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Acclimation of the photosynthetic apparatus to low light in a thermophilic Synechococcus sp. strain


Depending upon their growth responses to high and low irradiance, respectively, thermophilic Synechococcus sp. isolates from microbial mats associated with the effluent channels of Mushroom Spring, an alkaline siliceous hot spring in Yellowstone National Park, can be described as either high-light (HL) or low-light (LL) ecotypes. Strains isolated from the bottom of the photic zone grow more rapidly at low irradiance compared to strains isolated from the uppermost layer of the mat, which conversely grow better at high irradiance. The LL-ecotypes develop far-red absorbance and fluorescence emission features after growth in LL. These isolates have a unique gene cluster that encodes a putative cyanobacteriochrome denoted LcyA, a putative sensor histidine kinase; an allophycocyanin (FRL-AP; ApcD4-ApcB3) that absorbs far-red light; and a putative chlorophyll a-binding protein, denoted IsiX, which is homologous to IsiA. The emergence of FRL absorbance in LL-adapted cells of Synechococcus sp. strain A1463 was analyzed in cultures responding to differences in light intensity. The far-red absorbance phenotype arises from expression of a novel antenna complex containing the FRL-AP, ApcD4-ApcB3, which is produced when cells were grown at very low irradiance. Additionally, the two GAF domains of LcyA were shown to bind phycocyanobilin and a [4Fe-4S] cluster, respectively. These ligands potentially enable this photoreceptor to respond to a variety of environmental factors including irradiance, redox potential, and/or oxygen concentration. The products of the gene clusters specific to LL-ecotypes likely facilitate growth in low-light environments through a process called Low-Light Photoacclimation.

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DAB and JHG gratefully acknowledge support from the U. S. National Science Foundation (MCB-1613022). This research was also conducted under the auspices of the Photosynthetic Antenna Research Center (PARC), an Energy Frontier Research Center funded by the DOE, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC 0001035 (DAB). Molecular graphics and analyses performed with UCSF-Chimera, developed by the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco, were supported by NIH award P410GM103311.

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Correspondence to Donald A. Bryant.

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Soulier, N., Walters, K., Laremore, T.N. et al. Acclimation of the photosynthetic apparatus to low light in a thermophilic Synechococcus sp. strain. Photosynth Res (2022).

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  • Photosynthesis
  • Far-red light
  • Thermophilic cyanobacteria
  • Low-light photoacclimation
  • Allophycocyanin
  • Cyanobacteriochrome
  • GAF domain
  • Iron-sulfur cluster
  • Phycobiliprotein
  • IsiA