**Conflict of interest**

The main bottleneck of CGP production in Cyanobacteria is the relatively slow growth rate, which is much lower than in biotechnologically established bacteria. Conventional cultivation methods of cyanobacteria reach a biomass of roughly 1 g dry mass per liter [107]. To overcome this limitation, a new cultivation method was developed, using a two-tier vessel with

rapid growth of *Synechocystis* sp. PCC 6803 and *Synechococcus* sp. PCC 7002 up to 30 g CDM per liter [108]. *Synechocystis* sp. PCC 6803 strain BW86 was also used in this high-density cultivation setup. During this study, CGP amounts up to 1 g per liter were reached in 96 h. This is approximately four times higher compared to the maximum CGP yield observed during

In comparison, the recombinant *E. coli* strain DH1 harboring *cphA* from *Synechocystis* sp. PCC 6803 produces between 6.7 and 8.3 g CDM per liter culture in 16 h. CGP amounts during this fed-batch fermentations were between 21 and 24% of the CDM [27], resulting in a CGP production rate of 87.9 to 124.5 mg/l and hour. Although this exceeds the production rate in *Synechocystis* sp. PCC 6803 strain BW86 by a factor of 10, the recombinant *E. coli* requires terrific broth complex medium, while *Synechocystis* sp. PCC 6803 strain BW86 is cultivated in simple mineral medium and additionally sequesters hazardous greenhouse gas CO2

Considering these super ordinate factors, production of biopolymers with cyanobacteria may

CGP is well researched and its occurrence in cyanobacteria is known for more than 100 years. However, many questions are still open. Most obviously, the cell biology of the CGP granules remains largely unknown. In the last decades, research on CGP mainly focused on biotechnological purposes, like strain or process optimization. Most work has been carried out with short-chain CGP from recombinant producer strains; however the biophysical properties of the long-chain native CGP remain largely unexplored. So far, heterotrophic bacteria were mainly used to produce industrial biocompounds including CGP. In this chapter, we discussed the possibility of a cyanobacterial CGP production strain. The main disadvantages of cyanobacteria, their slower growth and the low abundance of product can be compensated using genetic engineering together with appropriate production processes. Future industry has to cope with the manifold challenges to counteract environmental pollution and climate change. The use of cyanobacteria in CGP production and, more generally, in biotechnological applications for bioproduct synthesis provides an environmentally friendly alternative to conventional biotechnological approaches.

This work was supported by grants from the DFG (Fo195/9), the research training group GRK 1708 and the Baden-Württemberg foundation grant 7533-10-5-92B. We thank Iris Maldener for provision of the electron micrographs of *Anabaena* sp. PCC 7120 and *Synechocystis* sp. PCC 6803. We would also like to give thanks to Rebeca Pérez for provision of light micrographs of

*Anabaena variabilis ATCC 29413* and *Nostoc punctiforme ATCC 29133.*

supply. By using this cultivation setup, it was possible to enable

membrane-mediated CO2

98 Cyanobacteria

**8. Conclusions**

**Acknowledgements**

conventional cultivation after 12 days [106, 109].

in fact become an alternative to heterotrophic bacteria.

The authors declare that they have no competing interests.
