Browsing by Author "Smart, Mariette"

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    A small-scale RNA isolation protocol useful for high-throughput extractions from recalcitrant plants
    (2010) Smart, Mariette; Roden, Laura Catherine
    Many plants indigenous to South Africa are rich in secondary and oxidizing compounds such as pigments, complex polysaccharides and polyphenols. This makes isolation of high quality RNA for analysis of gene expression difficult. Here we describe a cost-effective isolation protocol suitable for RNA extraction from recalcitrant plant species. This method uses small amounts of tissue, so is useful when material is limited, and is easy to process large numbers of samples at once. We have used the method successfully with mature leaves of Protea hybrid ‘Sylvia’, and species P. repens, Leucospermum hybrid ‘Succession’, resurrection plants Xerophyta humilis and Craterostigma pumilum, and mature needles of Pine (Pinus radiata). RNA was analyzed spectrophotometrically and was found to be of high purity with low levels of contaminating compounds. Electrophoretic analyses on denaturing formaldehyde agarose gels and an Agilent 2100 Bioanalyzer confirmed the presence of RNA of high integrity. This is the first description of plant RNA integrity number (RIN) values for these plants using the algorithm designed for analyses of plant RNA containing multiple ribosomal bands. The RNA could successfully be used for reverse transcription and gene amplification.
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    Open Access
    Characterisation of three novel α-L-arabinofuranosidases from a compost metagenome
    (2019-04-18) Fortune, Brent; Mhlongo, Sizwe; van Zyl, Leonardo J; Huddy, Robert; Smart, Mariette; Trindade, Marla
    Background: The importance of the accessory enzymes such as α-L-arabinofuranosidases (AFases) in synergistic interactions within cellulolytic mixtures has introduced a paradigm shift in the search for hydrolytic enzymes. The aim of this study was to characterize novel AFase genes encoding enzymes with differing temperature optima and thermostabilities for use in hydrolytic cocktails. Results Three fosmids, pFos-H4, E3 and D3 were selected from the cloned metagenome of high temperature compost, expressed in Escherichia coli and subsequently purified to homogeneity from cell lysate. All the AFases were clustered within the GH51 AFase family and shared a homo-hexameric structure. Both AFase-E3 and H4 showed optimal activity at 60 °C while AFase-D3 had unique properties as it showed optimal activity at 25 °C as well as the ability to maintain substantial activity at temperatures as high as 90 °C. However, AFase-E3 was the most thermostable amongst the three AFases showing full activity even at 70 °C. The maximum activity was observed at a pH profile between pH 4.0–6.0 for all three AFases with optimal activity for AFase H4, D3 and E3 at pH 5.0, 4.5 and 4.0, respectively. All the AFases showed KM range between 0.31 mM and 0.43 mM, Kcat range between 131 s− 1 and 219 s− 1 and the specific activity for AFase-H4, AFases-E3 and was 143, 228 and 175 U/mg, respectively. AFases-E3 and D3 displayed activities against pNP-β-L-arabinopyranoside and pNP-β-L-mannopyranoside respectively, and both hydrolysed pNP-β-D-glucopyranoside. Conclusion All three AFases displayed different biochemical characteristics despite all showing conserved overall structural similarity with typical domains of AFases belonging to GH51 family. The hydrolysis of cellobiose by a GH51 family AFase is demonstrated for the first time in this study.
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    Open Access
    Editorial for Special Issue “Water within Minerals Processing”
    (Multidisciplinary Digital Publishing Institute, 2022-03-14) Corin, Kirsten; Smart, Mariette; Manono, Malibongwe
    The products of mining are key to the technology development of the future [...]
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    Flowering in protea : a molecular and physiological study.
