Fed-batch cultivation of Arthrospira (Spirulina) platensis: Potassium nitrate and ammonium chloride as simultaneous nitrogen sources

Abstract

Arthrospiraplatensis was cultivated in minitanks at 13 klux, using a mixture of KNO(3) and NH(4)Cl as nitrogen source. Fed-batch daily supply of NH(4)Cl at exponentially-increasing feeding rate allowed preventing ammonia toxicity and nitrogen deficiency, providing high maximum cell concentration (X(m)) and high-quality biomass (21.85 mg chlorophyll g cells(-1); 20.5% lipids; 49.8% proteins). A central composite design combined to response surface methodology was utilized to determine the relationships between responses (X(m), cell productivity and nitrogen-to-cell conversion factor) and independent variables (KNO(3) and NH(4)Cl concentrations). Under optimum conditions (15.5mM KNO(3); 14.1mM NH(4)Cl), X(m) was 4327 mg L(-1), a value almost coincident with that obtained with only 25.4mM KNO(3), but more than twice that obtained with 21.5mM NH(4)Cl. A 30%-reduction of culture medium cost can be estimated when compared to KNO(3)-batch runs, thus behaving as a cheap alternative for the commercial production of this cyanobacterium.

Arthrospira (Spirulina) platensis cultivation in tubular photobioreactor: Use of no-cost CO2 from ethanol fermentation

“…This being so, the lowest mean P x value (0.381 g L À1 d À1 ) was obtained applying the feeding protocol III, followed by protocols II (0.412 g L À1 d À1 ) and I (0.460 g L À1 d À1 ). This last value was higher than that obtained by Rodrigues et al [5] for the same strain in Table 3 Influence of the CO 2 from cylinder and ethanol fermentation on mean values of X m (maximum cell concentration), P x (cell productivity), Y X/N (nitrogen-to-cell conversion factor), lipid and protein contents and respectively p values obtained from A. platensis open tank, and this result confirms the better performance of tubular closed photobioreactors. Because of the same reason, i.e.…”

“…These last ones, in solution, release ammonium ions that, under alkaline conditions, become ammonia; therefore, they are toxic at high concentrations [8] and, for this reason, it is recommended that only the necessary amount to sustain cell growth should be daily supplied to cultivations by the so-called fed-batch process [11] rather than to be entirely added at the beginning of a batch run. In this work, the simultaneous addition of two nitrogen sources was suggested by the promising results reported by Rodrigues et al [5] in open photobioreactor and using another kind of nitrogen feeding protocol.…”

“…Nevertheless, urea and ammonium salts have been successfully used as alternative sources, and where chosen especially because of their low acquisition cost [5]. In addition, this cyanobacterium uptakes nitrogen directly in the form of ammonia [6] when either of these sources is present in the cultivation medium, whereas nitrates require an enzymatic reduction to nitrite and then ammonia, thus consuming energy [7].…”

“…For these reasons, in order to reduce ammonia off-gassing, it would be preferable to cultivate A. platensis in closed photobioreactors [9,10] by the fed-batch process, in which small amount of this nitrogen source is daily added to cultivations [11]. The addition of only one kind of nitrogen source has been reported up to now by many authors [8][9][10][11]; however, Rodrigues et al [5] have recently applied the combined use of two nitrogen sources, one nitrate and the other ammonia-based, to A. platensis cultivation in open tanks, thus ensuring better results in terms of maximum cell concentration and biomass quality when compared to cultivations carried out with only one nitrogen source.…”

Biomass production by Arthrospira platensis under different culture conditions

“…The nitrogen assimilated by cyanobacteria is used primarily for cell growth, and its excess is stored as organic compounds, such as proteins (Rodrigues et al, 2010). This possibility of storing nitrogen allows this group of microorganisms to grow with small amounts of mineral.…”