Browsing by Author "Postma, Ferdinand"

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    Rhizofiltration of urban effluent : microbial ecology and conceptual treatment mechanisms
    (Stellenbosch : Stellenbosch University, 2016-03) Postma, Ferdinand; Botha, Alfred; Mouton, Marnel; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Polluted urban runoff is a challenge that is globally met by governing bodies employing best management practices (BMPs). One such BMP is rhizofiltration, a novel type of phytoremediation BMP designed to mimic riparian ecology, with the goal of rapidly filtering large volumes of urban runoff before it enters rivers. The physical, chemical and biological mechanisms behind pollutant removal within a rhizofiltration system however, are still largely unknown. The overall aim of this study was therefore to assess the ability of a pilot scale rhizofiltration system to reduce concentrations of the physico-chemical pollutants ammonium, chemical oxygen demand (COD), nitrate, phosphate, sulphate and suspended solids, as well as microbial indicators of faecal pollution, in simulated urban runoff. The faecal indicators included coliphages, faecal coliforms, potentially pathogenic yeasts (PPY) and Salmonella and/or Shigella. To achieve this study’s aim a conceptual model was first constructed to identify potential bacterial mechanisms of pollution removal and to estimate the effect of physico-chemical conditions on microbial communities within the rhizofilter medium. Then, the overall performance of the filter was measured with regard to its bioregeneration and sorption capacity for the abovementioned pollutants. Sorption equilibrium, for most of the pollutants in the simulated runoff percolating through the filter, was reached within 45 minutes. Partial bioregeneration of the filter medium occurred within a week for ammonium, COD, phosphate and sulphate, as well as for the microbial pollutants. Evidence was subsequently obtained supporting the hypothesis that this regeneration is brought about by microbial activity, since metagenomic (16S rDNA high throughput sequencing) and phospholipid fatty acid (PLFA) analyses revealed the presence of viable dynamic microbial populations within the rhizofilter medium. Significant correlations between relative quantities of microbial operational taxonomic units (OTUs) and nutrient concentrations were also uncovered. The rhizofilter plants selected for a microbial community distinct from an unplanted control, however, this did not relate to differences in filter performance. This phenomenon was ascribed to the rapid percolation rate and design of the rhizofilter which maximizes aeration of the filter medium. It was contended that these properties, combined with the composition of the simulated urban runoff, selected for functionally similar organisms. The Actinomycetales were the most abundant bacterial group in both the planted and unplanted filter media. However, the plants appeared to select for Mycobacteriaceae and nitrifiers identified as the Nitrospiraceae. Among the transient OTUs in the filter media were taxa associated with the human gut, including the Campylobacteraceae, Moraxellaceae, Porphyromonadaceae and Prevotellaceae, while the Enterobacteriaceae containing faecal coliforms were below the detection limit of the metagenomic analysis. Strains of four Candida species consistently occurred in the simulated urban runoff. The abundance of these PPY in the influent and effluent of the rhizofilter were affected by physico-chemical factors. Subsequent metagenomic analysis of the fungal community within the filter media revealed a low relative abundance of candidal PPY. In short, the rhizofilter design and wastewater composition selected for copiotrophic aerobic microorganisms capable of mineralizing potentially recalcitrant organic carbon and driving oxidative processes such as nitrification whilst removing human microbial commensialists and pathogens.
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    Yeasts and other culturable microorganisms associated with the nickel hyperaccumulator Berkheya coddii and its insect herbivore, Chrysolina clathrata
    (Stellenbosch : Stellenbosch University, 2013-03) Postma, Ferdinand; Botha, Alfred; Mesjasz-Przybylowicz, Jolanta; Przybylowicz, Wojciech; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: The heterogeneity and distribution of elements on earth is one of the key drivers that shape the biotic processes in any given environment. What we may consider as anomalies in an environment’s element composition often drives biological adaptation and speciation. Serpentine environments provide dramatic examples of the effect soil element composition has on life. The elevated heavy metal concentrations in these environments resulted in the adaptation of plants and insects endemic to these areas. Physiological adaptations of Berkheya coddii and its insect herbivore, Chrysolina clathrata, allowed them to exploit the nickel (Ni) rich serpentine soil of the Barberton Greenstone Belt. One of the driving forces behind these adaptations may involve interactions with microorganisms. However, the microbiology of serpentine environments is relatively unknown. In the current study we aimed to identify microorganisms that may have symbiotic relationships with C. clathrata and its diet, the herbaceous Ni hyperaccumulating plant B. coddii. Culture techniques were used to isolate bacteria and fungi from plants and the faeces of beetles that were reared under laboratory conditions. The identity of isolates was determined using morphology and molecular techniques. Several genera of filamentous fungi (Alternaria, Aspergillus, Bipolaris, Cladosporium, Epicoccum, Fusarium, and Penicillium), yeasts (Cryptococcus, Meyerozyma, and Rhodotorula), and endophytic bacteria (Bacillus and Lysinibacillus) were isolated from the leaves of B. coddii. Yeast species, representing the genera Candida, Cryptococcus, Debaryomyces, Meyerozyma and Wickerhamomyces were isolated from faeces of the beetles. The minimum inhibitory concentration (MIC) of Ni was determined for all isolates. The endophytic bacteria, filamentous fungi, Candida intermedia, Cryptococcus flavescens and Meyerozyma guilliermondii showed notable Ni resistance. The Ni resistant yeast strains were isolated from the faeces of the beetles where the yeasts were in close contact with Ni ions. A strain of M. guilliermondii was also found on leaves of B. coddii but this strain had lower resistance to Ni and occurred in much lower numbers than the faecal strain. Therefore, it seems that the gut of the beetle selects for Ni resistant yeasts. The role of the yeasts occurring in the gut of the beetle may be to metabolize waste products of the beetle or aid in the sequestration of Ni. Nitrogenous metabolic waste products are usually excreted by terrestrial insects as uric acid and/ or urea. Results obtained by UPLC-MS and colorimetry confirmed that uric acid and urea were present in the faeces of C. clathrata. Strains of the yeast species M. guilliermondii, C. flavescens and W. anomalus isolated from the beetle faeces used uric acid as sole carbon and nitrogen source. A strain of M. guilliermondii isolated from the faeces of C. clathrata sequestered Ni from an aqueous solution. Concluded from these findings, yeasts in the gut of C. clathrata, may play a role in the recycling of nitrogen and may play a role in the reduction of Ni toxicity in the insect.