Since microorganisms normally co-exist with other species in nature, they have developed complex metabolic and physiological responses as a result of such inter-species interactions. Biotic elicitation mimics the inter-species interactions in nature by introducing cell extracts, parts of cell wall, or dead cells into the culture of another species thus resulting in complex metabolic responses in the elicited microorganisms. In this thesis we report the exploitation of the interspecies interaction in order to enhance the antibiotic production by the model organism Streptomyces coelicolor. It produces four known antibiotics: actinorhodin, undecylprodigioisn, methylenomycin and the calcium dependent antibiotic. We investigated the production of actinorhodin and undecylprodigiosin only because of the lack of quantitative analytical methods for the other two. The pure cultures of S. coelicolor in a defined medium produce higher concentrations of actinorhodin compared with undecylprodigiosin. However, undecylprodigiosin is more important due to its antitumor activities. We introduced live and dead cells of E. coli, Bacillus subtilis and Staphylococcus aureus, separately, to the S. coelicolor culture. Investigations were performed on Petri dishes, shake flasks and 2 L bioreactors. The suitable amount of each elicitor bacterium was first determined based on its ability to grow in the S. coelicolor medium so that it did not overtake the growth of S. coelicolor. Growth of S. coelicolor and glucose consumption of the elicited cultures were studied and compared with those in the pure culture. Our results revealed an alteration in the antibiotic production pattern by S. coelicolor, such that undecylprodigiosin production was significantly enhanced and actinorhodin decreased. The maximum enhancement occurred in the culture elicited with the live cells of E. coli with an increase of 3.5-fold, whereas the minimum was with elicitation using S. aureus cells (2.1-fold increase). Also, a considerable suppression in the production of actinorhodin was observed upon elicitation with live cells of E. coli or S. aureus. Furthermore, another positive outcome of the elicitation was the earlier onset of undecylprodigiosin production by 24-35h compared to the pure culture of S. coelicolor. Moreover, this study showed that the dead cells of B. subtilis and S. aureus had the same elicitation effects as the live cells, contrary to the heat-killed cells of E. coli that had no such effect. Some optimisation experiments on the amount and the timing of the elicitation were performed and the optimal conditions were chosen that would increase undecylprodigiosin production. Elicitation in the bioreactor resulted in as much as six-fold increase in the production of undecylprodigiosin compared with the pure culture and approximately double that obtained in the shake flasks. The antimicrobial activities of the extracted actinorhodin and undecylprodigiosin on the elicitor bacteria were tested in agar diffusion tests. Undecylprodigiosin always inhibited the growth of the elicitor bacteria whereas actinorhodin was less effective. In addition, our results indicated that the interaction between S. coelicolor and E. coli was mediated via a molecule present in the E. coli culture, while no such evidence was found in the case of interaction with B. subtilis or S. aureus. The results showed that the elicitation with the cells of B. subtilis and S. aureus was not due to peptidoglycan or N-acetyl glucoseamine which is the constituents of the cell wall that may have been released by lyses during the culture process. Such inter-species interactions may form the basis of new strategies in the search for novel antibiotics and other bioactive compounds. They can also be used to increase the productivity of existing processes for antibiotics as it was found in this work.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:542707 |
| Date | January 2011 |
| Creators | Luti, Khalid Jaber Kadhum |
| Contributors | Mavituna, Ferda |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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