Babita Kumari

Water management — A tool for methane mitigation from irrigated paddy fields

Water drainage is considered to be one of the important practices that reduce the CH(4) efflux from paddy fields. In this study, four different drainage systems (continuous flooding, tillering stage drainage, mid-season drainage and multiple drainage) were compared to find out the best one, for attenuation of CH(4) emission from rice fields. Except for continuous flooding, from all the other three drainage systems, irrigation water from the paddy fields was drained out at the different stages of the crop cycle. Highest efflux of the methane was recorded from continuously flooded plots (346.6 mg/m(2)/day), followed by 9% less CH(4) efflux from tillering stage drainage (315.1mg/m(2)/day), 36.7% less efflux from mid-season drainage (219.3mg/m(2)/day) and the least 41% CH(4) efflux from multiple drainage plots (204.7 mg/m(2)/day). Among all the four different drainage systems applied, mid-season drainage and multiple drainage were found to be highly effective in mitigating methane efflux. Redox potential of the soil of the drainage system was found to be inversely proportional to the methane efflux from all the treatments.

Microbial Degradation of Alkanes

Petroleum hydrocarbons are introduced into the environment through excessive use of fuels and accidental spills during transportation and storage. Alkanes, a major fraction of crude oil, are saturated hydrocarbons and hence are chemically inert as non-polar molecules. However, a number of bacterial and fungal genera have been reported to degrade even high molecular weight alkanes in both aerobic and anaerobic conditions. The degradation process mainly involved enzymes such as methane monooxygenase (MMO), alkane hydroxylase and cytochrome P450 monooxygenase. Besides, a number of environmental factors affect the degradation of alkanes in soils.

In vitro degradation of fluoranthene by bacteria isolated from petroleum sludge.

An investigation was carried out for in vitro degradation of fluoranthene by four bacterial strains (PSM6, PSM7, PSM10 and PSM11) isolated from the petroleum sludge. Although all the strains registered their growth in MSM with 100 ppm fluoranthene, PSM11 growth was better than other strains. Growth of bacterial strains invariably corresponded to their degradation potential of fluoranthene. After 168 h of incubation, 61% fluoranthene was degraded by PSM11, followed by PSM10 (48%) and PSM6 (42%) and the least was recorded in PSM7 (41%). Besides, 11% loss in fluoranthene was attributed to abiotic factors. Thirty-eight times more activity of catechol 2,3-dioxygenase than catechol 1,2-dioxygenase showed that it played a significant role in fluoranthene degradation. Molecular weight of catechol 2,3-dioxygenase isolated from PSM11 was determined as ∼ 136 kDa by size exclusion chromatography and 34 kDa on denaturing SDS-PAGE, indicating tetrameric nature of the enzyme.

Bacterial degradation of pyrene in minimal salt medium mediated by catechol dioxygenases: Enzyme purification and molecular size determination

In vitro degradation of pyrene was studied in MSM by three bacterial strains individually, designated as BP10, NJ2 and P2. Among these strains, NJ2 was the highest degrader (60%) of pyrene, followed by BP10 (44%) and the least was P2 (42%) in MSM with pyrene (50 μg ml(-1)) in 8 days. During pyrene degradation, catechol 1,2 dioxygenase (C12O) activity was induced by 13 folds in BP10 and 17 folds in P2 as compared to catechol 2,3 dioxygenase (C23O). However, in NJ2, C23O activity was augmented 1.3 times more than C12O. This clearly indicated that C12O played a major role in pyrene degradation by BP10 and P2, while in NJ2, C23O contributed more to degradation process than C12O. Molecular weight of highly inducible C12O was determined as ~64 kDa by size exclusion chromatography and as ~32 kDa on denaturing SDS PAGE in BP10 which indicated dimeric nature of the enzyme.

