Researchers at Washington University in St. Louis have gained the first detailed insight into the way circadian rhythms govern global gene expression in Cyanothece, a type of cyanobacterium (blue-green algae) known to cycle between photosynthesis during the day and nitrogen fixation at night.
In general, this study shows that during the day, Cyanothece increases expression of genes governing photosynthesis and sugar production, as expected. At night, however, Cyanothece ramps up the expression of genes governing a surprising number of vital processes, including energy metabolism, nitrogen fixation, respiration, the translation of messenger RNA (mRNA) to proteins and the folding of these proteins into proper configurations.
Cyanothece is a unicellular bacterium that can capture energy from light and also fix atmospheric nitrogen. As part of a daily diurnal cycle, Cyanothece stores the products of photosynthesis and nitrogen fixation so that they can be used at the proper time. This ability makes Cyanothece an ideal system to understand how a unicellular organism balances and regulates complex processes in the same cell.
The findings have implications for energy production and storage of clean, alternative biofuels.
The study was published in the April online issue of the Proceedings of the National Academy of Science. The research was funded by the U.S. Department of Energy in the context of a Biology Grand Challenge project administered by the Environmental Molecular Sciences Laboratory at the Pacific Northwest National Laboratory.
Bacterial biological clock
"One of the mysteries in cellular physiology is this business of rhythm," said Himadri Pakrasi, Ph.D., the George William and Irene Koechig Freiberg Professor in Arts & Sciences and lead investigator of this project. "Circadian rhythm controls many physiological processes in higher organisms, including plants and people. Cyanothece are of great interest because, even though one cell lives less than a day, dividing every 10 to 14 hours, together they have a biological clock telling them when to do what over a 24-hour period. In fact, cyanobacteria are the only bacteria known to have a circadian behavior."
Why does such a short-lived, single-celled organism care what time it is? The answer, according to this study, is that the day-night cycle has a tremendous impact on the cell's physiology, cycling on and off many vital metabolic processes, not just the obvious ones.
Among the obvious cycling processes are photosynthesis and nitrogen fixation. It is difficult for one cell to perform these two functions because the processes are at odds with one another. Fixing nitrogen requires nitrogenase, a catalyst that helps the chemical reaction move forward. Unhelpfully, the oxygen produced by photosynthesis degrades nitrogenase, making nitrogen fixation difficult or impossible in photosynthetic organisms.
Other filamentous cyanobacteria perform photosynthesis and nitrogen fixation in different, separate cells. As a single-celled bacterium, however, Cyanothece cannot separate these antagonistic processes in space. But it can separate them in time.
Agreeing with previous studies, this study found that Cyanothece genes for photosynthesis turn on during the day and genes for nitrogen fixation turn on at night. The surprise is the tremendous impact the day-night cycle has on the overall physiology of the cell.
"It goes far beyond just the aspects of nitrogen fixation and photosynthesis," said Pakrasi, who also directs Washington University's International Center for Advanced Renewable Energy and Sustainability (I-CARES) to encourage and coordinate university-wide and external collaborative research in the areas of renewable energy and sustainability — including biofuels, carbon dioxide mitigation and coal-related issues. The university will invest more than $55 million in the initiative.
Cyanothece's 'Dark Period'
To see the effect of day-night cycles on the overall physiology of Cyanothece, lead author Jana Stöckel, Ph.D., Washington University post-doctoral researcher, and other members of this research team examined the expression of 5,000 genes, measuring the amount of messenger RNA for each gene in alternating dark and light periods over 48 hours. At a given time, the mRNA levels indicated what the cells were doing. For example, when the researchers identified high levels of many mRNAs encoding various protein components of the nitrogenase enzyme, they knew that the cells were fixing nitrogen at that time, in this case, during the dark periods.
Of the 5,000 genes studied, nearly 30 percent cycled on and off with changing light and dark periods. These particular genes, the study found, also govern major metabolic processes. Therefore, the cycling of mRNA transcription, Pakrasi said, "provides deep insight into the physiological behavior of the organism — day and night."
During the day, Cyanothece busies itself with photosynthesis. Using energy from sunlight, carbon dioxide from the atmosphere, and water, Cyanothece produces glucose, a sugar it stores in glycogen granules, filling its chemical gas tank. At night, the Cyanothece ramps up production of nitrogenase to fix nitrogen, as expected. Since nitrogen fixation requires a lot of energy, Cyanothece uses the glycogen stored through a process called respiration. Because respiration requires oxygen, the cells conveniently use up this by-product of photosynthesis, likely helping to protect nitrogenase from degradation.
Through this cyclic expression of genes, Cyanothece is essentially a living battery, storing energy from the sun for later use. This feat continues to elude scientists searching for ways to harness sunlight and produce energy on a large scale. With this in mind, a new project for the Pakrasi team seeks to use the machinery of Cyanothece — its energy storage strategy, its anaerobic conditions that protect important enzymes — as a biofactory to produce hydrogen from sunlight, the ultimate clean energy source.
Gayle Geren | EurekAlert!
Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute
Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy