Bacteria facing hostile environments can slow their metabolism to the limits of what would be considered alive. This previously unknown survival technique may help us better understand the development of some antibiotic resistance.
The fight against multidrug-resistant bacteria involves the creation of new antibiotics, but also a better understanding of the survival mechanisms that these microbes can adopt.
This resistance often occurs as a result of random mutations that give a bacterium and its offspring the ability to survive an antibiotic. These then become more and more numerous as the bacteria that are still susceptible to the antibiotic die.
However, there are other mechanisms by which these microbes can escape a difficult situation. Researchers at the University of Amsterdam have discovered a new method by which bacteria reduce their metabolic activity without stopping it, and at levels never seen before.
Nicknamed “zombie state” by some, this slowdown allows bacteria to survive while maintaining a level of activity leaving them the opportunity to quickly return to the load once the threat passed.
Bacteria do not all respond in the same way when food resources are lacking or living conditions become too difficult.
Some species will remain active by producing biofilms, walls that include bacterial colonies and allow them to live without being affected by external threats, such as antibiotics.
Other bacteria can go dormant and either stop their growth entirely or form what are called spores, extremely resistant capsules in which dehydrated bacteria can remain dormant for hundreds or even thousands of years.
Although very effective, only certain species of bacteria master this survival technique. In addition, this process requires a lot of energy to be put in place, and some bacteria are not able to emerge from this state when more favorable conditions are restored.
The researchers focused on a very common harmless bacterial species in the soil called Bacillus subtilis. This bacterium normally creates spores for survival, but researchers have noted that a mutant form that is unable to produce spores survives for months in almost pure water, with minimal access to nutrients.
However, the researchers realized that the bacteria were not dormant and that, even if the stress had made it take an unusual spherical shape, several biological processes continued to take place inside.
The bacterium could even continue to divide, even if it did so only once every four days, hundreds of times slower than the normal once every 40 minutes.
This activity slowed to the extreme, however came with one advantage: the bacterium was now much more resistant to oxidative stress and antibiotics.
Researchers have termed this process “oligotrophic growth”, that is, growth that takes place in an extremely nutrient-poor environment. If species other than B. subtilis master this survival technique, this could highlight the method used to survive antibiotics and offer a new target to researchers working to solve this problem.