Tecticornia sp. (Samphire)-A Promising Underutilized Australian Indigenous Edible Halophyte.

Salinization is gradually increasing over cropping soils and is challenging Governments in many countries, including Australia. There has been a high demand for utilizing arid and semi-arid land for sustainable food production. Currently, the main crops and forage plants are salt sensitive, while halophytes can tolerate a wide range of salinities. Samphire is an Australian indigenous edible halophyte and belongs to the genus Tecticornia. It is an underutilized, succulent plant growing on arid or semi-arid land. Most samphire species have a long history of use as food, but also as non-food (fodder and medicine), among indigenous communities in Australia, while scientific information is limited on their nutritional composition and potential bioactivity. The present study reports, for the first time, the nutritional composition, bioactive compounds (phytochemicals) and antioxidant capacity of six Australian grown samphire from different locations. The results showed that celosianin II and isocelosianin II could be identified as the predominant betalains (phytochemicals) in pigmented samphire species. Proximates and fiber varied significantly (p < 0.05) between the samphire species with a highest value of fiber of 46.8 g/100 g dry weight (DW). Furthermore, samphire could be identified as a valuable source of essential minerals and trace elements, such as iron (41.5 mg/100 g DW), magnesium (1.2 g/100 g DW) and sodium (16.7 g/100 g DW). The fatty acid profile, mainly palmitic, stearic, oleic, linoleic and α-linolenic acid, was similar among the studied species. Total phenolic content and DPPH-radical scavenging capacity were different (p < 0.05) between the six samphire samples. These initial results are very promising and indicate that Australian grown samphire may have the potential to be utilized as a functional food ingredient.

Development of High-Level Omega-3 Eicosapentaenoic Acid (EPA) Production from Phaeodactylum tricornutum.

Phaeodactylum tricornutum is a lipid-rich marine diatom that contains a high level of omega-3 polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA). In an effort to reduce costs for large-scale cultivation of this microalga, this study first established a New BBM medium (0.3 x strength BBM with only 3% of the initial phosphate level) to replace the traditional F/2 medium. Phaeodactylum tricornutum could grow in extremely low phosphate concentrations (25 µM), without compromising the EPA content. In the presence of sea salts, silicate addition was not necessary for high rate growth, high EPA content, or lipid accumulation in this species. Using urea as the sole nitrogen source tended to increase EPA contents per dry biomass (by 24.7%) while not affecting growth performance. The use of sea salts, rather than just sodium chloride, led to significantly improved biomass yields (20% increase) and EPA contents of total fatty acid (46-52% increase), most likely because it supplied sufficient essential elements such as magnesium. A salinity level of 35 led to significantly higher biomass yields compared with 20, but salinity had no significant influence on EPA content. EPA became the dominant fatty acid with average levels of 51.8% of total fatty acids during the exponential growth phase at 20 ppt in New BBM medium with sea salts.

Comprehensive Utilization of Marine Microalgae for Enhanced Co-Production of Multiple Compounds.

Marine microalgae are regarded as potential feedstock because of their multiple valuable compounds, including lipids, pigments, carbohydrates, and proteins. Some of these compounds exhibit attractive bioactivities, such as carotenoids, ω-3 polyunsaturated fatty acids, polysaccharides, and peptides. However, the production cost of bioactive compounds is quite high, due to the low contents in marine microalgae. Comprehensive utilization of marine microalgae for multiple compounds production instead of the sole product can be an efficient way to increase the economic feasibility of bioactive compounds production and improve the production efficiency. This paper discusses the metabolic network of marine microalgal compounds, and indicates their interaction in biosynthesis pathways. Furthermore, potential applications of co-production of multiple compounds under various cultivation conditions by shifting metabolic flux are discussed, and cultivation strategies based on environmental and/or nutrient conditions are proposed to improve the co-production. Moreover, biorefinery techniques for the integral use of microalgal biomass are summarized. These techniques include the co-extraction of multiple bioactive compounds from marine microalgae by conventional methods, super/subcritical fluids, and ionic liquids, as well as direct utilization and biochemical or thermochemical conversion of microalgal residues. Overall, this review sheds light on the potential of the comprehensive utilization of marine microalgae for improving bioeconomy in practical industrial application.

Effective Harvesting of Nannochloropsis Microalgae Using Mushroom Chitosan: A Pilot-Scale Study.

For efficient downstream processing, harvesting remains as one of the challenges in producing Nannochloropsis biomass, a microalga with high-value omega-3 oils. Flocculation is an effective, low-energy, low-cost method to harvest microalgae. Chitosan has been shown to be an effective food-grade flocculant; however, commercial chitosan is sourced from crustaceans, which has disadvantages including concerns over heavy-metal contamination. Thus, this study tests the flocculation potential of mushroom chitosan. Our results indicate a 13% yield of chitosan from mushroom. The identity of the prepared chitosan was confirmed by Fourier-transform infrared (FTIR) spectroscopy. Furthermore, results show that mushroom chitosan can be an alternative flocculant with >95% flocculation efficiency when tested in 100-mL jar and 200-L vertical column photobioreactor. Applications in a 2000-L raceway pond demonstrated that thorough mixing of mushroom chitosan with the algal culture is required to achieve efficient flocculation. With proper mixing, mushroom chitosan can be used to produce food-grade Nannochloropsis biomass suitable for the production of vegan omega-3 oils as a fish oil alternative.

Growth-promoting bacteria double eicosapentaenoic acid yield in microalgae.

High-yielding microalgae present an important commodity to sustainably satisfy burgeoning food, feed and biofuel demands. Because algae-associated bacteria can significantly enhance or reduce yields, we isolated, identified and selected highly-effective "probiotic" bacterial strains associated with Nannochloropsis oceanica, a high-yielding microalga rich in eicosapentaenoic acid (EPA). Xenic algae growth was significantly enhanced by co-cultivation with ten isolated bacteria that improved culture density and biomass by 2.2- and 1.56-fold, respectively (1.39 × 108 cells mL-1; 0.82 g L-1). EPA contents increased up to 2.25-fold (to 39.68% of total fatty acids). Added probiotic bacteria possessed multiple growth-stimulating characteristics, including atmospheric nitrogen fixation, growth hormone production and phosphorous solubilization. Core N. oceanica-dominant bacterial microbiomes at different cultivation scales included Sphingobacteria, Flavobacteria (Bacteroidetes), and α, γ-Proteobacteria, and added probiotic bacteria could be maintained. We conclude that the supplementation with probiotic algae-associated bacteria can significantly enhance biomass and EPA production of N. oceanica.

Evaluation of microalgae and cyanobacteria as potential sources of antimicrobial compounds.

In recent decades, marine microorganisms have become known for their ability to produce a wide variety of secondary bioactive metabolites. Several compounds have been isolated from marine microorganisms for the development of novel bioactives for the food and pharmaceutical industries. In this study, a number of microalgae were evaluated for their antimicrobial activity against gram-positive and gram-negative bacteria, including food and plant pathogens, using various extraction techniques and antimicrobial assays. Disc diffusion and spot-on-lawn assays were conducted to confirm the antimicrobial activity. To measure the potency of the extracts, minimum inhibition concentrations (MIultCs) were measured. Three microalgae, namely Isochrysis galbana, Scenedesmus sp. NT8c, and Chlorella sp. FN1, showed strong inhibitory activity preferentially against gram-positive bacteria. These microalgal species were then selected for further purification and analysis, leading to compound identification. By using a mixture of different chromatography techniques gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) and ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS), we were able to separate and identify the dominant compounds that are responsible for the inhibitory activity. Additionally, nuclear magnetic resonance (NMR) was used to confirm the presence of these compounds. The dominant compounds that were identified and purified in the extracts are linoleic acid, oleic acid, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). These compounds are the potential candidates that inhibit the growth of gram-positive bacteria. This indicates the potential use of microalgae and their antimicrobial compounds as biocontrol agents against food and plant pathogens.

Efficient Harvesting of Nannochloropsis Microalgae via Optimized Chitosan-Mediated Flocculation.

Food-grade rather than synthetic or chemical flocculants are needed for microalgae harvesting by settling, if used for food products. Chitosan is effective in harvesting freshwater microalgae, but it is expensive and typically not suitable for marine microalgae like Nannochloropsis. To minimize costs for food-grade flocculation, a number of potentially important parameters are considered, including chitosan solubility and optimized chitosan-mediated flocculation of Nannochloropsis sp. BR2 by a five-factor central composite design experiment. Results show that an optical density (440 nm) of 2 (0.23 g dry weight L-1), initial pH of 6, final pH of 10, and 22 ppm chitosan with a viscosity of 1808 cP provide optimum flocculation efficiency, which is predicted to be in the range of 97.01% to 99.93%. These predictions are verified on 4.5 and 8 L Nannochloropsis sp. BR2 cultures.

Soil bacterial diffusible and volatile organic compounds inhibit Phytophthora capsici and promote plant growth.

