Study of enhancement and inhibition phenomena and genes relating to degradation of petroleum polycyclic aromatic hydrocarbons in isolated bacteria

Polycyclic aromatic hydrocarbons (PAHs) are xenobiotic compounds, which being degraded by chemical, physical or biological methods. The latter is the safest and the cheapest one. Two bacterial strains ASU-01 and ASU-016 were isolated from different Egyptian petroleum contaminated sites. They were genetically identified based on the analysis of the nucleotide sequences of the 16S ribosomal PNA gene and the phylogenetic tree as Enterobacter hormaechei and Pseudomonas pseudoalcaligenes respectively. When pyrene as high molecular weight (HMW)-PAH was added as a sole carbon source, both strains could degrade it with efficiency 77.7 and 83.7% within 15 days of incubation, respectively. However, when it was mixed with low molecular weight (LMW)-PAHs, two opposite phenomena appeared. The first one was enhancement, which occurred with ASU-01. This strain shifted pyrene efficiency to 98.5%. The second phenomenon was inhibition occurred with ASU-016 which completely retarded pyrene degradation. Naphthalene dioxygenase (nahAc), and catechol dioxygenases (C12O and C23O) genes were detected in the two strains based on PCR. The detected genes were confirmed by determining the different specific activities of their translated protein (enzymes) on different PAHs. The maximum values of biosurfacatant production activity and cell-surface and percentage of cell-surface hydrophobicity (CSH) were detected during the exponential phase. These latter factors increased the bioavailability and consequently, the assimilation of PAHs.