A new report in the Proceedings of the National Academy of Sciences by Indiana University Bloomington scientists answers that form-and-function question for one bacterium, the aquatic Caulobacter crescentus, whose cells are anchored to solid objects by conspicuous and distinctive stalks.
"We've found the bacteria can take up nutrients with their stalks," said microbiologist Yves Brun, who led the study. "This is the first example that we know of in which a major feature of a bacterium's shape can be tied to a specific function."
Despite their tiny size and readiness for laboratory study, far less is known about the physiological utility of bacterial shapes than, say, the streamlined forms of fish, sharks and dolphins, or the elongated spires of pine and redwood trees.
Brun said C. crescentus' stalk acts as a sort of antenna that amplifies the uptake of organic phosphate from the surrounding environment. The narrow stalk adds little volume to the cell, and incoming nutrients diffuse toward the cell's main body, where nutrients are quickly assimilated by metabolic processes. Phosphate is an important molecule to all organisms. It is involved in DNA repair and duplication, the expression of DNA, the regulation of protein action, membrane synthesis and the transfer of energy within cells.
The scientists used fluorescence microscopy to see where organic phosphate enters C. crescentus cells. As a gram negative bacterium, C. crescentus has two membranes -- an outer membrane and an inner membrane, with a space called the "periplasm" in between. Experiments demonstrated initial entry of organic phosphate across the entire cell surface, including the stalk. Once across the outer membrane, the organic phosphate is converted to inorganic phosphate and diffuses from the stalk toward the cell body periplasm. When the phosphate reaches the periplasm, the phosphate is taken across the inner membrane and into the central part (cytoplasm) of the cell.
"The stalk essentially increases the cell's reach into the environment but without the cost of increasing the cell's volume and surface area, which would be expensive from an energetic standpoint," Brun said.
Using mathematical models, the scientists showed that absorption of a nutrient using an antenna was a far more efficient morphology for nutrient uptake than alternate cell shapes in which the stalk plays no special role. The models assume the bacteria encounter nutrients via diffusion from their surrounding medium.
"Our report makes the point that in calm aquatic environments where there is no mixing of the liquid and therefore the motion of nutrient molecules is dominated by diffusion, it is the cell's length that is the most important parameter for nutrient uptake," Brun said.
"Imagine the nutrient molecule as a tiny tennis ball undergoing diffusion, that is bouncing back and forth off other molecules in random directions. It is easy to imagine that the tennis ball will be just as likely to make contact with a baseball bat as it will a tennis racket. And the longer the baseball bat, the larger the number of diffusing tennis balls that will make contact. That's why the stalk seems to be so advantageous for the cell. This is in contrast to cases where there is mixing of the liquid and where total surface area -- not length -- becomes more important. The stalk shape is advantageous in both situations because it increases surface area with minimal increase in volume, and at the same time it can be 15 or more times longer than the cell body."
The implications of the group's discovery are two-fold, Brun said. If stalks improve the efficiency of the uptake of other nutrients, the structures and appropriate transport proteins could be added to bacteria commonly used in drug production and toxic spill clean-ups. Bacteria are often used as workhorses in the mass-conversion of one molecule to another. Improving the speed of uptake of a substrate molecule by the bacteria could hypothetically speed drug production. "If we could figure out how to get the bacteria used in bioremediation to make stalks, we could improve their ability to take up pollutants and up their efficiency," he said.
But Brun also says the discovery has ecological significance. "Bacteria with stalks and other prostheses are ubiquitous in all the earth's aquatic environments," he said. "Phosphorus is a limiting nutrient in determining the productivity of lakes and oceans. The stalked bacteria are central players in scavenging phosphorus in oceans and lakes, and reintroducing it into the food chain."
C. crescentus is an unusual bacterium whose lifespan encompasses two phases: a mobile "swarmer" phase, in which the cells have a single flagellum, and a sedentary "stalked" phase in which the cells shed their flagella, affix themselves to rocks or pebbles (or the sides of water pipes) with the help of a very sticky adhesive, and then grow a stalk.
In April, Brun and colleagues from Brown University reported in the Proceedings of the National Academy of Sciences that the polysaccharide adhesive C. crescentus uses to affix itself to solid objects appears to be the strongest glue produced in the natural world.
David Bricker | EurekAlert!
Could this protein protect people against coronary artery disease?
17.11.2017 | University of North Carolina Health Care
Microbial resident enables beetles to feed on a leafy diet
17.11.2017 | Max-Planck-Institut für chemische Ökologie
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
17.11.2017 | Physics and Astronomy
17.11.2017 | Health and Medicine
17.11.2017 | Studies and Analyses