The cyanide defense: How one bacterium inhibits predators with poison

December 19, 2017, American Society for Microbiology

Microbiologists in South Korea report this week in mBio that the bacterium Chromobacterium piscinae produces cyanide when under attack from Bdellovibrio bacteriovorus HD100, a microbial predator found in rivers and soils that ingests its prey from the inside out. The researchers found that the prey produced levels of cyanide high enough to inhibit, but not kill, the B. bacteriovorus HD100.

Experiments showed that C. piscinae produced the protective in a nutrient-rich broth. In a medium devoid of nutrients, it didn't produce the cyanide and was consumed. The researchers suspect that the bacteria likely uses some ingredient in the broth to produce the cyanide. That observation implies that a bacteria's defenses may depend on location - and, more generally, that bacteria may harbor protective mechanisms that are triggered in some environments, but not in others.

Studying such mechanisms may lead scientists to better understand how some protect themselves against antibiotics, says microbiologist and study leader Robert Mitchell. His lab at the Ulsan National Institute of Science and Technology, in South Korea, focuses on understanding how microbial prey protect themselves from predators. They are investigating how bacterial predators like B. bacteriovorus HD100 might be optimized as "living antibiotics" that can target bacterial pathogens.

The study suggests microbes may have means for resisting predation that only show up in certain environs. "Resistance may be present, but we're not finding it because we're not looking in the right conditions," he says. "This study is kind of like a warning. To understand how germs may resist treatment, we need to look at the actual conditions in the host."

The new findings in mBio align with work published earlier this year by Mitchell's group, which identified compounds in human blood that inhibit predation of infectious bacterial strains - like E. coli and Salmonella enterica - by B. bacteriovorus HD100.

When the researchers searched for clues for how C. piscinae resists predation, Mitchell says they didn't expect to find cyanide. Their investigation began when, in earlier experiments, they noticed the bacterium survived attacks in nutrient-rich media. In a nutrient-poor environment, however, the predator ate the prey.

Their first suspect was violacein, a metabolite produced by C. piscinae that is structurally similar to a compound they'd previously linked to predatory inhibition. However, experiments showed it wasn't responsible.

"We had to scour the literature to find anything else we didn't know," Mitchell says.

Ultimately, one of his students identified cyanide as the culprit. The researchers verified that C. piscinae produced large amounts of cyanide when cultured in nutrient-rich broth, and that those cultured in HEPES, a nutrient-poor buffer, didn't. Further experiments confirmed that cyanide does inhibit the B. bacteriovorus HD100. The cyanide didn't poison the C. piscinae. "Some of the data in our study suggests the can degrade it," Mitchell says.

The group now plans to look at how other predatory bacteria respond to cyanide, as well as other factors that can potentially inhibit or negatively impact predatory activity in microbes.

Explore further: Predatory bacteria as a new 'living' antibiotic

Related Stories

Predatory bacteria—the quest for a new class of antibiotics

October 11, 2017

In 2016, the World Health Organization named antibiotic resistance as "one of the biggest threats to global health, food security, and development today." The announcement cited a growing list of infections, such as tuberculosis ...

Defence at almost any price

December 13, 2017

Even bacteria have enemies – in water, for example, single-celled ciliates preferably feed on microbes. The microbes protect themselves against predators by employing a variety of tricks, which the ciliates, in turn, attempt ...

E. coli survives predatory bacteria by playing hide and seek

February 22, 2016

The majority of disease-causing bacteria in the body are rendered harmless by the protective effects of the immune system. Those that manage to escape the immune system can be killed by antibiotics, but bacteria are becoming ...

Recommended for you

Double the stress slows down evolution

December 6, 2018

Like other organisms, bacteria constantly have to fight to survive in hostile living conditions. Together with colleagues in Finland, researchers at the Max Planck Institute for Evolutionary Biology in Plön have discovered ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.