Bacterial survival switch triggered by growth rate
A team led by Rice University bioengineering researchers has decoded the mechanism that some bacteria use to make life-or-death decisions during extremely tough times.
Deciphering how bacteria respond to stress could yield new clues for combating food spoilage and for controlling food-borne pathogens. The new study was published in Molecular Systems Biology and sheds light on a long-standing debate about one of the field's fundamental questions: What causes stressed-out bacteria to make the drastic move to cease normal functions and form spores?
"What people in our field have long wondered is, How do spore-forming bacteria like Bacillus make this decision?" said study co-author Oleg Igoshin, associate professor of bioengineering at Rice and a senior investigator at Rice's Center for Theoretical Biological Physics (CTBP). "Is there a specific biochemical trigger that activates one of the network proteins or is sporulation more of a general physiological response?"
To form a hard-shelled spore, which can survive for years without food, the organism must pour its energy into sporulation. Becoming a spore too soon can lead to death by competition -- from neighbors that keep multiplying -- but delaying the decision can lead to death by starvation before the spore is complete.
"It's a high-stakes decision, which suggests that the decision mechanism has come about through intense evolutionary pressure," Igoshin said. "It's also possible that organisms have adopted this same mechanism to make other critical decisions."
B. subtilis is a common soil bacteria and a well-known survivor. It isn't harmful to humans and is even used as a probiotic in some traditional foods. It is so good at forming spores that it's the model organism of choice for biologists who study sporulation.
Almost a decade ago, Igoshin, a computational biologist, began studying the regulatory genes that B. subtilis uses to make sporulation decisions. He and members of his lab interpret the work of experimental collaborators and develop computer simulations to decipher the workings of the regulatory network, such as the switches, feedback loops and signal amplifiers, that B. subtilis uses to make its decision.
In 2012 Igoshin and graduate student Jatin Narula showed how the regulatory network employs a series of nested "feed-forward" loops to filter signal noise, and in 2015 they revealed the network's timing mechanism, a circuit that uses the organism's clock-like DNA replication cycle.
In the new study, which builds upon the 2015 work, Narula, Igoshin and collaborators used their computer model to show how a general physiological cue -- the slowdown of cellular growth -- can trigger B. subtilis' sporulation decisions. Igoshin said the sporulation network is very sensitive to the concentration of a key protein that the cell produces at an essentially constant rate. During starvation, when the cell's growth rate slows, the concentration of this protein builds up, and the bacteria are more likely to form spores. The theoretical work at Rice was experimentally tested in the lab of co-author Gürol Süel of the University of California at San Diego.
Experiments performed by two graduate students in Süel's lab, Anna Kuchina and Fang Zhang, confirmed the main model prediction: Only cells that slow down their growth beyond a threshold value proceed to sporulation. The experimental data indicated that the amount of sporulation network proteins -- but not the activity of the proteins -- was modulated by cell growth, a finding that contradicts the theory that there is a specific biochemical trigger for sporulation.
Igoshin said the finding has important implications for food safety and general microbiology.
"Sporulation by some of the close relatives of B. subtilis is a big hassle for the food-preservation industry because many of those spores can survive boiling temperatures," Igoshin said. "To kill those spores, you need to apply both heat and high pressure. So people have been looking for other methods to inhibit sporulation. If sporulation was triggered by a specific molecule, then perhaps a drug could be found to block that molecule, but our research suggests that sporulation is a general physiological response and that food safety engineers will need to look for other methods of control.
"Moreover, there is a good chance that this mechanism controls key decisions in other bacterial species," he said. "It ties to very basic bacterial physiology, and as a result, I think it may be universal."
Masaya Fujita of the University of Houston is also a co-author of the study. The research was supported by the National Science Foundation, the National Institutes of Health and the Howard Hughes Medical Institute.
The DOI of the Molecular Systems Biology paper is: 10.15252/msb.20156691
A copy of the paper is available at: http://msb.
Related B. subtilis research from Rice:
This release can be found online at news.rice.edu.
Follow Rice News and Media Relations on Twitter @RiceUNews.
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for best quality of life and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.
David Ruth | EurekAlert!
Single-stranded DNA and RNA origami go live
15.12.2017 | Wyss Institute for Biologically Inspired Engineering at Harvard
New antbird species discovered in Peru by LSU ornithologists
15.12.2017 | Louisiana State University
DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.
Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
15.12.2017 | Power and Electrical Engineering
15.12.2017 | Materials Sciences
15.12.2017 | Life Sciences