Biosurfactants surface-active substances synthesized by living cells (bacteria, yeast and fungi) They are amphiphilic compounds with a hydrophilic (amino-acid or peptides; di- or polysaccharides; anions or cations) and hydrophobic moieties (saturated or unsaturated fatty acid) (Mnif &Ghribi 2015a). Like chemical surfactants, biosurfactants are well known by their ability to decrease the surface and interfacial tension at the surface and interface respectively (Mnif &Ghribi 2015a). Owing their large diversity, environmentally friendly nature, non-toxicity, large biodegradability and possibility of large-scale production, a great interest was spotted onto biosurfactants in recent years. In addition to these properties, their numerous functional and biological activities and ability to function under extreme conditions of temperature, pH and salinity permit their application in various fields including food, agriculture, biomedical and environment (Mnif &Ghribi 2015a, Mnif &Ghribi 2015b, Mnif &Ghribi 2015c). They appear as best replacements of chemical surfactants and scientists focus on the research of new-biosurfactant producing microorganisms. When grown on immiscible or miscible substrates, these microorganisms synthesize a wide range of chemicals with surface active compounds, with diverse nature (Mnif &Ghribi 2015a). Owing their biochemical nature, biosurfactants are classified onto six groups including glycolipids, lipopeptides, phospholipids, lipopolysaccharides, neutral lipids and polymeric surfactants (Mnif &Ghribi 2015a). Glycolipids and lipopeptides consisting of a fatty acid chain linked to a carbohydrate and peptidic moieties respectively are among the most recognized biosurfactants with a high structural versatility and various functional activities (Mnif &Ghribi 2015a).
Lipopeptides, are characterized by diverse functional properties (emulsification/de-emulsification, dispersing, foaming, viscosity reducers, solubilizing and mobilizing agents, pore forming capacity) and endowed by different biological activities (antimicrobial; hemolytic; antiviral; antioxidant …) permitting their use in many domains (Mnif &Ghribi 2015c, Mnif &Ghribi 2015d). Especially, having the ability to emulsify, solubilize and mobilize hydrocarbon contaminants, lipopeptides increases their availability for microbial degradation (Mnif &Ghribi 2015c), (Mnif et al. 2014, Mnif et al. 2013b, Mnif et al. 2015a, Mnif et al. 2017a, Mnif et al. 2013a). They are very advantageous over synthetic emulsifiers for the enhancement of the bioremediation of hydrocarbon contaminated sites (Mnif &Ghribi 2015c, Mnif &Ghribi 2015d). Also, lipopeptide biosurfactants stimulates dyes bio-decolorization (Mnif et al. 2015b, 2015c, Mnif et al. 2016a). Moreover, they can be used in enhanced oil recovery and may be considered for other potential applications in environmental protection (Mnif &Ghribi 2015c). In addition, they can be applied in herbicides and pesticides formulations, detergents, healthcare and cosmetics, pulp and paper, coal, textiles, ceramic processing and food industries (Bouassida et al. 2018, Mnif &Ghribi 2015c).
Oil spills in the oceans causes great damage to local animal, plant life and disturb all the ecological equilibrium (Song et al. 2013). Due to increasing exploitation, production, transportation and storage, oil spread over a large area on sea surface causing great damage. The application of chemical dispersants, defined as a material that reduces the cohesive attraction between similar particles, is an efficient mean that help in the mechanic restoration of oil spills (Mnif et al. 2017b). Dispersant agents prevent insoluble particles to form aggregations with each other that keep insoluble particles in suspension and oil slicks are broken up. When they are sprayed onto oil slicks, they accelerate the dispersion of oil from the sea surface enhancing their removal (Guodong et al. 2015). During oil dispersion, the hydrophilic part of the surfactant turns towards the hydrophilic phase “the sea water” while the hydrophobic tail of the molecule turns towards the oil phase, leading to the formation of small oil droplets that are stabilized by the dispersant (Guodong et al. 2015, Pi et al. 2015). In addition to oil dispersion, dispersants agents have application in oil chemistry field as they have great role in desorption of hydrophobic molecules from rock surfaces enhancing their mobility and recovery. However, chemical dispersants have great hazardous effects to marine and soil ecosystems and cause great toxicities to living organisms (Kleindienst et al. 2015, Popovech 2017). Also, they can suppress the activity of oil degrading micro-organisms when applied to the oil-contaminated seawater to disperse surface slicks into smaller droplets that are presumed to be more bio-available to microorganisms (Kleindienst et al. 2015). So, an urgent need for natural and environment-friendly oil spill dispersants was developed (Guodong et al. 2015). Owing their great surface activity, biodegradability and non-toxicity, biosurfactants can be an eco-friendly alternative to chemical dispersants. Many previous reports described the use of biosurfactants as oil dispersants promoting therefore hydrocarbon decontamination and environment cleaning (Da Silva et al. 2017, Freitas et al. 2016, Rongsayamanont et al. 2017, Song et al. 2013).
Here, we report the screening and the identification of a newly biosurfactant producing bacterium. After that, biosurfactant purification and identification was studied by an acid precipitation followed by anionic exchange chromatography and High Performance Liquid Chromatography coupled to a mass Spectrometry. Aiming its potential use in bioremediation, we studied the surface tension decreasing capacity and the oil dispersant activity the produced biosurfactant along with the effect of different physic-chemical factors on these activities.