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    Cyanobacteria-microalgae consortia as bio- inoculants for enhancing soil fertility and plant growth
    (2024-05) Jose, Shisy; Bux, Faizal; Kumari, Sheena; Renuka, Nirmal; Ratha, Sachitra Kumar
    Modern agriculture that heavily utilizes synthetic fertilizers has raised significant environmental concerns worldwide. Microalgae-based bio-inoculants have become a more viable and eco- friendly option to reduce the reliance on chemical fertilizers for improving soil fertility and plant growth in agronomic practices. Indigenous microalgal species can colonize and thrive well under local conditions, making them well-suited for use as bio-inoculants. Additionally, it appears that using microalgal consortia of green microalgae and nitrogen (N)-fixing cyanobacteria could be beneficial because the green microalgae can supply carbon (C), the cyanobacteria can fix C and N in the soil. They both can produce agriculturally beneficial metabolites and improve soil nutrient availability. This synergistic relationship could enhance the overall effectiveness of bio- inoculants and promote sustainable agriculture practices. In this study, thirteen microalgal strains were isolated from agricultural fields of Durban, KwaZulu Natal, South Africa. Two N-fixing cyanobacteria (Nostoc sp. and Calothrix sp.) and two green microalgae (Desmodesmus armatus and Chlorella sp.) strains were selected and analyzed for metabolites of agricultural significance for the development of suitable microalgal consortia under N-deficient conditions. The amount of indole acetic acid (IAA) in biomass extracts from cyanobacteria (Calothrix sp. (2.54 ng g−1) and Nostoc sp. (1.52 ng g−1)) was significantly higher than in extracts from green microalgae (Chlorella sp. (0.32 ng g−1) and Desmodesmus armatus (0.20 ng g−1)). A completely randomized design was used to develop and evaluate eight microalgal consortia on a N-deficient medium with the selected microalgal strains. A significant improvement in biomass productivity, indole acetic acid production, nutrients viz C, N, phosphorus (P), potassium (K), calcium (Ca), copper (Cu), iron (Fe), and manganese (Mn) was observed in the selected consortium compared to the individual isolates. The microalgal consortium was further analyzed for biostimulant properties using seed germination assay in chili seeds. A significant increase in seedling length and leaf number was observed in seeds treated with biomass extracts of consortium compared to the control. The pot culture study also supported the effect of microalgal bio-inoculant on soil fertility, chili plant growth and native soil microbiomes. Soil enzyme activity increased significantly (p < 0.05) with microalgal treatments, with soil dehydrogenase activity (DHA), organic carbon (OC), soil chlorophyll (Chl), total polysaccharides (TP) and nutrients such as C, N, P, K and Mn being more enriched at 100 % and 50 % treatment applications in comparison to control (Cnt). Growth responses in terms of shoot and root (fresh and dry weight), root length and leaf number were significantly high in 50 % microalgal treatments (Al(50 %)+CF(50 %)) when compared to Cnt. With different soil nutrient parameters and microbiome (bacterial and fungal) indicators, we could successfully predict higher soil fertility and plant growth responses to microalgal inoculations. Results using 16SrRNA and ITS amplicon sequencing suggested that microalgal bio-inoculation improved the diversity and composition of native soil microbiome, leading to an increase in soil fertility, plant growth and yield. Further, shotgun metagenomics has confirmed a higher enzymatic activity involved in C, N, and P metabolisms in 50 % and 100 % microalgal treatment compared to the control. Potential shifts in microbial taxa and functional genes indicated that microalgal bio-inoculant was a major driver of microbial metabolic change. The findings from the study suggested that microalgal bio-inoculation improved the diversity and composition of native soil microbiomes, leading to an increase in soil fertility, plant growth, and yield in chili plants.
