#FEMSmicroBlog: Reviving the View - What it takes for a spore to germinate

02-05-2022

When bacterial spores awake, they germinate to convert into actively growing cells. The germination phase is brief and represents the first and most critical revival event. It was long thought that this event does not require the synthesis of new RNA and proteins. This dogma keeps being challenged as outlined in microLife in the review “Reviving the View: Evidence that Macromolecule Synthesis Fuels Bacterial Spore Germination”. Sigal Ben-Yehuda explains for the #FEMSmicroBlog how – in contrast to the current dogma – bacterial spore germination demands macromolecule synthesis. #FascinatingMicrobes

 

Bacilli bacteria form spores when starved

When starved of nutrients, bacteria from the Bacilli genus can enter a developmental process called sporulation. This process culminates in the production of a highly resilient long-lasting dormant spore, the most resilient cell type known!

Encased by multiple protecting shields, the dormant spore can withstand environmental challenges, including extremes of heat, desiccation, radiation and antibiotic treatment. As such, spore-forming pathogenic bacteria (e.g. Bacillus anthracis causing the anthrax disease) are highly resistant to antibacterial treatments and difficult to eradicate.

Before a spore starts to germinate, it is dormant and covered in spore coats.
Composition of a dormant spore.

Despite residing in a deep quiescent stage, the spore awaits tuned. It keeps communicating with its surrounding, capable of sensing the reappearance of nutrients via dedicated receptors. When nutrients become available, dormancy is ceased and the spore rapidly converts into an actively growing cell.

 

Coming out of bacterial hibernation with germination

The remarkable revival process initiates with a key event, termed germination. This event lasts only a few minutes during which the cell awakes. During germination, the morphology of the spore transits from a phase-bright to a phase-dark state, which can be readily monitored.

The broadly accepted view argues that germination occurs without the need for transcription or translation. This assessment heavily relies on studies, conducted mostly during the 1960s-70s, showing that Bacilli spores can undergo germination in the presence of RNA and protein synthesis inhibitors.

The contrast phase changes during the spore germination process.
The spore germination process. From Zhou et al. (2022).

However, these interpretations were questioned by other researchers at that time. They reasoned that the tested compounds could not cross the impermeable spore shells to reach their targets.  Hence, compounds, incapable of penetrating the spore core, seem unsuitable to report the occurrence of macromolecule synthesis.

The short review “Reviving the View: Evidence that Macromolecule Synthesis Fuels Bacterial Spore Germination”, published in microLife, challenges this notion and discusses experimental data on the awakening process of bacterial spores.

 

Bacteria seem to make RNA and proteins during germination

While following newly synthesized proteins during spore revival, studies revealed that translation indeed occurs during germination. These surprising results came from amino acid tagging experiments that followed newly synthesized proteins in the reviving spore. Furthermore, chemically increasing spore permeability allowed the introduction of ribosome-targeting antibiotics into the spore core to halt protein production. At the same time, spores derived from bacterial strains with mutations in translation factors were identified; they abort germination due to deficiency in protein synthesis.

These findings encouraged to probe for germination-induced transcription. Indeed, the immediate synthesis of transcripts at the onset of germination was detected. Interestingly, this process is dependent on the phosphorylation state of the housekeeping sigma factor A. Notably, both transcription and translation were found to be essential for completing the germination process.

This short review brings to light a collection of overseen investigations, carried out during the 1960s-70s, reinforcing this hypothesis. While this is a timely issue, it is also scientifically fascinating and still a controversial subject.

This discussion should be valuable to many researchers investigating organisms with a quiescent life form, including fungi spores and plant seeds. Furthermore, it can be critical for developing novel strategies to interfere with the germination of spores deriving from dangerous pathogens. Overall, this perspective redefines the process of spore germination and fundamentally challenges the way it is currently viewed.

 

About the author of this blog

Sigal Ben-Yehuda is a Professor at the Hebrew University of Jerusalem, Israel and an EAM member. She graduated from Tel-Aviv University and carried out her postdoctoral research in the laboratory of Prof. Richard Losick at Harvard studying the developmental process of sporulation in Bacillus subtilis. The current research in her lab focuses on spore dormancy and awakening, the characterization of intercellular nanotubes formed among neighbouring bacteria identified in her laboratory, and mechanisms of phage spread in multispecies communities.

About this blog section

The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.

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