Microalgal Aquafeeds As Part of a Circular Bioeconomy

Photosynthetic microalgae are unicellular plants, many of which are rich in pro-tein, lipids, and bioactives and form an important part of the base of the natural aquatic food chain. Population growth, demand for high-quality protein, and depletion of wildfish stocks are forecast to increase aquacultural fish demand by 37% between 2016 and 2030. This review highlights the role of microalgae andrecent advances that can support a sustainable‘circular’aquaculture industry. Microalgae-based feed supplements and recombinant therapeutic production offer significant opportunities to improve animal health, disease resistance,and yields. Critically, microalgae in biofloc, ‘green water’, nutrient remediation,and integrated multitrophic aquaculture technologies offer innovative solutions for economic and environmentally sustainable development in line with key UN Sustainability Goals

Design scenarios of outdoor arrayed cylindrical photobioreactors for microalgae cultivation considering solar radiation and temperature

Advancing microalgae biotechnologies requires the design of high efficiency, large scale outdoor photobioreactor systems. Here we present a predictive biomass productivity model to define system design parameters yielding high biomass productivities for a facility encompassing arrays of cylindrical photobioreactors (PBRs) in a sub-tropical location (Brisbane, Australia). The model analyses the temperature and the light distributed through the culture medium as a function of PBR height, diameter, spacing distance between reactors, biomass concentration and cultivation regime (continuous vs. batch; fixed vs. capped temperature control). Temporal changes in light and temperature were used to predict volumetric and areal productivities (Pvol and Pareal respectively) for three Chlorella strains (C. vulgaris, C. sp. 11_H5 and C. pyrenoidosa). A simple empirical relationship was derived to rapidly predict Pvol in PBR arrays based on the ratio of spacing distance and reactor height (L/H) if the Pvol of a single, unshaded PBR was known. For C. vulgaris under a continuous operation and variable temperature (within its maximum growth threshold), the highest Pvol in the range analysed was obtained at the smallest diameter (0.1 m), highest biomass concentration (1.5 g L−1) and largest L/H, (Pvol ~0.3 g L−1 d−1). In contrast, the highest Pareal (~50 t ha−1 yr−1) was found at higher diameters (0.15 and 0.3 m), a lower biomass concentration (0.3 g L−1) and low L/H (0.2–0.4); this was attributed to a higher overall culture volume per PBR and per area. Our predictions, based on light and temperature effects on productivity, suggest that attaining a high Pvol could reduce costs, energy and materials associated with water usage, harvest loads and PBRs; whereas attaining a Pareal toward its maxima could reduce costs associated with land. The model supports effective PBR array design and process optimisation to help minimise production cost

Membrane-protein crystallization in cubo: Temperature-dependent phase behaviour of monoolein-detergent mixtures

The lipidic cubic phase of monoolein has proved to be a matrix well suited to the production of three-dimensional crystals of membrane proteins. It consists of a single continuous bilayer, which is contorted in three-dimensional space and separates two distinct water channels. It has previously been proposed that on the addition of precipitants, membrane proteins embedded in the cubic phase migrate through the matrix to nucleation sites and that this process is dependent upon the stability of the lipidic cubic phase. Here, the effect of detergent type (C-8-C-12 glucosides, C-8-C-12 maltosides and C-7 thioglucoside) and concentration (1-3 x the critical micelle concentration; CMC) on cubic phase stability are reported in the form of the temperature-dependent phase behaviour (268-313 K) in 40% aqueous solution. The results are tabulated to show the best monoolein (MO)-detergent mixtures, mixing temperatures and crystallization temperatures identified. Monoolein-detergent mixtures suited for low-temperature in cubo crystallization of temperature-sensitive proteins are also reported for the first time. These mixtures can be prepared at low temperatures (mixed at less than or equal to 288 K) and remain stable at 277 K for a period of at least one month. They include MO- heptyl thioglucoside (1x and 3x CMC), MO-nonyl glucoside (3 x CMC), MO-octyl maltoside (3 x CMC), MO-nonyl maltoside (1 x CMC) and MO-decyl maltoside (1 x CMC)

High-throughput optimisation of light-driven microalgae biotechnologies

Microalgae biotechnologies are rapidly developing into new commercial settings. Several high value products already exist on the market, and systems development is focused on cost reduction to open up future economic opportunities for food, fuel and freshwater production. Light is a key environmental driver for photosynthesis and optimising light capture is therefore critical for low cost, high efficiency systems. Here a novel high-throughput screen that simulates fluctuating light regimes in mass cultures is presented. The data was used to model photosynthetic efficiency (PE, mol photon m) and chlorophyll fluorescence of two green algae, Chlamydomonas reinhardtii and Chlorella sp. Response surface methodology defined the effect of three key variables: density factor (D, 'culture density'), cycle time (t, 'mixing rate'), and maximum incident irradiance (I). Both species exhibited a large rise in PE with decreasing I and a minimal effect of t (between 3-20 s). However, the optimal D of 0.4 for Chlamydomonas and 0.8 for Chlorella suggested strong preferences for dilute and dense cultures respectively. Chlorella had a two-fold higher optimised PE than Chlamydomonas, despite its higher light sensitivity. These results demonstrate species-specific light preferences within the green algae clade. Our high-throughput screen enables rapid strain selection and process optimisation

