Biomass production and studies on Rhodopseudomonas palustris grown in an outdoor, temperature controlled, underwater tubular photobioreactor.

A temperature controlled underwater tubular photobioreactor was studied for 6 months in outdoor conditions to determine biomass production of Rhodopseudomonas palustris 42OL. Biomass output rate was very high during the study period. In July, productivity was about 75.0 g reactor(-1) d(-1) for a short period (5 days). The biomass yield averaged 0.7 g biomass dry weight (d.w.)xg acetic acid(-1). We also obtained a mean photosynthetic efficiency of 7.6% in winter and 7.1% in summer. Biomasses rich in pigments and a biodegradable thermoplastic polymer [poly-beta-hydroxybutyrate (PHB)] were obtained. During the summer, PHB was about 4.0% of the biomass d.w. The bacteriochlorophyll/carotenoid ratio was lower at midday than either in the morning or in the evening. The reduction in this ratio may have been a response of the Rhodopseudomonas cells to high irradiance (about 900 W m(-2)). A reduced rate of protein synthesis continued even in the dark. PHB and carbohydrates, synthesized in excess during the day, were used as substrates for night protein synthesis.