Enhancement of biomass and lipid productivity in ettlia sp. by interaction with wastewater indigenous bacteria

Abstract

For commercialization of biofuel from microalgae, economical obstacles in cultivation process must be overcome due to its extensive cost. In this study, mixture of swine and municipal wastewater (m-WW) was utilized as a substrate for cultivating Ettlia sp. YC001, one of the most robust microalgal species. Ettlia sp. YC001 grown in the m-WW showed higher pigments and biomass concentrations than ones grown in a conventional TAP medium, along with 25 % higher lipid productivity. In addition, during the cultivation of Ettlia sp. YC001, nutrients in m-WW, such as ammonium and phosphate, which are usually accounted as pollutants, were consumed about 90 % from initial amount. These results suggest that Ettlia sp. YC001 cultivation is possible in the wastewater, also achieving effective removal of pollutants at the same time. According to the m-WW cultivation results, we could find higher biomass productivity though initial nutrient concentration was similar to TAP medium. To investigate the clue of that, we focused on interaction between indigenous bacteria and Ettlia. Among thousands of bacteria existed in the wastewater, some of them have ability stimulate growth of photosynthetic organisms. There are many previous studies using plant growth promoting bacteria (PGPB) to promote the plant growth, along with successful commercialization. Microalgae, which are also photosynthetic organism similar to plants, may also be positively affected to these PGPB to enhance biomass productivity. With pyrosequencing-based analysis during cultivation in m-WW, dominant bacterial species was identified as Pedobacter sp.. To confirm the effect of co-cultivation, Pedobacter sp. was isolated. With co-cultivation with Ettlia sp. YC001, cell division stimulating effect of Pedobacter on Ettlia sp. YC001 was detected and biomass yield was also higher than pure Ettlia culture. Taken together, utilizing wastewater to substitute a conventional medium can be one of the solutions. Furthermore, wastewater indigenous bacteria have synergetic interaction with microalgae.