Nav: Home

Where wood is chopped, splinters must fall

January 22, 2016

Bacteria and other prokaryotes have been around for billions of years because they managed to develop successful evolutionary strategies for survival. For instance, they possess defense mechanisms that allow them to discriminate between self and non-self DNA in the event of a virus infection. These defense mechanisms are called restriction-modification systems and are based on the balance between the two enzymes M (methyltransferase) and R (restriction endonuclease). M tags endogenous DNA as self by methylating short specific DNA sequences--called restriction sites, and R recognizes unmethylated restriction sites as non-self and cleaves the DNA to render it harmless.

It has been suspected that the discrimination mechanism of restriction-modification systems may be imperfect and that also bacteria may experience autoimmunity issues because the number of restriction sites in many bacterial genomes is lower than expected. On the upside of potential mistakes, occasional cleavage of self-DNA could promote DNA recombination and contribute to genetic variation in microbial populations, thus facilitating adaptive evolution. On the downside however, it might lead to cell death and thus impose a fitness cost on bacterial populations. Despite these potential implications, autoimmunity in bacteria has not been directly observed so far.

Maros Pleska, a graduate student in the laboratory of C?lin Guet, an Assistant Professor at IST Austria, together with the teams of their colleagues Edo Kussell of New York University and Yuichi Wakamoto of Tokyo University, as well as IST Austria postdoc Tobias Bergmiller examine this scenario in their paper published on January 21, 2016, in Current Biology.

The authors studied two different restriction-modification systems originating from the bacterium Escherichia coli, named EcoRI and EcoRV (pronounced as "eco R one" and "eco R five"). Pleska and his colleagues analyzed populations as well as single cells carrying these restriction-modification systems and found that EcoRI is indeed prone to erroneously cleave self DNA while EcoRV is not. These autoimmune events are very rare and easily masked by the majority of unaffected cells, which is why, up until now, detection of bacterial autoimmunity was a major experimental challenge.

The authors managed to spot the rare events of bacterial autoimmunity and show that when they occur, the SOS response is triggered and specific proteins disengage to repair the damaged DNA. By comparing and counting nearly one hundred thousand bacterial colonies (see picture), the authors found out that under standard conditions, everything works just fine, but the ability to fix the damage is decreased in conditions where resources are scarce.

But why are some restriction-modification systems more likely to cause autoimmunity than others? Guet and his team found that the probability of cleaving self DNA is higher for more efficient restriction-modification systems--in this case EcoRI. It almost seems as if these systems are overeager at times in their attempt to protect the cell from harm. The result suggests the existence of an evolutionary tradeoff between enhanced protection against exogenous DNA and increased autoimmunity.

The autoimmunity work would not have been possible without the highly interdisciplinary team from Austria, Japan and USA, which was supported by a Young Investigator Human Frontier Science Grant to Guet, Kussell and Wakamoto that specifically supports high risk interdisciplinary projects, as well as a DOC OeAW Fellowship awarded to Pleska.
-end-


Institute of Science and Technology Austria

Related Bacteria Articles:

Conducting shell for bacteria
Under anaerobic conditions, certain bacteria can produce electricity. This behavior can be exploited in microbial fuel cells, with a special focus on wastewater treatment schemes.
Controlling bacteria's necessary evil
Until now, scientists have only had a murky understanding of how these relationships arise.
Bacteria take a deadly risk to survive
Bacteria need mutations -- changes in their DNA code -- to survive under difficult circumstances.
How bacteria hunt other bacteria
A bacterial species that hunts other bacteria has attracted interest as a potential antibiotic, but exactly how this predator tracks down its prey has not been clear.
Chlamydia: How bacteria take over control
To survive in human cells, chlamydiae have a lot of tricks in store.
Stress may protect -- at least in bacteria
Antibiotics harm bacteria and stress them. Trimethoprim, an antibiotic, inhibits the growth of the bacterium Escherichia coli and induces a stress response.
'Pulling' bacteria out of blood
Magnets instead of antibiotics could provide a possible new treatment method for blood infection.
New findings detail how beneficial bacteria in the nose suppress pathogenic bacteria
Staphylococcus aureus is a common colonizer of the human body.
Understanding your bacteria
New insight into bacterial cell division could lead to advancements in the fight against harmful bacteria.
Bacteria are individualists
Cells respond differently to lack of nutrients.

Related Bacteria Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...