Light History Influences the Response of the Marine CyanobacteriumSynechococcussp. WH7803 to Oxidative Stress    

Abstract

Marine Synechococcus undergo a wide range of environmental stressors, especially high and variable irradiance, which may induce oxidative stress through the generation of reactive oxygen species (ROS). While light and ROS could act synergistically on the impairment of photosynthesis, inducing photodamage and inhibiting photosystem II repair, acclimation to high irradiance is also thought to confer resistance to other stressors. To identify the respective roles of light and ROS in the photoinhibition process and detect a possible light-driven tolerance to oxidative stress, we compared the photophysiological and transcriptomic responses of Synechococcus sp. WH7803 acclimated to low light (LL) or high light (HL) to oxidative stress, induced by hydrogen peroxide (H 2 O 2 ) or methylviologen. While photosynthetic activity was much more affected in HL than in LL cells, only HL cells were able to recover growth and photosynthesis after the addition of 25 mM H 2 O 2 . Depending upon light conditions and H 2 O 2 concentration, the latter oxidizing agent induced photosystem II inactivation through both direct damage to the reaction centers and inhibition of its repair cycle. Although the global transcriptome response appeared similar in LL and HL cells, some processes were specifically induced in HL cells that seemingly helped them withstand oxidative stress, including enhancement of photoprotection and ROS detoxification, repair of ROS-driven damage, and regulation of redox state. Detection of putative LexA binding sites allowed the identification of the putative LexA regulon, which was downregulated in HL compared with LL cells but up-regulated by oxidative stress under both growth irradiances.

Connecting thermal physiology and latitudinal niche partitioning in marine Synechococcus

“…The sharp degradation of b-carotene, probably due to an impairment of the turnover of this antioxidant, observed for Synechococcus spp. A15-37, M16.1 and to a lesser extent WH7803, implies that the PSII of these strains were subjected to direct oxidative damages (Blot et al, 2011). Furthermore, oxidative stress is also thought to prevent the repair of the PSII key protein, D1 (Nishiyama et al, 2006), thus greatly enhancing PSII inactivation.…”

LexA protein of cyanobacterium Anabaena sp. strain PCC7120 exhibits in vitro pH-dependent and RecA-independent autoproteolytic activity

“…Oxidative stress arising due to high light intensity has been shown to modulate the expression of LexA, RecA and several SOS response genes in the cyanobacteria, Synechococcus and Prochlorococcus (Blot et al, 2011;Kolowrat et al, 2010). Though a direct correlation indicating increase in pH during oxidative stress has not been shown in cyanobacteria or other bacteria, reports on alkaline pH inducing oxidative stress and SOS response has been reported (Follmann et al, 2009;Maurer et al, 2005;Schuldiner et al, 1986).…”

“…In the marine unicellular cyanobacterial strains, Prochlorococcus marinus PCC9511 and Synechococcus sp. WH7803, several SOS-response genes are up-regulated during high light including lexA and recA, which are co-expressed (Blot et al, 2011;Kolowrat et al, 2010), contradicting the well established succession of LexA and RecA expression in other bacteria. Also, the expression pattern of LexA is influenced by high light intensity, but not by UV-B radiation in P. marinus (Kolowrat et al, 2010).…”

Sensing and Responding to UV-A in Cyanobacteria

“…Recently, H 2 O 2 has also been regarded as an important signal governing the expression of various genes, including antioxidants, photosynthetic genes, and signaling proteins such as kinase, phosphatase, and transcription factors [64,65,73,74]. Similarly, ROS may also act as a signal and/or second messenger enabling cyanobacteria to regulate the expression of a number of genes, resulting in protection from various environmental stresses, especially high and UV irradiance [11,101,102]. In the cyanobacterium Anabaena sp., UV-B-and UV-A-induced ROS production was detected in vivo using a ROS-sensitive probe [62,103,104].…”