Reduced light-harvesting antenna: Consequences on cyanobacterial metabolism and photosynthetic productivity

Abstract

Cyanobacteria are potential candidates for future photobiological hydrogen production. For this purpose, optimization of cyanobacterial metabolism and up-regulation of the linear electron flow aremandatory. One strategy to achieve this goal is the reduction of the photosynthetic antenna size. Here, we characterize the photosynthetic performance of two Synechocystis PCC 6803 antenna mutants in respect to culture density and light intensity under well-defined - continuous - cultivation conditions. The metabolic state of the mutants is defined by spectroscopic investigations and an in-depth proteomic analysis.

Our results show that both biotic (i. e. balanced photosystem 2 to photosystem 1 ratios, light tolerance) and abiotic parameters (i. e. light intensity, cell density) are important for the optimization of photosynthetic efficiency which, in turn, is a prerequisite for high-yield photobiological hydrogen production. While a complete loss of light-harvesting antenna - as observed in the PAL mutant - has a significant negative impact on robustness and fitness, the Olive mutant lacking only the phycocyanin subunits reaches higher cell densities in our photobioreactor setup. This results in higher time-space-yields. For this reason the Olive mutant is a promising candidate for the design of future hydrogen production.