Recent studies on production of biofuel and biopolyesters with anoxygenic phototrophic bacteria

Recent studies on the production of molecular hydrogen and biopolyesters by anoxygenic phototrophic bacteria are described in this paper. A halotolerant strain of Rhodobium marinum, an indigenous strain of Rhodopseudomonas palustris, and a mutant of the wild strain Rhodobacter capsulatus lacking hydrogenase activity, were investigated for hydrogen production. The penetration of light into a photobioreactor and the effect of light/dark cycles on hydrogen production were analyzed using Rba. sphaeroides. A combined system with hydrogen production by phototrophic bacteria and a fuel cell has been investigated for light energy conversion to electricity. The photobiological hydrogen production using the combination of a marine green alga Chlamydomonas sp. and a marine phototrophic bacterium Rhodovulum sulfidophilum, and spiral tubular and double-phase photobioreactors were investigated. As for the biopolyesters, a marine phototrophic bacterium, Rhodopseudomonas sp., was reported to accumulate poly-3-hydroxybutyrate (PHB) under microaerobic and photoheterotrophic conditions. The feasibility of a photoproduction process for both H-2 and the PHB-containing biomass of Rp. palustris have been tested using a tubular system with limiting amounts of fixed nitrogen. A method of producing polyhydroxyalkanoate from enzymatically treated crude sago starch was studied using Rba. sphaeroides. Induction of phototrophic bacterial growth from anaerobic granules under light conditions (100 muE m(-2) s(-1)) and the performance of a lighted upflow anaerobic sludge blanket (LUASB) reactor for PHB production and wastewater treatment were investigated. The average PHB production rate of the biomass in the effluent from the LUASB reactor was 6.6-14.0 mg l(-1)-reactor d(-1) using acetate-based media and the average PHB content based on the dry bacterial biomass was 15.1-25.3%. The PHB concentration increased by a secondary incubation of the effluent from the LUASB reactor with sodium acetate under anaerobic light conditions. The UASB granules can decompose a variety of organic substances; therefore, the LUASB method appears to be appropriate for wastewater treatment and the production of phototrophic bacteria and PHB from various wastewaters.