title: Bacillus cereus spores release alanine that synergizes with inosine to promote germination.
abstract: BACKGROUND
  The first step of the bacterial lifecycle is the germination of bacterial spores into their vegetative form, which requires the presence of specific nutrients. In contrast to closely related Bacillus anthracis spores, Bacillus cereus spores germinate in the presence of a single germinant, inosine, yet with a significant lag period.
  
  
  RESULTS
  We found that the initial lag period of inosine-treated germination of B. cereus spores disappeared in the presence of supernatants derived from already germinated spores. The lag period also dissipated when inosine was supplemented with the co-germinator alanine. In fact, HPLC-based analysis revealed the presence of amino acids in the supernatant of germinated B. cereus spores. The released amino acids included alanine in concentrations sufficient to promote rapid germination of inosine-treated spores. The alanine racemase inhibitor D-cycloserine enhanced germination of B. cereus spores, presumably by increasing the L-alanine concentration in the supernatant. Moreover, we found that B. cereus spores lacking the germination receptors gerI and gerQ did not germinate and release amino acids in the presence of inosine. These mutant spores, however, germinated efficiently when inosine was supplemented with alanine. Finally, removal of released amino acids in a washout experiment abrogated inosine-mediated germination of B. cereus spores.
  
  
  CONCLUSIONS
  We found that the single germinant inosine is able to trigger a two-tier mechanism for inosine-mediated germination of B. cereus spores: Inosine mediates the release of alanine, an essential step to complete the germination process. Therefore, B. cereus spores appear to have developed a unique quorum-sensing feedback mechanism to monitor spore density and to coordinate germination.
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America.
authors.forename: Tetyana
authors.initials: T
authors.lastname: Dodatko
authors.forename: Monique
authors.initials: M
authors.lastname: Akoachere
authors.forename: Stefan M
authors.initials: SM
authors.lastname: Muehlbauer
authors.forename: Forrest
authors.initials: F
authors.lastname: Helfrich
authors.forename: Amber
authors.initials: A
authors.lastname: Howerton
authors.forename: Christian
authors.initials: C
authors.lastname: Ross
authors.forename: Vicki
authors.initials: V
authors.lastname: Wysocki
authors.forename: Jürgen
authors.initials: J
authors.lastname: Brojatsch
authors.forename: Ernesto
authors.initials: E
authors.lastname: Abel-Santos
mesh_terms: D000409:Alanine / Q000378:metabolism*; D001409:Bacillus cereus / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D007288:Inosine / Q000378:metabolism*; D013171:Spores, Bacterial / Q000502:physiology*
chemical_list: D007288:Inosine; D000409:Alanine