Light is a ubiquitous energy source or environmental signal, organisms living in the photiczone were more or less affected by light. Different forms of geoluminescence or bioluminescence exist not only in hydrothermal areas but also in other deep-sea habitats such as cold seeps.

Many deep-sea animals are capable of emitting light at blue wavelengths. Whether deep-sea microorganism can sense and even utilize blue or other wavelengths of light is a focused issue.

However, due to the difficulty of deep-sea sample collection and deep-sea microorganism cultivation, the above concerns have not been solved.

Recently, the research team led by Prof. SUN Chaomin of Institute of Oceanology, Chinese Academy of Sciences (IOCAS), investigated the blue-light sensing mechanism of non-photosynthetic bacteria isolated from deep-sea cold seep.

The study was published in mSystems.

In this study, the sediment samples were collected by "Kexue" from the cold seep in the South China Sea, and a novel bacterial species named Spongiibacter nanhainus CSC3.9 from the deep-sea cold seep was isolated by a blue light-induction approach.

Consistently, compared with other wavelengths of light, the blue light (470nm) irradiation significantly promoted the growth of strain CSC3.9. However, the strain CSC3.9 did not possess genes encoding chlorophyll synthesis or rhodopsin, suggesting that strain CSC3.9 is not photosynthetic.

Proteomic results showed that BLUF (a kind of typical blue light photoreceptor) plays an important role in the blue light sensing process.

The researchers knocked out the gene encoding BLUF by molecular genetic method and found that the ability of BLUF to sense blue light was significantly reduced, which further verified the proteomic results. Consistent with the results of in vivo experiments, the BLUF protein expressed in vitro also showed specific blue light sensing activity.

The above proteomic, genetic and biochemical results comprehensively confirmed that blue light sensing protein BLUF mediates blue light perception of deep-sea bacteria and further activates acetyl-CoA synthesis pathway, which significantly enhances the tricarboxylic acid cycle (TCA) pathway to energy generation, and ultimately promotes the rapid growth of bacterial strains.

Notably, homologs of BLUF widely existed across the marine microorganisms (containing Spongiibacter species) derived from different environments including cold seeps, indicating that the distribution of light utilization by the non-phototrophic bacteria living in the ocean is broad and has been substantially underestimated. Thus, contribution of microbial-mediated light energy metabolism to the energy cycle of deep-sea ecosystems should be considered in future studies.

This study was funded by the Strategic Priority Research Program of the Chinese Academy of Sciences, Key Deployment Projects of Center of Ocean Mega-Science of the Chinese Academy of Sciences.

The proposed model about blue light sensing and utilization directly mediated by BLUF of S. nanhainus CSC3.9

Yeqi Shan, Ge Liu, Ruining Cai, Rui Liu, Rikuan Zheng, Chaomin Sun*. A deep-sea bacterium senses blue light via a BLUF-dependent pathway. mSystems, 2022, 7(1): e01279-21.

SUN Chaomin

Institute of Oceanology

E-mail: sunchaomin@qdio.ac.cn

(Editor: ZHANG Yiyi)