In the present economy, advancement in science and biotechnology have progressively aided mankind in the probe and exploration of natural resources. Different activities such as excavation of fossil fuels, crude oil exploration, crude-oil related products (kerosene, diesel, petrol) usage, arrival of agricultural chemicals and pharmaceutical products have eased the lifestyle of people worldwide. Unfortunately, a few of these interventions have a downside as the chemicals, solvents, and materials required for those developments may instigate health effects on the environment, humans, including the aquatic habitat (Valentín et al., 2013).
Numerous human activities have led to deliberate or accidental discharge of pollutants into the Earth’s ecological system as these contaminants pose a vast risk to human life, wellbeing and normal biological system (Chen et al., 2015). Any unwanted substances released into the environment are termed pollutants or contaminants. Pollutants are in existence for a while now, and life on Earth has always progressed amongst them (Korjus, 2014). The Earth is incessantly a polluted planet with pollutant similarities from, global warming, comets, space dust, organic dust, volcanic activities, smoke, comets, space dust, and acid rain (Korjus, 2014).
Poisonous chemicals contained in different materials in the Earth’s atmosphere can be absorbed on human skin, accumulate in the dust we inhale, or subsequently end up in the surrounding natural environment.
Substances that leach into the soil and water environment can indirectly affect humans, by absorption on different vegetables, fruits, fish, and other food products that end up on our eating table. The exhaustive utilization of substances, for example, oil hydrocarbons (such as saturated, unsaturated, polyaromatic, polycyclic aromatic hydrocarbons, and cycloalkanes), heavy metals (such as thallium, copper, zinc mercury, arsenic, iron, titanium, cadmium, nickel), pesticides, herbicides, air contaminants (carbon monoxide, ozone, acid rain, particulate matter), volatile organics (such as benzene, toluene, chloroform, ethylbenzene, xylenes), nitroaromatic compounds, organophosphorus compounds, trichloroethylene, perchloroethylene
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solvents, and chlorinated hydrocarbons can be intensely noxious thus inflicting extensive damage such as corrosive injuries, toxicity, and overall illness (Chen et al., 2015; Korjus, 2014; Megharaj et al., 2011). In some cases, some2
compounds are synthesized purposely to suit environmental requirements whereas in most cases, the burning of some chemicals such as polyvinylchloride, plastic, radioactive substances, inorganic substances, and organic compounds generate undesired toxic by-products. The destination of the above-listed pollutants is often the soil, lakes, river, and sea leading to bioaccumulation, and biomagnification effects over time. This, however, leads to deleterious and hazardous effect to both aquatic and terrestrial life (Liu et al., 2017; Valentín et al., 2013).
The discharge of crude oil, petroleum, hydrocarbons, heavy metals, and other various pollutants into the environment is a proportional range of approximately 2.0–8.8×106 metric tonnes annually (Hassanshahian and Cappello, 2013). Many pollutants introduced into the soil environment are degraded biologically while other pollutants have been toxic and not degradable to a number of the soil microbial community. Due to the detrimental consequences of hydrophobic pollutants, it is imperative to propose procedures to annihilate these environmental problems. Several conventional techniques such as alteration, volatilization, photo-oxidation, chemical oxidation, adsorption, landfilling, burning, and chemical treatments are extensively used in polluted sites clean-up, but these methods highlighted above are exceedingly costly, toxic, non-biodegradable and pose additional risks to the environment (Guntupalli et al., 2016; Patowary et al., 2018).
Anionic, non-ionic, cationic and mixed surfactants are different types of surfactants are able to remove concentrated hydrophobic compounds from liquid medium, groundwater, surface water and contaminated soil (Chaprão et al., 2015; Lai et al., 2009; Urum et al., 2006). Surfactants are standout amongst the profitable synthetic products and huge amounts are expended throughout the world for various purposes (Chakraborty et al., 2015). Be that as it may, the remaining surfactants in soil surroundings and receiving water bodies constitute probable danger to environmental conditions and human wellbeing (Chaprão et al., 2015).
