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Spore memory links different stages of the bacterial life cycle

Spore memory links different stages of the bacteriallife cycle

February 12, 2018

Scientists at the Max Planck Institute for Terrestrial Microbiology and BioQuant, the Center for “Quantitative Analysis of Molecular and Cellular Biosystems” of the University of Heidelberg have shown how “spore memory” gives rise to complex adaptive behaviors in microbes. The study was published in Nature Communications.

To cope with fluctuations in nutrient availability, many bacteria switch between growth and dormancy by making a spore. By tracking Bacillus subtilis through its adaptive life-cycle, the Max Planck Research Group of Dr. Ilka Bischofs were surprised to find that spores appeared to “remember” when they were made: upon arrival of new nutrients the spores that had formed early revived more successfully than spores that had formed later.

<div style="text-align: justify;">The phenotypic memory of <em>B. subtilis</em> spores can be visualized by tagging the enzyme Alanine dehydrogenase with a red fluorescent protein. Early-forming spores have higher enzyme levels than late forming spores (left) and thus they revive more efficiently in response to L-alanine (right).</div> Zoom Image
The phenotypic memory of B. subtilis spores can be visualized by tagging the enzyme Alanine dehydrogenase with a red fluorescent protein. Early-forming spores have higher enzyme levels than late forming spores (left) and thus they revive more efficiently in response to L-alanine (right).

The basis of this “memory” involves a metabolic enzyme that powers bacterial growth. Bacteria make the enzyme when the nutrient is available and stop its synthesis upon depletion. Although no new enzymes are made, the existing proteins are carried-over from one cell generation to the next until sporulation, upon which they are stored in the spore, awaiting new nutrients. In this way, spores obtain a stable so-called “phenotypic memory” of the growth and gene expression history of their progenitor cells that affects their future behavior. Since a considerable portion of a spore’s proteome is made prior to sporulation more proteins likely contribute to this memory.

Phenotypic memory has profound consequences for the production of spores. Similarly as for plant seeds or fish eggs, there is a tradeoff between quantity and quality: bacteria can either make many spores to revive in rich environments, or few but better spores that can also revive in scarce environments. On evolutionary time-scales, this tradeoff could thus drive adaptions to different ecological niches.

 

Reference

A. Mutlu, S. Trauth, M. Ziesack, K. Nagler, J. Bergeest, K. Rohr, N. Becker, T. Höfer and I. B. Bischofs
Phenotypic memory in Bacillus subtilis links dormancy entry and exit by a spore quantity-quality tradeoff
Nature Communications 9:69, 2018

 
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