Preserving spore dormancy

Many Firmicutes survive harsh conditions by forming dormant, resistant endospores that later resume growth through germination. Because germination abolishes spore resistance, developing spores must avoid responding to germinants too early. This thesis examines how sporulating bacteria prevent premature germination during spore development. In Bacillus subtilis, L-alanine and L-valine create a metabolic conflict: they are required for biosynthesis during sporulation but also act as strong germinants. Wild-type populations resolve this by collectively depleting extracellular alanine and valine before spores become fully responsive. When enzymes needed for their catabolism are absent, these amino acids accumulate and trigger premature germination. Alanine depletion is not simply general nutrient consumption, since amino acids are removed with different efficiencies. Other alanine-germinating Bacillus species also deplete alanine extensively, whereas non-spore-forming bacteria show no consistent pattern. This suggests that germinant choice is constrained by the ability to eliminate a potential germinant during sporulation. Experimental evolution showed that germinant sensing can adapt when clearance is disrupted. Suppressor populations restored stable, heat-resistant spore production despite alanine accumulation. Most adaptations tuned the germinant receptor rather than eliminating it, reducing responsiveness to L-alanine or increasing inhibition by D-alanine. This demonstrates tight coupling between germinant metabolism and sensing. Additional suppressors revealed that changes in the spore-envelope properties shape germinant exposure. Reduced envelope permeability likely limited germinant access to receptors, while altered amino acid transport suggested that uptake into the mother cell can raise intracellular germinant levels and promote premature germination. Mother-cell metabolism provides further protection by limiting alanine accumulation. Together, these findings show that B. subtilis prevents premature germination by clearing germinants at both population-wide and cellular levels, suggesting that germinant sensing and metabolism co-evolve.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Christian-Albrechts-Universität zu Kiel

Year

2026

Author dc:creator

• Kasu, Iqra Rafik

Contributors dc:contributor

• Lopez Garrido, Javier
• Bramkamp, Marc
• Holtgrewe Stukenbrock, Eva

• Spore formers
• Bacillus subtilis
• Sporulation
• Germination
• Metabolism
• Alanine
• Co-evolution

Repository record source_url

https://macau.uni-kiel.de/receive/macau_mods_00008405

OAI identifier oai:identifier

oai:macau.uni-kiel.de:macau_mods_00008405