Prochlorococcus and Synechococcus have Evolved Different Adaptive Mechanisms to Cope with Light and UV Stress

Abstract

Prochlorococcus and Synechococcus, which numerically dominate vast oceanic areas, are the two most abundant oxygenic phototrophs on Earth. Although they require solar energy for photosynthesis, excess light and associated high UV radiations can induce high levels of oxidative stress that may have deleterious effects on their growth and productivity. Here, we compared the photophysiologies of the model strains Prochlorococcus marinus PCC 9511 and Synechococcus sp. WH7803 grown under a bell-shaped light/dark cycle of high visible light supplemented or not with UV. Prochlorococcus exhibited a higher sensitivity to photoinactivation than Synechococcus under both conditions, as shown by a larger drop of photosystem II (PSII) quantum yield at noon and different diel patterns of the D1 protein pool. In the presence of UV, the PSII repair rate was significantly depressed at noon in Prochlorococcus compared to Synechococcus. Additionally, Prochlorococcus was more sensitive than Synechococcus to oxidative stress, as shown by the different degrees of PSII photoinactivation after addition of hydrogen peroxide. A transcriptional analysis also revealed dramatic discrepancies between the two organisms in the diel expression patterns of several genes involved notably in the biosynthesis and/or repair of photosystems, light-harvesting complexes, CO2 fixation as well as protection mechanisms against light, UV, and oxidative stress, which likely translate profound differences in their light-controlled regulation. Altogether our results suggest that while Synechococcus has developed efficient ways to cope with light and UV stress, Prochlorococcus cells seemingly survive stressful hours of the day by launching a minimal set of protection mechanisms and by temporarily bringing down several key metabolic processes. This study provides unprecedented insights into understanding the distinct depth distributions and dynamics of these two picocyanobacteria in the field.

Distribution of ultraphytoplankton in the western part of the North Pacific subtropical gyre during a strong La Niña condition: relationship with the hydrological conditions

“…Although surface Prochlorococcus cannot be accurately enumerated by flow cytometry due to their dim fluorescence (due to low pigment content in response to the strong irradiation), our results are consistent with the classical pattern and physiological properties of these microorganisms (Zhang et al, 2008;Mella-Flores et al, 2012). Mella-Flores et al (2012) described that in contrast to Prochlorococcus, Synechococcus have developed efficient mechanisms to cope with strong light such as in the surface layer. Similarly, Synechococcus were shown to have several advantages both in terms of nitrate and phosphate uptake in depleted nutrient conditions (Rippka et al, 2000;Moutin et al, 2002;Michelou et al, 2011).…”

Scratching Beneath the Surface: A Model to Predict the Vertical Distribution of Prochlorococcus Using Remote Sensing

“…Prochlorococcus numerically dominates vast expanses of the warm and strongly-stratified open ocean [13,15,34,45,46]. The sensitivity of the Prochlorococcus population as a whole to changes in physical forcing [12], such as decreased kinetic energy input to the water column, resulting in low turbulent mixing [44] and long-period internal oscillations in subsurface water masses that can lead to changes in nutrient supply from depth [39], makes this genus an ideal indicator of water-column dynamics.…”

Connecting thermal physiology and latitudinal niche partitioning in marine Synechococcus

“…A number of b-carotene molecules bound to the reaction centre II act as quenchers of singlet oxygen and under light, are regenerated through a repair cycle (Telfer 2005;Ishikita et al, 2007;Mella-Flores et al, 2012). This carotenoid is essential for the protection of reaction centres (Cazzaniga et al, 2012) and thus may be used as an indicator of oxidative stress intensity.…”