Physiological Properties of Photoautotrophic Microalgae and Cyanobacteria Relevant to Industrial Biomass Production

Photoautotrophic mass culture of microalgae is currently under investigation for social implementation, since such organisms are anticipated to be resources of alternative fuels and materials for reducing global warming. Production scale-up of culture systems and economy balance are great barriers for practical usage. In order to develop new culture systems such as attachment on solid surfaces or biofilms, we investigated various characteristics of photosynthesis in Chlorella, not only in liquid but also on filter membranes. In aquatic cultures, the photosynthetic rate was almost the same as the specific exponential growth rate at over 32 °C, suggesting that highly efficient cell growth was achieved at that temperature. The algal cells could fix about 50 mmol carbons per mole photons, at cloudy-day-level light intensities, which result to produce 1.2 g dry cell weight in calculation. Moreover, Chlorella could grow on a membrane surface at almost the same rate as in liquid. Similar tolerance to water deficiency was observed in a cyanobacterium, Synechocystis, in which gene expression responded in 30 min after the stress. Such a tolerance was also observed in other species of microalgae and cyanobacteria in photosynthesis.