By day, it uses iron in enzymes for photosynthesis to make carbohydrates; then by night, it appears to reuse the same iron in different enzymes to produce organic nitrogen for proteins.
The bacterium, Crocosphaera watsonii, is one of the few marine microbes that can convert nitrogen gas into organic nitrogen, which (just as it does on land) acts as fertilizer to stimulate plant growth in the ocean. So the ocean’s productivity is limited by nitrogen, which in turn is limited by scanty supplies of iron for the enzymes needed to make organic nitrogen.
This newfound capacity to conserve precious iron and use it in day-night shifts to satisfy two different metabolic demands reveals a surprising key to life on our planet, say scientists at Woods Hole Oceanographic Institution (WHOI) and Massachusetts Institute of Technology (MIT). They reported their findings Jan. 10 in the Proceedings of the National Academy of Sciences.
The scientists call the strategy “hot bunking,” referring to ships that sail with fewer bunks than sailors on board. The bunks are kept continuously hot, as sailors finishing night shifts hop into bunks newly emptied by sailors arising for day shifts.
Crocosphaera uses iron-containing nitrogenase enzymes to convert dissolved nitrogen gas into organic nitrogen (a process called nitrogen “fixing”). As the sun comes up, the bacterium breaks down these enzymes, releasing iron that can be used to make photosynthetic enzymes needed to convert dissolved carbon dioxide into carbohydrates. When the sun goes down, many of the photosynthetic enzymes are broken down, releasing the iron again to be recycled into nitrogenase.
Crocosphaera belongs to a subgroup of bacteria called cyanobacteria. “They have a bit of a Dr. Jekyll and Mr. Hyde lifestyle: photosynthetic by day and nitrogen-fixing by night,” said Mak Saito, a WHOI biogeochemist and lead author of the PNAS paper. Scientists previously knew cyanobacteria had this unusual dual-metabolic capacity, but they did not know how they could accomplish it with meager iron supplies.
The bacterium pays a price in energy needed to destroy and rebuild enzymes each day, but it’s worth it to maximize the use of scarce iron. The scientists estimate that by using the hot bunking strategy, the organism can survive with about 40 percent less iron than it would otherwise need. It allows Crocosphaera to thrive and produce life-sustaining organic nitrogen in iron-poor waters that would otherwise be less productive.
The surprising abundance of cyanobacteria in the ocean was discovered in the 1970s by WHOI microbiologist Stanley Watson and his colleagues Frederica Valois and John Waterbury and, who later continued their pioneering research to elucidate cyanobacteria’s critical ecological roles for the ocean and the planet. Crocosphaera watsonii is named after the late Dr. Watson.
Cyanobacteria have been notoriously difficult to culture in the laboratory. At WHOI, Waterbury, Valois and colleagues established methods to culture cyanobacteria routinely and reliably, and they maintain a collection of cyanobacteria cells in a new building called the Stanley W. Watson Laboratory. The collection is a sort of lending library of cells that provide cultures for scientists all over the world to study, including new generations of WHOI scientists working in the Watson Lab: Saito, graduate student Erin Bertrand, and lab associates Vladimir Bulygin and Dawn Moran.
They applied new biomedical research techniques to the study of the ocean: proteomics. As genomics studies the genes in an organism (its genome), proteomics studies the proteins made from instructions encoded in genes (its proteome).
“We wanted to know not only what could potentially be made from Crocosphaera’s genome, but also what proteins Crocosphaera actually did make,” Saito said.
A key part of the technique involves using mass spectrometers that distinguish and measure the various proteins in an organism by the infinitesimal differences in their masses. The researchers measured the inventory of iron-containing proteins during periods of dark and light. Nitrogen-fixing enzymes were largely absent during the day and present at night; iron-containing photosynthetic enzymes decreased during dark periods and reappeared during light periods. Thus, at any time of day, Crocsophaera required only about half the iron it would need if it maintained both sets of enzymes throughout the day.
To explore the implications of Crocosphaera’s hot bunking ability, scientists at MIT—Stephanie Dutkiewicz, Fanny Monteiro and Mick Follows—used a numerical model that simulates global ocean circulation, biochemistry, and ecosystem dynamics. The model showed that Crocosphaera’s ability to reduce its iron requirements allowed it to inhabit ocean regions with low levels of iron. It also allowed the same iron supply to support more growth of the cyanobacteria and more nitrogen fixation that supports other marine life higher up on the food chain.
Funding for the research came from the National Science Foundation, an Environmental Protection Agency Star Fellowship, the WHOI Ocean Life Institute, the NSF-funded Center for Microbial Research and Education, and the Center for Environmental Bioinorganic Chemistry at Princeton University. The paper was dedicated to co-author Vladimir Bulygin, who passed away in 2009.
The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment.
Media Relations | EurekAlert!
Global threat to primates concerns us all
19.01.2017 | Deutsches Primatenzentrum GmbH - Leibniz-Institut für Primatenforschung
Reducing household waste with less energy
18.01.2017 | FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbH
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
19.01.2017 | Earth Sciences
19.01.2017 | Life Sciences
19.01.2017 | Physics and Astronomy