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A rapidly growing world population has highlighted the need to significantly increase food production in the context of a world with accelerating soil and water shortages as well as climatic stressors. This situation has generated new interest in the application of liquid seaweed extracts because of their potent plant growth-enhancing properties through metabolic benefits, triggering disease response pathways and increasing stress tolerance. The basis for these benefits is complex and poorly understood. Liquid seaweed extracts are complex and have been demonstrated to possess novel mechanisms for increasing crop productivity. The benefits of seaweed extracts to crops have previously been reviewed in the context of the northern hemisphere, but not in the context of Australia, its crops and unique stressors. This review considers the application of seaweed extracts in Australian agriculture by (i) introducing the history of the Australian liquid seaweed extract industry and (ii) focusing on evidence of Australian research related to seaweed extract composition, plant growth properties during plant establishment, pathogenic disease and new approaches to phenotyping the biological efficacy of seaweed extracts. This type of research is essential for future Australian agriculture to develop effective strategies for the use of liquid seaweed extracts.

Microalgae are promising candidates for recycling of carbon dioxide (CO 2 ) into renewable bioproducts. However, the low biomass concentration of current suspension culture systems leads to high water requirements, inefficient harvesting and high liquid transportation costs. Despite ongoing research, these still propose a challenge to the economic viability of microalgal cultivation. Microalgal biofilms provide an alternative approach to biomass production that could resolve these challenges by growing the cells attached to a surface, surrounded by a self-produced matrix of polymers. Microalgal biofilms have much higher biomass concentrations than suspension cultures, and the attached cells are easy to separate from the cultivation medium. However, cultivating microalgal biofilms requires the development of a purposefully designed cultivation system, especially due to interactions between cells and surface, persistent gradients in the biomass and the effects of flow, which play a critical role for biofilm productivity. A range of systems has been employed for the cultivation of microalgal biofilms, with biomass productivities of up to 60 grammes dry weight (g(DW)) m −2  day −1 (dry weight per ground area) outdoors and up to 80 g(DW) m −2  day −1 under laboratory conditions, respectively. However, there is considerable variation of reported results along with experimental conditions, which limits the capability for quantitative comparisons with other systems and hinders the identification of the drivers and variables that dictate microalgal biomass formation. Development of standard conditions and representative species would be required for closing this gap and for realising the full potential of microalgal biofilm cultivation as a viable process for industrial biomass production.

Green synthesis of iron nanoparticles using a soil microalga, Chlorococcum sp. MM11, and their application in chromium remediation have been investigated. Spherical-shaped nanoiron was synthesized by treating the exponentially growing culture of Chlorococcum sp. with 0.1 M iron chloride solution for 48 h and incubating it under shaking in the dark. The appearance of a yellowish brown colour indicated the biotransformation of bulk iron into nanoiron. Morphological characteristics of nanoparticles with transmission electron microscopy (TEM) and dynamic light scattering (DLS) confirmed the presence of spherical-shaped nanoiron ranging in size from 20 to 50 nm. TEM imaging also revealed the localization of nanoiron on the microalgal cell surface, inside as well as outside the cell. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the involvement of carbonyl and amine bonds from polysaccharides and glycoproteins present in the algal cell wall in the bioreduction as well as capping of nanoiron. Phyco-synthesized iron nanoparticles were tested for their efficiency in reducing Cr(VI), a toxic environmental pollutant. The results showed that nanoiron reduced 92 % of 4 mg L −1 Cr(VI) to Cr(III) instantaneously, while bulk iron reduced only 25 %. Thus, iron nanoparticles with high reactivity, greater stability and environmentally benign and economically viable properties can be synthesized using phyco-nanofactories like Chlorococcum sp. MM11.

Streptophytes are one of the major groups of the green lineage (Chloroplastida or Viridiplantae). During one billion years of evolution, streptophytes have radiated into an astounding diversity of uni- and multicellular green algae as well as land plants. Most divergent from land plants is a clade formed by Mesostigmatophyceae, Spirotaenia spp. and Chlorokybophyceae. All three lineages are species-poor and the Chlorokybophyceae consist of a single described species, Chlorokybus atmophyticus. In this study, we used phylogenomic analyses to shed light into the diversity within Chlorokybus using a sampling of isolates across its known distribution. We uncovered a consistent deep genetic structure within the Chlorokybus isolates, which prompted us to formally extend the Chlorokybophyceae by describing four new species. Gene expression differences among Chlorokybus species suggest certain constitutive variability that might influence their response to environmental factors. Failure to account for this diversity can hamper comparative genomic studies aiming to understand the evolution of stress response across streptophytes. Our data highlight that future studies on the evolution of plant form and function can tap into an unknown diversity at key deep branches of the streptophytes.

