Identification and Characterization of the gerH Operon of Bacillus anthracis Endospores: a Differential Role for Purine Nucleosides in Germination
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan,1 The Institute for Genomic Research, Rockville, Maryland27vk, http://www.100md.com
Received 19 August 2002/ Accepted 18 November 20027vk, http://www.100md.com
ABSTRACT7vk, http://www.100md.com
We identified a tri-cistronic operon, gerH, in Bacillus anthracis that is important for endospore germination triggered by two distinct germination response pathways termed inosine-His and purine-Ala. Together, the two pathways allow B. anthracis endospores a broader recognition of purines and amino acids that may be important for host-mediated germination.7vk, http://www.100md.com
TEXT7vk, http://www.100md.com
Bacterial endospores are metabolically inactive and are capable of surviving extended periods of time under harsh environmental conditions but germinate rapidly in the presence of small molecules termed germinants (2). Work by Hachisuka demonstrated that the addition of exogenous adenosine and L-alanine was required for in vivo germination of Bacillus anthracis in the rat peritoneal cavity, thus establishing nucleosides as potentially contributing to in vivo germination (5). Germination is characterized by the hydration of the core and the breakup of the endospore cortex, though the molecular mechanisms underlying these activities remain undetermined (2, 9). Endospore germination results in the expulsion of Ca2+ and dipicolinic acid and the initiation of metabolic activity (11). Nutrient-triggered endospore germination is facilitated by ger operons, which are believed to encode germinant sensor proteins (9).
Identification and characterization of gerH in B. anthracis. In Bacillus cereus, gerI (gerIABC) is necessary for the triggering of germination by inosine and the disruption of gerIA or gerIB abolishes inosine-triggered germination (1). A BLAST search of the B. anthracis genome (http://www.tigr.org) with gerIA, gerIB, and gerIC from B. cereus (GenBank accession number AF067645) identified homologs in B. anthracis referred to here as gerHA, -B, and -C (open reading frames 02625, 02624, and 02623, respectively). The putative proteins encoded by gerHA, gerHB, and gerHC have 78, 92, and 89% amino acid identity, respectively, to their B. cereus GerI homologs. Unlike with B. cereus, inosine alone does not trigger B. anthracis endospore germination but acts as a potent cogerminant with several amino acids .ih2-i, 百拇医药
fig.ommittedih2-i, 百拇医药
Germination of B. anthracis Sterne 34F2 endospores in a subgerminal concentration of L-alanine plus L-amino acidsih2-i, 百拇医药
To determine a role for gerH in B. anthracis germination, a gerHA-null strain was constructed from the Sterne 34F2 (pXO1+, pXO2-) strain by using forward and reverse primers with 5' XmaI restriction sites (5'-TCCCCCCGGGCAAGAAGGTTTTGTAGAGGA-3', 5'-TCCCCCCGGGGATTGCATAGGCTTTTTAAC-3' ) to PCR amplify gerHA DNA (1.7 kb), which was cloned into pUC19 (New England Biolabs) and maintained in Escherichia coli XL1 Blue (American Type Culture Collection). A central section of gerHA (gerHA) was deleted and replaced by an erythromycin cassette, which had been amplified from pDG641 (Bacillus Genetic Stock Center), at the gerHA ClaI restriction site with appropriate primers (5'-CCATCGATGGGCGGTGTAGATGTTGATGA-3', 5'-CCATCGATGGACATGCTACACCTCCGGATA-3') (3). The resulting construct was transferred into the gram-positive shuttle vector pKSV7, creating pKSV7:gerHA:Erm, and maintained in E. coli GM272 (Bacillus Genetic Stock Center) (10). Electroporation of B. anthracis Sterne 34F2 was performed with polyethylene glycol-precipitated plasmid DNA (8). Transformants were plated on selective medium, and B. anthracis Sterne gerHA-null strains were obtained via allelic exchange, after curing of the plasmid vector containing wild-type gerHA (8). The identity of the null construct was confirmed by PCR and by Southern blotting.
Germinant surveys with an L-alanine-amino acid combination versus an inosine-amino acid combination. B. anthracis Sterne and gerHA-null endospores were preradiolabeled with 45Ca as described previously but with modified G medium (6, 7). Parental and gerHA-null strains exhibited similar vegetative growth kinetics (data not shown). The percentage of germination was measured as the percentage of 45Ca released from spores relative to the total amount of 45Ca contained in a sample (6, 12). Next, the binary combinations of germinants known to trigger germination in B. anthracis were tested to compare profiles of wild-type and gerHA-null strain phenotypes in MES (morpholineethanesulfonic acid) buffer at pH 8.0 by using 106 endospores/ml of germinant solution. Slight differences between the Sterne germination profiles reported here and those for Sterne (pXO1-, pXO2-) reported previously may result from strain differences or from slight variations in experimental conditions (4, 6). In our studies, MES buffer was used to minimize germination enhancement by monovalent ions. The gerH locus was required for germination with inosine-His, inosine-Met, inosine-Phe, inosine-Tyr, inosine-Val, and Ala-Tyr . The loss of Ala-Tyr-triggered germination in gerHA-null spores indicated that gerH also influenced a non-nucleoside-dependent germination pathway . Therefore, B. anthracis gerH facilitates germination via an inosine-amino acid pathway and, to a lesser extent, via an Ala-aromatic-amino-acid pathway. The presence of an aromatic ring structure is required for gerH-mediated germination, and Tyr cannot substitute for inosine with any amino acids other than Ala (6).
