Pulsating response to stress in bacteria `discovered`

Washington: If it`s chilly inside your house during the winter, you might just turn the heater on until it warms up outside. So biologists have long thought that cells would respond to their environment in a similar way.

But, now researchers at the California Institute of Technology are finding that cells can respond using a new kind of pulsating mechanism, instead of just shifting from one steady state to another and staying there.

According to them, the principles behind this process are surprisingly simple and could drive other cellular processes, revealing more about how the cells, and ultimately life, work.

In their experiment, the researchers studied how a bacterial species called B. subtilis responds to a stressful environment -- for example, one without food. In such conditions, the single-celled organism activates a large set of genes that help it deal with hardship, by aiding cell repair for instance.

Previously, biologists had thought the bacteria would handle stress by turning on the relevant genes and simply leaving them on until the stress goes away.

Instead, the researchers found that B. subtilis continuously flips these genes on and off.
When faced with more stress, it increases the frequency of these pulses. The pulsating action is like switching your heater on full blast for a brief period every few minutes, and turning it on and off more frequently if you want the house to be warmer.

"It`s a very different view of how a cell can respond to a particular stress," said lead researcher James Locke.

To make their finding, the researchers introduced a chemical to B. subtilis that inhibits the production of ATP, the energy-carrying molecules of cells.

They found that the stress induced by this chemical triggers interactions within a set of genes – collectively called a genetic circuit. This circuit, which contains a set of positive and negative feedback loops, generates sustained pulses of activity in a key regulatory protein called sigma B.

The researchers attached fluorescent proteins to the circuit, causing the cells to glow green when sigma B was activated. By making movies of the flashing cells, the team could then study the dynamics of the circuit.

The key to this pulsating mechanism is the variability inherent in how proteins are made, the researchers say.

This work provides a blueprint for how relatively simple genetic circuits can generate complex and dynamic behaviours in individual cells, the researchers say.

"We`re excited to think that similar mechanisms may occur in other cellular processes. It`d be interesting in the future to see which aspects of this circuit architecture also appear in more complex systems, such as mammalian cells," Locke said.


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