Rapid Harvest of Algae for Biofuel Production with the Aggregating Bacterium Bacillus sp. strain RP1137.

Abstract

Algal biofuels represent one of the most promising means of sustainably replacing liquid fuels. However significant challenges remain before algal based fuels become competitive with fossil fuels. One of the largest challenges is the ability to harvest the algae in an economic and low energy manner. In this dissertation I describe the isolation of the bacterium, Bacillus sp. strain RP1137, which can rapidly aggregate several algae that are candidates for biofuel production. This bacterium aggregates algae in a pH dependent and reversible manner and retains its aggregation ability after paraformaldehyde fixation. The optimal ratio of bacteria to algae is described as well as the robustness of aggregation at different salinities and temperatures. Aggregation is dependent on the presence of calcium or magnesium ions and likely occurs via charge neutralization through binding of calcium ions to the cell surface of both algae and bacteria. I show charge neutralization occurs at least in part through binding of calcium to negatively charged teichoic acid residues. A comparison of the aggregation efficiency of RP1137, Bacillus megaterium QM B1551 and Bacillus subtilis SMY showed that RP1137 and B1551 are equally efficient at aggregating algae while SMY does not aggregate algae. The genome of RP1137 was sequenced to understand the molecular underpinning of the mechanism of aggregation. The difference in aggregation phenotypes between the three bacilli was used to inform a genomic comparison which revealed two putative proteins that are predicted to be bound to the cell wall and are found only in RP1137 and B1551 but not SMY. This work characterizes the conditions under which Bacillus sp. RP1137 aggregates algae and the mechanism by which that aggregation occurs.