fig.ommittedif7t, 百拇医药
Germination of B. anthracis Sterne 34F2 in inosine plus L-amino acidsif7t, 百拇医药
Germinant studies indicate the testing of purine promiscuity with L-alanine but not with histidine. The degree to which purines could be substituted for each other with an amino acid cogerminant was determined for gerHA-null and Sterne endospores. Purine cogerminants (adenosine, guanosine, ATP, GTP, ITP) were substituted for inosine with 1 mM Ala in parental and gerHA-null strains. Each triggered germination to similar levels, with the sole exception of GTP plus Ala, with which the gerHA-null endospores responded more dramatically than did parental endospores . It is possible that a nonproductive interaction that interferes with GTP-Ala-triggered germination in parental, but not gerHA-null, endospores occurs between GTP and GerH proteins.if7t, 百拇医药
fig.ommittedif7t, 百拇医药
B. anthracis Sterne (parental strain; grey bars) and gerHA-null (black bars) endospore germination responses to a subgerminal concentration of alanine (A) and histidine (B) with purine nucleosides and nucleoside triphosphates. We used a subgerminal concentration of L-alanine (1 mM) (A) and a 10 mM concentration of histidine (B) with a 1 mM concentration of adenosine (ADE), inosine (INO), guanosine (GUA), ATP, ITP, or GTP. Purines and amino acids alone at the concentration used stimulated no endospore germination. Percent germination was calculated at 90 min as described in the text. Experiments were performed at pH 8 with 10 mM MES. Each experiment was performed in triplicate with three independent endospore preparations. Experimental error was calculated as 1 standard deviation from the mean.
The requirement of inosine for purine-His-triggered germination is absolute. Replacing inosine with any other purine in combination with His (10 mM) resulted in a total loss of germination. The ability of the gerHA-null strain to germinate via the purine-alanine pathway shows that gerH is not required for an inosine-based response to a subgerminal concentration of alanine. These data demonstrate, for the first time, differential responses to purines of B. anthracis endospores depending on the amino acid supplied as a cogerminant. The purine-Ala pathway exhibited a higher degree of purine promiscuity than the inosine-His pathway. The purines recognized by the purine-Ala pathway and the amino acids recognized by the inosine-His pathway allow a broad recognition of germinants that likely helps B. anthracis endospores recognize varieties of hospitable environments in which to germinate.);|, http://www.100md.com
Recently, the gerS operon in B. anthracis was characterized and was found to mediate the germination of B. anthracis endospores by germinants containing aromatic ring structures (6). Disruption of the gerS locus results in germinant profiles similar to that of the gerH-null strain. A functional relationship may also exist between gerS and gerH, though that relationship remains undefined. If the two loci are redundant, the loss of one should not abolish germination in response to a pair of cogerminants. Alternatively, it is possible that GerH and GerS are functionally redundant and that together they provide a critical number of germinant sensors required to facilitate germination.
ACKNOWLEDGMENTS+|], http://www.100md.com
We thank T. Dixon, J. Ireland, B. Thomason, S. Cendrowski, B. Heffernan, N. Fisher, and N. Bergman for their useful comments on this work.+|], http://www.100md.com
The sequencing of B. anthracis was supported by the ONR, DOE, NIAID, and DERA. This work was supported in part by the NIH grants AI-08649 and AI-40644 and ONR grants 14-00-1-0422, 14-01-1-1044, and 14-02-1-0061 (P.C.H.).+|], http://www.100md.com
REFERENCES+|], http://www.100md.com
Clements, M. O., and A. Moir. 1998. Role of the gerI operon of Bacillus cereus 569 in the response of spores to germinants. J. Bacteriol. 180:6729-6735.+|], http://www.100md.com
Foster, S. J., and K. Johnstone. 1990. Pulling the trigger: the mechanism of bacterial spore germination. Mol. Microbiol. 4:137-141.+|], http://www.100md.com
Guerot-Fleury, A., K. Shazand, N. Frandson, and P. Straigier. 1995. Antibiotic-resistance cassettes for Bacillus subtilis. Gene 167:335-336.+|], http://www.100md.com
Guidi-Rontani, C., Y. Pereira, S. Ruffie, J. C. Sirard, M. Wever-Levy, and M. Mock. 1999. Identification and characterization of a germination operon on the virulence plasmid pXO1 of Bacillus anthracis. Mol. Microbiol. 33:407-414.
