Abstract
BackgroundProduction of biofuels from microalgae has been recognized to be a promising route for a sustainable energy supply. However, the microalgae harvesting process is a bottleneck for industrialization because it is energy intensive. Thus, by displaying interactive protein factors on the cell wall, oleaginous microalgae can acquire the auto- and controllable-flocculation function, yielding smarter and energy-efficient harvesting.ResultsTowards this goal, we established a cell-surface display system using the oleaginous diatom Fistulifera solaris JPCC DA0580. Putative cell wall proteins, termed frustulins, were identified from the genome information using a homology search. A selected frustulin was subsequently fused with green fluorescent protein (GFP) and a diatom cell-surface display was successfully demonstrated. The antibody-binding assay further confirmed that the displayed GFP could interact with the antibody at the outermost surface of the cells. Moreover, a cell harvesting experiment was carried out using silica-affinity peptide-displaying diatom cells and silica particles where engineered cells attached to the silica particles resulting in immediate sedimentation.ConclusionThis is the first report to demonstrate the engineered peptide-mediated harvesting of oleaginous microalgae using a cell-surface display system. Flocculation efficiency based on the silica-affinity peptide-mediated cell harvesting method demonstrated a comparable performance to other flocculation strategies which use either harsh pH conditions or expensive chemical/biological flocculation agents. We propose that our peptide-mediated cell harvest method will be useful for the efficient biofuel production in the future.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0406-9) contains supplementary material, which is available to authorized users.
Highlights
Production of biofuels from microalgae has been recognized to be a promising route for a sustainable energy supply
Primary structure and gene expression level of frustulins of F. solaris In the present study, putative frustulin-like proteins were screened from F. solaris JPCC DA0580 genome using α1-frustulin of Cylindrotheca fusiformis [29] and ε-frustulin of Navicula pelliculosa [30] as the query sequences, whereas our previous study had utilized only α1-frustulin for the homology search, and resulted in revealing seven putative proteins [28]
Silica‐affinity peptide‐mediated cell harvesting using silica particles As a proof of concept, we investigated whether it is possible for the diatom cell-surface display system established here to mediate algal biomass harvesting
Summary
Production of biofuels from microalgae has been recognized to be a promising route for a sustainable energy supply. The current ratio derived from the microalgal biomass is desired to be more than 1 (i.e, energy production is higher than the consumption), in practice, it is difficult to achieve [14]. Towards this goal, tremendous efforts have been made to enhance TAG accumulation in target microalgal cells by means of cultivation techniques [15] as well as metabolic engineering [16]. Researchers determined that such approaches directing enhancement of energy production are not sufficient due to the significant energy consumption in their processes Decreasing this energy consumption during the microalgal biomass processing is critical to the practicality of microalgal biofuels
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