Quantification and regulation of pellet morphology in streptomyces hygroscopicus var; geldanus cultures
Ó Cléirigh, Cormac (2005) Quantification and regulation of pellet morphology in streptomyces hygroscopicus var; geldanus cultures. PhD thesis, Dublin City University.
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Streptomyces hygroscopicus var. geldanus, an actinomycete, produces a range of antibiotic compounds, one of which, Geldanamycin, is currently under investigation for its potential anticancer properties. Filamentous microbes, both bacterial and fungal, possess the ability to grow in a range of morphological forms in submerged fermentations. Secondary metabolite production by filamentous microorganisms is often dependent on the morphology of biomass aggregates within the culture and therefore morphological regulation in such fermentations is desirable in order to produce specific compounds of interest.
Morphological assessment of pellet formation and growth necessitated the development of an image analysis technique to allow high throughput morphological characterisation of microbial fermentation broths. An assessment of environmental and nutritional conditions for culturing S. hygroscopicus , concentrating specifically on the impact of nutrient broth composition, spore loading density and shear rate on the morphological and physiological profiles of the organism, was undertaken.
The formation of pelleted biomass in submerged fermentations occurs as a result of spore aggregation, hyphal aggregation or entanglement; each of which was identified as a potential morphological control strategy. The microbial polysaccharide xanthan gum was used to artificially regulate the apparent viscosity and hence the rheological characteristics of S. hygroscopicus fermentations broths and succeeded in controlling particle collision, aggregation and hence pellet formation. Control of broth surface tension through the introduction of surfactants, facilitates regulation of hydrophobic particle interaction, thus enabling regulation of hyphal aggregation and hence pellet formation in S. hygroscopicus cultures. Furthermore, we have identified the production of a previously unreported biosurfactant which appears to have significant effect on the morphology of the organism. Preliminary purification and characterisation of this molecules and an assessment of its usefulness as a morphological control agent in Streptomyces fermentations has been conducted.
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