**4.2 The use of** *Pseudomonas aeruginosa* **in the biodegradation and bioremediation of petroleum hydrocarbons**

Crude oil spills into marine (offshore) bodies or soil (onshore) environments are very toxic and dangerous to the ecosystem and could be detrimental to the well-being of life forms, air, water, and soil processes and could as well increase the potential of fire hazards [39]. Onshore spill of crude oil affects living forms in the habitat, reduces agricultural productivity, and pollutes groundwater and sources of potable water and living biota in flowing water bodies, among others [40]. Eliminating or limiting these adverse effects from crude oil spillage situations implies total prevention of the spillage where possible and amending the soil via the procedure known as bioremediation [41]. Some known methods used in remediating crude oil-polluted soils include physical separation, chemical degradation, photodegradation, and bioremediation [42]. However, bioremediation is gaining preference because of its comparative effectiveness, relatively lower costs, and eco-friendliness when compared to other techniques. Conversely, methods other than bioremediation used for oil-polluted soil remediation have shown potentials of leaving secondary metabolites, which are secondary residuals left after the primary crude oil pollutant has been removed [43]. These by-products can even exhibit higher toxicity levels than the parent crude oil pollutant. Fortunately, bioremediation technique usage detoxifies contaminants in crude oil and effectively removes pollutant by destroying them instead of transferring them to other medium [44].

Researchers have used plant species for bioremediation, in a process known as phytoremediation, but the deploying microorganisms as biologically mediated remediation of crude oil-polluted soil are still linked to the effectiveness of phytoremediation systems [45]. This is as result of the fact that microorganisms are still required in the rhizosphere of plants for efficient soil remediation via phytoremediation [58]. This makes the use of microorganisms for the remediation of soil polluted by crude oil spills of increasing interest to researchers and stakeholders involved in crude oil-polluted soil amendment. A good example of bacterial strains of microbes used in reported works for effective repair of crude oil-polluted soil is *Pseudomonas aeruginosa* [46]. In an attempt to degrade petroleum hydrocarbon,

*Pseudomonas* will normally release biosurfactant which will reduce crude oil from high molecular weight to low molecular weight. This is to enable the bacteria to utilize the petroleum hydrocarbon [47].
