Role of pH on antioxidants production by Spirulina (Arthrospira) platensis

Ability of an alkali-tolerant mutant strain of the microalga Chlorella sp. AT1 to capture carbon dioxide for increasing carbon dioxide utilization efficiency

An alkali-tolerant Chlorella sp. AT1 mutant strain was screened by NTG mutagenesis. The strain grew well in pH 6-11 media, and the optimal pH for growth was 10. The CO₂ utilization efficiencies of Chlorella sp. AT1 cultured with intermittent 10% CO₂ aeration for 10, 20 and 30min at 3-h intervals were approximately 80, 42 and 30%, respectively. In alkaline medium (pH=11) with intermittent 10% CO₂ aeration for 30min at 3-, 6- and 12-h intervals, the medium pH gradually changed to 10, and the biomass productivities of Chlorella sp. AT1 were 0.987, 0.848 and 0.710gL^-1d^-1, respectively. When Chlorella sp. AT1 was aerated with 10% CO₂ intermittently for 30min at 3-h intervals in semi-continuous cultivation for 21days, the biomass concentration and biomass productivity were 4.35gL^-1 and 0.726gL^-1d^-1, respectively. Our results show that CO₂ utilization efficiency can be markedly increased by intermittent CO₂ aeration and alkaline media as a CO₂-capturing strategy for alkali-tolerant microalga cultivation.

Growth promotion of Spirulina by steelmaking slag: application of solubility diagram to understand its mechanism

A solubility diagram was employed to understand growth promotion of Arthrospira (Spirulina) platensis by steelmaking slag (SMS). The growth promotion effect of 112 % of freshwater microalga A. platensis was obtained using 5 g/L SMS. However, metabolites, such as pigments, and protein content of A. platensis were not significantly affected. Several metals dissolved in Spirulina-Ogawa-Terui medium were detected by inductively coupled plasma atomic emission spectrometry just after the addition of SMS. The solubility diagram provides information on the chemical speciation of metal elements based on pH and concentration. It is a useful tool to understand the effect of metals on microalgal growth. The metal elements used to control microalgal growth are essential minerals but also act as a source of oxidative stress. Regarding the affecting mechanism of SMS, iron may be the primary element regulating microalgal growth via pathway involving reactive oxygen species, as revealed by superoxide dismutase assay.