AUG 11, 2015 08:58 AM PDT

The Secret Lives of Bacterial Toxins

WRITTEN BY: Kerry Evans
Bacteria spend a lot of time and energy avoiding detection by the immune system (no self-respecting pathogen gives up without a fight). One mechanism is to avoid being eaten by phagocytes, white blood cells charged with seeking out and destroying foreign invaders (the video below shows a phagocyte chasing bacteria in real-time). Some bacteria, such as Staphylococcus aureus, do this by forming impenetrable biofilms, while E. coli was shown to produce a protective cell-surface capsule after prolonged growth with phagocytes. Other species produce toxins to "poison" the host immune response.

A phagocyte (yellow) uses actin filaments to engulf bacteria (pink).




















ACD (for "actin crosslinking domain") is a toxin produced by a handful of bacterial species. Vibrio cholera and its close relative Vibrio vulnificus (bacteria that cause cholera and shellfish-associated food poisoning, respectively), along with Aeromonas hydrophila, all produce ACD.

Researchers knew that ACD effectively stopped immune cells from approaching and engulfing bacteria, but the precise mechanism of action was unclear. It was thought that ACD simply bound to actin monomers, preventing them from polymerizing into the functional filaments that allow immune cells to change their shape and engulf bacteria. This would require large amounts of ACD to be present in each host cell, however, researchers knew that only a small amount of ACD was required to disarm the host. This led David Heisler, a graduate student at The Ohio State University, to dig a little deeper. He suspected that ACD targeted other host proteins in addition to actin. Heisler and colleagues published their findings in the July 31 issue of Science.

In order to polymerize into filaments, actin monomers require the help of an additional protein called formin. Heisler demonstrated that in addition to binding actin, ACD effectively prevented formin from polymerizing free actin into functional filaments. Essentially, formin has a greater affinity to interact with ACD/actin complexes, than with actin alone. Thus, small amounts of ACD are able to start a chain reaction that "poisons" all of the actin in the cell.

Or, as senior author Dmitri Kudryashov puts it, "it appears that this toxin followed some of the most sophisticated battlefield strategies long before they were invented by humans: it recognizes that to win the war, one doesn't need to kill all the soldiers. All that is needed is to send in a spy to recruit a few soldiers who will betray their own army and neutralize the officers".



Sources: Eurekalert, The Scientist
About the Author
  • Kerry received a doctorate in microbiology from the University of Arkansas for Medical Sciences.
You May Also Like
OCT 14, 2019
Microbiology
OCT 14, 2019
Engineering Bacteria to be Tumor Assassins
Some cutting-edge techniques are being combined to create powerful and innovative therapeutics....
OCT 14, 2019
Cardiology
OCT 14, 2019
Stem Cells Improve Post Infarction Repair
Following a heart attack, tissues within the heart are often damaged. Once damaged, the heart is incapable of regeneration of these tissues. These dead are...
OCT 14, 2019
Microbiology
OCT 14, 2019
Colombia Declares a State of Emergency as Banana Fungus Reaches the Americas
Bananas: the world's most popular fruit, a major source of food for millions of people, and now, seriously threatened by fungus....
OCT 14, 2019
Microbiology
OCT 14, 2019
Using Peptides to Remodel the Microbiome
Now that we know so much more about the bacteria we carry in our bodies, it may be possible to start using that bacteria to improve our health....
OCT 14, 2019
Cell & Molecular Biology
OCT 14, 2019
A Protein Sensor That Helps a Stomach Bug Find a Good Home
A bacterial pathogen called Helicobacter pylori is known to colonize the stomach and cause ulcers....
OCT 14, 2019
Health & Medicine
OCT 14, 2019
Honey As An Antibacterial Against Methicillin-Resistant Staphylococcus Aureus
Honey has been used for its medicinal properties for thousands of years to treat wound infections, gastrointestinal ailments, and burns. Because of th...
Loading Comments...