Overexpressing Ferredoxins in Chlamydomonas reinhardtii Increase Starch and Oil Yields and Enhance Electric Power Production in a Photo Microbial Fuel Cell

Abstract

Ferredoxins (FDX) are final electron carrier proteins in the plant photosynthetic pathway, and function as major electron donors in diverse redox-driven metabolic pathways. We previously showed that overexpression of a major constitutively expressed ferredoxin gene PETF in Chlamydomonas decreased the reactive oxygen species (ROS) level and enhanced tolerance to heat stress. In addition to PETF, an endogenous anaerobic induced FDX5 was overexpressed in transgenic Chlamydomonas lines here to address the possible functions of FDX5. All the independent FDX transgenic lines showed decreased cellular ROS levels and enhanced tolerance to heat and salt stresses. The transgenic Chlamydomonas lines accumulated more starch than the wild-type line and this effect increased almost three-fold in conditions of nitrogen depletion. Furthermore, the lipid content was higher in the transgenic lines than in the wild-type line, both with and without nitrogen depletion. Two FDX-overexpressing Chlamydomonas lines were assessed in a photo microbial fuel cell (PMFC); power density production by the transgenic lines was higher than that of the wild-type cells. These findings suggest that overexpression of either PETF or FDX5 can confer tolerance against heat and salt stresses, increase starch and oil production, and raise electric power density in a PMFC.

The Development of Biophotovoltaic Systems for Power Generation and Biological Analysis

“…Some studies have used eukaryotic algae, predominantly either green algae, notably various species of Chlamydomonas, [26][27][28][29][30] Chlorella [31][32][33][34] and Dunaliella, [35] or diatoms, such as Phaeodactylum tricornutum and Thalassiosira pseudonana. [28] Green algae and diatoms are only very distantly related in evolutionary terms.…”

“…These are most commonly potassium ferricyanide, [10,15,16,20,26,28,29,31,58,81] and quinones such as 2,6-dichloro-p-benzoquinone (DCBQ), [14,30] 2-hydroxy-1,4-naphthoquinone (HNQ) [82][83][84][85] and 1,4-benzoquinone [24,86] (Figure 4). The major limitation of using such exogenous mediators for practical applications is that they may be toxic to the cells and expensive to scale up.…”

Enhancing Stability of Microalgae Biocathode by a Partially Submerged Carbon Cloth Electrode for Bioenergy Production from Wastewater

“…These values are higher than the working voltage (12-170 mV) from a photosynthetic algal MFC fed with food waste [9] or domestic wastewater [23]. The maximum values, rather than the average values for the parameters relative to electricity generation (e.g., working voltage, open circuit voltage/potential, current density), have traditionally been used in most studies [8][9][10]12,13]. Because those parameters vary remarkably with the change in DO caused by the different growth status of microalgae in the microalgae biocathode; for example, DO is usually very low in the start-up period or after replacement of the substrate in cathode chamber [9,10,12] and easily fluctuates with the shift in light/dark periods [8,12].…”

“…The maximum values, rather than the average values for the parameters relative to electricity generation (e.g., working voltage, open circuit voltage/potential, current density), have traditionally been used in most studies [8][9][10]12,13]. Because those parameters vary remarkably with the change in DO caused by the different growth status of microalgae in the microalgae biocathode; for example, DO is usually very low in the start-up period or after replacement of the substrate in cathode chamber [9,10,12] and easily fluctuates with the shift in light/dark periods [8,12]. The large variations render the average values for these parameters meaningless in the assessment of photosynthetic algal MFC performance.…”

“…Photosynthetic microalgae microbial fuel cell (MFC) could produce microbial lipid (could be converted to biodiesel [5]) and algal biomass besides electricity, while reducing greenhouse gas CO 2 by photosynthesis [6,7]. Many studies have demonstrated that the bioelectricity generation was correlated with oxygen availability in the cathode as O 2 is the electron acceptor [8][9][10]. Due to the high DO generated from photosynthesis, power generation of MFC with microalgae biocathode was reported to be higher than that of MFC with mechanical aeration cathode [8,11], abiotic-cathode, or air-cathode [12,13].…”