    (2012) Smart, Mariette; Roden, Laura; Cramer, Michael D
    Proteas have been extensively cultivated and are grown as floricultural crop plants in many parts of the world, including South Africa. However, the factors that influence the initiation of flowering in Protea have not been identified. From data gathered by the Protea Atlas Project it is evident that Protea spp. have greatly varying flowering times. Furthermore, flowering times between Protea spp. and their hybrid cultivars are also very different. Towards a better understanding of the factors involved in floral initiation in this cultivated crop, three aspects of flowering were investigated in this study. The carbon input into Protea inflorescence development was determined by measuring respiration rates and weights of developing structures. By manipulating source-sink ratios in plants, the carbon assimilatory capacities to support inflorescences were investigated in three cultivars and one wild-grown species of Protea which develop different sized flowers. As some Proteas flower in response to seasonal change, an orthologue of the floral inducer FLOWERING LOCUS T (FT), ProteaFT (ProFT), was isolated from ‘Carnival’ (P. compacta x P. neriifolia) and its expression pattern followed diurnally and seasonally. Finally, the functions of paralogous genes of Protea LEAFY (ProLFY) from ‘Carnival’ displaying sequence similarity to the meristem identity gene LEAFY from Arabidopsis thaliana, were investigated through heterologous expression studies in A. thaliana.
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    Identification and quantification of bacteria associated with cultivated Spirulina and impact of physiological factors
    (2016) Mogale, Motlalekgomo; Harrison, STL; Griffiths, Melinda J; Smart, Mariette
    Research into the use of 'algal' biomass for human consumption is receiving increased attention due to their favourable nutritional value, photosynthetic efficiency, and lower requirement of land and fresh water as compared to terrestrial crops. The Spirulina species, also known as Arthrospira, is of particular interest due to its high protein content and nutritional value. Open raceway pond systems are popularly used for commercial industrial scale cultivation of microalgae due to their economic feasibility. These open cultivation systems are, however, susceptible to contamination by other microorganisms. This raises concerns relating to suitability for human ingestion and the need to control bacterial growth to prevent contamination by pathogens and to minimise the overall bacterial load. Further, bacterial contamination in processed (harvested and dried) Spirulina biomass has been reported, suggesting that some of these contaminants may end up in the market ready product where appropriate processing approaches are not used. This study sought to identify the microorganisms that typically contaminate Spirulina cultivation ponds, to understand their interaction with Spirulina biomass during cultivation and to evaluate the vulnerabilities of these contaminants, in order to generate strategies for controlling their populations during open pond cultivation. The main objectives of this study were therefore: • To quantify the bacterial load in processed Spirulina powder from a single pilot facility to ascertain the presence of the contaminant in the final product derived from the outdoor pond system used as a case study, and to quantify the bacterial load in the outdoor cultivation cultures. • To identify and characterize the bacteria associated with these Spirulina cultures and processed powder from a pilot operation carried out in Franschhoek, South Africa, with a particular focus on evaluating the likelihood for pathogens. • To establish the dynamics of the relationship between Spirulina and bacterial growth under different environmental conditions including pH, salinity and temperature. • To develop practical methods to control and minimize contamination.
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    Linking microbial community dynamics and performance of a biological sulphate reducing system using a mixed volatile fatty acid stream as electron donor
    (2021) Motleleng, Liabo; Harrison, Susan; Smart, Mariette
