Can the optimisation of pop-up agriculture in remote communities help feed the world?

Threats to global food security have generated the need for novel food production techniques to feed an ever-expanding population with ever-declining land resources. Hydroponic cultivation has been long recognised as a reliable, resilient and resource-use-efficient alternative to soil-based agricultural practices. The aspiration for highly efficient systems and even city-based vertical farms is starting to become realised using innovations such as aeroponics and LED lighting technology. However, the ultimate challenge for any crop production system is to be able to operate and help sustain human life in remote and extreme locations, including the polar regions on Earth, and in space. Here we explore past research and crop growth in such remote areas, and the scope to improve on the systems used in these areas to date. We introduce biointensive agricultural systems and 3D growing environments, intercropping in hydroponics and the production of multiple crops from single growth systems. To reflect the flexibility and adaptability of these approaches to different environments we have called this type of enclosed system ‘pop-up agriculture’. The vision here is built on sustainability, maximising yield from the smallest growing footprint, adopting the principles of a circular economy, using local resources and eliminating waste. We explore plant companions in intercropping systems to supply a diversity of plant foods. We argue that it is time to consume all edible components of plants grown, highlighting that nutritious plant parts are often wasted that could provide vitamins and antioxidants. Supporting human life via crop production in remote and isolated communities necessitates new levels of efficiency, eliminating waste, minimising environmental impacts and trying to wean away from our dependence on fossil fuels. This aligns well with tandem research emerging from economically developing countries where lower technology hydroponic approaches are being trialled reinforcing the need for ‘cross-pollination’ of ideas and research development on pop-up agriculture that will see benefits across a range of environments

The role of a disulfide bridge in the stability and folding kinetics of Arabidopsis thaliana cytochrome c6A

Cytochrome c 6A is a eukaryotic member of the Class I cytochrome c family possessing a high structural homology with photosynthetic cytochrome c 6 from cyanobacteria, but structurally and functionally distinct through the presence of a disulfide bond and a heme mid-point redox potential of + 71 mV (vs normal hydrogen electrode). The disulfide bond is part of a loop insertion peptide that forms a cap-like structure on top of the core α-helical fold. We have investigated the contribution of the disulfide bond to thermodynamic stability and (un)folding kinetics in cytochrome c 6A from Arabidopsis thaliana by making comparison with a photosynthetic cytochrome c 6 from Phormidium laminosum and through a mutant in which the Cys residues have been replaced with Ser residues (C67/73S). We find that the disulfide bond makes a significant contribution to overall stability in both the ferric and ferrous heme states. Both cytochromes c 6A and c 6 fold rapidly at neutral pH through an on-pathway intermediate. The unfolding rate for the C67/73S variant is significantly increased indicating that the formation of this region occurs late in the folding pathway. We conclude that the disulfide bridge in cytochrome c 6A acts as a conformational restraint in both the folding intermediate and native state of the protein and that it likely serves a structural rather than a previously proposed catalytic role. © 2011 Elsevier B.V. All rights reserved

The bioenergetic role of dioxygen and the terminal oxidase(s) in cyanobacteria

AbstractOwing to the release of 13 largely or totally sequenced cyanobacterial genomes (see http://www.kazusa.or.jp/cyano and www.jgi.doe.gov/), it is now possible to critically assess and compare the most neglected aspect of cyanobacterial physiology, i.e., cyanobacterial respiration, also on the grounds of pure molecular biology (gene sequences). While there is little doubt that cyanobacteria (blue-green algae) do form the largest, most diversified and in both evolutionary and ecological respects most significant group of (micro)organisms on our earth, and that what renders our blue planet earth to what it is, viz. the O2-containing atmosphere, dates back to the oxygenic photosynthetic activity of primordial cyanobacteria about 3.2×109 years ago, there is still an amazing lack of knowledge on the second half of bioenergetic oxygen metabolism in cyanobacteria, on (aerobic) respiration. Thus, the purpose of this review is threefold: (1) to point out the unprecedented role of the cyanobacteria for maintaining the delicate steady state of our terrestrial biosphere and atmosphere through a major contribution to the poising of oxygenic photosynthesis against aerobic respiration (“the global biological oxygen cycle”); (2) to briefly highlight the membrane-bound electron-transport assemblies of respiration and photosynthesis in the unique two-membrane system of cyanobacteria (comprising cytoplasmic membrane and intracytoplasmic or thylakoid membranes, without obvious anastomoses between them); and (3) to critically compare the (deduced) amino acid sequences of the multitude of hypothetical terminal oxidases in the nine fully sequenced cyanobacterial species plus four additional species where at least the terminal oxidases were sequenced. These will then be compared with sequences of other proton-pumping haem–copper oxidases, with special emphasis on possible mechanisms of electron and proton transfer

