For the purpose of environmental protection, governments and international organizations have enacted strict regulations for controlling the process of overexploitation and possibly inappropriate release of PCO throughout the world. While these regulations have effectively contributed to minimizing the pollution of environment by the PCO, they can unfortunately be relatively ineffective in the face of contamination that occurs accidentally or unintentionally. Whatever the causes, when the pollution by the PCO occurs, multiple and diverse ecotoxicological effects are produced in both terrestrial and aquatic environments. The application of physical methods for removing the PCO from the aquatic environment can be a difficult, expensive and inefficient process, and the use of chemical surfactants as remediating agents is no longer favored because of their toxic effects on the biota of targeted area.
Therefore, bioremediation, defined as the use of microorganisms to degrade pollutants owing to their diverse metabolic capabilities, is considered as an evolving method for the degradation and removing of many environmental pollutants including hydrocarbons. The biodegradation of PCO by microorganisms has been the subject of many excellent reviews during the past decade and a considerable number of investigations has reported that bacteria are the most active microorganisms in crude oil degradation, and several bacteria are even known to feed exclusively on hydrocarbons.
Microorganisms, dwelling in the PCO, have exceptional biological capabilities to tolerate the toxicity of this complex and they therefore presumed to be promising emulsifier-degraders of PCO in the aquatic environments. Following this logic, the main purpose of the current work was to isolate, if existed, the PCO-inhabiting microorganisms in the objective of their identification, characterization and studying their possible potentiality as emulsifier-degraders of the PCO. Seven bacterial strains were therefore purely isolated and one of them was selected by its remarkable ability to consume the PCO.
A newly published paper in the Journal of Frontiers in Microbiology describes a set of PCO-inhabiting bacterial species, one of which, identified as Bacillus safensis PHA3, produces an efficient biosurfactant which was characterized as a glycolipid. Fourier transform infrared spectrometer, nuclear magnetic resonance, Thin layer chromatography, HPLC, and GC-MS analysis of the purified biosurfactant revealed that the extracted molecule under investigation is likely a mannolipid molecule with a hydrophilic part as mannose and a hydrophobic part as hexadecanoic acid (C16:0). The data reveal that: (i) PHA3 is a potential producer of biosurfactant; (ii) pre-adding of the purified glycolipid enhanced the degradation of PCO by approximately; (iii) the highest emulsifying activity of biosurfactant was found against the PCO and the lowest was against the naphthalene; (iv) the optimal PCO-emulsifying activity was found at 30–60∘C, pH 8 and a high salinity. An orthologous gene encodes a putative β-diglucosyldiacylglycerol synthase (β-DGS) was identified in PHA3 and its transcripts were significantly up-regulated by exogenous PAHs, i.e., pyrene and benzo(e)pyrene but much less by mid-chain n-alkanes (ALKs) and fatty acids. Subsequently, the accumulation of β-DGS transcripts coincided with an optimal growth of bacteria and a maximal accumulation of the biosurfactant. Of particular interest, the authors found that PHA3 actively catalyzed the degradation of PAHs notably the pyrene and benzo(e)pyrene but was much less effective in the mono-terminal oxidation of ALKs. The outcome of this work will support the global efforts to identify new microorganisms with promising activities in removing the petroleum-origin pollutants from the aquatic environment.