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Title: Morphological and physiological adaptations of prosthecate bacteria to growth in low nutrient environments
Author: Morgan, Philip
ISNI:       0000 0001 3421 1269
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1985
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Prosthecate bacteria are usually observed in oligotrophic (low nutrient) environments and have been proposed as "model" oligotrophic bacteria since they possess a number of adaptations for growth under very low nutrient conditions. This project was designed to study selected prosthecate bacteria and attempt to relate their ecology to physiological and morphological adaptations, in particular the production of a motile swarmer cell stage. Ecological investigations showed that the prosthecate bacteria were ubiquitous in the oligotrophic fresh water environments examined. A variety of morphological types were observed in populations which also included large numbers of morphologically "typical" cells, demonstrating that there exists a large variety of oligotrophic bacteria. The responses of these bacteria to increasing nutrient concentrations suggested that currently accepted definitions of oligotrophy are in need of reconsideration. Caulobacter crescentus CB1S, Hyphomicrobium X and Rhodomicrobium vanniel1i Rm5 were studied in detail in both batch and continuous culture with respect to nutrient effects on cell morphology and cell type expression. All three organisms produced elongated prosthecae with increasing nutrient stress under both carbon and phosphate—1imi ted conditions, an observation somewhat in contradiction with reports suggesting that prosthecae function as specialised phosphate uptake sites. The production of «warmer cells was enhanced under conditions of nutrient stress, supporting the proposition that swarmer cells function as specialised survival and dispersal cells. R, vannlelli was chosen for investigations into the intermediary metabolism of prosthecate bacteria with respect to adaptions to oligotrophy and differential cell type expression. Unlike other Rhodospirillaceae this organism was shown to possess an incomplete tricarboxyllc acid (TCA) cycle under anaerobic conditions broken at 2-oxoglutarate dehydrogenase and lacked NADH oxidase activity but these enzymes were present under aerobic conditions. Of the glyoxylate shunt enzymes, malate synthase activity was detected but isocltrate lyase was absent. The TCA cycle enzymes, Ribulose—1,5-bl«phosphate carboxylase/oxygenase (RUBISCO) and phosphoenolpyruvate carboxylase possessed similar activities and Inhibitor patterns in both swarmer and prosthecate cells and therefore the physiological adaptations of the swarmer cells remain largely unknown. This work has demonstrated the success and ubiquity of prosthecate bacteria in the oligotrophic fresh water ecoystem although it must be emphasised that there exist a large number of non-prosthecate bacteria in these environments. The roles of the prosthecae and swarmer cells in this competitiveness are as yet not fully clear but appear to be of importance in view of observed responses to nutrient limitation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QR Microbiology