Bacterial spores that hibernate millions of years offer key insights into evolution

Like a bear that falls into a deep sleep when winter arrives, bacterial spores can also remain dormant for a long time and then “wake up” to function with an extraordinary genetic memory system. 

A new study at the Hebrew University of Jerusalem (HU) discovered key insights into their evolutionary strategies to survive that could potentially impact fields such as microbiology, biotechnology, and medicine. 

Bacterial spores are the most dormant form of bacteria since they undergo minimal metabolism, respiration, and reduced enzyme production. Chemical disinfectants like chlorine bleach can kill bacteria, but they can’t wipe out spores. High-temperature sterilization under high pressures destroys spores and bacteria. 

The research headed by Prof. Sigal Ben Yehuda and her HU team has unveiled a fascinating facet of bacterial dormancy, as it explains the mechanism by which dormant bacterial spores uphold and activate an enduring transcriptional program upon revival, showcasing an amazing genetic memory system. 

They said their discovery was very important, as it unravels the mechanisms governing how these organisms retain vital genetic information during years of dormancy. Understanding this process not only sheds light on bacterial survival in harsh conditions but also holds broader implications that impact a variety of scientific and medical fields. Such knowledge could lead to strategies to control pathogens, enhance biotechnological processes, and deepen our understanding of dormant states across different life forms.

Spores serve as a survival mechanism against adverse conditions. Bacterial spores are among the longest-living cellular forms on Earth, and they can be revived after millions of years of inactivity. Bacterial spores are among the longest-living cellular forms on Earth, with reports evoking their revival capacity from 25- to 40-million-year-old amber. 

and even from a 250-million-year-old primary salt crystal.

They encapsulate the organism’s genetic material and essential components, remaining dormant until conditions become favorable for germination. 

The study, just published in the journal Molecular Cell under the title “Dormant bacterial spores encrypt a long-lasting transcriptional program to be executed during revival,” highlights the discovery of a central chromosomal domain within dormant spores. This domain hosts core RNA polymerase (RNAP) that remains bound to specific intergenic promoter regions during dormancy. These regions exert control over genes crucial for essential cellular functions, such as the production of rRNAs and tRNAs.

Upon emergence from dormancy, the RNA polymerase inside these spores promptly launches the copying of vital genetic instructions and recruits necessary components for transcription like sigma factors, swiftly activating essential genes necessary for cellular functions. The study also observed a similar process in disease-causing bacteria that form spores, suggesting a common strategy among various organisms to reinitiate functions after dormancy.

The research also uncovered the pivotal role of spore DNA-compacting proteins in this process. Mutants lacking these proteins displayed scattered RNAP localization, resulting in disorganized gene expression during germination. This underscores the significance of maintaining proper chromosomal structure in preserving the transcriptional program crucial for spore revival.

Ben Yehuda commented that the research “suggests that the structure of the spore chromosome is designed to uphold a blueprint for gene activity by pausing RNA polymerase, in a standby mode, ready to resume gene expression when conditions favor revival. This mechanism’s relevance might extend beyond bacteria, offering valuable insights into maintaining enduring gene activity plans across various organisms that undergo dormant life stages.”