Bacteria-mediated aerobic degradation of hexacosane in vitro conditions

In vitro degradation of hexacosane (C26H54), a HMW n-alkane, was studied in MSM by two bacterial strains i.e., Pseudomonas sp. BP10 and Stenotrophomonas nitritireducens E9, isolated from petroleum sludge, in isolation and combination. The results revealed that both the strains were able to metabolize hexacosane by 82% in isolation and 98% in their consortium after 7days. An enhancement of 16% in hexacosane degradation by the consortium indicated an additive action of bacterial strains. However, in control, a degradation of 21% was attributed to abiotic factors. During incubation with hexacosane, both the bacteria continued to multiply in isolation and consortium, which reflected that hexacosane was utilized by bacteria as a carbon and energy source. Activities of alkane hydroxylase and alcohol dehydrogenase were differentially expressed in isolation and combination, indicating their involvement in hexacosane degradation. Enhanced cell surface hydrophobicity and emulsification index and reduced surface tension also supported the degradation process.

Microbe-induced changes in metal extractability from fly ash

A low cost and eco-friendly technology to bioremediate toxic metals associated with fly ash dumps that contaminate ground and surface water in and around fly ash settling ponds, was investigated. The impact of augmentation of fly ash tolerant bacterial strains, isolated from Typha latifolia growing naturally on fly ash dumps, was studied for metal extractability. It was observed that most of the bacterial strains either induced the bioavailability of Fe, Zn and Ni or immobilized Pb, Cr, Cu, Cd in the fly ash. However, there were few exceptions also. In case of Ni, eight strains enhanced metal mobility, while others caused metal immobilization. The findings also suggest that metal solublization and immobilization are specific to bacterial strains. While induced bioavailability of metals by bacteria may be used to accelerate the phytoextraction of metals from fly ash by hyper accumulator plants, immobilization of metals can check their migration to water reservoirs and reduce the human suffering in affected areas. Thus, bacteria serve the dual purpose and may result in the microbe- assisted phytoremediation of contaminated sites.

Fluoride distribution and contamination in the water, soil and plants continuum and its remedial technologies, an Indian perspective– a review

Fluorine is an essential element required in trace amounts but gets toxic for human beings at levels more than 1.5 mg F- L-1 primarily through drinking contaminated water. It is the 13th most abundant element and constitutes about 0.06-0.09% in the earth crust. It is electronegative in aqueous medium forming fluoride ion (F-). Fluoride contamination in the environment occurs mostly due to anthropogenic and geogenic sources. Fluoride is widely distributed in all components of environment, air (0.1-0.6 μg L-1) soils (150-400 mg Kg-1) rocks (100-2000 mg Kg-1), plant (0.01-42 mg Kg-1) and water (1.0-38.5 mg L-1). Human beings and animals are being exposed to F- primarily from water (0.2-42.0 mg L-1) and plants (0.77-29.5 μg g-1). Fluorosis, a health hazard due to F- is a major problem in many countries across the world affecting about 200 million people globally. In India, > 62 million people in twenty states are facing problem due to F-. The most affected states are Rajasthan (7670 habitations), Telangana (1,174 habitations) and Karnataka (1122 habitations). To mitigate this problem, there is an urgent need to understand the current status and brief knowledge of F- geochemistry. The objective of this review is to highlight different sources of F- that contaminate different environmental matrices including plants, the extent of contamination level in India, uptake, translocation and toxicity mechanism in plants. The review also highlights currently available mitigation methods or technologies through physio-chemical and biological means.

Bacteria Induced Degradation of Anthracene Mediated by Catabolic Enzymes

Abstract This investigation evaluated the ability of three bacterial strains, Pseudomonas aeruginosa PSA5, Rhodococcus sp. NJ2, and Cronobacter sp. PSM10, isolated from the petroleum hydrocarbon contaminated soil, for the degradation of anthracene at very high concentration (1000 ppm) in minimal salt media (MSM). A maximum degradation of 94% was attained by PSA5, followed by PSM10 (84%) and a minimum was recorded for NJ2 (78%) after 10 days of incubation periods. Specific activities of catabolic enzymes like C120, C230, 3,4‐PCD, and 4,5‐PCD were recorded that indicates anthracene gets mineralized by these strain through O‐phthalate pathway. However aromatic rings of anthracene dominantly cleavage through ortho cleavage pathway by Pseudomonas aeruginosa PSA5 and Cronobacter sp. PSM10 while through meta cleavage by Rhodococcus sp. NJ2. Biosurfactant production by these strains during degradation of anthracene was also confirmed through the reduction of surface tension of media and formation of emulsification for 24 h with benzene.