Isolation and characterization of oleaginous yeasts for biodiesel production and usage of pretreated livestock wastewater as a low cost feedstock

Abstract

Biodiesel is one sustainable alternative to fossil-based liquid fuels. Among various feedstock, oleaginous microbes, cells able to accumulate lipid over 20% of their dry masses, have received increasing attention due to their exceptionally high lipid productivity. Microalgae and heterotrophic yeasts are two of the most promising and thus studied cell types. Microalgae generally grow photoautotrophically and hence accumulate lipid through photoautotrophic metabolism, only requiring carbon dioxide as a sole carbon source and light as an energy source. Slow growth and low final cell density are two fatal disadvantages of these photoautotrophs in relation to their usage as fuel feedstock. Oleaginous yeasts, on the other hand, have much higher growth rate and lipid productivity. The final cell density can even reach a commercially viable level relatively easily. One critical caveat is their requirement of growth substrates, which constitutes approximately half of total fuel production cost. Accordingly, one success key of heterotroph-based fuel production is to find sufficiently cheap feedstock. It is equally important to obtain potent yeast trains. These two critical issues were therefore be addressed in this master thesis. First, several oleaginous yeasts were isolated particularly from carbon-rich environments such as mine drainage, spoil, and soil, based on my assumption that in this condition oil-degrading microbes proliferate. My working hypothesis for this was that good oil degraders are also able to accumulate lipid well, as their lipid synthesis must be metabolically linked to lipid degradation. After isolation, each of the 4 isolated yeasts was sequenced for identification. Among these 4 kinds of yeasts were selected for detail characterization. Growth rate was employed as parameter, as it, together with lipid content, would be one determining factor for commercialization. Various culture conditions, such as carbon source, temperature, and pH, were examin...