Abstract
Increased tolerance to light stress in cyanobacteria is a desirable feature for their applications. Here, we obtained a high light tolerant (Tol) strain of Synechocystis sp. PCC6803 through an adaptive laboratory evolution, in which the cells were repeatedly sub-cultured for 52 days under high light stress conditions (7000 to 9000 μmol m−2 s−1). Although the growth of the parental strain almost stopped when exposed to 9000 μmol m−2 s−1, no growth inhibition was observed in the Tol strain. Excitation-energy flow was affected because of photosystem II damage in the parental strain under high light conditions, whereas the damage was alleviated and normal energy flow was maintained in the Tol strain. The transcriptome data indicated an increase in isiA expression in the Tol strain under high light conditions. Whole genome sequence analysis and reverse engineering revealed two mutations in hik26 and slr1916 involved in high light stress tolerance in the Tol strain.
Highlights
Increased tolerance to light stress in cyanobacteria is a desirable feature for their applications
The Tol strain showed higher high light (HL) tolerance compared with PCC6803, i.e., the growth of the Tol strain did not decrease under 7000 μmol m−2 s−1 and even under 9000 μmol m−2 s−1 (Fig. 1)
PCC6803 was obtained by an Adaptive laboratory evolution (ALE) experiment under extreme HL stress condition (9000 μmol m−2 s−1)
Summary
Increased tolerance to light stress in cyanobacteria is a desirable feature for their applications. Because high light (HL) stress is one of the major obstacles in the bio-production of cyanobacteria, it is highly desired to develop an HL tolerant strain for enhancing their growth and production rate of various bio-molecules for industrial applications Cyanobacteria can adapt their cellular system to survive under HL stress conditions by reducing their light-harvesting antenna size[3] and decreasing contents of chlorophyll and photosystem I (PSI)[4,5,6]. They possess some mechanisms for preventing photoinhibition by allowing excess light energy to escape, such as state transition[7], heat dissipation[8], energy dissipation from phycobilisome and photosystem II (PSII)[9,10], and synthesis and maintenance of protein complexes in thylakoid membrane by chaperone proteins[11]. We aimed to reveal HL tolerance mechanisms in the evolved strain by fluorescence analyses of their photosystem as well as by transcriptome analysis
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