Enhanced productivity of a lutein-enriched novel acidophile microalgae grown on urea

Abstract

Coccomyxa acidophila is an extremophile eukaryotic microalga isolated from the Tinto River mining area in Huelva, Spain. C. acidophila accumulates relevant amounts of b- carotene and lutein, well-known carotenoids with many biotechnological applications, especially in food and health-related industries. The acid culture medium (pH <2.5) that prevents outdoor cultivation from non-desired microorganisms growth is one of the main advantages of acidophile microalgae production. On the opposite, acidophile microalgae growth rates are usually very low if compared to common microalgae growth rates. In this work, we show that phototrophic cultivation on urea efficiently enhances growth and productivity of an acidophile microalga up to typical values for common microalgae, therefore approaching acidophile algal production towards suitable conditions for feasible outdoor production. Algal productivity and potential for carotenoid accumulation were analyzed as a function of the nitrogen source supplied. Several nitrogen conditions were assayed: nitrogen starvation, nitrate and/or nitrite, ammonia and urea. Among them, urea clearly led to the best cell growth (~ 4 ´ 108 cells/mL at the end of log phase). Ammonium led to the maximum chlorophyll and carotenoid content per volume unit (220 mg/mL and 35 mg/mL, respectively). When urea was added as only C and N source, no significant differences in growth rates were found between batch cultures grown with urea and those grown on nitrate as sole nitrogen source [0.12 ± 0.02 d -1 (cellular data, 1st experiment) or 0.44 ± 0.02 d -1 (chlorophyll data, 2nd experiment)]. Lutein accumulated up to 3.55 mg/g in those photoautotrophic cultures grown on urea. In addition, algal growth in a shaded culture revealed the first evidence for an active xanthophylls cycle operative in acidophile microalgae.