What doesn’t kill you makes you stronger
Bacteria can overcome environmental challenges by killing nearby bacteria and incorporating their DNA.
Every year, antibiotics save millions of lives, but this may not last forever. The bacteria that cause infections are getting smarter and continuously evolve genes to become resistant to antibiotics, which makes it harder to kill them. In many cases, using stronger drugs can bypass this problem, but some ‘super-bugs’ are developing resistance to every drug we have. For example, the bacterium Acinetobacter baumannii has recently been classified as a global threat that kills thousands of people every year, which placed it on a top six ‘most wanted’ list for multi drug-resistant bacteria. Worryingly, this drug resistance seems to develop faster than ‘standard’ evolution would allow, making it difficult to keep up with developing new effective drugs.
One way bacteria can shortcut the evolution of resistance is through a process called horizontal gene transfer, in which they collect resistance genes from other bacteria. Some bacteria can speed up this gene transfer by actively killing their neighbors to extract their DNA. However, until now, this process has not been observed directly, and it was not fully understood where and when killing neighbors becomes important for gene transfer.
Now, Cooper, Tsimring and Hasty have studied a relative of A. baumannii called A. baylyi. Together with another type of bacteria that contained green fluorescence genes, A. baylyi was placed onto a surface that allowed both species to grow. As the two types of bacteria grew together, A. baylyi started to kill the other one and stole their genes. This happened so often that some started to become fluorescent, which could be observed in real time under a microscope. A. baylyi also stole genes for antibiotic resistance, and when an antibiotic was added, the bacteria with the stolen resistance genes kept growing and dividing, while the others were killed.
Cooper et al. then developed a mathematical model to quantify and simulate this killing-enhanced horizontal gene transfer. The results showed that killing other bacteria made gene transfer more effective when the number of A. baylyiwas high and the number of ‘victims’ was low — and also when they were together for a shorter period.
This work may help to explain how Acinetobacter and similar bacteria develop drug resistance so quickly. A next step will be to measure and compare gene transfer parameters in different types of bacteria. A better understanding of how, where, and when gene transfer happens, may in the future help to guide strategies to fight resistance.
To find out more
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