Morphogenesis and differentiation in Rhodomicrobium

• Main Author: France, Andrew D
• Format: Dissertation
• Language: English
• Published: University of Warwick 1978
• Subjects: QH Natural history; QR Microbiology

Differentiation and morphogenesis in the budding photosynthetic bacterium Rhodomicrobium vannielii (Rm5) was investigated using batch and continuous culture techniques. A previously undocumented 'simplified' vegetative cell cycle was identified. 'Simplified' Rm 5 cells (with a developmental cycle resembling that of the prosthecate Hyphomicrobium) were isolated from the late exponential growth phase of batch cultures, or from continuous cultures grown under high CO2 tensions. Expression of this cell type appears to be under environmental control although the possibility that such cells may be mutants has not been overlooked. Previous studies have associated swarm cell production with mother cells comprising multicellular arrays, but the existence of 'simplified' cells suggests that microcolony formation is not a prerequisite for swarm cell synthesis. The characteristics of this unusual cell type and the morphology and physiology were compared with cells of Rhodomicrobium expressing the ’normal’ developmental cycle. Soluble protein extracts of ’simplified’ Rm 5 cells were compared with those of the other cell types by polyacrylamide gel electrophoresis. Since reproducibility of results was difficult to achieve under batch culture conditions, the possibility of using a chemostat to perform simple physiological studies and optimise growth conditions was investigated. Experiments were performed in order to try and elucidate whether or not 'simplified' Rm 5 cells were mutations, or a form of cellular expression in response to particular environmental conditions. Although growth of Rm 5 is accompanied by obligate differentiation, life cycle variations such as exospore production and swarm cell formation are almost certainly environmentally induced. Preliminary investigations were made as to the effect of different environmental conditions on cellular expression in Rm 5. Light intensity, pH and CO2 tension were involved with swarm cell production and development, whereas the presence of trace elements was a probable requirement for successful exospore formation.