The cultural characteristics of various mucoid strains of Ps. aeruginosa were examined, a wide variation in the time when the polymer was produced, the levels synthesised and the composition of the polymer occurred. The only similarity between these strains is that they produced an acetylated polyuronide. Mucoid strains were found to be highly unstable in ammonia limited chemostat cultures. Small colonies appeared at a high rate which led to a rapid displacement of the parental type indicating that some of these variants possessed a competitive advantage over the wild type. Ultimately selection for a non mucoid strain with a higher yield of biomass on the growth-limiting substrate occurred. The pathway for the biosynthesis of alginate appears to differ very little from the reaction sequences proposed in both Az. vinelandii and Fucus gardneri. In the study of enzymes involved in the biosynthesis by PAO strains similarities occurred to the biosynthetic pathway of colanic acid found in E.coli. The wild type contains all the enzymes necessary to produce alginate but it is not expressed. Synthesis of alginate leads to an increase in the levels of enzymes involved in the formation of the presursor GDP-Mannuronic acid. In non mucoid strains both sup+ and sup 7, GDP-Mannose dehydrogenase was absent. Also in these strains either GDP-Mannose pyrophosphorylase or phosphomannose isomerase was absent. In some sup strains elevated levels of certain carbohydrate enzymes were found. The regulation/repression of the enzymes is complex but the pathway lacks the fine control mechanisms present in other biosynthetic pathways. Synthesis of alginate led to an increase in resistance to carbenicillin and a decrease in resistance to tetracycline. In salts increase in resistance to EDTA and SDS. This effect was greatly magnified in salts deficient media. In salts deficient media both mucoid and sup + and sup strains were more resistant to deoxycholate; in salts media this was not observed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660612 |
| Date | January 1979 |
| Creators | Piggott, Nigel H. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11257 |
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