One of the promising techniques to restore contaminated environments is the utilization of bioremediation innovations, which is an eco-accommodating, financially productive, and supportable method. Bioremediation is an ecologically-sound technique encompassing the usage of natural biological processes to cleanse or remove pollutants through biochemical solubilization or mineralization. It is the most interesting strategy by which microbes, microalgae, green plants and/or their enzymes use for hydrocarbon biodegradation and bioremediation (Korjus, 2014; Mani and Kumar, 2014; Mnif et al., 2015). They have been recognized as extensive substitutes for regular strategies in settling natural ecological issues (Mnif et al., 2015). Likewise, biodegradation by natural microbial population characterizes one of the significant mechanisms by which hydrophobic contaminants can be expelled or diminished from nature. Biodegradation is a natural process that
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involves the transformation and breakdown of organic contaminants principally by microbial organisms into simpler substances. The microbial organisms transform the contaminants through their metabolic or enzymatic processes (Katyal and Morrison, 2007; Thomson, 2012). Some physicochemical, just as biological parameters determine the extent of hydrocarbons biodegradation. Due to the exceedingly hydrophobic nature of hydrophobic pollutants, different factors such as low water solubility, strong soil particles attachment, and low biological availability of oil pollutants have constrained the mass transfer proportion to biodegradation and bioremediation. Also, oil and petroleum contaminants are often adsorbed and absorbed onto soil particles, might be available as a liquid or a solid phase (Bezza and Nkhalambayausi Chirwa, 2015; Chaprão et al., 2015;
Paria, 2008).
Both eco-friendly techniques highlighted above involves the production of surface-active molecules of microbial origin termed “biosurfactant” which aid in the solubilization and remediation of hydrophobic pollutants, petroleum hydrocarbons, oil-related products, and not limited to heavy metals. Biosurfactants (BioSs) are amphiphilic compounds, produced by specific microorganisms (Parthipan et al., 2017; Sharma et al., 2015). BioS synthesis by microorganisms is either secreted intracellularly by being partly attached to the cell membrane or as an extracellular release to the medium. The former mechanism arises commonly when the microorganism is grown in substrates that are insoluble in water. BioSs produced intracellularly assist in nutrient uptake, neutralization of toxic elements, and further ease carbon molecule storage (Ndlovu, 2017).
Furthermore, BioSs enable microorganisms to have a surface activity which assists in lowering the surface tension between multiple interphases (liquid-liquid, liquid-air, liquid-gas, and liquid-solid), thus rendering the substrate and aid the mobility of microorganisms in unfriendly environments (Van Hamme et al., 2006).
The BioS molecules which contain the hydrophobic group (water repelling such as unsaturated or saturated hydrocarbon chains or fatty acids) and hydrophilic ends (water-loving, such as, acid, cations, or anions, peptide, mono-, di- or polysaccharides) mediates the surface interactions at the interface (Sharma et al., 2015). The dual nature of BioSs permits the dissolution of both polar and non-polar solvents (Smyth et al., 2010a; Smyth et al., 2010b). Depending on the chemical structure and microorganisms that produce these compounds, BioS are biological-chemical complexes that consist of an extensive kind of biomolecules such as fatty acids, dicarboxylic acids, fatty acid amides, lactones, alkyl glycosides, and sugar molecules (Ndlovu, 2017; Youssef et al., 2005). The main classes include polymeric compounds, lipopeptides, phospholipids, particulate surfactants, and glycolipids. BioSs have several advantages when compared to chemically produced counterparts. Such advantages involve non-toxicity, extensive foaming activities, biodegradability, ecological
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acceptability, high selectivity, environmentally friendliness, and effectiveness at extreme environments (Bezza and Nkhalambayausi Chirwa, 2015; Chrzanowski et al., 2012; Hirata et al., 2009). As such, BioSs are well- thought-out as a preeminent option to synthetic surfactants in augmenting solubilization, bioavailability, biodegradation, and bioremediation of hydrophobic pollutants (Mnif et al., 2015). These favorable properties make BioSs suitable in scope of applications, for example, food, agriculture, oil industries, cosmetics, environmental, pharmaceutics, and biotechnological processes (Bezza and Nkhalambayausi Chirwa, 2015;
Mnif et al., 2014; Pacwa-Płociniczak et al., 2011).