'Bug memories' could help fight looming crisis

While it's known bacteria are sometimes able to remember past environments, it's less well understood when and how. Photo / 123RF

Even bacteria have memories - and learning more about them could help combat the grave and growing threat of antimicrobial resistance.

"Bacterial memory" is a relatively unexplored area of science - but a New Zealand-led project aims to shed much more light.

"Many people consider memory to be a trait only animals have," said Dr Olin Silander, a senior lecturer in genetics at Massey University.

"But memory is a more general phenomenon – it's when your experiences in the past affect how you behave in the future."

While it's known bacteria sometimes do this, it's less well understood when and how.

One critical process to understand was why bacteria responded the way they did when antibiotics appeared in their environment.

"We know that bacteria can respond to the presence of antibiotics by slowing or shutting down their metabolism, thereby protecting themselves from the antibiotic and preventing cell death," Silander said.

"It is important for us to understand when this can happen, what levels of antibiotic are required to trigger this response, how long this response lasts, and whether this response can protect the bacteria from antibiotics they have not yet seen.

"As antibiotic resistance is on the rise both in New Zealand and globally, this might help us to better treat infections and prevent bacteria from becoming transiently resistant to antibiotic treatment."

Already, an estimated 700,000-plus people worldwide die each year due to drug-resistant infections.

But the toll could be much more devastating when even today's easily-treatable diseases were found harder to combat.

One recent landmark report estimated that, without urgent action, antimicrobial resistance would kill 10 million people a year by 2050 - more than will die from cancer.

For Silander and his team, answering the vital questions around memory meant observing single bacterial cells for many many generations, and tracking how long their memories lasted.

It also required being able to control the environmental conditions that bacteria grew in, and to follow those epigenetic processes that took place in the cells - changes that were inherited across generations, yet didn't affect the sequence of their DNA.

Naturally, watching single bacterial cells grow was a challenging prospect, particularly as they were very small and grew very quickly.

"If we want to watch one cell for just 10 generations - approximately five hours - during that time it will produce more than 1000 daughters and granddaughters and great granddaughters," Silander said.

"We have to be able to track just one single cell and ignore all of its offspring – otherwise those daughter cells literally just get in the way and prevent us from seeing the one cell we are interested in.

"If we can't track single cells, we can't measure how long their memory is."

It was also very challenging to track epigenetic changes in single cells.

"Novel DNA sequencing technology might allow us to simultaneously track genetic and epigenetic changes in single cells, and we are currently testing the best methods to do this.

"However, for the most part this is uncharted territory."

In the new project, supported with a $895,000 Marsden Fund grant, Silander and international colleagues will draw on a range of cutting-edge technologies.

"Because one of our primary goals is to observe the behaviour in single bacterial cells, we will need to use new methods to look at single cells for long periods of time.

"We will use high-powered microscopy and microfluidics to isolate bacteria so we can watch them grow and react to the environment."

"With luck, we will be able to make some small steps forward in understanding the range of environmental conditions that bacteria can sense, including their abilities to sense, react and remember when they have encountered even small amounts of antibiotics."