Assessing impacts of cyanide treatments on soil microbial community composition and structure

Background/Question/Methods

Cyanide was first introduced commercially over a century ago, and since has been used or produced in many industries including: metal plating, gold mining, gas production, and pharmaceutical production. In the USA 10 million tons of road salt representing an environmental input of 700 tons of iron cyanide are used each year. The known problems with cyanide are its deleterious threats to both human and environmental health. The resiliency of certain communities may hold the key to cyanide remediation.  The objective of this study is to evaluate the short term impact of cyanide treatment on soil microbial community composition and structure. A microcosm study was performed in which replicate soil microcosms were treated once with 2 different cyanide compounds (KCN and K2Ni(CN)₄^-2) and sampled over time for whole community DNA and subsequent 16S rRNA gene sequence analysis. 

Results/Conclusions

Phyla that are commonly found in dominance in soils were also found in the treated soils with CN (Actinobacteria, Proteobacteria, and Firmicutes) as each of them showed immediate response to the presence of CN. Relative abundance of Actinobacteria and Firmicutes were surpressed by between 5-15% in both KCN and K2Ni(CN)₄^-2 treatments. Actinomycetes were the only taxanomic group at the Order level to show a significant surpression in response to KCN over time starting at 7.9% of sequences and dropping to below 2% of sequences. Orders lactobacillales and xanthomonadales showed significant differences (P<0.05) at each time step between the two treatments. Clustering and principal coordinate analysis at 3% dissimilarity showed the grouping of early samples with each other, as well as samples which have had time to equilibriate grouped each other as well. Species were identified for the 100 most abundant OTUs, of which 62 OTUs actually had known identities according to the ribosomal database, suggesting novelty in the bacterial communities associated with cyanide. Further studies, perhaps in metagenomics, that could characterized the genomic functions and adaptations of these unknown species that survive in the presence of cyanide.