Isolation of a high-ammonium-tolerant Monoraphidium sp. and evaluation of its potential for biodiesel production

Abstract

The economic challenges of microalgae biodiesel production, including the energy burden and water shortage, can be addressed simultaneously by using wastewater as a nitrogen source. However, as a major form of nitrogen, ammonium is toxic to most microalgae strains, which limits the use of ammonium-containing wastewater. High-ammonium-tolerant algal strains remain to be explored. In this study, a microalgal strain named HDMA-01, which was isolated from Lake Dongfeng in China, was selected using a high ammonium medium. Phylogenetic analysis suggested that HDMA-01 belongs to the genus Monoraphidium (Selenastraceae, Sphaeropleales), and both 18S ribosomal DNA and ITS sequences of HDMA-01 appeared to be new molecular records of the Monoraphidium species. HDMA-01 can multiply vigorously using acetic acid and ammonium in TAP medium, reaching a density of 2 ×107 mL−1 within 7 days. HDMA-01 showed strong tolerance for ammonium. At a high ammonium concentration of 14 mM, HDMA-01 achieved maximum biomass and lipid productivity of 78.9 mg L−1 day−1 and 13.8 mg L−1 day−1, which is the highest among other Monoraphidium strains under similar cultivation conditions. Together with its ideal fatty acid profile, HDMA-01 has great potential for development as a promising strain used in biodiesel feedstock and high-ammonium tolerance biotechnology.