Polychlorinated biphenyls: Biodegradative indigenous soil microorganisms and genetically modified alfalfa symbiont Sinorhizobium meliloti

Biodegradation of Polychlorinated Biphenyls (PCBs), toxic environmental pollutants, is considered the most cost-effective cleanup technique available. This study provides data on known and unknown microorganisms indigenous to soils contaminated with PCBs. The Colony Forming Unit (CFU) counts were used to quantitate growth of microorganisms and estimate the effect of PCBs toxicity. Dechlorination of PCBs was estimated by chlorine (Cl- ) release assay (at 460 nm) and by High Performance Liquid Chromatography (HPLC). The plasmid pPE43, which is a subclone containing ohb DNA region and relevant genes for PCB degradation, was electroporated into Sinorhizobium meliloti. Unidentified microorganisms that had the ability to degrade 2', 3, 4 PCB were isolated from highly to moderately contaminated soils. The higher the concentration of 2 ', 3, 4 PCB in the soil, the greater was the ability of the microorganisms, isolated from the soil, to deplete the pollutant. Indigenous unidentified cultures were at least equal and sometimes better than known PCB degraders such as Comamonas testosteroni and Rhodoccocus sp. tested. Moreover, mixed cultures were more potent than single cultures. The presence of plants significantly increased the rhizosphere CFU counts and the amount of PCB depleted was irrelevant to the origin and nature of the microorganisms. The PCB depletion and growth of Sinorhizobium meliloti electrotransformants, in the presence of the alfalfa plant were significantly enhanced. Genetically modified nitrogen-fixing Sinorhizobium meliloti USDA 1936 and its symbiont, the alfalfa plant, are ideal choices for cleaning up PCB contaminated soil and in fertilizing the soil as green manure, thus reclaiming vast acreages of abandoned toxic soils.