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Theses and dissertations (Applied Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/6

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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.