Phototrophic microorganisms are promising resources for green biotechnology. Compared to heterotrophic microorganisms, however, the cellular economy of phototrophic growth is still insufficiently understood. We provide a quantitative analysis of light-limited, light-saturated, and light-inhibited growth of the cyanobacterium Synechocystis sp. PCC 6803 using a reproducible cultivation setup. We report key physiological parameters, including growth rate, cell size, and photosynthetic activity over a wide range of light intensities. Intracellular proteins were quantified to monitor proteome allocation as a function of growth rate. Among other physiological acclimations, we identify an upregulation of the translational machinery and downregulation of light harvesting components with increasing light intensity and growth rate. The resulting growth laws are discussed in the context of a coarse-grained model of phototrophic growth and available data obtained by a comprehensive literature search. Our insights into quantitative aspects of cyanobacterial acclimations to different growth rates have implications to understand and optimize photosynthetic productivity.

• Keywords
• computational biology, growth model, infectious disease, light limitation, microbiology, photoinhibition, phototrophic growth laws, proteome allocation, resource allocation, systems biology,
• MeSH
• Biotechnology MeSH
• Photosynthesis genetics   MeSH
• Phototrophic Processes genetics   MeSH
• Proteome genetics   MeSH
• Cyanobacteria genetics   growth & development   metabolism   MeSH
• Light MeSH
• Synechocystis genetics   growth & development   MeSH
• Cell Size MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Proteome MeSH

Photoautotrophic growth depends upon an optimal allocation of finite cellular resources to diverse intracellular processes. Commitment of a certain mass fraction of the proteome to a specific cellular function typically reduces the proteome available for other cellular functions. Here, we develop a semi-quantitative kinetic model of cyanobacterial phototrophic growth to describe such trade-offs of cellular protein allocation. The model is based on coarse-grained descriptions of key cellular processes, in particular carbon uptake, metabolism, photosynthesis, and protein translation. The model is parameterized using literature data and experimentally obtained growth curves. Of particular interest are the resulting cyanobacterial growth laws as fundamental characteristics of cellular growth. We show that the model gives rise to similar growth laws as observed for heterotrophic organisms, with several important differences due to the distinction between light energy and carbon uptake. We discuss recent experimental data supporting the model results and show that coarse-grained growth models have implications for our understanding of the limits of phototrophic growth and bridge a gap between molecular physiology and ecology.

• Keywords
• Cellular protein economy, Cyanobacteria, Microbial growth laws, Photosynthesis, Resource allocation, Systems biology,
• MeSH
• Bacterial Proteins physiology   MeSH
• Models, Biological * MeSH
• Phototrophic Processes physiology   MeSH
• Cyanobacteria growth & development   MeSH
• Synechococcus growth & development   MeSH
• Cell Enlargement MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Bacterial Proteins MeSH