Biodegradation of environmental significant inorganics using aerobic bacteria found in Blesbokspruit Wetland, South Africa

Abstract

The Blesbokspruit wetland is known to be one of the imperative wetlands in Republic of South Africa (RSA), located in region of Ekurhuleni, Gauteng Province. A continuous discharge towards the Blesbokspruit wetland from effluents coming from the nearby Grootvlei mine, paper production company (South African Pulp and Paper Industries) and other anthropogenic activities accompanied with environmental impurities which include cyanide-residues has been witnessed within the wetland. Cyanide compounds depict distinct characteristics depending on chemical bindings with other elements which determines their severity and stability of the compound. Cyanides are either classified as either organic or inorganic cyanides and they are regarded as environmental significant contaminants. Biodegradation processes have proved to be an ideal tool to degrade environmental significant contaminants due to its cost effectiveness, eco-friendly and durability. The environmental significant inorganic placed under study is thiocyanate and its biodegradability using microorganisms isolated from soil, water and sludge within Blesbokspruit wetland. Among the most problematic inorganics found in wetlands are cyanides, particularly thiocyanate, which are toxicophores due to their cyanide content. Studies have shown that cyanides are present in effluents channelled by mining industries, which results in the deterioration of the Blesbokspruit wetland. Microorganisms were isolated and identified using universal primers 16S-27F and 16S-1492R, targeting 16S rDNA sequence. Indicator plate technique was applied in order to detect microorganisms with thiocyanate biodegradation capabilities, where phenol red aided as an indicator to distinguish microorganisms that can degrade thiocyanate by observing a colour change from red to pink. Later, thiocyanate degrading isolates and mixed culture were inoculated in minimal media without addition of a carbon or nitrogen source and 1/10th minimal medium containing a 24-hour starved culture was further inoculated in batch conical flasks containing minimal media with thiocyanate (SCN) either 150 mg SCN-/L or 250 mg SCN-/L. The sampling intervals were done every 24 hour-interval for a duration of 5 days, whereby the absorbance of microbial growth was measured at 600 nm and ammonium-nitrogen was measured with use of Merck Spectroquant Pharo 300. The results have shown that only few bacterial isolates were more effective compared to the bacterial consortium with regards to biodegrading thiocyanate, whereas the highest biological thiocyanate removal efficiency achieved in this study was 97.44 % and 95.71 % under 150 mg SCN-/L and 250 mg SCN-/L by Exiguobacterium sp., respectively. Most of bacterial isolates gave less biological thiocyanate removal efficiency as compared to bacterial consortium which was dominantly comprised by Pseudomonas sp. It was concluded that aerobic bacteria obtained at the Blesbokspruit wetland were capable of biodegrading thiocyanate which is deemed as an environmental significant inorganic. The greater concentration amounts of thiocyanate, most bacteria seemed to be susceptible to exposure, although few bacteria exhibited some form of resistance to some extent. Most of these bacteria were able nitrify the available ammonium-nitrogen.