12-07: Ultrastructural analysis of cell wall deconstruction in the green alga Chlorella vulgaris

Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Bryon S. Donohoe1, Henri G. Gerken2, Philip T. Pienkos2 and Eric P. Knoshaug2, (1)Biosciences Center, National Renewable Energy Laboratory, Golden, CO, (2)National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO
The unicellular green alga, Chlorella vulgaris has been identified as a strong candidate feedstock and model strain for algal biofuels, yet its robust cell wall is a substantial barrier to the efficient release of lipid bodies. Due to the chemical complexity of the polymers, and the structural complexity of the architecture, there is still a significant knowledge gap in our understanding of C. vulgaris cell walls. Our approach to fill this gap has been to survey the impact of a broad range of enzymes on cell walls by colony growth inhibition and changes in permeability by flow cytometry. To compliment these techniques and explore the nanoscale architecture of the algal cell wall we have employed transmission electron microscopy (TEM) to directly visualize structural changes in cell walls with application of degrading enzymes. We have also examined how components of the secretory pathway may have reorganized in response to cell wall deconstruction. Highlights of this analysis include the dramatic and complex effects of lysozyme on the cell walls. TEM micrographs revealed the complete loss of the hair-like fiber layer of the outer wall surface, swelling of the outer layers, and a peeling or dissolution of material from the outer cell wall. Physical parameters of cell wall deconstruction have been defined and quantified including cell wall thickness, density, and delamination. This work serves as a foundation for determining what key architectural changes and the level of structural disruption will be required to eventually generate a self-lysing phenotype.
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