Several seaweed species have been successfully tested for their biofilter potential for integrated multi-trophic aquaculture (IMTA). In this study, Saccharina latissima bioremediation potential was assessed over 12 months with respect to the yield, phosphorous (P) and nitrogen (N) content and removal. The experiment took place at two commercial cultivation areas: in close proximity to a blue mussel and fish farm (IMTA) and at a reference site, both situated outside Horsens Fjord in Denmark. The maximum biomass yield over the first growing season was achieved in August (1.08 ± 0.09 and 1.51 ± 0.13 kg fresh weight (FW) m −1 ) and September (0.92 ± 0.18 and 1.49 ± 0.16 kg FW m −1 ). Yield was significantly higher at the IMTA compared to the reference site in August ( P  < 0.05). A second growing season did not improve biofiltration efficiency. The highest N and P removal was achieved in August and September. Again, the IMTA location showed better N and P removal compared with the reference site in August: 5.02–7.02 g N and 0.86–1.23 g P m −1 of cultivation line ( P  < 0.05). S. latissima shows potential for assimilation and removal of nutrients, particularly nitrogen. Seasonal variations of seaweed biofilter efficiency, condition, and potential applications should be taken into account when evaluating the best suited harvest time. For Horsens Fjord, our results showed that the harvest time should take place in August–September in order to achieve maximum biofiltration efficiency (including N and P in epiphytes). However, for human consumption, it is better to harvest in May when the seaweed is free of epiphytes.

Seaweeds are important sources of bioactive compounds with potential use in functional foods and nutraceutical products. This study aims to investigate the extraction efficiency of phlorotannins and antioxidant compounds of a South Australian brown seaweed Ecklonia radiata by enzymatic and microwave-assisted enzymatic extraction in order to evaluate their uses as potential functional food ingredients. A selected group of carbohydrases (Viscozyme, Celluclast, and Ultraflo) and proteases (Alcalase, Neutrase, and Flavourzyme) has been applied to improve the extraction efficiency, alone and intensified with microwave heating, using conventional acid-base and water extractions as controls. The antioxidant activities of the extracts were evaluated using both ferric reducing ability of plasma (FRAP) and oxygen radical absorbance capacity (ORAC) assays. Significantly higher yields in total phlorotannin content (TPC) and antioxidant activities of the extracts were achieved by enzymatic and microwave-assisted enzymatic extraction. Microwave-assisted Viscozyme extraction for 5 to 30 min was the most effective process with an extraction yield achieved of 52 %. The extract had a TPC of 4.4 g phloroglucinol equivalents (PGE).100 g −1 dry weight (DW) and antioxidant activities of 29.7 mmol FeSO 4 equivalents.100 g −1 DW and 740.1 μmol Trolox equivalents (TE).g −1 DW. In contrast, the conventional acidic extraction for 24 hours resulted in a TPC of 3.4 g PGE.100 g −1 DW and antioxidant activities of 21.1 mmol FeSO 4 equivalents.100 g −1 DW and 512.4 μmol TE.g −1 DW. Extracts of brown seaweed E. radiata have potential for use in value-added products for nutritional purposes, using the microwave-assisted enzymatic extraction techniques.

Increased global demands for food have raised interest for seaweed as a healthy and sustainable food source. At the same time, the large amounts of microplastic in the oceans have raised concern in relation to pollution of seafood including sea vegetables. The aim of this study was to examine sorption of fluorescent polystyrene (PS) microplastic particles to edible macroalga (seaweed) Fucus vesiculosus, and to investigate to what extent adsorbed PS particles could be washed off, using an industrial relevant method. PS microplastic particles (diameter of 20 μm) were used in a concentration of 2.65 mg L−1 (corresponding to 597 particles per mL) in filtrated seawater (50 mL) to treat F. vesiculosus distal tips in blue cap flasks (100 mL) placed in a rotary box for 2 h. Results showed sorption of PS microplastic particles to F. vesiculosus analysed by microscopy and a significant reduction of 94.5% by washing. These results were based on high microplastic concentrations, not comparable to natural conditions/concentrations. Nonetheless, this study provides methodological and mechanistic insights into procedures for investigating the sorption of microplastics to seaweed, for which there is currently no established standardised method.

