Costs and Limitations of Marine Synechococcus Blue-Green Chromatic Acclimation

Abstract

Benefits and trade-offs of blue/green chromatic acclimation (CA4) have received limited study. We investigated the energetic costs associated with executing chromatic acclimation using a fluorescence-based calculation of light use efficiency. Using laboratory cultures and artificial light environments, we show that the delayed response to acclimation known to occur in marine Synechococcus acclimating strains (generalists) in green light do not reduce light use efficiency in green light, but that only one generalist, RCC307, with a much smaller range of acclimation, had higher light use efficiency than blue and green light specialist strains. Generalists with a wider acclimation range either had the same or >30% lower light use efficiencies in blue and green light environments. From this work, we propose that advantages from CA4 may not be geared at direct competition with other Synechococcus specialists with fixed pigment types, but may serve to expand the ecological range of Synechococcus in spectral competition with other genera. As all eight Synechococcus strains tested had higher light use efficiency in green light, regardless of a fixed or flexible light harvesting strategy, we add evidence to the suitability of the Synechococcus genus to greener ocean niches, whether stable, or variable.

Differential acclimation kinetics of the two forms of Type IV chromatic acclimaters occurring in marineSynechococcuscyanobacteria

“…1). In this context, (Lovindeer et al, 2021) also recently showed that CA4-capable Synechococcus strains were characterized by much higher light use efficiency in GL than in BL, often associated with faster growth rate. The latter difference with our results can be explained by the fact that the blue LEDs used in this previous study had a peak at 440 nm, mainly absorbed by Chl a (Amax = 440 nm) but very poorly by PUB (Amax = 495 nm), resulting in strong limitation of the production of chemical energy by photosynthesis in their BL condition.…”

Effect of Rising Temperature and Carbon Dioxide on the Growth, Photophysiology, and Elemental Ratios of Marine Synechococcus: A Multistressor Approach

“…Growth of the cultures was monitored via raw chlorophyll fluorescence measurements using a Turner Fluorometer (Turner Designs Trilogy, model 7200, San Jose, CA, USA). The chlorophyll in vivo module (blue module model 7200-043) was used for the measurements [10]. Chlorophyll fluorescence analysis facilitates near instantaneous measurement of prime aspects of photosynthetic light capture and electron transport [35].…”

“…Specific growth rate µ (d −1 ) was determined from the raw chlorophyll fluorescence measurements using the following equation [10,14]:…”

“…The focus of our study was on the picocyanobacteria, Synechococcus, which has an extensive oceanic distribution, ranging from coastal to open ocean habitats that extend deep into temperate climate zones [8,9]. They are 0.6-2 µm in diameter and possess light-harvesting pigment-protein complexes called phycobilisomes [10,11]. As a component of the picophytoplankton, Synechococcus accounts for 40% of global ocean primary productivity and can be temporally or regionally important contributors to carbon fixation owing to their seasonal dominance [12,13].…”

Modeling Ocean Color Niche Selection by Synechococcus Blue‐Green Acclimaters

“…Maximum growth rates reported in Table S1 were the average exponential growth rates across all five strains in green light (0.7 day −1 max,green ; E p ) and blue light (0.5 day −1 max,blue ; E p ). Photosynthetic efficiencies were estimated following the method of Lovindeer et al (2021), assuming proportionality between growth rate (day −1 ) and the light available for growth, which was a product of the growth light intensity (μmol photons m −2 day −1 ), the absorption cross section of photosystem II (converted from Å 2 to m 2 ), and the proportion of open reaction centers available for light capture and measured by variable fluorescence (F v /F m , dimensionless). Fluorescence parameters were measured on a custom-build miniature Fluorescence Induction and Relaxation System (Maxim Gorbunov) with blue excitation.…”