    Mining for the recovery of minerals and coal can result in acid mine drainage (AMD) which presents an environmental risk. Acid mine drainage, as the name suggests, is acidic run-off water from mostly mine waste dumps. It affects water quality by lowering its pH and increasing its metal and sulphate loading, thus making it unsuitable for use by many forms of life. AMD must therefore be treated before entering nearby water systems and soils. An effective treatment technology is considered as the one that can result in water neutralisation and removal of metals and sulphate. Biological sulphate reduction (BSR) technologies, mediated by sulphate reducing bacteria (SRB), have attracted attention as a sulphate remediation strategy as they offer a cheap alternative to other sulphate removal technologies such as chemical approaches. In addition, the concomitant generation of alkalinity and soluble sulphide assist in neutralisation and heavy metal removal. One of the challenges associated with BSR is the supply of a cost-effective carbon source which also acts as an electron donor for the anaerobic reduction of sulphate. Studies have reported that both the choice of carbon source and electron donor and the microbial communities present influence the sulphate reduction process, the former frequently defining technoeconomic feasibility. The feed sulphate concentration and residence time, together defining the volumetric sulphate loading rate, have also been reported to influence the efficacy of the sulphate reduction process and needs to be optimised for the microbial community present and the chosen electron donor. The identification and characterisation of the microbial communities involved and investigating how these change with changes in operating conditions is crucial in the optimisation of BSR processes. Currently, there are no commonly used molecular tools which can be used for routine analysis of SRB communities in real time and on a regular basis and cost effectively. This makes it difficult to understand the link between changes in the mixed BSR microbial community structure and process performance. The study presented in this thesis had three main objectives. Firstly, to evaluate the use of an anaerobic digestate, obtained from a partially anaerobically digested Cyanobacteria species (Arthrospira platensis, commonly known as Spirulina), as a carbon source and electron donor for BSR. Secondly, to validate, optimise and apply the molecular tools for analysis of the relative abundances of species within the mixed BSR microbial community in this study. Thirdly, to compare the microbial community dynamics and performance of BSR using the complex anaerobic digestate as carbon source and electron donor to BSR using a single electron donor source, lactate. Chemostat studies using a mixed SRB consortium were carried out using anaerobic digestate, characterised as containing a mixture of acetate, propionate and butyrate, as a carbon source and electron donor for BSR. Upon reaching steady-state, the concentrations of sulphate, bicarbonate, acetate, propionate and butyrate were measured and used to estimate the BSR kinetics and reaction stoichiometry. A 16S rRNA gene survey of the BSR inoculum used for this thesis was performed by constructing a 16S rRNA gene clone library and analysis of the diversity of clones was performed using amplified ribosomal DNA restriction analysis (ARDRA). These 16S rRNA sequences were used to provide insight into the diversity and phylogenetic relatedness of the bacterial community and key species within the mixed BSR inoculum. In silico analysis of the 16S rRNA sequences captured from the clone library was performed to design novel genus specific quantitative real-time PCR (qPCR) primers and to validate the specificity of previously published primers. Fluorescence in situ hybridisation (FISH) techniques were optimised for the visual characterisation of this microbial community. FISH and qPCR were then applied to assess how the mixed microbial community structure was affected by the changes in the volumetric sulphate loading rate (VSLR), mediated through dilution rate and feed sulphate concentration, when anaerobic digestate (mixed carbon source) and lactate (simple carbon source) were used as an electron donor for BSR. The results obtained were used to examine and compare the link between microbial community dynamics and performance of sulphate reducers between the mixed and the simple carbon source. The results obtained from this thesis suggested the simultaneous utilisation of all the three volatile fatty acids (acetate, propionate and butyrate) present in anaerobic digestate which contributed to the robustness of the chemostat reactors as indicated by higher sulphate, propionate and butyrate conversion efficiencies. The kinetic profiles of the volumetric sulphate reduction rate (VSRR) obtained with anaerobic