Quantitative analysis of the effects of morphological changes on extracellular electron transfer rates in cyanobacteria
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(2020) 13:150 Okedi et al. Biotechnol Biofuels https://doi.org/10.1186/s13068-020-01788-8
Open Access
METHODOLOGY
Quantitative analysis of the effects of morphological changes on extracellular electron transfer rates in cyanobacteria Tonny I. Okedi1 , Adrian C. Fisher1,2 and Kamran Yunus1*
Abstract Background: Understanding 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. Results: The 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. Conclusion: A 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. Keywords: Morphology, Extracellular electron transfer, Cyanobacteria, Synechococcus elongatus sp. PCC7942, Mass transfer Background Biophotovoltaics (BPVs) promise a low-cost sustainable pathway for wastewater bioremediation with ondemand electricity or chemicals production. This is achieved by employing exoelectrogenic photosynthetic microorganisms requiring solar radiation and nutrients such as nitrates and phosphates that can be derived from *Correspondence: [email protected] 1 Department of Chemical Engineering and Biotechnology, University of Cambridge, Phillipa Fawcett Drive, Cambridge CB3 0AS, UK Full list of author information is available at the end of the article
wastewater. Electrical current generation in cellular BPVs has been demonstrated using various oxygenic photosynthetic microorganisms including eukaryotic microalgae such as Chlorella vulgaris [1, 2] and Chlamydomonas reinhardtii [3–5] as well as marine and fresh water species of prokaryotic cyanobacteria such as Arthrospira maxima [6], Synechocystis sp. PCC6803 [7–16] and Synechococcus sp. P
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