Handbook of Bioremediation

Handbook of Bioremediation

Physiological, Molecular and Biotechnological Interventions
2021, Pages 591-602
Handbook of Bioremediation

Chapter 37 - Physiological and molecular basis of plants tolerance to linear halogenated hydrocarbons

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Abstract

Halogenated hydrocarbons are produced when hydrogen atoms of a hydrocarbon are substituted by one or more halogens. These occur naturally but majority of the halogenated hydrocarbons are synthetic. These are synthesized as industrially valuable materials, or produced as a by-product during chemical reactions, or being released as a result of burning of municipal waste. Halogenated hydrocarbons are ubiquitous in our environment as are found in water, marine systems, soil, sewage and air, but most commonly as groundwater contaminants. Halogenated hydrocarbons may be carcinogenic and are also involved in ozone destruction leading to global warming, which thereby result in decreased photosynthesis rate in plants.

Dehalogenases (hydrolases and hydratases) catalyze the hydrolytic reaction to replace chlorine and fluorine atoms from linear halohydrocarbon compounds. Haloalkane dehalogenases (EC 3.8.1.5.) cleave carbon-halogen bond of aliphatic halogenated hydrocarbons, resulting in the formation of an alcohol, a proton, and a halide ion. Several microorganisms have been isolated and reported, which are capable of degrading aliphatic organochlorine compounds such as 1,2-dichloroethane (1,2-DCA) that is degraded by bacteria. Xanthobacter autotrophicus GJ10 dehalogenates 1, 2-DCA by substituting chlorine atom with a hydroxyl group leading to the formation of chloroethanol.

Trichloroethylene, one of the common halogenated hydrocarbons, is a big environmental contaminant. Poplar trees showed genetic response to trichloroethylene and several putative detoxification genes were differentially regulated as was evident by microarray studies. It was also observed that detoxification genes like cytochrome P450s, glycosyltransferases, glutathione-S-transferases, and ATP-binding cassette transporters take part in TCE degradation in poplar species. In addition, it has been reported that popular endophytic bacteria can degrade TCE more effectively, thus enhancing plant tolerance against this organic pollutant.

The proposed chapter will discussed the types, chemistry, and transport of aliphatic halogenated hydrocarbons in plants. Plant genes and bacterial endophytes involved in plant tolerance against halogenated hydrocarbons will also be highlighted in this chapter.

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