Master of Science in Chemical Engineering (MSChE)
Considerable interest in alternative energy has stimulated research in biofuels, particularly microalgal biofuels. In particular, strains of algae that accumulate lipids to be used for biofuels must be adapted to outdoor growth and resistant to invasive species. Differential gene expression in a Louisiana algae/cyanobacteria co-culture consisting of approximately 97% Chlorella vulgaris and 3% Leptolyngbya sp. possessing these traits was examined. Possible reasons for the enhanced growth of the co-culture relative to a Chlorella monoculture were reviewed, including cyanobacterial symbiosis and chemicals produced by cyanobacteria or bacteria that could influence the growth of Chlorella. The co-culture and Chlorella monoculture were cultivated at scalar irradiance levels of 180 and 400 µmol/m2-sec and nitrate levels corresponding to 50% and 100% of the nitrate levels of Bold’s Basal Medium. Dry biomass and cell counts were measured for the cultures initially, in the early exponential phase, in the late exponential phase, and at the end of the growth period. Lipid content was measured in the late exponential phase and at the end of the growth period. Total RNA was extracted and suppression subtractive hybridization was performed. Expressed sequence tags corresponding to putatively differentially expressed genes were sequenced, yielding one-hundred and five putatively differentially expressed genes. Quantitative PCR was performed on nine genes to compare gene expression in Chlorella in the co-culture and monoculture. All nine genes showed statistically significant expression level differences between the Chlorella vulgaris in the co-culture and in the monoculture for cultures grown at the same irradiance and nitrate levels. Evidence from the gene expression experiments, combined with observations in the literature, suggest the possible effect of a cyanobacteria-produced substance such as microcystins by the Leptolyngbya sp. Second, two Photosystem II genes were upregulated in the Chlorella monocultures, and one Photosystem I gene was upregulated in the co-cultures. Finally, the upregulation of a gene for an oil globule associated protein was found in the co-culture Chlorella. A homologous protein has been found in similar green algae, and further study of it in Chlorella is expected.
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Tate, John Joseph, "Differential Gene Expression in a Louisiana Strain of Microalgae" (2012). LSU Master's Theses. 3945.