and the DT50 was 0.91 day.

Bacterial degradation of monocrotophos and phyto- and cyto-toxicological evaluation of metabolites

The bacterium Serratia marsescens strain JAS16 was isolated from agricultural soil which had prior exposure to monocrotophos for three years. The strain JAS16 tolerated up to 1200 mg L–1 monocrotophos and degraded the insecticide (1000 mg L–1) at a degradation rate constant of 136 d−1 (DT50 = 3.7 d). In soil, the degradation rate constant was 105 d−1 (DT50 = 4.8 d). A schematic pathway is being proposed from the degraded products derived from gas chromatography--mass spectrometry (GC-MS). The phytotoxicity of degradation products to Vigna radiata, Vigna unguiculata, and Macrotyloma uniflorum and the genotoxicity to Allium cepa roots were found to be low. A cost-effective powder-based formulation was achieved with the isolate. The isolate remained viable during the storage and also multiplied with a higher colony forming units (CFU) load g–1 for over a period of seven weeks of storage.

Evaluation of the production of exopolysaccharide by plant growth promoting yeast Rhodotorula sp. strain CAH2 under abiotic stress conditions

The capability of plant growth promoting microbes to survive under abiotic stresses has important significance for improving plant growth and productivity. Among the various plant growth promoting biomolecules produced by microbes, exopolysaccharide (EPS) help microbes to survive in inhospitable environments and endure environmental stressful conditions. In the present study, a yeast strain CAH2 was isolated from Beta vulgaris rhizosphere soil and identified as Rhodotorula sp., based on the partial 18S rRNA gene sequence analysis. Rhodotorula sp. strain CAH2 was found to tolerate higher concentrations of Al (6 mM), NaCl (150 mM) and PEG-6000 (15%, w/v). The strain CAH2 was shown to produce 7.5 g L-1 of EPS in the production medium with sucrose and yeast extract as a carbon and nitrogen sources, respectively. The EPS yield was increased constantly with increasing concentrations of Al, NaCl and PEG-6000. The structural feature of EPS studied through FT-IR and NMR spectral analysis confirmed the presence of glucose, mannose and galactose. The yeast strain CAH2 was produced multiple plant growth promoting traits in the presence and absence of abiotic stresses. Finally, these results indicate that the production of EPS could be safeguard the plant growth promoting Rhodotorula sp. strain CAH2 from unfavourable environmental conditions.

BIODEGRADATION OF CHLORPYRIFOS AND 3,5,6-TRICHLORO-2-PYRIDINOL BY FUNGAL CONSORTIUM ISOLATED FROM PADDY FIELD SOIL

Pesticides are considered as one of the most serious environmental pollutants, which are frequently used in the control of agricultural and domestic pests. Biodegradation of chlorpyrifos and its 3,5,6-trichloro-2-pyridinol (TCP) were studied in mineral medium and soil with fungal consortium consisting of JAS1 and JAS4 strains which were isolated from paddy field soil. The fungal consortium was spiked with 300 mg l chlorpyrifos which was degraded completely within 12 h of incubation in the mineral medium along with the major metabolite TCP. The course of the degradation process was studied using HPLC and FTIR analyses. Two experiments were carried out in soil which included the addition of nutrients (Carbon, Nitrogen and Phosphorous) with fungal consortium and fungal consortium without addition of nutrients. In both the experiments, chlorpyrifos (300 mg kg -1 soil) and its metabolite TCP were degraded within 24 h and 48 h, respectively. These results showed that the chlorpyrifos degrading fungal consortium had the potential to degrade the pesticide from contaminated soil.