Optimising light conditions increases recombinant protein production in Chlamydomonas reinhardtii chloroplasts

The green alga Chlamydomonas reinhardtii provides a platform for cheap, scalable and safe production of complex proteins. Despite the fact that chloroplast gene expression in photosynthetic organisms is tightly regulated by light, most expression studies have analysed chloroplast recombinant protein production under constant light. Here, the influence of light period and intensity on expression of green fluorescent protein (GFP) and a GFP-bacterial-lysin (PlyGBS) fusion protein was analysed. Protein yields were strongly influenced by the light period (6–24 h d), the light intensity (0–450 μE m s) and trophic condition. Heterotrophic conditions showed low yields of both recombinant proteins due to low growth rates, despite high protein accumulation per cell. Mixotrophic conditions exhibited the highest yields for GFP (4 mg·L·d) under constant light at 35 μE m s and GFP-PlyGBS (0.4 mg·L·d) under a light period of 15 h d and 35 μE m s. This is due to the high growth rates and cellular protein content. For GFP-PlyGBS the maximum increase in cellular protein accumulation was ~24-fold, and in total protein yield ~10-fold, in comparison to constant light conditions (~200 μE m s). The highest yields under photoautrophic conditions were obtained under a 9 h d light period. GFP yielded 1.2 mg·L·d and GFP-PlyGBS 0.42 mg·L·d. This represented a ~5-fold increase in cellular protein accumulation for GFP-PlyGBS in comparison to constant light conditions (~200 μE m s). Optimising light conditions to balance growth and protein expression can significantly enhance overall recombinant protein production in C. reinhardtii cultures

Trading Off Global Fuel Supply, CO2 Emissions and Sustainable Development

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

Surveying a Diverse Pool of Microalgae as a Bioresource for Future Biotechnological Applications

Jakob G, Wolf J, Bui TVL, et al. Surveying a Diverse Pool of Microalgae as a Bioresource for Future Biotechnological Applications. Journal of Petroleum & Environmental Biotechnology. 2013;4(05):153.Resource limitation is an escalating concern given human expansion and development. Algae are increasingly recognised as a promising bioresource and the range of cultivated species and their products is expanding. Compared to terrestrial crops, microalgae are very biodiverse and offer considerable versatility for a range of biotechnological applications including the production of animal feeds, fuels, high value products and waste-water treatment. Despite their versatility and capacity for high biomass productivity on non-arable land, attempts to harness microalgae for commercial benefit have been limited. This is in large part due to capital costs and energy inputs remaining high, the necessity of identifying ‘suitable’ land with proximal resource and infrastructure availability and the need for process and strain optimisation. Microalgae represent a relatively unexplored bioresource both for native and engineered strains. Success in this area requires (1) appropriate methods to source and isolate microalgae strains, (2) efficient maintenance of motherstocks, (3) rapid strain characterisation and correct matching of strains to applications, (4) ensuring productive and stable cultivation at scale, and (5) ongoing strain development (breeding, adaptation and engineering). This article illustrates a survey and isolation of over 150 local microalgae strains as a bioresource for ongoing strain development and biotechnological applications

Bacterial mechanosensitive channels: models for studying mechanosensory transduction

Significance: Sensations of touch and hearing are manifestations of mechanical contact and air pressure acting on touch receptors and hair cells of the inner ear, respectively. In bacteria, osmotic pressure exerts a significant mechanical force on their cellular membrane. Bacteria have evolved mechanosensitive (MS) channels to cope with excessive turgor pressure resulting from a hypo-osmotic shock. MS channel opening allows the expulsion of osmolytes and water, thereby restoring normal cellular turgor and preventing cell lysis. Recent Advances: As biological force-sensing systems, MS channels have been identified as the best examples of membrane proteins coupling molecular dynamics to cellular mechanics. The bacterial MS channel of large conductance (MscL) and MS channel of small conductance (MscS) have been subjected to extensive biophysical, biochemical, genetic, and structural analyses. These studies have established MscL and MscS as model systems for mechanosensory transduction. Critical Issues: In recent years, MS ion channels in mammalian cells have moved into focus of mechanotransduction research, accompanied by an increased awareness of the role they may play in the pathophysiology of diseases, including cardiac hypertrophy, muscular dystrophy, or Xerocytosis. Future Directions: A recent exciting development includes the molecular identification of Piezo proteins, which function as nonselective cation channels in mechanosensory transduction associated with senses of touch and pain. Since research on Piezo channels is very young, applying lessons learned from studies of bacterial MS channels to establishing the mechanism by which the Piezo channels are mechanically activated remains one of the future challenges toward a better understanding of the role that MS channels play in mechanobiology