Distribution of biphenyl degraders in soil samples in Mosul-Iraq

Abstract

This work aimed to study the distribution of biphenyl degrading isolates from different soils in Nineveh governorate. Fifty five soil samples were collected from reeds soil, sandy soil, landfill soil, oil refinery soil, agricultural soil, sulfur station soil, garden soil, and sewage contaminated soil. Nine isolates were diagnosed based on their cultural characteristics and 16S rRNA gene sequence. Five isolates belonged to Rhodococcus, and the other four were diagnosed as Extensimonas perlucida, Achromobacter sp., Microbacterium barkeri, and Pseudomonas luteola. The sequences were submitted to NCBI and given the initials RM. Our results showed that the soil samples with the highest source of biphenyl degraders was Mishraq sulfur station soil (33.33%) followed by sewage soil (28.57%). On the other hand no biphenyl degraders were isolated from oil refinery soils, agricultural soils and garden soils. Growth rates of the nine biphenyl degraders varied with different strains reflecting the efficiency of their enzymes in degrading biphenyl. Two sets of primers were used to detect dioxygenases used by the isolates. The primer BPHD-f3 and BPHD-r1 was used to amplify a 524bp DNA fragment from the Rieske non-heme iron dioxygenase gene expected to be used in the initial step of biphenyl degradation and was found in 5/9 biphenyl degrading isolates. The second set of primers (DOalpha-2 and DOalpha-3) was designed to target angular dioxygenase genes involved in the first step of aromatic hydrocarbon degradation other than biphenyl. Interestingly, our results showed that E. perlucida and Pseudomonas luteola RM9 contains an angular dioxygenase gene that is probably involved in degrading other aromatic compounds besides biphenyl.