Swarming bacteria “scream” when they die, warning their fellow bacteria of danger. These screams are not audible; instead, they are chemical alarms that the bacteria broadcast while on they are close to death, an action commonly referred to as necrosignaling.
Through necrosignaling, bacteria alert their fellow bacteria to presence of a looming threat and save the majority of the swarm (a bacterial colony that is on the move). When confronted by a threat such as antibiotics, the bacteria’s chemical death cries can provide survivors enough time to go through mutations that develop antibiotic resistance, scientists have reported in a study.
Several species of bacteria swim around with the support of long tail-like structures referred too as flagella, which helps them swiftly. And occasionally, bacteria such as Escherichia coli (E. coli) gather in the billions and use their flagella to move together over solid surfaces, as a swarm. “Bacterial swarms are metabolically active and grow robustly,” the researchers wrote. For that reason, the scientists suspected that swarms might also have their own methods for evolving antibiotic resistance, which might be different from those of individual bacteria.
Researchers previously noted that when swarming bacteria came into contact with antibiotics, about 25% of the roaming colony perished. The deceased bacteria seemed to somehow protect the survivors – surviving cells appeared to actively move away from the antibiotics after a portion of the swarm died. However, it is unclear what guided the bacteria’s behaviour.
In a new study, scientists observed swarms of E. coli bacteria as they clashed with antibiotics, to unravel how decreased cells might help save the rest of the swarm.
Signals from the Deceased
The researchers discovered that deceased E. coli in the swarm released a necrosignal: a protein that linked the outer membranes of the living cells in the swarm. With these dying chemical “screams,” the deceased bacteria activated mechanisms in the membranes of the live cells “to start pumping out the antibiotics,” a researcher mentioned. This might suggest that the compound communicated “a state of emergency,” signalling to the other living bacteria to the presence of danger, the study suggests.
The cascade of genes turned on by necrosignals not only shielded the surviving swarm from antibiotics but promoted future resistance to the compounds that killed their comrades. Furthermore, the scientists figured out that subpopulations of swarm bacteria were genetically variable; some were quicker to catch onto an antibiotic than others. Swarms of bacteria may collectively cultivate different subpopulations as an evolutionary survival method – if new antibiotics kill the vulnerable members of the swarm, their deaths will help shield the remaining members.
According to researchers who took part in this study, “dead cells are helping the community survive”. The findings suggest that in dense bacteria swarms, exposure to low doses of antibiotics could actually promote the acquisition of antibiotic resistance. This is an important consideration for research methodologies for tackling bacterial infections, researchers added.
Ultimately, understanding how we can work around these necrosignals with antibiotics can improve the overall effectiveness of antibiotics. There will most probably be more studies surrounding the topic in the future. These results do offer an insight into the bacterial world that could also be tested against other forms of bacteria and possibly even viruses. If this principle extended to the behaviour of viruses as well this could open new approaches for epidemiologists to synthesize new medications to tackle epidemics and hopefully pandemics. But unfortunately, because of the vast array of bacteria and viruses there are in the world, scientists can never rest on their loins. The world of bacteria influences everything we do so scientists will continue to research.