Long-term Culture Characteristics of Sterile Ulva spp. (Chlorophyta)

Sterile mutants of green algae in the genus Ulva have the potential to grow stably and are expected to be a suitable food or feed resource containing various nutrients, such as proteins and minerals. In this study, we isolated U. lactuca and U. pertusa from Tokyo Bay and Imari Bay, respectively, in Japan and evaluated their growth rates using a model reactor at Imari. The newly isolated U. lactuca had a growth rate of approximately 11.4 g-dry·m−2·d−1, which is estimated to be seven times greater than the rice yield in paddy fields, while repeatedly cultured U. lactuca had a growth rate of 8.1 g-dry·m−2·d−1. We also demonstrated that this species could be produced in subculture. Heavy metal analysis showed that after culture production, As, Cr, Pb, and Zn were present at concentrations of 0.1 ppm or less and Cd and Hg were below the detection limit for both Ulva species, indicating that long-term cultured sterile Ulva species have almost no accumulation of heavy metals and so would meet safety requirements for use in foods and feeds. Based on these findings, we designed a new type of efficient production system for sterile mutant Ulva spp. using enriched seawater.