Abstract
BackgroundUnderstanding the extracellular electron transport pathways in cyanobacteria is a major factor towards developing biophotovoltaics. Stressing cyanobacteria cells environmentally and then probing changes in physiology or metabolism following a significant change in electron transfer rates is a common approach for investigating the electron path from cell to electrode. However, such studies have not explored how the cells’ concurrent morphological adaptations to the applied stresses affect electron transfer rates. In this paper, we establish a ratio to quantify this effect in mediated systems and apply it to Synechococcus elongatus sp. PCC7942 cells grown under different nutritional regimes.ResultsThe results provide evidence that wider and longer cells with larger surface areas have faster mediated electron transfer rates. For rod-shaped cells, increase in cell area as a result of cell elongation more than compensates for the associated decline in mass transfer coefficients, resulting in faster electron transfer. In addition, the results demonstrate that the extent to which morphological adaptations account for the changes in electron transfer rates changes over the bacterial growth cycle, such that investigations probing physiological and metabolic changes are meaningful only at certain time periods.ConclusionA simple ratio for quantitatively evaluating the effects of cell morphology adaptations on electron transfer rates has been defined. Furthermore, the study points to engineering cell shape, either via environmental conditioning or genetic engineering, as a potential strategy for improving the performance of biophotovoltaic devices.
Highlights
Understanding the extracellular electron transport pathways in cyanobacteria is a major factor towards developing biophotovoltaics
Putative unmediated pathways found in literature are (1) an outer membrane c-type cytochrome (Omc) in direct contact with the anode; and (2) electrically conductive extracellular appendages that extend beyond the cell outer membrane in direct contact with the anode [13, 20, 21]
PCC7942 cells grown under continuous light with an intensity of 70 μmol m−2 s−1 (3x the light intensity used in this study) have a reported doubling time of 8.7 ± 0.7 h [31]
Summary
Understanding the extracellular electron transport pathways in cyanobacteria is a major factor towards developing biophotovoltaics. Stressing cyanobacteria cells environmentally and probing changes in physiology or metabolism following a significant change in electron transfer rates is a common approach for investigating the electron path from cell to electrode. Such studies have not explored how the cells’ concurrent morphological adaptations to the applied stresses affect electron transfer rates. Biophotovoltaics (BPVs) promise a low-cost sustainable pathway for wastewater bioremediation with ondemand electricity or chemicals production. Mediated electron transport introduces mass transfer phenomena to BPV systems which are known to limit the power output of electrochemical power devices such as fuel cells and batteries
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