Some living things can switch off their life functions in adverse circumstances and survive decades without any metabolism. Now a team led by Gürol M. Süel from the University of California San Diego has found out how such living beings, despite complete inactivity, notice when it is time to wake up again. As the working group in »Science« reports, spores of the bacterium bacillus subtilis measure the nutrient content of the environment because in its presence potassium flows out of the cell. Only when the potassium concentration falls below a certain threshold will they wake up. In this way, they prevent them from being woken up by random, insufficient signals.
The working group treated the bacterial spores with short pulses of L-alanine, a nutrient that serves as a wake-up signal in B. subtilis. She found that a short pulse wakes up only a small fraction of the spores. However, a second pulse, quite a while later, woke up more than half of the spores. The group interprets this to mean that each environmental signal gradually changes an internal state of the cell until this state reaches a threshold value.
On the basis of theoretical considerations and computer models, the team suspected that the inner state sought could be the electrochemical potential of the cell generated by high concentrations of potassium ions. According to this model, L-Alanin opens pores in the membrane of the spores, so that potassium flows out and the potential decreases. If the potential is low enough, the cell wakes up. However, these channels close again without the nutrient, so that the threshold is only reached at a high nutrient concentration in which the channels open again and again.
This explains the waking behavior of the bacteria in the first attempt. The first nutrient pulse was not enough to wake up a significant part of the spores. But he lowered her potassium supply, and the spores cannot fill it. As a result, they were already much closer to the threshold and more spores in the second nutrient pulse. With this mechanism, the spores can almost count on how much nutrients they encounter - and with it whether it is worth waking up. The whole process is purely passive, so the measurement process does not use energy except the one with which the bacterium pumped potassium in spore formation. As a result, such spores can survive for decades and still wake up when the conditions are favorable.
