Isolation of aroclor۱۲۵۴ degrading bacteria in contaminated soil by transformer oil

ABSTRACT- Aerobic biodegradation is an environmental-friendly biological method that allows micro organisms to remove persistent organic pollutants. Aroclor۱۲۵۴ is a mixed compound containing polychlorinated biphenyls (PCBs) along with persistent organic materials. There is no estimate of Aroclor۱۲۵۴ usage and its release into the environment in Iran. A transformer manufacturing plant in Shiraz (located in southwest of Iran) uses transformer oils containing Aroclor۱۲۵۴. Soil samples contaminated by transformer oil were taken from the manufacturing plant’s site and were tested for the presence of certain bacteria, level of degradation and pH. In all samples, ۱۳ bacterial strains were isolated on C-media, and their growth was measured using a spectrophotometer. Of the isolated strains, eight could degrade Aroclor۱۲۵۴. Of these eight strains, three showed weak growth (OD between ۰.۱ to ۰.۱۹۵), three showed low growth (OD between ۰.۲ to ۰.۳) and two showed good growth (OD between ۰.۳ to ۰.۵). Some of the strains grew well during the first week, but their growth decreased and eventually stopped in the second week. For all the growth media on which the bacteria from the soil was separated and cultured, pH decreased as the bacterial growth increased. For some media, in which bacterial growth had stopped, pH increased after ۱۴ or ۲۱ days but it was always below ۷.۰. This indicated that environmental pH or increasing carbon dioxide levels were not suitable for the growth of these strains. However, this trend was not observed in bacteria belonging to Pseudomonas, Curtobacterium and Burkholderia. These bacteria could grow and degrade Aroclor۱۲۵۴ even at pH of ۴.۵. In fact, their degradation efficiency increased at a constant pH of about ۵.۵.