Abstract
Survival of photosynthetic cyanobacteria is challenged by environmental contaminations like heavy metals. Among them, deciphering the regulatory mechanisms for cadmium (Cd) in cyanobacteria would facilitate the construction of Cd-resistant strains. In this study, the DNA-Affinity-Purified-chromatin immunoprecipitation assay was employed to identify the direct targets of Sll0649, which was a Cd2+-related response regulator identified in our previous work in model cyanobacteria Synechocystis sp. PCC 6803. As a result, the promoter region of slr0946 encoding the arsenate reductase was enriched fourfolds by quantitative real time PCR analysis. Further, deletion of slr0946 led to a sensitive phenotype to Cd2+ stress compared with the wild type (WT) and the sensitive phenotype of Δslr0946 could be rescued by complementation assay via introducing slr0946 back into Δslr0946. Finally, individually overexpression of slr0946 as well as two Cd2+-related genes identified priviously (i.e., sll1598 and slr0798) in WT could significantly improve the tolerance of Synechocystis sp. PCC 6803 to Cd2+. This study provided a better understanding of the tolerance mechanism to Cd2+ in cyanobacteria and also feasible strategies for tolerance modifications to heavy metals in the future.
Highlights
Photosynthetic cyanobacteria are a large group of Gram-negative prokaryotes able to utilize CO2 and sunlight directly for growth (Gao et al, 2016), playing a pivotal role in the global carbon and nitrogen cycling as well as in some bioremediation applications (Rahman et al, 2011)
Though various metals were required for growth, survival of cyanobacteria is challenged by heavy metals like arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb), which are increasingly spread out in the environment through human activities (Cassier-Chauvat and Chauvat, 2015)
A RR encoding gene sll0649 was identified involved in Cd2+ stress response in Synechocystis and sll0649 exhibited more sensitive phenotype to Cd2+ than wild type (WT) (Chen et al, 2014b)
Summary
Photosynthetic cyanobacteria are a large group of Gram-negative prokaryotes able to utilize CO2 and sunlight directly for growth (Gao et al, 2016), playing a pivotal role in the global carbon and nitrogen cycling as well as in some bioremediation applications (Rahman et al, 2011). Cd2+ is toxic to cyanobacteria even at a low concentration it is important to investigate the response mechanisms of cyanobacteria to Cd2+ and modified the tolerance to Cd2+. Sas et al (2006) monitored the effect of Cd2+ on the photosynthetic activity of model cyanobacteria Synechocystis slr0946 Involving Cadmium Tolerance sp. PCC 6803 (hereafter Synechocystis), founding that Cd2+ could penetrate rapidly into the cells and blocked the photosynthetic activity by altering the whole-chain electron transport (Sas et al, 2006). A better understanding of the regulation mechanisms of cyanobacteria to Cd2+ would benefit the tolerance modifications of cyanobacteria in the future
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