Abstract
The continuous accumulation of recalcitrant xenobiotic compounds into the ecosystem released from various sources caused a serious global concern. Xenobiotics compounds are carcinogenic, mutagenic, causing teratogenic effect and persist over a long period of time in the environment. Therefore there is an urgent need for the detoxification of these compounds. Biodegradation is a technique that employs natural biological processes to completely degrade toxic contaminants from the environment. The microorganisms possess a wide range of catabolic biodegradation pathways and, thus, use these toxic xenobiotics as the sole source of carbon and energy. Bacteria and fungi are source of xenobiotic degradation. For the development of successful and improved bioremediation processes, understanding of the biochemical and molecular aspects of xenobiotics biodegradation is required. The chapter aims to provide an overview of xenobiotic compounds, factors affecting biodegradation, the metabolic pathways and genetic adaptation in microorganisms for degradation of recalcitrant xenobiotic compounds.
TopXenobiotic Compounds
The word, xenobiotic is a combination of two distinct roots “xeno” and “biotic.” The word xeno is derived from Greek which means strange, unnatural, or different while biotic is a word that implies life. Xenobiotic, therefore, refers to an organic compound that imitates natural biochemicals that are crucial for life, but are strange and unnatural. The xenobiotic compounds are highly thermostable thus persists in the environment. Xenobiotics are often toxic to life. Also, they may not be recognized by biochemical processes in plants and microorganisms and are thus resistant to degradation in the environment. Primarily, xenobiotics are those compounds that are alien to a living individual and have a propensity to accumulate in the environment. Xenobiotics include many compounds that are used in both industrial and agricultural activities. The major xenobiotics include pesticides, fuels, solvents, alkanes, polycyclic hydrocarbons (PAHs), antibiotics, synthetic azo dyes, pollutants (dioxins and polychlorinated biphenyls), polyaromatic, chlorinated and nitro- aromatic compounds. The main issue with xenobiotic compounds is the toxicity threat they pose to public health. It is quite shocking that some xenobiotic compounds (phenols, biphenyl compounds, phthalates, etc.) act as endocrine disruptors (Borgeest, Greenfeld, Tomic, & Flaws, 2002).
Key Terms in this Chapter
Mesophile: Mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 20 and 45 °C.
Thermophile: Thermophile is an organism a type of extremophile that thrives at relatively high temperatures, between 41 and 122 °C.
Bioremediation: Bioremediation is a waste management technique that involves the use of organisms to remove or neutralize pollutants from a contaminated site.
Biosorption: It is a physiochemical process that occurs naturally in certain biomass which allows it to passively concentrate and bind contaminants onto its cellular structure.
Xenobiotic: Xenobiotics are those compounds that are alien to a living individual and have a propensity to accumulate in the environment.
Mineralization: The decomposition or oxidation of the chemical compounds in organic matter into plant-accessible forms.
Co-Metabolism: The simultaneous degradation of two compounds, in which the degradation of the second compound (the secondary substrate) depends on the presence of the first compound (the primary substrate).
Surfactants: The compounds that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants.
Biomagnification: It is a process in which chemical substances become more concentrated at each higher trophic level. Such chemical substances tend to be difficult to be removed from animal and plant tissues.