title: Memory of Germinant Stimuli in Bacterial Spores.
abstract: Bacterial spores, despite being metabolically dormant, possess the remarkable capacity to detect nutrients and other molecules in their environment through a biochemical sensory apparatus that can trigger spore germination, allowing the return to vegetative growth within minutes of exposure of germinants. We demonstrate here that bacterial spores of multiple species retain memory of transient exposures to germinant stimuli that can result in altered responses to subsequent exposure. The magnitude and decay of these memory effects depend on the pulse duration as well as on the separation time, incubation temperature, and pH values between the pulses. Spores of Bacillus species germinate in response to nutrients that interact with germinant receptors (GRs) in the spore's inner membrane, with different nutrient types acting on different receptors. In our experiments, B. subtilis spores display memory when the first and second germinant pulses target different receptors, suggesting that some components of spore memory are downstream of GRs. Furthermore, nonnutrient germinants, which do not require GRs, exhibit memory either alone or in combination with nutrient germinants, and memory of nonnutrient stimulation is found to be more persistent than that induced by GR-dependent stimuli. Spores of B. cereus and Clostridium difficile also exhibit germination memory, suggesting that memory may be a general property of bacterial spores. These observations along with experiments involving strains with mutations in various germination proteins suggest a model in which memory is stored primarily in the metastable states of SpoVA proteins, which comprise a channel for release of dipicolinic acid, a major early event in spore germination.
  
  
  OBJECTIVE
  Cellular memory is defined as a sustained response to a transient environmental stimulus, and yet its generation and storage have not been described in bacterial spores. We demonstrate here that bacterial spores of multiple species retain memory of transient exposures to germinant stimuli that can result in altered responses to subsequent exposure. Memory was induced by activation of germinant receptors (GRs) or by GR-independent germinants and was accessed by both GR-dependent and GR-independent germinants. Analysis of effects on memory of exposure to GR-dependent and GR-independent germinants as well as in spores lacking various germination proteins suggests a model in which memory is stored primarily in metastable states of SpoVA proteins which comprise a channel for release of spore dipicolinic acid. Spore memory can also significantly reduce the concentration of nutrient germinants necessary to trigger germination, and this may be used to respond to low levels of nutrient germinants.
authors.affiliation: Department of Physics, East Carolina University, Greenville, North Carolina, USA.
authors.forename: Shiwei
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Computational and Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Faeder
authors.affiliation: Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Setlow
authors.affiliation: Department of Physics, East Carolina University, Greenville, North Carolina, USA liy@ecu.edu.
authors.forename: Yong-qing
authors.initials: YQ
authors.lastname: Li
mesh_terms: D001409:Bacillus cereus / Q000187:drug effects* / Q000502:physiology; D001412:Bacillus subtilis / Q000187:drug effects* / Q000502:physiology; D001426:Bacterial Proteins / Q000378:metabolism*; D016360:Clostridioides difficile / Q000187:drug effects* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000378:metabolism*; D010848:Picolinic Acids / Q000378:metabolism*; D015398:Signal Transduction; D013171:Spores, Bacterial / Q000187:drug effects* / Q000502:physiology; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D010848:Picolinic Acids; C004860:dipicolinic acid