Characterization of arsenate reduction by arsenic tolerant lvllcrobacterjum foljoruj'vf strain szllsolated from gold ores

Arsenic is a metalloid of global concern that primarily exists in two inorganic forms of severe toxicity, As (III) and As (V). The reduction of As (V) to As (III) increases toxicity, mobility and bioavailability of arsenic. Understanding how microorganisms reduce As (V) is important to elucidate As (V) reduction mechanism and inevitably, discover approaches to minimise its toxic impact on the environment. This study was aimed at investigating the capability of arsenic tolerant Microbacterium foliorum strain SZ1 isolated from gold ores to undergo As (V) reduction to As (III). This strain demonstrated complete reduction of 1 mM As (V) achieved within 120 hours under aerobic condition indicating a possible mechanism of detoxification through regulation of ars operon. Further optimization of factors enhancing As (V) reduction capacity of strain SZ1 resulted in complete reduction of 1 mM As (V) achieved within 36 hours in Tris minimal medium supplemented with 10 mM sucrose and 0.1 % (w/v) tryptone at pH 7. The effect of cell adaptation or acclimation towards As (V) reduction was investigated. Well-adapted strain SZ1 recorded complete reduction of 0.5 mM As (V) to 3 mM As (V) within 18 hours to 42 hours incubation. Exopolysaccharides (EPS) was observed to be secreted during reduction of As (V) and subjected to further characterization through chemical analysis of neutral carbohydrate and protein contents and Fourier transform infra-red (FT-IR) analysis. As As (V) concentration increased, so did the protein and carbohydrates concentration of EPS, indicating that EPS played an important role in enabling strain SZ1 to resist and reduce arsenic. Haldane inhibition model was used to fit the reduction rate at different initial As (V) concentrations and the parameters µmax, Ks and Ki were determined to be 0.14 h-1, 0.39 mM and 35.3 mM, respectively. In addition, presence of As (III) as the final product was further confirmed by detection through high performance liquid chromatography (HPLC) analysis. Field emission scanning electron microscopy analysis (FESEM) showed that cells grown in the presence of As (V) exhibited distinct changes in cell morphology and presence of EPS. Exploration of the draft genome of M. foliorum SZ1 identified the presence of ars operon (arsC-arsC-ACR3-arsT-arsC-arsR-arsC) and another two stand-alone genes, arsC and arsB which further confirmed SZ1’s tolerance towards high concentration of arsenic. From the screening of plant growth promoting (PGP) traits, strain SZ1 was able to produce siderophores and indole acetic acid which highlighted its potential use in microbe-assisted arsenic phytoremediation. This is the first study that elucidates the characterization of As (V) reduction by M. foliorum SZ1

Cyanide degradation by pseudomonas pseudoalcaligenes strain W2 Isolated from mining effluent

Cyanide is highly toxic to the living organisms as it inhibits respiration system in the cell mitochondria. Cyanide is commonly used in gold extraction process and its discharge into the environment not only causes pollution but it also brings harm to the surrounding population. Chemical treatment is expensive and the use of hazardous compound can exacerbate the problem. Biodegradation offers cheap and safe alternative as it overcomes the problems faced by chemical treatment. In this study, indigenous bacteria from mining wastewater were isolated. Cyanide degradation was done via shake flask method. A bacterium, designated W2 was found able to grow in the mining wastewater. 16S rRNA analysis identified the strain as Pseudomonas pseudoalcaligenes which could tolerate up to 39 mg/L cyanide concentration and growth was depleted at 52 mg/L. 60% cyanide degradation was achieved in wastewater containing medium. End-product analysis from high performance liquid chromatography (HPLC) detected formamide implicating the role of cyanide hydratase in cyanide degradation. It can be concluded that P. pseudoalcaligenes is capable of biodegrading cyanide and its potential in wastewater treatment containing cyanide is feasible

Biosorption of as (iii) by non-living biomass of an arsenic-hypertolerant Bacillus cereus strain SZ2 isolated from a gold mining environment: equilibrium and kinetic study

The ability of non-living biomass of an arsenic-hypertolerant Bacillus cereus strain SZ2 isolated from a gold mining environment to adsorb As (III) from aqueous solution in batch experiments was investigated as a function of contact time, initial As (III) concentration, pH, temperature and biomass dosage. Langmuir model fitted the equilibrium data better in comparison to Freundlich isotherm. Themaximum biosorption capacity of the sorbent, as obtained from the Langmuir isotherm, was 153.41 mg/g. The sorption kinetic of As (III) biosorption followed well the pseudo-second-order rate equation. The Fourier transform infrared spectroscopy analysis indicated the involvement of hydroxyl, amide and amine groups in As (III) biosorption process. Field emission scanning electron microscopy-energy dispersive X-ray analysis of the non-living B. cereus SZ2 biomass demonstrated distinct cell morphological changes with significant amounts of As adsorbed onto the cells compared to non-treated cells. Desorption of 94%As (III)was achieved at acidic pH 1 showing the capability of non-living biomass B. cereus SZ2 as potential biosorbent in removal of As (III) from arsenic-contaminated mining effluent

Cyanide degradation by Pseudomonas pseudoalcaligenes strain W2 isolated from mining effluent

Cyanide is highly toxic to the living organisms as it inhibits respiration system in the cell mitochondria. Cyanide iscommonly used in gold extraction process and its discharge into the environment not only causes pollution but it alsobrings harm to the surrounding population. Chemical treatment is expensive and the use of hazardous compound canexacerbate the problem. Biodegradation offers cheap and safe alternative as it overcomes the problems faced by chemicaltreatment. In this study, indigenous bacteria from mining wastewater were isolated. Cyanide degradation was done viashake flask method. A bacterium, designated W2 was found able to grow in the mining wastewater. 16S rRNAanalysisidentified the strain asPseudomonas pseudoalcaligeneswhich could tolerate up to 39 mg/L cyanide concentration andgrowth was depleted at 52 mg/L. 60% cyanide degradation was achieved in wastewater containing medium. End-productanalysis from high performance liquid chromatography (HPLC) detected formamide implicating the role of cyanidehydratase in cyanide degradation. It can be concluded thatP. pseudoalcaligenesis capable of biodegrading cyanideand its potential in wastewater treatment containing cyanide is feasible