title: Cultivation of Acidophilic AlgaeGaldieria sulphurariaandPseudochlorellasp. YKT1 in Media Derived from Acidic Hot Springs.
abstract: Microalgae possess a high potential for producing pigments, antioxidants, and lipophilic compounds for industrial applications. However, the cultivation of microalgae comes at a high cost. To reduce the cost, changes from a closed bioreactor to open pond system and from a synthetic medium to environmental or wastewater-based medium are being sought. However, the use of open pond systems is currently limited because of contamination by undesirable organisms. To overcome this issue, one strategy is to combine acidophilic algae and acidic drainage in which other organisms are unable to thrive. Here, we tested waters from sulfuric acidic hot springs (Tamagawa, pH 1.15 and Tsukahara, pH 1.14) in Japan for the cultivation of the red algaGaldieria sulphuraria074G and the green algaPseudochlorellasp. YKT1. Both of these spring waters are rich in phosphate (0.043 and 0.145 mM, respectively) compared to other environmental freshwater sources. Neither alga grew in the spring water but they grew very well when the waters were supplemented with an inorganic nitrogen source. The algal yields were ∼2.73 g dry weight/L forG. sulphurariaand ∼2.49 g dry weight/L forP. sp. YKT1, which were comparable to those in an autotrophic synthetic medium.P. sp. YKT1 grew in the spring waters supplemented either of NH4+, NO3-or urea, whileG. sulphurariagrew only when NH4+was supplemented. ForP. sp. YKT1, the spring water was adjusted to pH 2.0, while forG. sulphuraria, no pH adjustment was required. In both cases, no additional pH-buffering compound was required. The phycocyanin of the thermophilicG. sulphurariais known to be more thermostable than that from theSpirulina platensiscurrently used in phycocyanin production for commercial use. The phycocyanin content inG. sulphurariain the Tsukahara water supplemented with NH4+was 107.42 ± 1.81 μg/mg dry weight, which is comparable to the level inS. platensis(148.3 μg/mg dry weight).P. sp. YKT1 cells in the Tamagawa water supplemented with a nitrogen source formed a large amount of lipid droplets while maintaining cellular growth. These results indicate the potential of sulfuric hot spring waters for large-scale algal cultivation at a low cost.
authors.affiliation: Department of Cell Genetics, National Institute of GeneticsMishima, Japan; Japan Science and Technology Agency, Core Research for Evolutionary Science and TechnologyKawaguchi, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Hirooka
authors.affiliation: Department of Cell Genetics, National Institute of GeneticsMishima, Japan; Japan Science and Technology Agency, Core Research for Evolutionary Science and TechnologyKawaguchi, Japan; Department of Genetics, Graduate University for Advanced StudiesMishima, Japan.
authors.forename: Shin-Ya
authors.initials: SY
authors.lastname: Miyagishima
keywords: acidic hot spring water; biomass; lipid droplets; nitrogen source; phosphorus; phycocyanin