digestate were well matched with the kinetics observed in previous studies when single carbon sources and electron donors were used for BSR. At a feed sulphate concentration of 1.0 g l-1 , the oxidation of acetate, propionate and butyrate and concomitant sulphate reduction were observed across the dilution rates of 0.0083 to 0.083 h -1 . The stoichiometry of BSR utilising propionate and butyrate as carbon and electron donor suggested that by increasing feed sulphate concentrations from 1.0 to 2.5 and 5.0 g l-1 acetogenic reactions were favoured at the higher dilution rates of 0.042 and 0.083 h-1 . However, increasing the feed sulphate concentration at the lower dilution rates of 0.0083 to 0.021 h-1 did not alter the oxidation of volatile fatty acids (VFAs) and concomitant sulphate reduction, suggesting that the sensitivity of the propionate and butyrate oxidisers was related to specific growth rate rather than the sulphate loading. A previous mathematical model developed by Moosa et al. (2002) was used to determine microbial growth constants (μmax and Ks) and energetic coefficients (Yx/s) for SRB at each feed sulphate concentration to describe the microbial growth kinetics obtained with anaerobic digestate. A 16S rRNA gene survey, performed by 16S rRNA library construction and 16S rRNA gene amplicon sequencing, revealed a more diverse microbial community in the inoculum obtained from a lactate operated BSR reactor than previously reported. qPCR was used to confirm the presence and relative abundance of these species within the reactors receiving anaerobic digestate or lactate as carbon source and electron donor. The 16S rRNA sequences captured were found to have high similarity to well- known SRB species belonging to the Desulfomicrobium, Desulfovibrio, Desulfuromonas, Desulfobulbus and Desulfocurvus genera. Other “non-traditional SRB” species belonging to the Firmicutes and Citrobacter genera containing a specific molecular target for the detection of SRBs, the dissimilatory sulphite reductase gene (dsrAB), within their genomes were also detected. DsrAB is the key enzyme catalysing the last and main energy-generating step during sulphate reduction. Non-SRB species present were identified as members of the Sphaerochaeta, Synergistetes, Chloroflexi, Mesotoga, Acholeplasma, Bacteriodetes, Petrimonas and Bacteriodes genera. A 16S rRNA gene survey by 16S rRNA variable region amplification from metagenomic DNA extracted from microbial biomass associated with continuous stirred tank reactors (CSTRs) operated on anaerobic digestate or lactate was performed to validate the qPCR results and assist with the identification of the “other SRB” and nonSRB species. The 16S rRNA gene survey suggested the presence of 13 known SRB species Desulfomicrobium groups (Desulfomicrobium hypogeium and Desulfomicrobium aestuarii), Desulfovibrio species (D. aminophilus, D. vulgaris, D. desulfuricans, D. intestinalis, D. oxamicus, and D. sulfodismutans), Desulfobulbus oligotrophicus, Desulfocurvus vexinensis, Desulfococcus biacutus, Desulfarculus baarsii, Desulfomonile tiedjei and Desulfobacca acetoxidans in CSTRs operated on anaerobic digestate. Only up to 10 SRB species, Desulfomicrobium hypogeium, Desulfomicrobium aestuarii, Desulfovibrio groups (Desulfovibrio aminophilus, Desulfovibrio vulgaris, Desulfovibrio desulfuricans, Desulfovibrio intestinalis, Desulfovibrio sulfodismutans, Desulfovibrio mexicanus, Desulfobulbus oligotrophicus and Desulfocurvus vexinensis were observed in reactors with lactate, suggesting that the multiple VFAs present in the anaerobic digestate (acetate, propionate and butyrate) were able to support a more diverse SRB community than a single electron donor (lactate). Various non-SRB bacterial genera as well as known elemental sulphur reducing bacteria Desulfuromonas acetexigens and Dethiosulfovibrio acidaminovorans were also found to be present, with the latter being associated only with the lactate operated reactor. qPCR results indicated that despite being present in high proportions at the lowest VSLRs, the Desulfomicrobium species were washed out of the reactors at higher VSLRs regardless of carbon source and electron donor was provided. Species from the Desulfovibrio genera, which were present at lower abundances than the Desulfomicrobium species, were more resistant to changes in dilution rates and remained present within the reactors at the higher VSLRs, 0.104 and 0.208 g l-1 h -1 . In the reactors operated on anaerobic digestate, the decline in the abundance of Desulfovibrio species at VSLRs of 0.052 and 0.104 g l-1 h -1 , correlated with a noticeable decline in sulphate conversion from 60.4 to 49.4% at feed sulphate of 2.5 g l-1 , and from 66.9 to 22.6% at feed sulphate of 5.0 g l-1 . These findings suggest that Desulfovibrio species may play a critical role in sustained sulphate reduction at lower VSLRs. 