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    Evaluation of toxicity and biochemical characterisation of a microalgal diatom
    (2023-05) Beekrum, Lamees; Amonsou, Eric Oscar; Odhav, Bharti; Lalloo, Raj
    One ofthe critical challengesthat we face in the 21st century isthe need to feed an ever-increasing human population with increasingly limited natural resources. Microalgae have emerged as a potentialsolution for global food security as a sustainable biological food source for humans due to their nutrient-rich composition, particularly rich protein and bioactive compoundsthat provide potential benefits for human health. By establishing microalgae as a new food platform, we can increase the supply of these essential productsto address global demandsin a more efficient and environmentally sustainable way. These under-exploited organisms have been consumed in the human diet for thousands of years. Microalgae cultivation does not compete with land and resources required for traditional crops and has a superior yield compared to terrestrial crops. Diatoms are a major group of microalgae in the phytoplankton community and have the potential to be engineered into cell factoriesforthe sustainable production of bioactive compoundsin food and nutraceutical industries. This study aimed to characterise a rapidly growing marine diatom in terms of its toxicity and biochemical profile. This was done by evaluating the safety profile and biochemical composition, characterising the soluble protein, and investigating the carbohydrate profile with specific emphasis of β-glucan and its effect of cardioprotective properties on ferric-induced oxidative cardiac injury in a rat model. Based on Basic Local Alignment Search Tool (BLAST) analysis, the strain showed the closest similarity to Amphora sp. (JF834543.1) with 99.5% and istherefore represented as Amphora sp., accession number MW721231. The bacterial reverse mutation assay found no evidence of mutagenicity on the methanolic, aqueous, and hexane extracts of Amphora sp. and was found to exert low levels of cytotoxicity against Peripheral Blood Mononuclear Cells (PBMC). A 28- day acute oral toxicity assessment on male Wistar rats showed an absence of adverse effects and mortality in the rats. The biomass exhibited a low lipid profile, modest protein content, notable amino acid content, and excellent carbohydrate and mineral content. Results of this study for antioxidant assays displayed low to moderate activities. Protein extracted using three-phase partitioning (TPP) treatment showed that the protein concentration and total amino acid content were substantially higher in the protein-enriched biomass extract when compared to the dried biomass. The solubility of the protein-enriched biomass extract increased with the increase in pH within the range of pH 2 to pH 12. The biomass consisted of a simple monosaccharide profile comprising glucose, rhamnose, and mannose, and a β-glucan content of approximately 9%. The cardioprotective properties ofthe β-glucan extract on ferric-induced oxidative cardiac injury did not improve the glutathione (GSH) level significantly, it led to increased superoxide dismutase (SOD) and catalase activities, while depleting malondialdehyde (MDA), NO (nitric oxide), low-density lipoprotein cholesterol levels, and simultaneously elevating triglycerides and high-density lipoprotein (LDL) cholesterol levels. GC-MS analysis revealed a complete depletion of the lipid metabolites. Our results advocate the protective capabilities of the β-glucan extract against ferric-induced oxidative cardiac injury as portrayed by its ability to stall oxidative stress and modulate cardiac lipid metabolism while inhibiting the acetylcholinesterase and lipase activities. These results display that the β-glucan extract could be utilized as an alternative for the development of nutraceuticals for maintaining cardiac health. The diversity of food bioactive molecules obtained from microalgae makes these microorganisms a bioresource with full potential of exploitation in the food industry. The richness of compounds in microalgae can contribute to develop an algal-based food industry, focusing on producing and utilizing microalgae for innovative functional food products. Overall, this study demonstrated the potential utilization of the diatom, Amphora sp. as a potential ingredient and nutraceutical in foods.
