No description available.

Here I present results from three field studies and one manipulative experiment that explored some of the factors that may influence belowground communities at multiple spatial scales. In the first field study I found that the abundance of two groups of soil mites was positively related to soil pore volume in two contrasting habitats. Hence, by limiting abundance, soil pore volume could indirectly influence species richness of mites. In another field study, using a spatial design, I found that the variation in community composition of soil mites and microbes within habitats was related to the variation in soil properties and plant community composition. However, the relative influence of these factors depended on the degree to which they varied within a habitat. Similarly, using a multi-site field study I found that soil properties, plant community composition and also precipitation influenced the composition of the microbial and mite communities within the landscape. This study also showed that the species richness of soil mites within a site was related to the degree of variation in soil properties and vegetation within the site. Finally, a manipulative field experiment showed that species richness of soil fauna was related to small-scale heterogeneity in soil physical properties, and that both the abundance and composition of belowground communities was related to the organic horizon thickness. Overall, my work shows a general positive relationship between species richness of soil biota and heterogeneity across spatial scales, and that the composition of belowground communities is related to the variation in soil properties, plant community composition and climate.

This study was designed to show what dissemules may be carried by selected genera of Odonata, where the dissemules may be predominantly carried on the selected insects and to relate the behavior of the selected Odonata to frequency of occurrence of micro-organisms on the insects.

The structures of the exopolysaccharides from a number of strafos of the bacterial genus KlebsieUa have been investigated and compared. ·All of these polysaccharides have been shown to be composed of regularly repeated oligosaccharide units containing -glucuronic acid and three to five hexose residues, with pyruvic acid ketal and 0-acetyl groups also present in some of the polysaccharides. Graded acid hydrolysis, monitored by gel-permeation chromato graphy, has been used to study the degradation of each polysaccharide to the structurally significant oligosaccharides and fragments of higher molecular weight which are clearly aggregates of these units. In all cases both acidic and neutral oligosaccharides have been isolated in a high degree of purity, which has permitted their characterisation by standard techniques, including partial acid hydrolysis and methylation analysis, and the use of proton magnetic resonance spectroscopy and measurement of optical rotatory power to determine the nature of anomeric linkages. The polysaccharides from Klebsiella K4 and X.pnev.moniae ( oxytoca variant) have been shovm to have linear tetra- and pentasaccharide repeating units respectively, while the structures of those from serotypes K27 and K64 have been found to be more complex, consisting of branched hexasaccharide repeating units with pyruvic acid ketallinked to one sugar residue. In addition, the fungal polysaccharides from two strains of c1yptococcus neoformans have been investigated and shovm to be chemically equivalent. The evidence obtained from partial acid hydrolysis, methylation analysis and Smith-degradation studies performed on one of these polysaccharides is consistent with a structure in which a linear (l-+3)- linked chain of -mannose residues is substituted at position C-2 by either g-glucuronic acid or ll_-xylose. This represents one of the few complete characterisations of a Cryptococcus polysaccharide to be achieved up to the present.

No description available.

Methods currently available for the detection and enumeration of genetically modified micro-organisms in the environment include culturing methods, direct microscopic detection and nucleic hybridization techniques. The aim of this project was to develop luminescence as a molecular based-marker system in Pseudomonas fluorescens. The lux genes, originally isolated from Vibrio fischeri, were introduced into Ps. fluorescens on plasmid vectors and on the chromosome. The efficiency of these two strategies for the detection of Ps. fluorescens in soil was assessed. Luminometry was used to estimate biomass concentration during growth. The sensitivity of luminescence detection was greater for the plasmid marked Ps. fluorescens in both liquid culture and soil, however, cellular light output was less closely linked to biomass concentration. Enumeration of cells by luminometry was only possible for growing cells as light output is correlated with microbial activity. The lux chromosomal marker was stable in liquid culture for at least 200 generations and in soil for up to 135 days. The plasmid borne lux genes had a half-life of 20 generations in liquid culture. After inoculation in sterile soil, plasmid loss was only observed during cellular growth. The frequency of transfer of the lux genes from Ps. fluorescens, by conjugation and transformation, was assessed in liquid culture. Mobilisation of these genes by three self transmissible plasmids was negligible due to the instability of these vectors in this host. Transformation of Ps. stutzeri with lux genes, by cell contact, was at frequencies below levels of detection. Luminescence provided a valuable marker for tracking pseudomonads in soil. Detection of marked strains by luminometry provided a sensitive, rapid and non-extractive technique for enumeration of growing cells and measurement of microbial activity. As the chromosomally encoded lux genes were stable, regardless of growth conditions, and emitted sufficient levels of light to enable visual enumeration of colonies by eye, this was considered the best system for long term risk assessment studies.

