No description available.

The effect of <I>L. terrestris </I>on the transport of marked bacterial inocula in the absence of percolating water was investigated using repacked soil microcosms over a 10 day period. The microcosms consisted of cylindrical cores containing loamy sand. The bacterial inoculum was applied in filter paper disks to the surface of soil cores containing <I>L. terrestris </I>and to control cores. Destructive analysis of cores was carried out 5 and 10 days after inoculation to facilitate enumeration of marked bacterial inocula at 3 depths in the soil. Significantly greater vertical transport of marked bacteria occurred in cores containing <I>L. terrestris. </I>The effect of <I>L. terrestris </I> on the dispersal of marked bacteria in the presence of percolating water was investigated using both repacked soil cores and larger intact cores over a one month period. Bacterial inocula were again applied in filter paper disks to the surface of cores and the cores subjected to simulated rainfall events at 3 day intervals. Concentrations of marked bacteria in leachate were determined and destructive harvests of cores carried out after 24 days. The results from repacked soil cores demonstrated that cores containing earthworms were associated with early breakthrough, higher percentage recovery and greater numbers of marked bacteria in the leachate than control cores without earthworms. Results from intact soil cores demonstrated that cores containing earthworms were associated with different bacterial leaching patterns, higher percentage recovery and greater numbers of bacteria in the leachate than control cores. For both repacked and intact cores, the presence of earthworms in cores led to transport of marked bacteria to greater depths in the soil. Plaster of Paris impregnation of repacked and intact cores highlighted the importance of earthworm burrowing in providing pathways for bypass water flow and hence bacterial transport through soil. Results from the use of interdisciplinary methods developed and adapted in this study identify the importance of earthworms in the fate of microbial inocula in soil and the potential for use of earthworms in biotechnology.

Survival of P. fluorescens 10586s FAC510 was studied in liquid culture and soil microcosms in the presence of the ciliate C. steinii and the flagellate Cercomonas sp. Both protozoa caused a reduction in bacterial viable cell concentration, however the ciliate caused a greater decrease in abundance. Starvation of the bacterial prey caused a reduction in grazing rates of both the ciliate and flagellate, indicating the lower nutrional quality of starved as opposed to non-starved cells. Manipulation of the physiological state of prey cells, by starvation, had much the same effect as observed when bacterial prey resources are reduced. Luminescence provided a valuable marker for monitoring P. fluorescens 10586s FAC510 in liquid culture and soil, since detection by luminometry provided a sensitive, rapid, and non-extractive technique for measurement of microbial activity. In the presence of C. steinii, bacterial activity increased, whilst predation by Cercomonas sp. caused a reduction. The different responses of the bacterial inoculum may reflect the divergent balance between bacterial turnover, leading to nutrient regeneration, and grazing strategies, which are selective of the two protozoa. The distribution of bacterial cells in the soil pore network was manipulated by adjustment of the antecedant matric potential prior to inoculation. The ability to predominantly place bacterial and protozan cells in specific pore size classes was confirmed by partial chloroform fumigation and resin impregnated sections of soil.

No description available.

The aim of this work was to develop and test a mathematical model for DNA transfer by conjugation which considered spatial separation of cells on surfaces. Model parameters include the initial donor and recipient numbers, maximum specific population growth rate, microcolony radial extension rate, maximum cell yield, maximum incubation time, standard deviation of the mean intercellular distance (σ), cellular area and area available for colonization. Sensitivity analysis indicated that growth areas and σ had the greatest effects on conjugation. The model was extended to consider the presence of a strain that did not conjugate and its effect on plasmid transfer. Filter matings with <I>Pseudomonas fluorescens</I> MON787 RP4 as the plasmid donor and <I>P. fluorescens</I> MON787 R <I>lux</I> as recipient were used to test the model. Model predictions were generally accurate but transconjugants were consistently underestimated. This was attributed to intercellular distances not following a strict Gaussian distribution. Nevertheless, predicted and experimental data were qualitatively similar, which increased confidence in the validity of the mechanisms proposed. Conjugation occurred over a wide range of cell densities, donor to recipient ratios, nutrient levels and incubation temperatures. Starved cells retained the capacity to conjugate, but plasmid transfer frequency was higher in the presence of nutrient. Above a minimum level, conjugation ability was not enhanced by nutrients. Temperature affected conjugation ability, the optimum being 20°C - 30°C. The presence of a nonconjugative strain decreased conjugation, by leading to earlier nutrient exhaustion and growth arrest which limited meetings between donor and recipient microcolonies. The model and the experimental system demonstrate the importance of spatial effects on conjugation. Description and prediction of gene transfer in natural environments will require models of greater complexity, and more sophisticated experimental testing, but this study provides a basis for theoretical descriptions of gene transfer in heterogeneous natural environments, such as soil and biofilms on solid surfaces in aquatic environments.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 6 uppsatser.