Occurrence of Far-Red Light Photoacclimation (FaRLiP) in Diverse Cyanobacteria.

Fei Gan,Donald Bryant,Gaozhong Shen

doi:10.3390/life5010004

Abstract

Cyanobacteria have evolved a number of acclimation strategies to sense and respond to changing nutrient and light conditions. Leptolyngbya sp. JSC-1 was recently shown to photoacclimate to far-red light by extensively remodeling its photosystem (PS) I, PS II and phycobilisome complexes, thereby gaining the ability to grow in far-red light. A 21-gene photosynthetic gene cluster (rfpA/B/C, apcA2/B2/D2/E2/D3, psbA3/D3/C2/B2/H2/A4, psaA2/B2/L2/I2/F2/J2) that is specifically expressed in far-red light encodes the core subunits of the three major photosynthetic complexes. The growth responses to far-red light were studied here for five additional cyanobacterial strains, each of which has a gene cluster similar to that in Leptolyngbya sp. JSC-1. After acclimation all five strains could grow continuously in far-red light. Under these growth conditions each strain synthesizes chlorophylls d, f and a after photoacclimation, and each strain produces modified forms of PS I, PS II (and phycobiliproteins) that absorb light between 700 and 800 nm. We conclude that these photosynthetic gene clusters are diagnostic of the capacity to photoacclimate to and grow in far-red light. Given the diversity of terrestrial environments from which these cyanobacteria were isolated, it is likely that FaRLiP plays an important role in optimizing photosynthesis in terrestrial environments.

Highlights

Chlorophototrophic bacteria, i.e., bacteria that use bacteriochlorophylls and/or chlorophylls (Chls) to produce energy for growth, are a diverse group of organisms that currently occur in seven phyla: Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, Firmicutes, Acidobacteria, and Gemmatimonadetes [1,2,3]
Gan et al [28] found that the Leptolyngbya JSC-1 genome encodes paralogous genes for the core subunits of PS I, PS II, and PBS that are expressed in far-red light (FRL)
We have shown in this study that the capacity to perform Far-Red Light Photoacclimation (FaRLiP) is positively correlated with the presence of photosynthetic gene clusters similar to the one originally identified and characterized in Leptolyngbya JSC-1 [28]

Summary

Introduction

Chlorophototrophic bacteria, i.e., bacteria that use bacteriochlorophylls and/or chlorophylls (Chls) to produce energy for growth, are a diverse group of organisms that currently occur in seven phyla: Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, Firmicutes, Acidobacteria, and Gemmatimonadetes [1,2,3]. Cyanobacteria are unique among chlorophototrophs by virtue of their ability to photo-oxidize water and evolve oxygen, a reaction that has globally important consequences. Mostly Prochlorococcus, marine Synechococcus, and Trichodesmium species, are presently estimated to contribute ≥25% of primary production on Earth [6,7]. Reliable values for cyanobacterial primary production in terrestrial environments are more difficult to estimate, but cyanobacteria are thought to be major contributors to both terrestrial photosynthesis and nitrogen fixation [7,8]. One study suggested that total terrestrial photosynthesis by cyanobacteria is likely to be greater than half, and perhaps equivalent to, their activity in oceans [7]. Cyanobacterial photosynthesis could globally account for as much as half the CO2 fixation and oxygen evolution on Earth

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