Biopolyesters and Related Valuable Products in Phototrophic Microbes

Poly(3-hydroxyalkanoates) are widely used environmentally sound bioplastic produced by numerous microbes including anoxygenic and oxygenic photosynthetic bacteria. Similarly to heterotroph microbes, the photosynthetic microbes can accumulate these polyester-type storage materials under nutrient limitation such as nitrogen, phosphorous or sulfur starvation. A number of purple non-sulfur, sulfur photosynthetic and cyanobacteria can produce PHA of various compositions. The amount, type, length and monomer composition of the PHA strongly depend on the nutrients and the growth conditions, and the light intensity also seriously affects the yield. While anoxygenic photosynthetic microbes need external inorganic or organic electron source, for photosynthetic CO2 fixation, the oxygenic microbes, cyanobacteria can gain electron from water splitting. In principle, anoxygenic photochemolitoautotrophic and cyanobacteria can produce PHA from CO2 as sole carbon source, but addition of organic substrates significantly improves the yield. PHA can also be decomposed by the cells under certain conditions and the PHA metabolism has connections to other metabolic routes including glycogen metabolism. There are several approaches for improving the production rate and yield and – for this purpose – a number of artificially genetically modified microorganisms, metabolic routes were constructed.

Keywords: Bacteria, Biocompatible bioplastics, CO2 fixation, Cyanobacteria, Microbial storage materials, Photosynthetic microbes, Polyhydroxyalkanoates (PHA), Purple photosynthetic bacteria.