Biology Reference
In-Depth Information
capture and storage, and the sustainable production of biofuels, thanks to their (1)
simple nutritional requirements, (2) physiological robustness, (3)metabolic plasticity,
and(iv)thepowerfulgeneticsofsomemodelstrains.Becauseoftheirphotoautotro-
phiclifestyle,cyanobacteriaareinevitablychallengedbytoxicreactiveoxygenspecies
generated by photosynthesis (and respiration), especially under intense illumination
whenthelight-drivenelectrontransportexceedswhatneededfortheassimilationof
inorganic substrates.This review summarizeswhat is known regarding the defences
against oxidative stress in cyanobacteria, emphasizing on the central role of gluta-
thione and the wealth of glutathione-dependent enzymes, which have been well
conservedthroughoutevolution.Wealsoreportonwhatcanbe inferred inthis field
byminingtheinformationprovidedbythe70sequencedgenomesofmorphologically
andphysiologicallydiversecyanobacteria.
1. INTRODUCTION
1.1. The Fundamental and Biotechnological Interests
of Cyanobacteria
Cyanobacteria, formerly termed blue-green algae, are the only prokaryotes
that perform the oxygen-evolving photosynthesis. These ancient microor-
ganisms (∼3 × 10
9
years) are regarded as the progenitors of the oxygen-
rich atmosphere of our planet (
Schopf, 2011
) that enabled the evolution of
the vital respiration pathway, and as the ancestors of the plant chloroplast
(
Archibald, 2009
). In colonizing most waters (fresh, brackish and marine)
and terrestrial (including deserts) environments, cyanobacteria have evolved
as the largest and most diverse groups of bacteria (
Shi & Falkowski, 2008
).
They display different forms ranging from unicellular morphologies (spheri-
cal and cylindrical) to complex multicellular (filamentous) forms, which can
fix atmospheric nitrogen (N
2
) and establish symbioses with other organisms
(fungi, bryophytes, gymnosperms, angiosperm, and the water fern
Azolla
filiculoides
). Consequently, cyanobacteria are good model systems to study
the impact of changing conditions on the physiology (
Battchikova et al.,
2010
;
Hagemann, 2011
;
Kirilovsky, 2010
;
Singh et al., 2009
), morphol-
ogy (
Vermaas et al., 2008
), division (
Marbouty, Saguez, Cassier-Chauvat, &
Chauvat, 2009
;
Miyagishima, Wolk, & Osteryoung, 2005
) and differentia-
tion (
Mariscal & Flores, 2010
) of microbial cells. Furthermore, cyanobacte-
ria being the most abundant photosynthetic organisms on Earth (
Scanlan
et al., 2009
), they support a large part of the biosphere in using solar energy
to (1) renew the oxygenic atmosphere (
Partensky, Hess, & Vaulot, 1999
);
(2) play important roles in global biogeochemical cycles (assimilation and
sequestration of carbon and nitrogen); and (3) make up organic assimilates
essential to the food chain. Cyanobacteria convert captured solar energy