Mutants, overexpressors, and interactors of Arabidopsis plastocyanin isoforms

Two homologous plastocyanin isoforms are encoded by the genes PETE1 and PETE2 in the nuclear genome of Arabidopsis thaliana. The PETE2 transcript is expressed at considerably higher levels and the PETE2 protein is the more abundant isoform. Null mutations in the PETE genes resulted in plants, designated pete1 and pete2, with decreased plastocyanin contents. However, despite reducing plastocyanin levels by over approximately 90%, a pete2 null mutation on its own affects rates of photosynthesis and growth only slightly, whereas pete1 knockout plants, with about 60-80% of the wild-type plastocyanin level, did not show any alteration. Hence, plastocyanin concentration is not limiting for photosynthetic electron flow under optimal growth conditions, perhaps implying other possible physiological roles for the protein. Indeed, plastocyanin has been proposed previously to cooperate with cytochrome c(6A) (Cyt c(6A)) in thylakoid redox reactions, but we find no evidence for a physical interaction between the two proteins, using interaction assays in yeast. We observed homodimerization of Cyt c(6A) in yeast interaction assays, but also Cyt c(6A) homodimers failed to interact with plastocyanin. Moreover, phenotypic analysis of atc6-1 pete1 and atc6-1 pete2 double mutants, each lacking Cyt c(6A) and one of the two plastocyanin-encoding genes, failed to reveal any genetic interaction. Overexpression of either PETE1 or PETE2 in the pete1 pete2 double knockout mutant background results in essentially wild-type photosynthetic performance, excluding the possibility that the two plastocyanin isoforms could have distinct functions in thylakoid electron flow

Growth of microalgae using nitrate-rich brine wash from the water industry

© 2018 Safe and accepted limits for nitrates in drinking water are exceeded in around one-third of the groundwater bodies in Europe. Whilst anion exchange (AEX) is an effective technology to strip nitrates, the regeneration of AEX resins using saturated sodium chloride (brine) results in a significant quantity of nitrate-rich saline waste, which is currently disposed of at a substantial cost to the water industry. The aim of this research was to evaluate the viability of using AEX brine wash as a nutrient source to support microalgal growth. Experiments were carried out at laboratory and pilot scales to test which algal species were able to grow on brine wash, to determine the optimal nitrate concentration within modified growth media, and to identify whether the origin of the brine wash affected the nitrate uptake potential. In small scale laboratory experiments, five marine algal species were able to grow in modified f/2 growth media containing nitrate sourced from the brine wash. Further experiments showed that three species could grow on the modified media at nitrate concentrations from 5 to 274 mg L −1 . P. tricornutum could remediate up to 6.5 mg nitrate in 50 mL cultures in laboratory scale experiments, up to 570 mg at 10 L scale and 1700 mg at 100 L scale. We found that the origin of the brine wash did not significantly affect the growth of the cultures or the amount of nitrate removal from the modified media. The algal biomass could be used effectively in biogas production in small-scale trials, although with < 10% the yield from P. tricornutum biomass from standard f/2 medium. Our results suggest that it may be possible to derive value from brine wash as a sustainable source of nitrate for the growth of microalgae in bulk after optimisation.European Union (project no. 215G) INTERREG IVB ‘Energetic Algae’ (EnAlgae

Cytochrome c6A: discovery, structure and properties responsible for its low haem redox potential

Cytochrome c6A is a unique dithio-cytochrome of green algae and plants. It has a very similar core structure to that of bacterial and algal cytochromes c6, but is unable to fulfil the same function of transferring electrons from cytochrome f to Photosystem I. A key feature of cytochrome c6A is that its haem midpoint potential is more than 200 mV below that of cytochrome c6 (Em≈+340 mV) despite both cytochromes having histidine and methionine residues as axial haem-iron ligands. One salient difference between the haem pockets is that a valine residue in cytochrome c6A replaces a highly conserved glutamine residue in cytochrome c6. This difference has been probed using site-directed mutagenesis, X-ray crystallography and protein film voltammetry studies. It has been found that the stereochemistry of the glutamine residue within the haem pocket has a destabilizing effect and is responsible for tuning the haem's midpoint potential by over 100 mV. This large effect may have contributed to the evolution of a new biological function for cytochrome c6A.</jats:p