The impact of bioaugmentation on metal cyanide degradation and soil bacteria community structure

Metal cyanides are significant contaminants of many soils found at the site of former industrial activity. In this study we isolated bacteria capable of degrading ferric ferrocyanide and K₂Ni(CN)₄. One of these bacteria a Rhodococcus spp. was subsequently used to bioaugment a minimal medium broth, spiked with K₂Ni(CN)₄, containing 1 g of either an uncontaminated topsoil or a former coke works site soil. Degradation of the K₂Ni(CN)₄ was observed in both soils, however, bioaugmentation did not significantly impact the rate or degree of K ₂Ni(CN)₄ removal. Statistical analysis of denaturing gradient gel electrophoresis profiles showed that the topsoil bacterial community had a higher biodiversity, and its structure was not significantly affected by either K₂Ni(CN)₄ or bioaugmentation. In contrast, profiles from the coke works site indicated significant changes in the bacterial community in response to these additions. Moreover, in both soils although bioaugmentation did not affect rates of biodegradation the Rhodococcus spp. did become established in the communities in broths containing both top and coke works soil. We conclude that bacterial communities from contaminated soils with low biodiversity are much more readily perturbed through interventions such as contamination events or bioaugmentation treatments and discuss the implications of these findings for bioremediation studies.