Even among bacteria there are those that go by the Estonian proverb “Wake up early, go to bed late”, as scientists at the University of Tartu have managed to show. Now the same scientists are looking for a way to make all bacteria act this way, as it would make treatment of the diseases they cause much easier.
In an article published at the beginning of April in Scientific Reports, an offshoot journal of the renowned science journal Nature, Arvi Jõers and Tanel Tenson show how bacterial cells awake from dormancy. It turns out that bacteria possess something resembling memory, and those that drop off last will be the first to wake up.
It is quite common for bacteria to enter the state of dormancy, as Jõers, a senior researcher, explains. “There are periods when bacteria have a lot to eat; then they run dry of the food and a famine begins. During evolution, bacteria have acquired a variety of mechanisms to survive such train of events. When the food runs out, bacteria enter into a state of dormancy, comparable to the hibernation of bears”.
When food sources recover, bacteria wake up and start reproducing. Scientists already knew that some bacteria wake up quicker, while others take more time. It happens this way despite the fact that each bacterium in a colony is genetically identical to the others.
The differences make survival possible
This unevenness has an evolutionary explanation – if the future is unclear, there is a point in bringing about individuals with different properties among the bacteria population. “Presumably some of them are optimal in the future environment, but we don’t know which ones”, Jõers explains. “It’s a bit like choosing a portfolio for a pension fund. We don’t know exactly which stock works the best. We buy many different ones, just in case, as some are supposed to bring profit”.
“When the environment is good and it remains this way, the best strategy is to begin quick growth immediately”, Jõers says. “But catastrophes can happen in the environment as well, such as heatwave, increased ultraviolet radiation, antibiotic treatment. In an environment impacted by things like this, hibernation turns out to be the best choice, as bacteria really endure in this state”.
Jõers and Tenson performed experiments with E. coli, a bacterium quite common in the human organism, which in certain circumstances might cause diseases. After producing fluorescent proteins in bacteria so that the activity level of a single cell could be observed, they noticed that the way bacteria wake up from the dormancy is not random, as was thought before.
“We showed that the time when a bacterium enters into dormancy at the end of a growth cycle influences the time when it wakes up in the next cycle”, Jõers says. “Some bacteria drop off a little earlier while the others still thrive, using up the last energy the environment has to offer, thus falling ‘asleep’ a bit later. This difference is enough to make waking time differ, too”.
In addition, the scientists found out that bacteria are able to evaluate how quickly they should wake up. “When the environment is a little better, when it includes some substance that ‘tastes better’ to the bacteria, more of them wake up”, Jõers says. With E. coli, glucose – grape sugar – was the reason. Even if it was available in only a small amount, bacteria interpreted the signal as favourable and started waking up much quicker than with other nutrients.
“It seems that although in dormancy, bacteria still somehow get that it is an especially good situation and immediate awakening pays off”.
“Sleeping” bacteria are communicating
Understanding the behaviour of bacteria can open up new ways to beat diseases. “The trouble is that when a bacterium is in dormancy, it is almost impossible to kill it with antibiotics”, according to Jõers. “It is a medical problem of quite a substantial kind, actually”.
“When we are able to understand what controls whether a bacterium is active and receptive to antibiotics or, conversely, in hibernation, we might be able to somehow affect it”, he adds.
“We have some tentative data that bacteria might communicate between each other. It seems that if growth is predisposed, growing bacteria signals to those that haven’t awakened yet that the environment is good – they can wake up, too”, as Jõers describes the current research.
“The thing that makes the latter bacteria wake up as well is probably some kind of molecule secreted by the bacteria that has already awakened”, he says. After the possible discovery of this molecule, there might be a way to deceive the pathogens in the organism, luring them all into an active state.
“We ‘broadcast’ the specific signal into the environment, so everyone begins wanting to grow, thus making it easier to kill them”, says Jõers in describing the desirable outcome of the study. “At this moment, we are actively searching for the molecule. We don’t yet know what it is, but we are working on it”.
Arko Olesk is a science journalist.
The Estonian version of this article was first published in the Estonian daily Postimees.
Jõers A, & Tenson T (2016). Growth resumption from stationary phase reveals memory in Escherichia coli cultures. Scientific reports, 6 PMID: 27048851