Polycyclic aromatic hydrocarbons (PAHs) are a large group of chemicals. They represent an important concern due to their widespread distribution in the environment, their resistance to biodegradation, their potential to bioaccumulate and their harmful effects. Several pilot treatments have been implemented to prevent economic consequences and deterioration of soil and water quality. As a promising option, fungal enzymes are regarded as a powerful choice for degradation of PAHs. Phanerochaete chrysosporium, Pleurotus ostreatus and Bjerkandera adusta are most commonly used for the degradation of such compounds due to their production of ligninolytic enzymes such as lignin peroxidase, manganese peroxidase and laccase. The rate of biodegradation depends on many culture conditions, such as temperature, oxygen, accessibility of nutrients and agitated or shallow culture. Moreover, the addition of biosurfactants can strongly modify the enzyme activity. The removal of PAHs is dependent on the ionization potential. The study of the kinetics is not completely comprehended, and it becomes more challenging when fungi are applied for bioremediation. Degradation studies in soil are much more complicated than liquid cultures because of the heterogeneity of soil, thus, many factors should be considered when studying soil bioremediation, such as desorption and bioavailability of PAHs. Different degradation pathways can be suggested. The peroxidases are heme-containing enzymes having common catalytic cycles. One molecule of hydrogen peroxide oxidizes the resting enzyme withdrawing two electrons. Subsequently, the peroxidase is reduced back in two steps of one electron oxidation. Laccases are copper-containing oxidases. They reduce molecular oxygen to water and oxidize phenolic compounds.

Bioremediation for degradation of hydrocarbons is a widely used alternative for the recovery of contaminated sites. The current study aimed to use Alcanivorax borkumensis crude enzyme preparation as an agent for enhanced microbial hydrocarbons biodegradation in contaminated water and soil. The inoculum and hydrocarbons concentration have a remarkable effect on the biodegradation with the crude enzymes. The high enzymatic production reaching 145.71 U/mg for alkane hydroxylase, 3628.57 U/mg for lipase and 2200 U/mg for esterase led to a significant degradation efficiency of the different concentrations of petroleum hydrocarbon substrates reaching 73.75% for 5000 ppm of hexadecane, 82.80% for 1000 ppm of motor oil, 64.70% for 70 ppm of BTEX and 88.52% for 6000 ppm of contaminated soil. The study suggested that Alcanivorax borkumensis is a potential hydrocarbon-degrading bacterium with higher enzymatic capacities for bioremediation of hydrocarbon-polluted environment.

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This study investigates motor oil (3, 5, 7.5 and 10% (v v)) as a sole carbon source for the production of Alcanivorax borkumensis in shake flasks and a 5 L bench-scale fermenter in comparison to the standard media. Shake flask studies showed a significant and higher cell growth (p=0.000038), lipase (p = 0.006900) and alkane hydroxylase production (p = 0.000921) by Alcanivorax borkumensis when motor oil was used as the substrate. Based on Tukey post-hoc tests, 5% motor oil concentration was selected as the optimal substrate concentration. The 5 L fermenter experiments conducted using motor oil at 5% (v v) concentration, under controlled conditions exhibited significant and higher alkane hydroxylase and lipase activities (55.6 U mL (p = 0.018418) and 208.30 U mL (p =  0.020087), respectively) as compared with those of motor oil at 3% (v v) and n-hexadecane at 3% (v v) concentration which was used as control. Cell growth was significantly higher when motor oil (3 or 5%) was used as a substrate (p =  0.024705). Enzymatic degradation tested on two different polycyclic aromatic hydrocarbons (PAHs) contaminated groundwaters showed 37.4% removal after 5 days with a degradation rate of 196.6 ppb day and 82.8% removal after 10 days with a degradation rate of 217.54 ppb day for the 1st site and an almost complete biodegradation with 95% removal and 499.02 ppb day removal rate after only 5 days for the 2nd site.

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