Chromatic Acclimation in Cyanobacteria: A Diverse and Widespread Process for Optimizing Photosynthesis

Abstract

Chromatic acclimation (CA) encompasses a diverse set of molecular processes that involve the ability of cyanobacterial cells to sense ambient light colors and use this information to optimize photosynthetic light harvesting. The six known types of CA, which we propose naming CA1 through CA6, use a range of molecular mechanisms that likely evolved independently in distantly related lineages of the Cyanobacteria phylum. Together, these processes sense and respond to the majority of the photosynthetically relevant solar spectrum, suggesting that CA provides fitness advantages across a broad range of light color niches. The recent discoveries of several new CA types suggest that additional CA systems involving additional light colors and molecular mechanisms will be revealed in coming years. Here we provide a comprehensive overview of the currently known types of CA and summarize the molecular details that underpin CA regulation.

MpeV is a lyase isomerase that ligates a doubly linked phycourobilin on the β-subunit of phycoerythrin I and II in marine Synechococcus

“…Marine cyanobacteria in the genus Synechococcus are the second most abundant oxygenic phototrophs and contribute significantly to global ocean primary productivity and carbon cycling (1). Synechococcus are widespread in part because of their efficiency at harvesting available light using their antenna, or phycobilisome (PBS), which is tuned to absorb light colors from portions of the visible spectrum in which chlorophyll absorbs poorly (2)(3)(4). Marine isolates of Synechococcus have a complex PBS structure comprised of up to four highly pigmented phycobiliproteins (PBP).…”

“…The PBS core is made of allophycocyanin and is surrounded by 6 to 8 rods made of phycocyanin and up to two types of phycoerythrin (PEI and PEII). These extended rod structures increase the spectral range of the PBS light harvesting capabilities ( Figure 1) (1,3,(5)(6)(7). PEI and PEII are homologous PBP, each composed of an α-and a β-subunit arranged in a heterohexameric (αβ)6 torus and stacked with the help of linker polypeptides to form the distal portion of the rods (Figure 1) (4,8,9).…”

“…strain RS9916 possesses the ability to alter the ratio of the blue light-absorbing chromophore phycourobilin (PUB) [absorbance maximum (λmax) ~495 nm] and the green light-absorbing chromophore phycoerythrobilin (PEB) (λmax ~545 nm) on the distal portion of the PBS rods, a phenomenon known as type IV chromatic acclimation (CA4) (3,6,(35)(36)(37)(38)(39). During CA4, the PUB to PEB ratio (PUB:PEB) is adjusted to be higher in blue light and lower in green light in order to optimize light capture in changing light color environments (3,31,35,36,39,40). All CA4 strains contain one of the two genomic island configurations, CA4-A or CA4-B, each encoding transcritional activators and a lyase or a lyase-isomerase (36).…”

Far-Red Light Absorbing Photosynthetic Pigments in Cyanobacteria: Steady-State Fluorescence Detection, Time-Resolved Fluorescence Spectroscopy, and Confocal Laser Scanning Microscopy

“…This adaptation is performed via the shifts in PE (green light absorbing PBP) and PC (red light absorbing PBP) content. The knowledge on this phenomenon termed complementary chromatic adaptation (CA) has been comprehensively reviewed [16,17].…”

Diurnal Regulation of In Vivo Localization and CO2-Fixing Activity of Carboxysomes in Synechococcus elongatus PCC 7942

“…The extraordinary ability of cyanobacteria to survive in diverse ecosystems and adapt to extremes of environmental stress is ascribed to their metabolic robustness and tunability [ 1 ]. As cyanobacterial cells rely directly on light for photosynthesis, their abilities to respond to changes in the environmental light conditions are indispensable [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. A typical example is the natural diurnal cycles that synchronize to the rotation of the Earth.…”