Life science
Cell factories, Fermentation, Bioproduction, Metabolic engineering

Creation of High Light Stress Tolerant Green Cell Factory ofCyanobacteria
図１ 清水Graduate School of Information Science and Technology
Professor Hiroshi Shimizu

Researchmap https://researchmap.jp/hiroshi_shimizu/?lang=en

Associate Professor Yoshihiro Toya

Researchmap https://researchmap.jp/ytoya/?lang=en

Cyanobacteria are promising host microorganisms for theproduction of industrial bio-molecules because these cells candirectly fix carbon dioxide through the Calvin Benson cycle andconvert it into target compounds using light energy. However, excess light, such as in summer, damages their photosystem andinhibits photosynthetic activity. 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 rates of growth and production of various bio-molecules forindustrial applications. Here, we obtained a HL tolerant (Tol) strainof Synechocystis sp. PCC6803 through an adaptive laboratory
evolution (ALE). Although the growth of the parental strain almost
stopped when exposed to 9,000 μmol m-2 s-1 light, no growth inhibition was observed in the Tol strain. We identified two mutations inthe genome involved in HL stress tolerance in the Tol strain.

▍Background & Results

ALE experiment is a method used to induce tolerance against
stress conditions. A serially passaged culture is performed undera stress environment with decreasing the growth rate, which allows
the selection of mutants with improved growth phenotypes. In thepresent study, an evolved strain of Synechocystis sp. PCC6803
was obtained through an ALE experiment under HL stress conditions. We identified key mutations involved in the HL tolerance using whole genome sequencing and reverse engineering. Although
the growth of the parental strain almost stopped when exposed
to 9,000 μmol m-2 s-1 light, no growth inhibition was observedin the Tol strain. Excitation-energy flow was affected because ofphotosystem II damage in the parental strain under HL conditions,whereas the damage was alleviated and normal energy flow wasmaintained in the Tol strain. Whole genome sequence analysis
and reverse engineering revealed two mutations in the genome involved in HL stress tolerance in the Tol strain.

Passaged culture
under stress conditionk m @Sh i m i zu L ab

ParentalstrainEvolvedstrains

High light stress

Single colony
isolation

図２Fig.
清水1 Adaptive laboratory evolution under high light stress condition

40 µmol m s-2

Cell concentration(OD730)Life science

Abstract

4000 µmol m s-1-2

7000 µmol m s-1-2

9000 µmol m s-1-2

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ParentalstrainEvolvedstrain

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48

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Time (h)

02448

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02448

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0244872Time (h)Time (h)Time (h)Parental Evolved
strainstrainParental Evolved
strainstrainParental Evolved
strainstrainParentalstrain
EvolvedstrainFig. 2 Cell growth of the high light stress tolerant strain▍ Significance of the research and Future perspective
To create green cell factories by cyanobacteria, HL stress tolerance is a critical issue to realize a development of industrially
useful bioprocesses. ALE and systems biology including omics
analysis, in silico cell modelling and experimental analysis would
provide better understanding and superior designability of photosynthetic organisms.

P a t e n t
Yoshikawa, Katsunori; Ogawa, Ken-ichi; Toya, Yoshihiro et al. Mutations in hik26 and slr1916 lead to high-light stress tolerance in Synechocystis sp.
PCC6803. Communications Biology. 2021; 4(1): 343. doi: 10.1038/s42003-021-01875-y
UR
L https://resou.osaka-u.ac.jp/ja/research/2021/20210316_1
K e y w o r d photosynthesis, adaptive laboratory evolution, genome analysis, high light stress tolerance, cell factories
Tr e a t i s e