In the last 20 years, there has been an increasing interest in using various seaweed extracts as prophylactic and/or therapeutic agents in aquaculture. Up until now, most studies on the direct antimicrobial effect of seaweeds have taken place in various parts of Asia, particularly in India. All groups of seaweeds exhibit significant antimicrobial properties against many infectious agents of fish and shrimp, but the genera that appear to exhibit a broader range of antibacterial properties are Asparagopsis spp. (red seaweed) and Sargassum spp. (brown seaweed). The activity can be affected by many factors and the method of extraction is one of the most important ones, as the extracts that are produced using organic solvents appear more efficient. In fish, almost all published information on bacterial pathogens comes from in vitro screenings, where extracts of different seaweed species were tested against many bacterial species. On the other hand, in shrimp, the studies have been focusing on the antimicrobial effects of seaweed extracts mainly against many Vibrio species. Regarding the viral pathogens, in fish, there is only one published study on fish viruses (IHNV and IPNV), while in shrimp there are many studies on WSSV. There are only two published studies on fish parasites ( Ichthyophonus hoferi and Neobendenia spp.) and no studies on pathogenic fish and shrimp fungi. Interestingly, there are no published studies on salmons and carps, the main fish species that are extensively farmed. When the antimicrobial properties were studied in vivo, the seaweed extracts were either incorporated directly in the feeds (dry or live) or added directly into the water in which the fish and shrimp were reared. In the last case, the water-soluble antimicrobial seaweed substances affected the communication between the bacterial pathogens, rather than their growth. The development of parasites was also affected. In addition, one study indicated that short-term immersion of shrimp in seaweed extracts appeared to have a therapeutic effect against Vibrio parahaemolyticus . On the other hand, incorporation of the extracts into the feeds appeared to be an effective delivery method for the prevention and treatment of different infectious diseases. Up until now, there are no complete studies on the pharmacodynamics and pharmacokinetics of seaweed extracts in fish or shrimp. However, the findings indicate that they can reduce the bacterial load within the tissues. Another issue that has not been examined yet is the applicability of using these extracts on a commercial scale. Currently, the increased extraction cost inhibits the extensive use of these extracts. Other methodologies, such the production of synthetic analogues with similar properties, may decrease the production cost. Based on the published studies, seaweed extracts exhibit promising antimicrobial properties, but further research is needed before the complete potential of seaweed extracts is assessed.

The girdle structure of Proschkinia (Bacillariophyta) is described in detail, showing the form of the unusual, channelled bands and how they link together. The significance and potential function of the more complex band structure is discussed in relation to its occurrence in other diatom genera and to other potential stabilising elements. Although some similarities in girdle structure are seen with the diatom genus Undatella, there is currently no evidence of a close phylogenetic relationship between these genera. Based on the current molecular data, Proschkinia is most closely related to the genus Fistulifera, with which it shares a distinctive valve feature, a fistula. Because of the traditional focus on valve morphology, far less is known of the girdle structure within the diatoms, despite its importance for maintaining cell integrity and allowing cell growth. The importance of studying the girdle structure as well as the valve morphology in diatoms in relation to their phylogeny and ecology is stressed.

Since the discovery of the type species Chlorella vulgaris in 1890 by Beijerinck, a large number of coccoid green algae have been isolated and assigned to the genus Chlorella Beij. primarily on the basis of morphologic similarities. Based on literature review and a survey of curators of algae culture collections, our study aims to review and organize the taxonomy of Chlorella to correlate with the commercial names currently in use in Europe for food products. In particular, an inventory of the specific species or strains of Chlorella traditionally consumed in Europe is made. Chlorella pyrenoidosa , C. vulgaris , and Chlorella luteoviridis are the three species of Chlorella listed in the Novel Food Catalogue as having been on the market and consumed before 15 May 1997, and hence not subject to the Novel Food Regulation. However, as a consequence of revisions of the systematics of Chlorella , it appears that these names are not always in conformance with the current taxonomy. This is the case for the taxon C. luteoviridis which is no longer valid as it has been renamed as Heterochlorella luteoviridis . Furthermore, the review of revisions operated in algal culture collections shows that some strains had been incorrectly identified as C. pyrenoidosa or C. vulgaris . This result suggests that other species, which were known as C. pyrenoidosa or C. vulgaris at that time, might have been consumed in Europe before 1997. Therefore, the list of Chlorella species not subject to the Novel Food Regulation could possibly be extended to additional species not only strictly related to “true” Chlorella genus.