Enterococcus species are found in faeces of mammals, birds, insects, reptiles, but also soil, plants and water. These bacteria can also be isolated from animal products such as milk, cheese and meat. This study was aimed at isolating Enterococcus species from communal and commercial cattle faecal and water samples. A further objective was to determine the antibiotic resistance profiles of the isolates as well as some of the potential factors and mechanisms that could be responsible for their resistance to antibiotics. A total of 79 cattle faecal and water samples were collected from the communal and commercial farms. Sixty-five faecal samples were collected from commercial (33 healthy and 16 diarrhoeal cattle) and communal (16 healthy cattle) farms. Twelve water samples were collected from the commercial farms and 2 from the communal farm. From all the samples collected, 129 Enterococcus isolates were identified. Isolates, which included Enterococcus faecium (E. faecium), Enterococcus avium (E. avium), Enterococcus durans (E. durans) and Streptococcus bovis I (Sc. bovis !), were isolated from bovine faeces and water samples, while E. avium was only isolated from water at the communal farm. Furthermore, isolates from the healthy and diarrhoeal commercial cattle included E. faecium, E. avium, E. durans and Sc. bovis I. E. faecium and E. avium species were also isolated from the commercial farm cattle water sources. However, E. faecium was the predominant species in communal cattle faecal and water samples. On the other hand, E. avium was dominant in. commercial cattle faecal and water samples. Multiple antibiotic resistance (MAR) was observed in enterococci from all samples at both farm types. The predominant MAR phenotype that was prevalent in all enterococci species was GENSMX- NAL-NIT-KAN-STR All isolates showed an MAR index above 0.2 (water; 0.58 to 0.68 and faeces; 0.6 to l. 7). Cluster analysis based on antibiotic inhibition zone diameter data, resulted in dendrograms that showed a similar relationship of Enterococcus isolates from the two farms. Between 13% and 50% of Enterococcus isolates from cattle faeces and water samples from communal and commercial farms were resistant to vancomycin and oxytetracycline. In general, 11% of all the Enterococcus isolates from the cattle faeces was resistant to vancomycin. Thirty one per cent of the isolates from cattle water sources were resistant to both drugs. Vancomycin Resistant Enterococcus (VRE) genes conveying the vanC phenotype were obtained from E. durans and E. avium. This was an unexpected result. The tet A, tet Band tet C genes were not obtained from any of the Enterococcus species. Further studies on antibiotic resistance should be undertaken especially in rural areas, where farmers could be using over-the-counter medicines such as tetracycline even when it is not necessary. It was speculated in this study that there could be a development of potential reservoirs of antibiotic resistance in farmlands. In order to prevent the distribution of MAR organisms or their transferable resistance genes, a sensible use of antibiotics is necessary in veterinary medicine, animal husbandry and human medicine. / MSc. (Agriculture) North-West University, Mafikeng Campus, 2006

Most attempts to monitor the effects of introductions of Genetically Modified Micro-organisms (GMMs) have centred on the enumeration of specific populations. However for a significant perturbation to be measured, changes of between 100% and 300% (0.3 and 0.5 on a log scale) are necessary for the impact to be significant. Standard population measurements, assessing the survival, dissemination and effect on total indigenous populations do not give an indication of the functioning of the ecosystem. A range of soil enzyme assays have been developed as alternatives to population measurements. Assays for determining chitobiosidase, N-acetyl glucosaminidase, beta-glucosidase, beta-galactosidase, acid phosphatase, alkaline phosphatase, phosphodiesterase, aryl sulphatase and urease activities from small soil samples were developed. These assays were employed to assess the impact of microbial inoculation into the rhizosphere of crop plants and compared to traditional microbial population measurements. The impact of a chromosomally modified Pseudomonas fluorescens (SBW25) in the wheat rhizosphere using a large intact core microcosm was studied with a combined substrate addition of urea, colloidal chitin and glycerophosphate. The substrate addition caused an increase in the soil chitobiosidase, N-acetyl glucosaminidase aryl sulphatase and urease activities but did not affect acid and alkaline phosphatase and phosphodiesterase activity. Seed inoculated with P. fluorescens caused significant increases in rhizosphere chitobiosidase and urease activities and a significant decrease in alkaline phosphatase activity. Inoculation with the bacteria in the presence of substrate gave opposing effects to those treatments without substrate addition. Using these enzyme assays perturbations of less than 20% could be detected. Two strains of Pseudomonas fluorescens were compared in microcosm experiments one with a functional modification of strain F113 with repressed production of the antibiotic 2,4-diacetylphloroglucinol (DAPG), to create the DAPG negative strain F113 G22. The other, SBW25 EeZY 6KX, with nonfunctional modifications consisting of marker genes (LacZY, xylE and kan') only. Both were assessed, along with the corresponding wild types (F113 and SBW25), for their effects upon the indigenous microflora, plant growth and rhizosphere soil enzyme activities. Significant perturbations were found in the indigenous bacterial population structure, with the F113 (DAPG+) strain causing a shift towards slower growing colonies (K strategists). The DAPG+ strain also significantly reduced, in comparison with the other inocula, the total Pseudomonas populations. The survival of the F113 strains were an order of magnitude lower than the SBW25 strains. The DAPG+ strain caused a significant decrease in the shoot to root ratio in comparison to the control and other inoculants. The F113 (DAPG+) inocula resulted in higher alkaline phosphatase, phosphodiesterase and aryl sulphatase activities than the other inoculants and lower beta glucosidase, beta galactosidase and N-acetyl glucosaminidase activities. These results indicate that the soil enzymes are extremely sensitive to perturbations in the rhizosphere ecosystem and are sensitive enough to measure the impact of GMM inoculation.

No description available.

No description available.