Growth of Cyanobacteria Is Constrained by the Abundance of Light and Carbon Assimilation Proteins

Abstract

Summary: Cyanobacteria must balance separate demands for energy generation, carbon assimilation, and biomass synthesis. We used shotgun proteomics to investigate proteome allocation strategies in the model cyanobacterium Synechocystis sp. PCC 6803 as it adapted to light and inorganic carbon (Ci) limitation. When partitioning the proteome into seven functional sectors, we find that sector sizes change linearly with growth rate. The sector encompassing ribosomes is significantly smaller than in E. coli, which may explain the lower maximum growth rate in Synechocystis. Limitation of light dramatically affects multiple proteome sectors, whereas the effect of Ci limitation is weak. Carbon assimilation proteins respond more strongly to changes in light intensity than to Ci. A coarse-grained cell economy model generally explains proteome trends. However, deviations from model predictions suggest that the large proteome sectors for carbon and light assimilation are not optimally utilized under some growth conditions and may constrain the proteome space available to ribosomes. : Jahn et al. used shotgun proteomics to investigate resource allocation strategies in the model cyanobacterium Synechocystis as it adapted to light and carbon limitation. They found that cells reorganize their proteome following a growth optimization strategy but deviate from this strategy to keep protein reserves even under nutrient-replete conditions. Keywords: cyanobacteria, cellular economy, resource allocation, light limitation, carbon limitation, coarse-grained model, bet-hedging, shotgun proteomics