The United Nations Conference on Climate Change (Paris 2015) reached an international agreement to keep the rise in global average temperature 'well below 2°C' and to 'aim to limit the increase to ...1.5°C'. These reductions will have to be made in the face of rising global energy demand. Here a thoroughly validated dynamic econometric model (Eq 1) is used to forecast global energy demand growth (International Energy Agency and BP), which is driven by an increase of the global population (UN), energy use per person and real GDP (World Bank and Maddison). Even relatively conservative assumptions put a severe upward pressure on forecast global energy demand and highlight three areas of concern. First, is the potential for an exponential increase of fossil fuel consumption, if renewable energy systems are not rapidly scaled up. Second, implementation of internationally mandated CO2 emission controls are forecast to place serious constraints on fossil fuel use from ~2030 onward, raising energy security implications. Third is the challenge of maintaining the international 'pro-growth' strategy being used to meet poverty alleviation targets, while reducing CO2 emissions. Our findings place global economists and environmentalists on the same side as they indicate that the scale up of CO2 neutral renewable energy systems is not only important to protect against climate change, but to enhance global energy security by reducing our dependence of fossil fuels and to provide a sustainable basis for economic development and poverty alleviation. Very hard choices will have to be made to achieve 'sustainable development' goals.
Summary
The global population is predicted to increase from ~7.3 billion to over 9 billion people by 2050. Together with rising economic growth, this is forecast to result in a 50% increase in fuel ...demand, which will have to be met while reducing carbon dioxide (CO2) emissions by 50–80% to maintain social, political, energy and climate security. This tension between rising fuel demand and the requirement for rapid global decarbonization highlights the need to fast‐track the coordinated development and deployment of efficient cost‐effective renewable technologies for the production of CO2 neutral energy. Currently, only 20% of global energy is provided as electricity, while 80% is provided as fuel. Hydrogen (H2) is the most advanced CO2‐free fuel and provides a ‘common’ energy currency as it can be produced via a range of renewable technologies, including photovoltaic (PV), wind, wave and biological systems such as microalgae, to power the next generation of H2 fuel cells. Microalgae production systems for carbon‐based fuel (oil and ethanol) are now at the demonstration scale. This review focuses on evaluating the potential of microalgal technologies for the commercial production of solar‐driven H2 from water. It summarizes key global technology drivers, the potential and theoretical limits of microalgal H2 production systems, emerging strategies to engineer next‐generation systems and how these fit into an evolving H2 economy.
This review article considers Earth as an energy-storing (photosynthetic) and energy-consuming (metabolic) system. We evaluate whether and how photosynthetic, solar fuel-production systems can be ...engineered and deployed sufficiently rapidly to supplant enough fossil fuel supply to sustain a complex human economy and natural ecosystems over the long term. Geophysical, ecological, economic, technological and political constraints are quantified. We consider the potential to innovate and scale up promising systems such as microalgal and artificial photosynthetic systems to economic viability within a time frame meaningful for mitigating the effects of climate change and fuel-supply limitations. A future global society powered sustainably by solar fuels is forecast to require increased global photosynthetic productivity, through increased photon-conversion efficiency and production area. Increasing the efficiency of socioeconomic energy utilisation is also important. Meeting these challenges on the required time scale demands historically unprecedented technical progress, highlighting the need for both advanced international policy frameworks and scientific excellence. Based on evidence from a broad range of fields, a multiscale systems optimisation approach is identified as important, to integrate analyses from the scale of the global climate, economy and energy systems, down to the nanoscale of light-harvesting and carbon-fixing machinery that drives photosynthesis.
Dry weight biomass is an important parameter in algaculture. Direct measurement requires weighing milligram quantities of dried biomass, which is problematic for small volume systems containing few ...cells, such as laboratory studies and high throughput assays in microwell plates. In these cases indirect methods must be used, inducing measurement artefacts which vary in severity with the cell type and conditions employed. Here, we utilise flow cytometry pulse width data for the estimation of cell density and biomass, using Chlorella vulgaris and Chlamydomonas reinhardtii as model algae and compare it to optical density methods. Measurement of cell concentration by flow cytometry was shown to be more sensitive than optical density at 750 nm (OD750) for monitoring culture growth. However, neither cell concentration nor optical density correlates well to biomass when growth conditions vary. Compared to the growth of C. vulgaris in TAP (tris-acetate-phosphate) medium, cells grown in TAP + glucose displayed a slowed cell division rate and a 2-fold increased dry biomass accumulation compared to growth without glucose. This was accompanied by increased cellular volume. Laser scattering characteristics during flow cytometry were used to estimate cell diameters and it was shown that an empirical but nonlinear relationship could be shown between flow cytometric pulse width and dry weight biomass per cell. This relationship could be linearised by the use of hypertonic conditions (1 M NaCl) to dehydrate the cells, as shown by density gradient centrifugation. Flow cytometry for biomass estimation is easy to perform, sensitive and offers more comprehensive information than optical density measurements. In addition, periodic flow cytometry measurements can be used to calibrate OD750 measurements for both convenience and accuracy. This approach is particularly useful for small samples and where cellular characteristics, especially cell size, are expected to vary during growth.