16S rRNA gene amplicon data validated the qPCR data showing that increasing the VSLR, resulted in a change in the SRB community structure and a decrease in the proportion of total SRB within the microbial community. In agreement with the FISH and qPCR findings, Desulfomicrobium hypogeium was identified as the most abundant operational taxonomic unit (OTU) belonging to SRB present at the lowest dilution rate (D) tested (0.0083 h-1 , retention time (RT = 1/D) of 5 d) when anaerobic digestate was used as an electron donor for BSR. Washout of most SRB species was also observed when the dilution rate was increased from 0.0083 to 0.042 h-1 (RT of 5 to 1 d) in these reactors. Species such as Desulfovibrio sulfodismutans, Desulfomonile tiedjei, the acetate oxidiser Desulfococcus biacutus and the elemental sulphur reducing Desulfuromonas acetexigens were found to tolerate higher VSLRs of 0.104 and 0.208 g l-1 h -1 (dilution rate of 0.042 h-1 ), suggesting fast enough growth rates to remain in these reactors at the higher dilution rate of 0.042 h-1 . A decrease in the abundance of the incomplete propionate oxidiser Desulfobulbus oligotrophicus correlated to a decrease in propionate oxidation at a VSLR of 0.104 and 0.208 g l-1 h -1 suggesting that this SRB was responsible for the oxidation of propionate and concomitant sulphate reduction observed in these reactors. Similar to the reactors receiving anaerobic digestate, increasing the dilution rate from 0.0083 to 0.042_h -1 (RT of 5 to 1 d) resulted in washout of most SRB OTUs in CSTRs operated on lactate. At a feed sulphate concentration of 10.0 g l-1 , increasing the dilution rate from 0.0083 to 0.042 h-1 resulted in an increase in the proportion of the lactate oxidiser Desulfocurvus vexinensis from 25 to 98% of the total SRB proportion. At this dilution rate (0.042 h-1 ), other SRB species observed were the lactate oxidisers Desulfovibrio sulfodismutans and Desulfobulbus oligotrophicus which can oxidise lactate and the product of its incomplete oxidation, propionate. Although the abundance of these two SRB at the dilution rate of 0.042 h-1 was much lower than that of Desulfocurvus vexinensis, studies with anaerobic digestate suggested Desulfobulbus oligotrophicus which was abundant at only 0.004% and was identified as the only propionate degrader in the CSTR resulted in propionate conversion of 21.7%. This suggested that the less abundant Desulfovibrio sulfodismutans and Desulfobulbus oligotrophicus may have also played a role in sulphate reduction at the dilution rate of 0.042 h-1 in the CSTR with lactate. In addition, Desulfocurvus vexinensis and Desulfobulbus oligotrophicus were able to function at a VSLR of 0.42 g l-1 h -1 which suggests these two SRB species could be used effectively to reduce sulphate to hydrogen sulphide in wastewaters with higher VSLRs of up to 0.42 g l-1 h -1 when lactate was provided as an electron donor for BSR. The acetate specialist, Desulfobacca acetoxidans, the butyrate oxidiser Desulfarculus baarsii and the propionate oxidiser Desulfobulbus oligotrophicus, were able to function at a VSLR of 0.208 g l-1 h -1 suggesting that a combination of these three SRB species could be used in BSR treatment processes with VSLRs of up to 0.208 g l-1 h -1 where anaerobic digestate is provided as an electron donor. The ability for anaerobic digestate to support diverse SRB communities even at higher VSLRs may add to the robustness of the reactors to maintain sulphate reduction even at high VSLRs. This thesis showed that both the presence and diversity of SRB species are subject to the carbon source and VSLR. To the author's knowledge, this is the first study to indicate the relationship between the change in SRB community structure and sulphate reduction performance when anaerobic digestate (a complex carbon source) is used as a carbon source and electron donor for BSR. Results from this thesis suggest that the use of a mixed volatile fatty acid stream generated for the partial digestion of a suitably digestible biomass may be used as electron donor and carbon source to support a robust BSR process for the treatment of AMD. Using a mixed volatile fatty acid stream also has potential to result in the development of a more economically viable AMD treatment process.
