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Title: Production of antimicrobial compounds by marine epiphytic bacteria under conditions which mimic their natural environment
Author: Yan, Liming
Awarding Body: Heriot-Watt University
Current Institution: Heriot-Watt University
Date of Award: 2002
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The aim of this work was to investigate the production of antimicrobial compounds by marine epiphytic bacteria. This work was carried out by devising a "niche mimic bioreactor", in which physical and chemical conditions were similar to the original ecological niche from which the bacteria were isolated. A modified roller bottle bioreactor was designed to mimic the intertidal environment and could facilitate the production of antimicrobial compounds by two marine isolates. Biofilm formation by these bacteria was found to be the key requirement for this observation. An Air- Membrane Surface (AMS) bioreactor was therefore constructed to allow growth of attached bacteria within a biofilm. A Bacillus licheniformis strain, EI-34-6, isolated from the surface of the marine alga Palmaria palmala, produced bacitracin and a red pigment when cultivated using the AMS bioreactor but not using standard shake flask cultures. Glycerol and ferric iron were necessary for the production of both antimicrobial compounds and the red pigment. Further investigation into the mechanism of this induction showed that a small amount of the cell-free spent medium from the AMS culture of this isolate could induce the corresponding shake flask culture to produce bacitracin and the red pigment. Glycerol or ferric iron was not necessary for the production of inducer compounds. Furthermore, metabolites from the shake flask culture, which had been induced to produce bacitracin and the red pigment, were able to continue to induce other non-producing shake flask cultures. In addition, a small amount of cell-free spent medium from B. subtilis DSMIOT grown using the AMS bioreactor also induced B. licheniformis strain EI-34-6 to produce bacitracin and the red pigment in shake flask cultures. However, the spent medium from B. subtilis DSMIOT shake flask culture could not elicit this production. These results suggest the presence of a biofilm specific and cross-species signalling system which can elicit, in planktonic bacterial cells, the type of metabolism normally observed in cells grown in a biofilm. Based on this discovery, the AMS bioreactor was improved and it allowed a further nine Bacillus isolates to be obtained, which exhibited a similar phenomenon. The observations suggest a novel strategy to discover new antimicrobial compounds by taking advantage of their signalling system to reveal new metabolic pathways in marine microorganisms
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available