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 six 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 d.w. × g 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-ß-hydroxybutyrate (PHB)] were obtained. During the summer, PHB was about 4.0 % of the biomass dry weight. 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.