Cyanobacteria Change Their Genetic Activity After Sunset

Cyanobacteria, often called blue-green algae, are found globally in different forms, ranging from single-celled organisms to long filamentous chains. Although they play a crucial role in many ecosystems, most studies of their behaviour have been conducted in controlled laboratory settings with constant lighting.

Image credit: Elif Bayraktar/Shutterstock.com

*Important notice: mBio publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

However, recent research conducted by scientists at the Marine Biological Laboratory (MBL) has revealed that filamentous cyanobacteria are significantly influenced by the natural day-night cycle. The findings of this research were published in mBio.

Through examination of gene expression in the cyanobacterium Nostoc punctiforme, researchers found that cells prioritize metabolic processes during daylight, carefully synchronizing photosynthesis and carbon assimilation to support cell division. At night, however, the cells shift their focus to regulating genome repair and activating a range of genetic elements.

I think this is a benchmark study that reveals that lab cultures under stable conditions may not undergo the same genetic or genomic dynamics that they would reveal in the wild. So, this was a necessary step toward mimicking natural, environmental conditions and then seeing which genes are activated by these more natural conditions.

Blair Paul, Study Senior Author and Research Scientist, Marine Biological Laboratory

The research also uncovered an unexpected finding: mobile genetic elements were seen moving in and out of the N. punctiforme genome. These elements were transported by viruses called phages. The researchers found that transposons were active during nighttime hours.

Furthermore, the investigation identified particular genes referred to as diversity-generating retroelements. These genes aid swift mutation at particular locations within the genome. According to Paul, these retroelements are frequently present in the numerous species of cyanobacteria, with a higher prevalence in multicellular species. The findings of this study indicated that these retroelements remain active throughout the entire day-night cycle.

Resilient Multicellular Cyanobacteria

Multicellular cyanobacteria are “widespread terrestrially, and also in marine environments, while several of them are associated with plants. They occupy most niches on the planet where there’s sunlight.” Paul said.

N. punctiforme serves as a model system in laboratory settings for investigating the functional specialization of cells within these cyanobacteria, which aids in their adaptation to environmental challenges.

Despite extensive research on the day-night cycles of single-celled cyanobacteria, Paul noted that "comparatively little was known about the circadian rhythm in multicellular cyanobacteria." This gap is due to the common laboratory practice of maximizing growth rates using constant illumination.

Understanding the natural behavior of these microorganisms is crucial due to their role as primary producers, which Paul described as "the vital foundation for an ecosystem."

He also notes that "relatives of these cyanobacteria form harmful algal blooms," generating toxins, occasionally potent neurotoxins. Therefore, a deeper grasp of their genome dynamics "can help us understand how these organisms thrive in the wild."

The genomes of these multicellular cyanobacteria are considerably more extensive than those of their single-celled counterparts, approximately 8 million "letters" in length, versus about 3 million. Consequently, it is not unexpected that while specific genes identified in this study as linked to day-night cycles were previously recognized in other cyanobacteria types, others were entirely novel.

Paul stated, "They're different, but could have a similar function tied to the cellular clock" and will be explored further.

Despite their small size, cyanobacteria exert a significant influence on ecosystems. Their presence "can be massive, affecting the chemistry and biology of major biomes, like that of the global ocean," as stated by Paul. Furthermore, their mobile genetic components have the potential to alter the genetic makeup of nearby microorganisms.

What genetic vehicles are these cyanobacteria disseminating in an ecosystem? Are those beneficial to other microorganisms, or are they most often deployed against adversaries? Those are pretty open-ended questions.

Blair Paul, Study Senior Author and Research Scientist, Marine Biological Laboratory

*Important notice: mBio publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.