AUG 11, 2015 8:58 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
JUL 19, 2021
Cell & Molecular Biology
ATP & GTP Are Common in Biology - But What About CTP?
JUL 19, 2021
ATP & GTP Are Common in Biology - But What About CTP?
Adenosine triphosphate (ATP) is a molecule that provides crucial energy to activate a wide array of biological processes ...
JUL 25, 2021
Cell & Molecular Biology
Fungal Pathogens Can Grow on Microplastics
JUL 25, 2021
Fungal Pathogens Can Grow on Microplastics
Microplastics are being found throughout our world; they're in the oceans, in soil, and in our bodies, among other place ...
AUG 05, 2021
Cell & Molecular Biology
Concrete-Loving Bacteria Might be Helpful to Us
AUG 05, 2021
Concrete-Loving Bacteria Might be Helpful to Us
Some bacteria love to live in inhospitable environments that might be excessively hot, dry, or under intense pressure, e ...
AUG 10, 2021
Microbiology
Herbal Medicine May Help Restore the Microbiome, Treat Gulf War Illnesses
AUG 10, 2021
Herbal Medicine May Help Restore the Microbiome, Treat Gulf War Illnesses
About one-third of Gulf war veterans have chronic and unexplained medical issues that include gastrointestinal disorders ...
SEP 06, 2021
Microbiology
Imbokodo Trial Shows HIV Vaccine Candidate Isn't Effective Enough
SEP 06, 2021
Imbokodo Trial Shows HIV Vaccine Candidate Isn't Effective Enough
HIV vaccines have remained elusive in part because the virus has a powerful ability to mutate, and there are so many str ...
SEP 08, 2021
Microbiology
Authorities Work to Contain Nipah Virus Outbreak in India
SEP 08, 2021
Authorities Work to Contain Nipah Virus Outbreak in India
Nipah virus is one of the world's deadliest viruses. It has caused several small outbreaks in Southeast Asia since it em ...
Loading Comments...