UV-A radiation increases biomass yield by enhancing energy flow and carbon assimilation in the edible cyanobacterium
Nostoc sphaeroides
Authors: Chen Zhen , Yuan Zu-Wen , Luo Wei-Xin , Wu Xun , Pan Jin-Long , Yin Yong-Qi , Shao Hai-Chen , Xu Kui , Li Wei-Zhi , Hu Yuan-Liang , Wang Zhe , Gao Kun-Shan , Chen Xiong-Wen 
Published: February 2024

ABSTRACT

Ultraviolet (UV) A radiation (315–400 nm) is the predominant component of solar UV radiation that reaches the Earth’s surface. However, the underlying mechanisms of the positive effects of UV-A on photosynthetic organisms have not yet been elucidated. In this study, we investigated the effects of UV-A radiation on the growth, photosynthetic ability, and metabolome of the edible cyanobacterium
Nostoc sphaeroides
. Exposures to 5–15 W m
−2
(15–46 µmol photons m
−2
s
−1
) UV-A and 4.35 W m
−2
(20 μmol photons m
−2
s
−1
) visible light for 16 days significantly increased the growth rate and biomass production of
N. sphaeroides
cells by 18%–30% and 15%–56%, respectively, compared to the non-UV-A-acclimated cells. Additionally, the UV-A-acclimated cells exhibited a 1.8-fold increase in the cellular nicotinamide adenine dinucleotide phosphate (NADP) pool with an increase in photosynthetic capacity (58%), photosynthetic efficiency (24%),
Q

A

re-oxidation, photosystem I abundance, and cyclic electron flow (87%), which further led to an increase in light-induced NADPH generation (31%) and ATP content (83%). Moreover, the UV-A-acclimated cells showed a 2.3-fold increase in ribulose-1,5-bisphosphate carboxylase/oxygenase activity, indicating an increase in their carbon-fixing capacity. Gas chromatography–mass spectrometry-based metabolomics further revealed that UV-A radiation upregulated the energy-storing carbon metabolism, as evidenced by the enhanced accumulation of sugars, fatty acids, and citrate in the UV-A-acclimated cells. Therefore, our results demonstrate that UV-A radiation enhances energy flow and carbon assimilation in the cyanobacterium
N. sphaeroides
.

IMPORTANCE

Ultraviolet (UV) radiation exerts harmful effects on photo-autotrophs; however, several studies demonstrated the positive effects of UV radiation, especially UV-A radiation (315–400 nm), on primary productivity. Therefore, understanding the underlying mechanisms associated with the promotive effects of UV-A radiation on primary productivity can facilitate the application of UV-A for CO
2
sequestration and lead to the advancement of photobiological sciences. In this study, we used the cyanobacterium
Nostoc sphaeroides
, which has an over 1,700-year history of human use as food and medicine, to explore its photosynthetic acclimation response to UV-A radiation. As per our knowledge, this is the first study to demonstrate that UV-A radiation increases the biomass yield of
N. sphaeroides
by enhancing energy flow and carbon assimilation. Our findings provide novel insights into UV-A-mediated photosynthetic acclimation and provide a scientific basis for the application of UV-A radiation for optimizing light absorption capacity and enhancing CO
2
sequestration in the frame of a future CO
2
neutral, circular, and sustainable bioeconomy.