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.