Comparison of Polyhydroxyalkanoates Biosynthesis, Mobilization and the Effects on Cellular Morphology in Spirulina platensis and Synechocystis sp. UNIWG

Filamentous Spirulina platensis and unicellular Synechocystis sp. UNIWG showed capability of synthesizing poly(3-hydroxybutyrate) [P(3HB)j under nitrogen starvation conditions with a maximum accumulation of up to 10 and 14 wt% of the cell dry weight (CDW), respectively under mixotrophic culture conditions. Intracellular degradation (mobilization) of P(3HB) granules by both strains was initiated by the restoration of a nitrogen source. The mobilization of P(3HB) was faster in S. platensis (80% degradation in a period of 8 days) than in Synechocystis sp. (57% degradation in a period of 10 days). Transmission electron microscopy (TEM) revealed that the mobilization of P(3HB) involved changes in granule quantity and morphology. P(3HB) granules became irregular in shape and the boundary region was less defined. Ultrastructural analysis also revealed that Synechocystis sp. UNIWG cells from the growth phase was covered with pilus-like structures. However, these pilus-like structures were not observed in cells from the polyhydroxyalkanoate (PHA) accumulation phase. It is suggested that these pilus-like structures may play an important role for the survival of this cyanobacterium under stress conditions.