Poly(3-hydroxybutyrate) (PHB) is a biobased and biodegradable polymer with properties comparable to polypropylene and therefore has the potential to replace conventional plastics. PHB is intracellularly accumulated by prokaryotic organisms. For the cells PHB functions manly as carbon and energy source, but all possible functions of PHB are still not known. Synechocystis (cyanobacteria) accumulates PHB using light as energy and CO2 as carbon source. The main trigger for PHB accumulation in cyanobacteria is nitrogen and phosphorous depletion with simultaneous surplus of carbon and energy. For the above reasons, obtaining knowledge about external factors influencing PHB accumulation is of highest interest. This study compares the effect of continuous light exposure and day/night (16/8 h) cycles on selected physiology parameters of three Synechocystis strains. We show that continuous illumination at moderate light intensities leads to an increased PHB accumulation in Synechocystis salina CCALA 192 (max. 14.2% CDW - cell dry weight) compared to day/night cycles (3.7% CDW). In addition to PHB content, glycogen and cell size increased, while cell density and cell viability decreased. The results offer new approaches for further studies to gain deeper insights into the role of PHB in cyanobacteria to obtain bioplastics in a more sustainable and environmentally friendly way.

BEST Bioenergy and Sustainable Technologies GmbH Inffeldgasse 21b 8010 Graz Austria

Department of Food Chemistry and Biotechnology Faculty of Chemistry Brno University of Technology Purkynova 118 61200 Brno Czech Republic

Faculty of Science Charles University Vinicna 7 12844 Prague Czech Republic

Institute of Environmental Biotechnology Department of Agrobiotechnology IFA Tulln University of Natural Resources and Life Sciences Vienna Konrad Lorenz Straße 20 3430 Tulln Austria

Institute of Parasitology Biology Centre The Czech Academy of Sciences Branisovska 31 37005 Ceske Budejovice Czech Republic

Institute of Scientific Instruments The Czech Academy of Sciences Královopolská 147 61264 Brno Czech Republic

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