Abstract

Several studies have described that cyanobacteria use blue light less efficiently for photosynthesis than most eukaryotic phototrophs, but comprehensive studies of this phenomenon are lacking. Here, we study the effect of blue (450 nm), orange (625 nm), and red (660 nm) light on growth of the model cyanobacterium Synechocystis sp. PCC 6803, the green alga Chlorella sorokiniana and other cyanobacteria containing phycocyanin or phycoerythrin. Our results demonstrate that specific growth rates of the cyanobacteria were similar in orange and red light, but much lower in blue light. Conversely, specific growth rates of the green alga C. sorokiniana were similar in blue and red light, but lower in orange light. Oxygen production rates of Synechocystis sp. PCC 6803 were five-fold lower in blue than in orange and red light at low light intensities but approached the same saturation level in all three colors at high light intensities. Measurements of 77 K fluorescence emission demonstrated a lower ratio of photosystem I to photosystem II (PSI:PSII ratio) and relatively more phycobilisomes associated with PSII (state 1) in blue light than in orange and red light. These results support the hypothesis that blue light, which is not absorbed by phycobilisomes, creates an imbalance between the two photosystems of cyanobacteria with an energy excess at PSI and a deficiency at the PSII-side of the photosynthetic electron transfer chain. Our results help to explain why phycobilisome-containing cyanobacteria use blue light less efficiently than species with chlorophyll-based light-harvesting antennae such as Prochlorococcus, green algae and terrestrial plants.

Highlights

  • Almost 140 years ago, professor Theodor Engelmann showed that light color plays an important role in photosynthesis (Engelmann 1882)

  • Photosynthesis Research (2018) 138:177–189 were confirmed by Emerson and Lewis, who showed that the phycobiliproteins of cyanobacteria and red algae play a key role in light-harvesting for photosynthesis (Emerson and Lewis 1942)

  • Our results show that the cyanobacterium Synechocystis sp

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Summary

Introduction

Almost 140 years ago, professor Theodor Engelmann showed that light color plays an important role in photosynthesis (Engelmann 1882). We know that these phycobiliproteins make up specialized light-harvesting antennae, called phycobilisomes (PBSs), consisting of an allophycocyanin core and stacked rods of phycocyanin often in combination with phycoerythrin. These phycobiliproteins consist of an apo-protein and one or more chromophores, known as bilins, including phycocyanobilin absorbing orange light (620 nm), phycoerythrobilin absorbing green light (545 nm), and phycourobilin absorbing blue-green light (495 nm) (Grossman et al 1993; Tandeau de Marsac 2003; Six et al 2007). Recent reviews on the structure and function of PBSs are provided by Tamary et al (2012), Watanabe and Ikeuchi (2013), and Stadnichuk and Tropin (2017)

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