3. Electronic Theses and Dissertations (ETDs) - All submissions
Permanent URI for this communityhttps://wiredspace.wits.ac.za/handle/10539/45
Browse
3 results
Search Results
Item The impact of organic compost on the infectivity and virulence of entomopathogenic nematodes and their bacterial symbionts as biocontrol agents(2019) Khumalo, Nolwandle NolenA safer and greener alternative to chemical pesticides includes the use of entomopathogenic nematodes (EPNs) and their endosymbiotic bacterial pathogens as biocontrol agents. Entomopathogenic nematodes of the genera Steinernema and Heterorhabditis cause disease in insect pests, killing them within 48 hours, with the help of their highly virulent insect pathogenic bacterial symbionts belonging to the genera Xenorhabdus and Photorhabdus, respectively. The efficacy of EPNs in the field is affected by abiotic and biotic factors, thus understanding the soil ecosystem and its interaction with EPNs will aid in improving the application of EPNs in many agricultural soils post application. The research project focused on isolating and identifying locally adapted EPNs and their bacterial symbiont isolated from the North West province in the Magaliesburg region. Investigating factors affecting the survival, virulence, and persistence of EPNs in the soil, by the use of adding soil amendments such as organic compost namely mulch, organic compost, professional potting mix, organic lawn dressing mixed with loamy soil and coarse river in soils undergoing progressive dehydration. The effects of different soil composition on the behaviour and host-seeking efficiency within the soil profile and EPN response to desiccation tolerance was also investigated. EPNs were retrieved and harvested using the soil baiting technique with Galleria mellonella and White trap method respectively. PCR amplification of the 18S rDNA and 16S rDNA sequencing of the PCR amplicon was used to establish the phylogenetic affinities of EPN isolates and their bacterial symbiont using GenBank sequence database respectively. The presumptive Heterorhabditis species and Steinernema species isolated were found to show high affinity to H. bacteriophora (MG334257.1) and S. khoisanae (MH697401.1) respectively. The symbiont bacteria only isolated of H. bacteriophora was identified as Photorhabdus luminescence subsp. laumondi (KT963833.1). The use of organic compost did not have any detrimental effect on EPNs. The Mulch soil amendment resulted in the highest insect mortality rate across different application concentration (mass: mass basis) when mixed with loamy soil. It was observed that virulence and efficacy decreased over 7 days of progressive dehydration. In soil profile larvae locating behavioural studies, H. bacteriophora was found to be a cruise predator (search and forage) in search of a new host. Soil composition affected host locating ability of H. bacteriophora infective juveniles (IJs). H. bacteriophora IJs were able to survive desiccation tolerance with resuscitation by rehydration with water for a period of 8 weeks however infectivity and survival of IJs to locate the host were affected. Overall the type of compost used based on its feedstock iii composition, the concentration of nutrients and organic matter mixed with a specific type of soil texture had a significant effect on the infectivity and survival of H. bacteriophora IJs in the soil. In conclusion soil physical structures affects EPNs infectivity post application and the knowledge obtained will be used to improve soil application strategies and formulation products so that EPNs can be used as commercially viable biocontrol agents.Item Effect on oral streptococci of exposure to penicillin and its relevance in infective endocarditis prophylaxis(1996-03) Mclure, William . Peter. JohnThe survival of bacteraemic isolates of viridans streptococci, after the administration to subjects of prophylactic antibiotic cover, has been widely reported in the literature. This study demonstrated that the cause of bacteraemia was as a result of phenotypic tolerance amongst populations of bacteria, and both proposed a mechanism responsible for the appearance of this form of tolerance and the design of a model to evaluate candidate drugs for infective endocarditis (IE) prophylaxisItem Evaluating the productivity of selected in vitro culture techniques for the production of a locally isolated entomopathogenic nematode(2018) Matlhabe, OfentseEntomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis have gained interest as biocontrol agents of insect pests due to their ability to search and kill soil dwelling insects. Some members of the Oscheius genus have been shown to have insecticidal abilities as a result of their association with bacteria in the Serratia genus. This has led to the consideration of the Oscheius as an EPN genus. The biocontrol potential serves as an incentive for studying EPNs and various production methods for their commercial use as biopesticides. A putative EPN was isolated from soil samples collected at Brits in the North West Province of South Africa. 18S rDNA based identification indicated that it belonged to the Heterorhabditis genus however, phylogenetic analysis and symptoms on Galleria mellonella larvae suggested that the nematode may belong to the Oscheius genus. The bacterial symbiont associated with this nematode was found to be a strain of Serratia marcescens, through 16S rDNA based sequencing and phylogenetic analysis. Various in vitro production methods were evaluated for their effect in the production of Oscheius L8 MCB. These include monoxenic and axenic culturing, growth media supplementation, and production in solid and liquid state. Axenic cultures were found to produce high maximum yields of EPNs (78 600 EPNs/ml) compared to monoxenic cultures (53 833 EPNs/ml). It was concluded that axenic culturing was efficient for the production of this species. Oscheius L8 MCB was cultured in NB supplemented with varying concentrations of oil and glucose. Supplementation of NB with 2% canola produced a significant amount of EPNs in reduced culture times, but NB supplemented with 4% canola oil and 25mg/ml glucose increased nematode yield but prolonged the culture time. It is noted that media composition (with regards lipid and carbohydrate content) plays an important role in nematode yield and culture time and thus optimization of these components is critical for efficient nematode production. Solid state and liquid state production of Oscheius L8 MCB showed that solid state cultures allowed for early IJ production, whereas liquid state culturing produced the highest IJ yield (36 000 IJs/ml). The reduced culture period, makes solid state production more cost effective and preferable for mass production. However, liquid production can still be used as it offers the benefits of high nematode yeild and efficient recovery of nematodes from culture. The in vitro methods of EPN production have been reported to have an effect on the efficacy of the EPNs against insect hosts. Dose-response assays showed that in vivo produced EPNs resulted in high G. mellonella larvae mortality at lower concentrations compared to solid and liquid in vitro methods. Larvae infected with in vivo produced Oscheius L8 MCB produced a high number of emerging IJs compared to larvae infected with EPNs produced using axenic in vitro culturing methods. The differences between mortality and IJ emergence in larvae infected with solid state and liquid state cultured EPNs were marginal. Therefore, it is concluded that axenic culturing methods may reduce the efficacy of Oscheius L8 MCB against insect hosts.