Browsing by Author "Michael, A."

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    Antioxidants activity of the cyanobacterium, Arthrospira (Spirulina) fusiformis cultivated in a low-cost medium
    (ACADEMIC JOURNAL, 2018-08) Michael, A.; Kyewalyanga, M.S.; Mtolera, M.S.; Lugomela, C.V.
    Spirulina species are known to have a good nutritional profile and antioxidant properties against reactive oxygen species. However, little is known about the antioxidant contents and the scavenging ability of Arthrospira fusiformis, cultivated under various conditions. This study aimed at evaluating the content of antioxidants (total phenols, total flavonoids, β-carotene, and lycopene) and the activity of A.fusiformis produced using low-cost culture (LCMA) and standard culture (Zarrouk) media. The results revealed that A. fusiformis is rich in antioxidants and it possesses high scavenging and chelating activities. Interestingly, the LCMA was superior over the Zarrouk medium as it resulted in spirulina with a higher amount of antioxidants and lower EC50 values. In this context, production of natural antioxidants can be maximized through the use of cost-saving, inorganic culture medium.
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    Biomass and nutritive value of Spirulina (Arthrospira fusiformis) cultivated in a cost-effective medium
    (SPRINGER NATURE, 2019-12-23) Michael, A.; Kyewalyanga, M.S.; Lugomela, C.V.
    Introduction Cultivation of spirulina at commercial-scales relies on analytical grade–based media, which are expensive and so are the product. Purpose This study assessed the biomass, proximate composition, and other useful compounds in Spirulina (Arthrospira fusiformis) produced with a cost-effective culture medium (LCMA), and the results were compared with those from a standard Zarrouk medium–grown spirulina. Methods The LCMA medium was formulated by using a commercial NPK10-20-20 fertilizer as a source of the three major nutrients for spirulina growth, and other three ingredients from Zarrouk medium. The experiment was conducted for 28 days in the glass aquaria under indoor conditions. Standard analytical methods were applied for the determination of proximate composition, chlorophyll, minerals, and vitamins in the spirulina biomass. Result The LCMA medium showed the best growth conditions by accumulating higher chlorophyll content (0.99 ± 0.02%) and dry weight (0.75 ± 0.01 g/100 ml) as well as attaining higher optical density (2.06 at day 15) earlier than the Zarrouk medium. The results of the proximate analysis for spirulina cultured in the LCMA medium were of good quality, with the protein contributing more than 50% of its dry matter. It was further noticed that the LCMA was an ideal medium for optimization of vitamins and some minerals since it recorded a significant amount of most of the analyzed vitamins together with the minerals sodium and potassium compared with the Zarrouk medium. Conclusion It is suggested that LCMA medium could be used as the alternative and cheap medium for maximization of biomass and production of useful biochemical compounds in spirulina species.
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    Evidence of localised upwelling in Pemba Channel (Tanzania) during the southeast monsoon
    (ELSEVIER, 2020-12-07) Painter, S.C.; Sekadende, B.; Michael, A.; Noyon, M.; Shayo, S.; Godfrey, B.; Mwadini, M.; Kyewalyanga, M.
    Oceanographic and biogeochemical observations collected in Pemba Channel, a deep-water (800 m) channel separating Pemba Island from mainland Tanzania, during the South East monsoon indicate the presence of active upwelling along the western edge of Pemba Island. Surface salinity values, nutrient concentrations and the presence of coccolithophore species previously reported from the mid to lower euphotic zone all suggest up welling from at least 80–100 m depth. The surface waters of the channel were characterised with low NO3 − :PO4 3− (0.68:1) and NO3 − :Si (0.04:1) ratios far below the Brzezinski-Redfield ratio indicating the presence of N-limitation and the possibility that these waters may be susceptible to anthropogenic N inputs. Surface NO3 − concentrations averaged 0.09 ± 0.10 μmol L− 1 but increased to 0.5 μmol L− 1 in the centre of upwelling where coincidentally both integrated nutrient concentrations and surface POC/PON pools were approximately 2-fold higher than the channel average. Despite its significance for local productivity upwelling is tentatively estimated, via stoichio metric assumptions, to enhance local productivity by only 20%. The modest productivity response to upwelling may be explained by picoplankton (0.2–2 μm) dominance of the phytoplankton community with this size-class representing ~80% of total chlorophyll-a. Nevertheless, important spatial variability was identified in larger size fractions and supported by taxonomic analyses with indications that the distribution of Chaetoceros spp. alone may be particularly relevant for understanding the variability in larger (>20 μm) chlorophyll-a size fractions. The location of upwelling has previously been shown to host large concentrations of small pelagic fish thus management of this regionally important resource would benefit from additional investigation of the underlying physical mechanism driving upwelling and subsequently how trophic interactions and ecosystem productivity are influenced.