Background
By co‐culturing selected microalgae and heterotrophic microorganisms, the growth rate of microalgae can be improved even under atmospheric conditions with a low CO2 concentration. However, ...the detailed mechanism of improvement of proliferative capacity by co‐culture has not been elucidated. In this study, we investigated changes in the proliferative capacity of the green alga Chlamydomonas reinhardtii by co‐culturing with Escherichia coli.
Main Methods and Major Results
In the co‐culture, the number of C. reinhardtii cells reached 2.22 × 1010 cell/L on day 14 of culture. This was about 1.9 times the number of cells (1.16 × 1010 cell/L) on day 14 compared to C. reinhardtii cells in monoculture. The starch content per cell in the co‐culture of C. reinhardtii and E. coli on the 14th day (2.09 × 10−11 g/cell) was 1.3 times higher than that in the C. reinhardtii monoculture (1.59 × 10−11 g/cell), and the starch content per culture medium improved 2.5 times with co‐cultivation. By analyzing the gene transcription profiles and key media components, we clarified that E. coli produced CO2 from the organic carbon in the medium and the organic carbon produced by photosynthesis of C. reinhardtii, and this CO2 likely enhanced the growth of C. reinhardtii.
Conclusions
Consequently, E. coli plays a key role in promoting the growth of C. reinhardtii as well as the accumulation of starch which is a valuable intermediate for the production of a range of useful chemicals from CO2.
Graphical and Lay Summary
In this study, we investigated changes in the proliferative capacity of the green alga Chlamydomonas reinhardtii by co‐culturing with Escherichia coli. It was clarified for the first time that co‐culture with C. reinhardtii and E. coli promotes the growth of C. reinhardtii and the starch production. In the future, it is expected that the co‐culture system consisting of C. reinhardtii and E. coli will be developed to produce a range of useful chemicals from CO2.
Microalgal production technologies are seen as increasingly attractive for bioenergy production to improve fuel security and reduce CO2 emissions. Photosynthetically derived fuels are a renewable, ...potentially carbon-neutral and scalable alternative reserve. Microalgae have particular promise because they can be produced on non-arable land and utilize saline and wastewater streams. Furthermore, emerging microalgal technologies can be used to produce a range of products such as biofuels, protein-rich animal feeds, chemical feedstocks (e.g. bioplastic precursors) and higher-value products. This review focuses on the selection, breeding and engineering of microalgae for improved biomass and biofuel conversion efficiencies.
ABC toxins are pore-forming virulence factors produced by pathogenic bacteria. YenTcA is the pore-forming and membrane binding A subunit of the ABC toxin YenTc, produced by the insect pathogen ...Yersinia entomophaga. Here we present cryo-EM structures of YenTcA, purified from the native source. The soluble pre-pore structure, determined at an average resolution of 4.4 Å, reveals a pentameric assembly that in contrast to other characterised ABC toxins is formed by two TcA-like proteins (YenA1 and YenA2) and decorated by two endochitinases (Chi1 and Chi2). We also identify conformational changes that accompany membrane pore formation by visualising YenTcA inserted into liposomes. A clear outward rotation of the Chi1 subunits allows for access of the protruding translocation pore to the membrane. Our results highlight structural and functional diversity within the ABC toxin subfamily, explaining how different ABC toxins are capable of recognising diverse hosts.
The use of fossil fuels is now widely accepted as unsustainable due to depleting resources and the accumulation of greenhouse gases in the environment that have already exceeded the “dangerously ...high” threshold of 450 ppm CO
2
-e. To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable, but also capable of sequestering atmospheric CO
2
. Currently, nearly all renewable energy sources (e.g. hydroelectric, solar, wind, tidal, geothermal) target the electricity market, while fuels make up a much larger share of the global energy demand (∼66%). Biofuels are therefore rapidly being developed. Second generation microalgal systems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane and biohydrogen. Biodiesel is currently produced from oil synthesized by conventional fuel crops that harvest the sun’s energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approximately 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to represent the only current renewable source of oil that could meet the global demand for transport fuels. The main advantages of second generation microalgal systems are that they: (1) Have a higher photon conversion efficiency (as evidenced by increased biomass yields per hectare): (2) Can be harvested batch-wise nearly all-year-round, providing a reliable and continuous supply of oil: (3) Can utilize salt and waste water streams, thereby greatly reducing freshwater use: (4) Can couple CO
2
-neutral fuel production with CO
2
sequestration: (5) Produce non-toxic and highly biodegradable biofuels. Current limitations exist mainly in the harvesting process and in the supply of CO
2
for high efficiency production. This review provides a brief overview of second generation biodiesel production systems using microalgae.
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