Enhancing plasma membrane NADPH oxidase activity increases current output by diatoms in biophotovoltaic devices
Biophotovoltaic (BPV) devices employ the photosynthetic activity of microalgae or cyanobacteria to harvest light energy and generate electrical current directly as a result of the release of electrons from the algal cells. NADPH oxidases (NOX) are plasma-membrane enzymes that transport electrons from the cytosol to generate extracellular superoxide anions, and have been implicated in BPV output. In this study, we investigated NOX activity in the diatoms Phaeodactylum tricornutum and
... tum and Thalassiosira pseudonana in an attempt to understand and enhance NOX and BPV function. We found that NOX activity was linked to defined growth regimes and growth phases, and was light dependent. Crucially, current output in a BPV device correlated with NOX activity, and levels of up to 14 μA per 10 6 cells (approximately 500 mA·m −2 ) were obtained. Expression of two putative P. tricornutum NOX genes (PtNOX1 and PtNOX2) was found to correspond with the observed growth patterns of superoxide anion production and power output, suggesting that these are responsible for the observed patterns of NOX activity. Crucially, we demonstrate that NOX activity levels could be enhanced via semicontinuous culturing, pointing to the possibility of maintaining long-term power output in BPV devices.