Microorganisms normally co-exist with other species in nature, so it is necessary for them to develop their own ability to survive in their habitat competing for the common nutritional resources. Following millions of years of competition with such interspecies interactions, microorganisms would have developed the mechanisms of recognition of the presence of a competitor and the defense mechanisms to produce some bioactive compounds such as antibiotics to fight with other species. As the largest antibiotic-producing genus, Streptomyces species produce most antibiotics that are currently used in medicine and agriculture. Streptomyces coelicolor A3(2) that belongs to Streptomyces species can produce many compounds with bioactivities including four known antibiotics; undecylprodigiosin and actinorhodin which are pigmented, and the other two that are colourless, methylenomycin and calcium-dependent antibiotic (CDA). Because undecylprodigiosin has been found to have immunosuppressive and anti-cancer activities and can be used as a novel drug for breast cancer treatment, it has become an active research topic. However, in laboratory conditions, the production of undecylprodigiosin by Streptomyces coelicolor is very low in pure culture. The hypothesis of this research was that the production of secondary metabolites, especially antibiotics, would increase in the presence of another microbial species as this would create competition. The aim of this research was therefore, to investigate the effect of interaction with live and dead cells as well as cell-free supernatant of E. coli culture on antibiotics production by Streptomyces coelicolor MT1110 and wild-type Streptomyces coelicolor A3(2) cultures. With the elicitation by E. coli C600 (live cells and supernatant), S. coelicolor MT1110 and wild-type S. coelicolor A3(2) produced 3.5-fold undecylprodigiosin concentration than the pure culture and the production level of actinorhodin decreased to one fifth of the pure culture. In the bioreactor experiment of wild-type S. coelicolor A3(2), the elicitation by E. coli (live cells and supernatant) reduced the maximum actinorhodin concentration by two thirds and increased undecylprodigiosin concentration by 2.5-fold. In a set of experiments, phthalic acid was used for the elicitation of S. coelicolor MT1110. When elicited with 15 Î¼M phthalic acid, the maximum actinorhodin concentration was 3.684 mg/L, which was one-third of the concentration obtained in the pure S. coelicolor culture; the maximum undecylprodigiosin concentration was 1.676 mg/L which was 1.5- fold of that achieved in the pure culture. A kinetic model of S. coelicolor was developed in order to obtain quantitative comparisons of experimental results. Furthermore, Metabolic Flux Balance Analysis (MFBA) was applied to some of the experimental results using a previously developed metabolic model and integrating phthalic acid metabolism with it in order to test the feasibility of using MFBA as a computational tool for the development mechanisms of microbial interactions, and the design of the relevant experiments. Indeed, both the kinetic model and the MFBA gave encouraging preliminary prediction of the experimental results. They are however, not perfect and need further development. If they can be refined, they can be additional research tools in the future research in the microbial inter-species interactions and especially for the search for and production of novel antibiotics.
|Date of Award||31 Dec 2018|
- The University of Manchester
|Supervisor||Ferda Mavituna (Supervisor) & Robin Curtis (Supervisor)|