Characterization of Germination Receptors of Bacillus cereus ATCC 14579

Specific amino acids, purine ribonucleosides, or a combination of the two is required for efficient germination of endospores ofBacillus cereus ATCC 14579. A survey including 20 different amino acids showed thatl -alanine,l -cysteine,l -threonine, andl -glutamine are capable of initiating the germination of endospores ofB. cereus ATCC 14579. In addition, the purine ribonucleosides inosine and adenosine can trigger germination of the spores. Advanced annotation of theB. cereus ATCC 14579 genome revealed the presence of seven putative germination (ger ) operons, termedgerG ,gerI ,gerK ,gerL ,gerQ ,gerR , andgerS . To determine the role of the encoded putative receptors in nutrient-induced germination, disruption mutants were constructed by the insertion of pMUTIN4 into each of the seven operons. Four of the seven mutants were affected in the germination response to amino acids or purine ribonucleosides, whereas no phenotype could be attributed to the mutants with disruptedgerK ,gerL , andgerS loci. The strain with a disruptedgerR operon was severely hampered in the ability to germinate: germination occurred in response tol -glutamine but not in the presence of any of the other amino acids tested. ThegerG mutant showed significantly reducedl -glutamine-induced germination, which points to a role of this receptor in thel -glutamine germination signaling pathway.gerR ,gerI , andgerQ mutants showed reduced germination rates in the presence of inosine, suggesting a role for these operons in ribonucleoside signaling. Efficient germination by the combination ofl -glutamine and inosine was shown to involve thegerG andgerI operons, since the germination of mutants lacking either one of these receptors was significantly reduced. Germination triggered by the combination ofl -phenylalanine and inosine was lost in thegerI mutant, indicating that both molecules are effective at the GerI receptor.