Efficient open cultivation of cyanidialean red algae in acidified seawater

Shunsuke Hirooka,Haruko Kuroiwa,Mio Ohnuma,Shin-Ya Miyagishima,Tsuneyoshi Kuroiwa,Reiko Tomita,Takayuki Fujiwara

doi:10.1038/s41598-020-70398-z

Abstract

Microalgae possess high potential for producing pigments, antioxidants, and lipophilic compounds for industrial applications. However, their open pond cultures are often contaminated by other undesirable organisms, including their predators. In addition, the cost of using freshwater is relatively high, which limits the location and scale of cultivation compared with using seawater. It was previously shown that Cyanidium caldarium and Galdieria sulphuraria, but not Cyanidioschyzon merolae grew in media containing NaCl at a concentration equivalent to seawater. We found that the preculture of C. merolae in the presence of a moderate NaCl concentration enabled the cells to grow in the seawater-based medium. The cultivation of cyanidialean red algae in the seawater-based medium did not require additional pH buffering chemicals. In addition, the combination of seawater and acidic conditions reduced the risk of contamination by other organisms in the nonsterile open culture of C. merolae more efficiently than the acidic condition alone.

Highlights

Cyanidiales grow at a very low pH, which reduces the risk of contamination by other organisms
Given the above information and assumptions, here we show that C. merolae, Cyanidium caldarium, and Galdieria sulphuraria can be cultured in natural seawater supplemented with inorganic nitrogen and phosphorus sources, iron, and a trace metal mix
As a first step to develop a cultivation system of cyanidiales in acidified seawater, we examined whether the three cyanidialean red algae C. merolae 10D, Cy. caldarium RK-1, and G. sulphuraria 074 W grew in an inorganic medium containing a concentration of NaCl that was equivalent to the amount in seawater and under our culture conditions

Summary

Introduction

Cyanidiales grow at a very low pH, which reduces the risk of contamination by other organisms. C. merolae has the following features that are potentially useful for industrial applications, which are not present in Cyanidium spp. and Galdieria spp. Similar to many other microalgae, the cells of Cyanidium spp. and Galdieria spp. are enclosed by a rigid cell wall[19] that requires mechanical processing to be disrupted to release their cellular contents. We show that the acidified seawater reduces the risks of microbial contamination in outdoor open cultivation. Because acidophilic freshwater algae have been identified in many other eukaryotic lineages, the combination of acid and seawater are likely useful for the open cultivation of other microalgae to reduce the risk of contamination and costs associated with their cultivation

Methods

Results

Conclusion