Have Your Cake and Eat It Too: Bacteria Can Hedge Their Bets When Living in Unpredictable Environments

by Daria Kaptsan

New research suggests that bacteria divide their risk when facing the unknown, by allowing a sub-population to develop alternative pathways to survive.

This new study is an outcome of collaborative work by Marie Sklodowska-Curie ITN NORA partners from the Norwegian University of Life Sciences and the University of East Anglia in the United Kingdom.

The study has been performed in the model soil denitrifying bacterium Paracoccus denitrificans and such bet-hedging is a novel discovered fitness trait.

When oxygen is limited

Generally, bacteria use oxygen, as it is a preferable electron acceptor. When oxygen becomes a limiting factor for growth, the transcription of denitrification enzymes under tight regulation will be initiated. The denitrification enzymes are nitrate-, nitrite-, nitric oxide- and nitrous oxide- reductases. However this process requires a lot of energy and it is uncertain if anoxic condition will last long.

Scientists suggested a strategy that would secure survival under oxygen depletion to the fraction of population that expresses nitrite reductase, and minimize the energy costs for the fraction that does not.

Old hypothesis, new tools

Last decade it has been speculated that only a minor fraction of P. denitrificans population switches to denitrification when oxygen starts to deplete, and to support this hypothesis the dynamic modeling approach has been used. This approach postulates that: “initial transcription of the nirS gene is stochastic with a low probability (r=0.5% h-1), consistent with only a fraction of cells switching to denitrification in response to oxygen depletion”.

To support the hypothesis and to provide the experimental proof, two young researches within NORA group, Pawel Lycus and Manuel-Soriano-Laguna and their PI’s, have developed molecular tools to investigate this phenomenon. The young scientists have used genetic engineering to develop a fluorescent construct. The fluorescent red protein mCherry was fused to nitrite reductase (NirS). The maturation of mCherry is rapid and allows to see the results soon after activating transcription. This way they could capture the small fraction of bacterial population that has expressed anaerobic respiration machinery and to deliver a strong proof of a concept.

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