Phb-rich Biomass and Bioh2 Production by Means of Photosynthetic Microorganisms

Abstract

Polyhydroxyalkanoates (PHAs) are a family of biopolyesters produced by many bacteria as intracellular
\nstorage carbon and energy source. Poly-β-hydroxybutyrate (PHB) is probably the most common type of PHA.
\nIt is biodegradable and renewable, with relevant thermoplastic properties along with adjustable thermal and
\nmechanical properties. The thermoplastic properties of PHB and its biodegradability make it a potential
\nalternative to petroleum-based plastics. Several microorganisms growing in the dark and/or in the light
\nproduce PHB. The polymer is mainly accumulated in the cytoplasm of cells when microorganisms are growing
\nunder conditions of stress. If purple non-sulfur photosynthetic bacteria (PNSB) are grown under nitrogen
\nstarvation conditions, a photoevolution of molecular hydrogen occurs as well. The PHB amount increases
\nwhen carbon and energy sources are in excess, but the growth is limited, for example, by the lack of a
\nnitrogen, phosphorous or sulfur source. This work deals the possibility of producing PHAs by photosynthetic
\nmicroorganisms belonging to cyanobacteria and PNSB. Different culture broths, with and without organic
\ncarbon sources, were investigated to maximize PHA production by photosynthetic microorganisms. An
\nunbalanced agro-industrial wastewater has been also investigated in the present study. It concerns the olive
\nmill wastewater (OMW) containing significant reusable carbon fractions suitable for an eco-efficient
\nvalorization by feeding photosynthetic processes. The maximum PHA concentration in a cyanobacterium drybiomass
\nwas 317 mg/L, when growing cells in a medium with a low content of acetic acid (LAC). In PNSB drybiomass
\nthe maximum PHB content was 215 mg/L, when growing PNSB in a synthetic medium. A
\nsimultaneous H2 co-production (1,295 mL/L of culture) was cumulated as well, at the end of the process.