Effects of different nitrogen sources on cell growth of Haematococcus pluvialis at “green stage”

Abstract:

[Background] The unicellular green microalga Haematococcus pluvialis can synthesize astaxanthin which possess super antioxidant properties. H. pluvialis is an excellent microalga for commercial production of high-value natural astaxanthin. [Objective] The current study is to investigate effects of different nitrogen (N) sources on growth of H. pluvialis, with a view to develop the optimized N nutrition technology system for increasing biomass and astaxanthin yield of H. pluvialis. [Methods] Therefore, NaNO3 (NO3–-N) and NH4Cl (NH4+-N) were selected as two different N sources for the culture of H. pluvialis strain 797, respectively. At the same time, Hepes pH buffer was added into the media to keep pH stability. The measurements included pH changes of alga suspension culture media, cell growth rate at vegetative growth stage (“green stage”), chlorophyll content in cells and algal biomass. [Results] The results presented here demonstrated that the specific growth rate, biomass, chlorophyll a and b content in algal cells were higher in the NO3–-N media than in the NH4+-N media. Different N sources showed a significantly effect on pH in H. pluvialis suspension culture media. NH4Cl led to pH reduction in the culture media, whereas NaNO3 resulted in pH increase in the media. The addition of Hepes pH buffer successfully stabilized the pH in the culture media and thus, greatly promoted growth of H. pluvialis, with NH4Cl+Hepes showing much significant in this regard. It is the pH change in the algal suspension culture media caused by two different N sources that resulted in the obvious difference of H. pluvialis’s cell growth, biomass, and other features at “green stage” between the two N source treatments. [Conclusion] Addition of Hepes buffer into the media of either NO3–-N or NH4+-N could effectively stabilize the pH in microalga suspension culture media, and consequently, significantly promoted H. pluvialis’s cell growth and biomass accumulation at vegetative growth stage.

Key words:Haematococcus pluvialis, Nitrogen sources, pH value, NaNO3, NH4Cl