Inorganic cyanide and nitrile compounds are distributed widely in the environment, chiefly as a result of anthropogenic activity but also through cyanide synthesis by a range of organisms including higher plants, fungi and bacteria. The major source of cyanide in soil and water is through the discharge of effluents containing a variety of inorganic cyanide and nitriles. Here the fate of cyanide compounds in soil and water is reviewed, identifying those factors that affect their persistence and which determine whether they are amenable to biological degradation. The exploitation of cyanides by a variety of taxa, as a mechanism to avoid predation or to inhibit competitors has led to the evolution in many organisms of enzymes that catalyse degradation of a range of cyanide compounds. Microorganisms expressing pathways involved in cyanide degradation are briefly reviewed and the current applications of bacteria and fungi in the biodegradation of cyanide contamination in the field are discussed. Finally, recent advances that offer an insight into the potential of microbial systems for the bioremediation of cyanide compounds under a range of environmental conditions are identified, and the future potential of these technologies for the treatment of cyanide pollution is discussed.

Aims:  To study how repeated applications of an herbicide bromoxynil to a soil, mimicking the regime used in the field, affected the degradation of the compound and whether such affects were reflected by changes in the indigenous bacterial community present. Methods and Results:  Bromoxynil degradation was monitored in soil microcosms using HPLC. Its impact on the bacterial community was determined using denaturing gradient gel electrophoresis (DGGE) and quantitative PCR of five bacterial taxa (Pseudomonads, Actinobacteria, α‐Proteobacteria, Acidobacteria and nitrifying bacteria). Three applications of 10 mg kg−1 of bromoxynil at 28‐day intervals resulted in rapid degradation, the time for removal of 50% of the compound decreasing from 6·4 days on the first application to 4·9 days by the third. Bacterial population profiles showed significant similarity throughout the experiment. With the addition of 50 mg kg−1 bromoxynil to soil, the degradation was preceded by a lag phase and the time for 50% of the compound to be degraded increased from 7 days to 28 days by the third application. The bacterial population showed significant differences 7 days after the final application of bromoxynil that correlated with an inhibition of degradation during the same period. Conclusions:  These analyses highlighted that the addition of bromoxynil gave rise to significant shifts in the community diversity and its structure as measured by four abundant taxa, when compared with the control microcosm. These changes persisted even after bromoxynil had been degraded. Significance and Impact of the Study:  Here we show that bromoxynil can exert an inhibitory effect on the bacterial population that results in decreased rates of degradation and increased persistence of the compound. In addition, we demonstrate that molecular approaches can identify statistically significant changes in microbial communities that occur in conjunction with changes in the rate of degradation of the compound in the soil.

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 K2Ni(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.

The analysis of the bacterial community within the soil using DGGE showed acrylonitrile (ACN) could lead to the selection of significantly similar communities. Moreover, Rhodococcus sp. AJ270 was successfully established in the soil community. High GC G+-bacteria also responded positively to ACN addition. Bioaugmentation or carbon addition had no impact on the rate or degree of ACN degradation. ACN could be readily degraded by the soil bacteria, however, the community structure was significantly affected by its addition as well as by the addition of carbon or Rhodococcus sp. AJ270. The bioaugmentation of the soil with this strain was successful, in that the organism became established within the community. ACN addition to a soil produces statistically significant changes in the bacterial community.

Aims:  Bromoxynil degradation by soil micro‐organisms has been shown to be co‐oxidative in character. In this study, we investigate both the impact of the application of increasing bromoxynil concentrations on soil‐derived bacterial communities and how these changes are reflected in the degradation of the compound. Our aim was to test the hypothesis that the addition of bromoxynil to a soil‐derived bacterial community, and the availability of a readily utilizable carbon source would have an impact on bromoxynil degradation, and that would be reflected in the bacteria present in the soil community. Methods and Results:  Degradation of bromoxynil was observed in soil‐derived communities containing 15 mg l−1, but not 50 mg l−1 of the compound, unless glucose was added. This suggests that the addition of carbon stimulates co‐oxidative bromoxynil degradation by the members of the bacterial community. Measurable changes in the bacterial community indicated that the addition of bromoxynil led to deterministic selection on the bacterial population, i.e. the communities observed arise through the selection of specific micro‐organisms that are best adapted to the conditions in the soil. The addition of bromoxynil was also shown to have a negative impact on the presence of α and γ‐proteobacteria in the soil community. Conclusion:  Bromoxynil degradation is significantly inhibited in bacterial soil communities in the absence of readily accessible carbon. The application of bromoxynil appears to exert deterministic selection on the bacterial community. Significance and Impact of the Study:  This study highlights the effects of increasing bromoxynil concentrations on a model bacterial population derived from soil. Soil communities show qualitative and quantitative differences to bromoxynil application depending on the availability of organic carbon. These findings might have implications for the persistence of bromoxynil in agricultural soils.