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    Trends and novel strategies for enhancing lipid accumulation and quality in microalgae
    (Elsevier, 2016) Singh, Poonam; Kumari, Sheena K.; Guldhe, Abhishek; Rawat, Ismail; Misra, Rohit; Bux, Faizal
    In order to realize the potential of microalgal biodiesel there is a need for substantial impetus involving interventions to radically improve lipid yields upstream. Nutrient stress and alteration to cultivation conditions are commonly used lipid enhancement strategies in microalgae. The main bottleneck of applying conventional strategies is their scalability as some of these strategies incur additional cost and energy. Novel lipid enhancement strategies have emerged to research forefront to overcome these challenges. In this review, the latest trends in microalgal lipid enhancement strategies, possible solutions and future directions are critically discussed. Advanced strategies such as combined nutrient and culti-vation condition stress, microalgae–bacteria interactions, use of phytohormones EDTA and chemical additives, improving light conditions using LED, dyes and paints, and gene expression analysis are described. Molecular approaches such as metabolic and genetic engineering are emerging as the potential lipid enhancing strategies. Recent advancements in gene expression studies, genetic and metabolic engineering have shown promising results in enhancing lipid productivity in microalgae; however environmental risk and long term viability are still major challenges.
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    Biodiesel from microalgae: A critical evaluation from laboratory to large scale production
    (Elsevier, 2013) Rawat, Ismail; Ranjith Kumar, R.; Mutanda, Taurai; Bux, Faizal
    The economically significant production of carbon-neutral biodiesel from microalgae has been hailed as the ultimate alternative to depleting resources of petro-diesel due to its high cellular concentration of lip-ids, resources and economic sustainability and overall potential advantages over other sources of biofu-els. Pertinent questions however need to be answered on the commercial viability of large scale production of biodiesel from microalgae. Vital steps need to be critically analysed at each stage. Isolation of microalgae should be based on the question of whether marine or freshwater microalgae, cultures from collections or indigenous wild types are best suited for large scale production. Furthermore, the determination of initial sampling points play a pivotal role in the determination of strain selection as well as strain viability. The screening process should identify, purify and select lipid producing strains. Are natural strains or stressed strains higher in lipid productivity? The synergistic interactions that occur nat-urally between algae and other microorganisms cannot be ignored. A lot of literature is available on the downstream processing of microalgae but a few reports are available on the upstream processing of mic-roalgae for biomass and lipid production for biodiesel production. We present in this review an empirical and critical analysis on the potential of translating research findings from laboratory scale trials to full scale application. The move from laboratory to large scale microalgal cultivation requires careful plan-ning. It is imperative to do extensive pre-pilot demonstration trials and formulate a suitable trajectory for possible data extrapolation for large scale experimental designs. The pros and cons of the two widely used methods for growing microalgae by photobioreactors or open raceway ponds are discussed in detail. In addition, current methods for biomass harvesting and lipid extraction are critically evaluated. This would be novel approach to economical biodiesel production from microalgae in the near future. Glob-ally, microalgae are largest biomass producers having higher neutral lipid content outcompeting terres-trial plants for biofuel production. However, the viscosities of microalgal oils are usually higher than that of petroleum diesel.
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    Improving the feasibility of producing biofuels from microalgae using wastewater
    (Taylor and Francis, 2013-10-08) Rawat, Ismail; Bhola, Virthie; Ranjith Kumar, R.
    Biofuels have received much attention recently owing to energy consumption and environmental concerns. Despite many of the technologies being technically feasible, the processes are often too costly to be commercially viable. The major stumbling block to full-scale production of algal biofuels is the cost of upstream and downstream processes and environmental impacts such as water footprint and indirect greenhouse gas emissions from chemical nutrient production. The technoeconomics of biofuels production from microalgae is currently unfeasible due to the cost of inputs and productivities achieved. The use of a biorefinery approach sees the production costs reduced greatly due to utilization of waste streams for cultivation and the generation of several potential energy sources and value-added products while offering environmental protection. The use of wastewater as a production media, coupled with CO2 sequestration from flue gas greatly reduces the microalgal cultivation costs. Conversion of residual biomass and by-products, such as glycerol, for fuel production using an integrated approach potentially holds the key to near future commercial implementation of biofuels production.