Biotic interactions through diffusible and volatile organic compounds (VOCs) are frequent in nature. Soil bacteria are well-known producers of a wide range of volatile compounds (both organic and inorganic) with various biologically relevant activities. Since the last decade, they have been identified as natural biocontrol agents. Volatiles are airborne chemicals, which when released by bacteria, can trigger plant responses such as defence and growth promotion. In this study, we tested whether diffusible and volatile organic compounds (VOCs) produced by soil bacterial isolates exert anti-oomycete and plant growth-promoting effects. We also investigated the effects of inoculation with VOC-producing bacteria on the growth and development of Capsicum annuum and Arabidopsis thaliana seedlings. Our results demonstrate that organic VOCs emitted by bacterial antagonists negatively influence mycelial growth of the soil-borne phytopathogenic oomycete Phytophthora capsici by 35% in vitro. The bacteria showed plant growth promoting effects by stimulating biomass production, primary root growth and root hair development. Additionally, we provide evidence to suggest that these activities were deployed by the emission of either diffusible organic compounds or VOCs. Bacterial VOC profiles were obtained through solid phase microextraction (SPME) and analysis by gas chromatography coupled with mass spectrometry (GC-MS). This elucidated the main volatiles emitted by the isolates, which covered a wide range of aldehydes, alcohols, esters, carboxylic acids, and ketones. Collectively, twenty-five VOCs were identified to be produced by three bacteria; some being species-specific. Our data show that bacterial volatiles inhibits P. capsici in vitro and modulate both plant growth promotion and root system development. These results confirm the significance of soil bacteria and highlights that ways of harnessing them to improve plant growth, and as a biocontrol agent for soil-borne oomycetes through their volatile emissions deserve further investigation.

LED power efficiency of biomass, fatty acid, and carotenoid production in Nannochloropsis microalgae.

The microalga Nannochloropsis produces high-value omega-3-rich fatty acids and carotenoids. In this study the effects of light intensity and wavelength on biomass, fatty acid, and carotenoid production with respect to light output efficiency were investigated. Similar biomass and fatty acid yields were obtained at high light intensity (150 µmol m-2 s-1) LEDs on day 7 and low light intensity (50 µmol m-2 s-1) LEDs on day 11 during cultivation, but the power efficiencies of biomass and fatty acid (specifically eicosapentaenoic acid) production were higher for low light intensity. Interestingly, low light intensity enhanced both, carotenoid power efficiency of carotenoid biosynthesis and yield. White LEDs were neither advantageous for biomass and fatty acid yields, nor the power efficiency of biomass, fatty acid, and carotenoid production. Noticeably, red LED resulted in the highest biomass and fatty acid power efficiency, suggesting that LEDs can be fine-tuned to grow Nannochloropsis algae more energy-efficiently.

Gene expression profiling of astaxanthin and fatty acid pathways in Haematococcus pluvialis in response to different LED lighting conditions.

Haematococcus pluvialis is a green microalga of major interest to industry based on its ability to produce large amounts of astaxanthin. Biosynthesis of astaxanthin and its mono- and di-esters was significantly stimulated under 150 µmol m-2 s-1 of white LED (W-150) compared with lower light intensities, but the highest astaxanthin amounts were produced under 70 µmol m-2 s-1 of blue LED (B-70). Transcripts of astaxanthin biosynthesis genes psy, crtO, and bkt2 were upregulated under W-150, while psy, lcy, crtO, and crtR-B were upregulated by B-70. Total fatty acid content and biosynthesis genes fata and all dgat genes were induced under W-150, while C18:3n6 biosynthesis and dgat2a expression were specifically stimulated by B-70 which was correlated to astaxanthin ester biosynthesis. Nitrogen starvation, various LEDs and the identified upregulated genes may provide useful tools for future metabolic engineering to significantly increase free astaxanthin, its esters and fatty acid precursors in H. pluvialis.

A biorefinery for Nannochloropsis: Induction, harvesting, and extraction of EPA-rich oil and high-value protein.

Microalgae have been studied as biofactories for almost four decades. Yet, even until today, many aspects of microalgae farming and processing are still considered exploratory because of the uniqueness of each microalgal species. Thus, it is important to develop the entire process of microalgae farming: from culturing to harvesting, and down to extracting the desired high-value products. Based on its rapid growth and high oil productivities, Nannochloropsis sp. is of particular interest to many industries for the production of high-value oil containing omega-3 fatty acids, specifically eicosapentaenoic acid (EPA), but also several other products. This review compares the various techniques for induction, harvesting, and extraction of EPA-rich oil and high-value protein explored by academia and industry to develop a multi-product Nannochloropsis biorefinery. Knowledge gaps and opportunities are discussed for culturing and inducing fatty acid biosynthesis, biomass harvesting, and extracting EPA-rich oil and high-value protein from the biomass of Nannochloropsis sp.