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    Synthesis of monodisperse silver nanoparticles for antibacterial purposes
    (2018) Adam, Sarah; Kooyman, Patricia; Smart, Mariette; Harrison, Sue
    Safe drinking water is a scarcity for many in the developing world. Currently, 884 million people, 48% of whom live in sub-Saharan Africa, are without access to even basic drinking-water services (WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation, 2017). This has a severe impact on the health of those living in such communities, which is why the universal access to safe and affordable drinking water has been made a priority by the United Nations. There is an undeniable need for change so that the lives of these many millions of people may be improved. Silver nanoparticles have great potential in being used in water disinfection applications because of their high antibacterial activity and broad antimicrobial spectrum (Qu, Alvarez, & Li, 2013). Development in this area is critical, particularly in advancing technology to allow greater accessibility to clean drinking water for people in poor, rural areas in developing countries. Incorporating nanotechnology into current water disinfection systems, as well as developing new water treatment nanotechnology, shows promise in addressing this issue. However, much research needs to be done first before this can become a reality (Q. Li et al., 2008). There is particular concern about the toxicity aspects of silver nanoparticles, both in humans and towards the environment. Whilst the current study does not investigate their toxicity, it is important to highlight the need to fully understand the human and environmental impacts nanoparticles may have in assessing their applicability in microbial control. Literature indicates that, although the role of silver nanoparticles themselves in the antibacterial mechanism cannot be excluded entirely, it is the silver ions that are mostly responsible for their antibacterial activity (Foldbjerg, Jiang, Miclăuş, et al., 2015; Le Ouay & Stellacci, 2015; Panacek et al., 2006; Xiu, Zhang, Puppala, Colvin, & Alvarez, 2012). Sotiriou & Pratsinis (2010) found that silver nanoparticles of smaller than 10 nm had a negligible antibacterial effect in comparison to the ions they released. Thus, to isolate just the effect of the released silver ions, it was desired to prepare uniformly sized particles of smaller than 10 nm. Controlling the size of the formed particles requires consideration of parameters that affect their nucleation and growth (Thanh et al., 2014). These can be thermodynamic, kinetic or stoichiometric parameters. It is on this basis that the work described herein was developed. This study aimed to synthesise silver nanoparticles suitable for use in water disinfection applications by exploring how preparation conditions affect the particle size and distribution. To do this, two different aqueous chemical reduction preparation methods were performed and reaction conditions such as surfactant concentration, agitation rate, synthesis temperature, and method of chemical addition were varied to produce monodisperse silver nanoparticles with an average size of smaller than 10 nm. This study also aimed to investigate the antibacterial efficacy of silver nanoparticles deposited on quartz fibre filters against E. coli. Two silver nanoparticle syntheses procedures were extensively investigated. Method One (AL-Thabaiti et al, 2008) uses ascorbic acid as the reducing agent and SDS (sodium dodecyl sulphate) as the surfactant whilst Method Two (Yang, Yin, Jia, & Wei, 2011) uses aniline as the reducing agent, DBSA (dodecylbenzenesulfonic acid) as the surfactant and NaOH (sodium hydroxide) as the ‘activating’ chemical. The surfactant concentrations, agitation rates, synthesis temperature, reducing agent concentrations and methods of chemical addition were varied for each of these synthesis procedures and the effect thereof on particle size was investigated. Both synthesis methods produced fcc metallic silver nanoparticles with (111) and (200) lattice planes, confirmed by studying nanoparticle d-spacings. For Method One, the unaltered synthesis procedure produced the smallest particles with a numberbased mean size of 3.6 ± 3.8 nm and a volume-based mean particle size of 15.4 ± 6.4 nm. For Method Two, which is performed at 90 °C, the ‘hot’ injection of NaOH into the system resulted in the production of the smallest nanoparticles with a number-based mean particle size of 6.7 ± 5.4 nm and a volumebased mean particle size of 22.3 ± 10.9. Removing excess surfactant and collecting these nanoparticles in powder form would facilitate antibacterial efficacy studies, however this proved to be difficult. Additionally, the presence of large nanoparticles in both samples, as evidenced from the volume-based size distributions, means that in assessing antibacterial activity of the nanoparticles, it will be difficult to interpret whether the bactericidal effect is due to silver ions or because of an interaction between the bacteria and the actual nanoparticles. Antibacterial efficacy studies were therefore not performed on these synthesised silver nanoparticles. Silver nanoparticles deposited on quartz fibre filters via spark ablation were prepared at Delft University of Technology. SEM revealed that the deposited nanoparticles on the filters had a mean particle size ranging from 25 to 70 nm. Studies using E. coli (ATCC® 25922™) did not conclusively demonstrate antibacterial activity of the filters. It is believed the large particle size, and thus slow dissolution into silver ions, may be the reason for the lack of evidence of bactericidal activity over the 24-hour experimental period. The results of this study indicate how small changes in synthesis parameters can have a significant effect on nanoparticle size and uniformity, morphology, and degree of agglomeration. This reveals the importance in specifying exact parameters used in nanoparticle preparation to allow for better reproducibility, including vessel size, mixing speed, and rate of chemical addition. This work also showed that it is important to quantify the release of silver ions from silver nanoparticles before performing antibacterial efficacy assessments. Since silver ions are the most important factor in the antibacterial action of silver nanoparticles, understanding their rate of release will allow for improved experimental design thus producing useful results. There is great potential for the use of silver nanoparticles for disinfection, as evidenced particularly by the antibacterial efficiency of Ag+ against E. coli (ATCC® 25922™). However, improvements in both the synthesis of silver nanoparticles and methods of assessing their bactericidal efficacy are clearly necessary. This study has highlighted the challenges that may be faced in the pursuit of efficiently and safely using silver nanoparticles for water treatment and disinfection. Numerous recommendations for future studies have been put forward. These include: further optimisation of the nanoparticle synthesis procedure so as to produce particles of the desired size and acquire them in powder form, performing a thermodynamic estimation of the equilibrium silver ion concentration as a function of silver nanoparticle size to quantify the effect nanoparticle size will have on bactericidal activity, and using more realistic water conditions for antibacterial efficacy experiments to simulate the environment in which silver nanoparticles will be applied.
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    The effect of microbial load and water recycling on the flotation performance of a PGM bearing ore
    (2022) Wabatagore, Vushe; Smart, Mariette; Corin, Kirsten
    Mineral processing requires large quantities of water for its operations. With the continuing move to reduce freshwater withdrawal and mine water discharge, the mineral industry has been applying water recycling and reuse to improve water use efficiency. Previous studies on the use of remediated water as supplementary point source water and water recycling within the flotation circuit have shown that these practices affect the flotation process performance. It is therefore important to understand the effect that components within recycled and reclaimed water may have on flotation performance. While research on the effects of the abiotic components such as ions on flotation is well represented in literature, the effects of biotic water components, particularly microorganisms, on flotation performance still remain understudied and poorly understood. This study aimed to contribute to our understanding of the effects microbes have on the flotation performance of a PGM bearing ore from the Bushveld IgneousComplex in South Africa. In addition, the effects of xanthate collectors such as Sodium Ethyl Xanthate (SEX) and Sodium Isobutyl Xanthate (SIBX), widely employed in sulphide mineral beneficiation, on microbial growth were also considered. Results suggest that the presence of microbial cells and recycling of flotation waters increase water and solids recovery, while the metal grade recoveries were negatively affected. The microbial community used in this study could proliferate in the presence of up to 240 ppm for SEX and 480 ppm for SIBX, with an increase in the lag phase of growth observed with increasing collector concentrations. The presence of microbes at a concentration of 109 cells/ml resulted in the compete removal of 60 ppm collector from solution, both SEX and SIBX, from solution within a 2-hour time period. Outcomes of this study include a method for the measurement of microbial activity within a mineral slurry, which will further facilitate studying the effects of microorganisms on flotation systems. The work presented in this dissertation revealed that the presence of microbial consortia studied here negatively affected metal (Cu and Ni) grades attesting to the detrimental effect posed by the usage of microbial laden water for flotation operations. Further, the microbial consortium showed that it can facilitate the bioremoval of xanthate from solution which could affect the recovery of valuable minerals during flotation operations. This mechanistic framework, explaining the mechanisms by which the microbes affect flotation and the detrimental effects posed by microbes found in flotation waters is an actionable (fundamental) for the mining industry. From the present study, it is recommended that researchers should assess the microbial load present in flotation waters prior to their usage for flotation operations as high microbial load proved to be detrimental as far as flotation performance is concerned on a laboratory scale. Conclusively, the knowledge generated from this study builds on the ongoing scientific efforts decoding the effects of naturally prevailing microbes in flotation waters.