Bacterial research grows better understanding

Last updated 16:51 08/04/2014

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Bacteria are much better at fighting off infection than previously thought, an Otago University study shows.

The findings have implications for improving the understanding of how bacteria evolve, including the spread of antibiotic resistance genes.

The research team, some members of which came from the Netherlands, investigated an adaptive immune system called CRISPR-Cas found in half of the bacterial species.

Through the system, bacteria create a genetic memory of specific past infections by plasmids - small mobile DNA molecules that can move between organisms - and viruses.

The system stole samples of an invader's genetic material and stored them in a memory bank so it could immediately recognise future exposures and neutralise the attack, team leader Peter Fineran, from the university's microbiology and immunology department, said.

It had been thought invaders with enough mutations could evade the immune system because the system would not recognise them.

"What we have now discovered is that while the viruses and plasmids can evade direct recognition by acquiring multiple mutations, the system is primed to quickly generate a new immunity by grabbing a new sample of the mutated genetic material," Fineran said.

"It's a remarkably flexible and robust immune system for such simple single-celled organisms."

The bacterial immune system could stop bacteria from acquiring antibiotic resistance genes moved around by plasmids, which could pass between different bacterial species.

The challenge was to work out how to apply that information directly. Understanding the processes could lead to ways to tweak the system.

"We know we can get this system to be quite rapid at removing plasmids that have antibiotic resistance on them in the lab," Fineran said.

"If we knew a way to tweak the system in an applied setting, then we would be able to potentially reduce the chance of bacteria developing resistance."

A war between bacteria and viruses underpinned everything from how global nutrient cycles operated to how human pathogens evolved.

For example, bacteria that caused cholera and diphtheria had been infected by viruses that provided genes coding for toxins. That converted the bacteria into significant human pathogens.

Fineran said that in the most extreme case, researchers had found bacteria with nearly 600 snippets of information in their memory bank representing different exposures to infection.

"What's really quite amazing about these systems is they actually pass the memory [of invaders' genetic material] on to all the daughter cells. It's a heritable memory," he said.

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