Hachisuka, Y. 1969. Germination of B. anthracis spores in peritoneal cavity of rats and establishment of anthrax. Jpn. J. Microbiol. 13:199-207.}j&3}, 百拇医药
Ireland, J. A. W., and P. Hanna. 2002. Amino acid- and purine ribonucleoside-induced germination of Bacillus anthracis {Delta} Sterne endospores: gerS mediates responses to aromatic ring structures. J. Bacteriol. 184:1296-1303.}j&3}, 百拇医药
Kim, H. U., and J. M. Goepfort. 1974. A sporulation medium for Bacillus anthracis. J. Appl. Bacteriol. 37:265-267.}j&3}, 百拇医药
Koehler, T. M., Z. Dai, and M. Kaufman-Yarbray. 1994. Regulation of the Bacillus anthracis protective antigen gene: CO2 and a trans-activating element activate transcription from one of two promoters. J. Bacteriol. 176:586-595.}j&3}, 百拇医药
Moir, A., E. H. Kemp, C. Robinson, and B. M. Corfe. 1994. The genetic analysis of bacterial spore germination. J. Appl. Bacteriol. 77:9S-16S.}j&3}, 百拇医药
Smith, K., and P. Youngman. 1992. Use of a new integrated vector to investigate compartment specific expression of the Bacillus subtilis spoII gene. Biochimie 74:705-711.}j&3}, 百拇医药
Stewart, G., K. Johnstone, E. Hagelberg, and D. J. Ellar. 1981. Commitment of bacterial spores to germinate. A measure of the trigger reaction. Biochem. J. 198:101-106.}j&3}, 百拇医药
Suzuki, J. B., R. Booth, and N. Grecz. 1971. In vivo and in vitro release of Ca [45] from spores of Clostridium botulinum type A as further evidence for spore germination. Res. Commun. Chem. Pathol. Pharmacol. 2:16-23.(Matthew A. Weiner Timothy D. Read and Philip C. Hanna)
Received 19 August 2002/ Accepted 18 November 20027vk, http://www.100md.com
ABSTRACT7vk, http://www.100md.com
We identified a tri-cistronic operon, gerH, in Bacillus anthracis that is important for endospore germination triggered by two distinct germination response pathways termed inosine-His and purine-Ala. Together, the two pathways allow B. anthracis endospores a broader recognition of purines and amino acids that may be important for host-mediated germination.7vk, http://www.100md.com
TEXT7vk, http://www.100md.com
Bacterial endospores are metabolically inactive and are capable of surviving extended periods of time under harsh environmental conditions but germinate rapidly in the presence of small molecules termed germinants (2). Work by Hachisuka demonstrated that the addition of exogenous adenosine and L-alanine was required for in vivo germination of Bacillus anthracis in the rat peritoneal cavity, thus establishing nucleosides as potentially contributing to in vivo germination (5). Germination is characterized by the hydration of the core and the breakup of the endospore cortex, though the molecular mechanisms underlying these activities remain undetermined (2, 9). Endospore germination results in the expulsion of Ca2+ and dipicolinic acid and the initiation of metabolic activity (11). Nutrient-triggered endospore germination is facilitated by ger operons, which are believed to encode germinant sensor proteins (9).
Identification and characterization of gerH in B. anthracis. In Bacillus cereus, gerI (gerIABC) is necessary for the triggering of germination by inosine and the disruption of gerIA or gerIB abolishes inosine-triggered germination (1). A BLAST search of the B. anthracis genome (http://www.tigr.org) with gerIA, gerIB, and gerIC from B. cereus (GenBank accession number AF067645) identified homologs in B. anthracis referred to here as gerHA, -B, and -C (open reading frames 02625, 02624, and 02623, respectively). The putative proteins encoded by gerHA, gerHB, and gerHC have 78, 92, and 89% amino acid identity, respectively, to their B. cereus GerI homologs. Unlike with B. cereus, inosine alone does not trigger B. anthracis endospore germination but acts as a potent cogerminant with several amino acids .ih2-i, 百拇医药
fig.ommittedih2-i, 百拇医药
Germination of B. anthracis Sterne 34F2 endospores in a subgerminal concentration of L-alanine plus L-amino acidsih2-i, 百拇医药
To determine a role for gerH in B. anthracis germination, a gerHA-null strain was constructed from the Sterne 34F2 (pXO1+, pXO2-) strain by using forward and reverse primers with 5' XmaI restriction sites (5'-TCCCCCCGGGCAAGAAGGTTTTGTAGAGGA-3', 5'-TCCCCCCGGGGATTGCATAGGCTTTTTAAC-3' ) to PCR amplify gerHA DNA (1.7 kb), which was cloned into pUC19 (New England Biolabs) and maintained in Escherichia coli XL1 Blue (American Type Culture Collection). A central section of gerHA (gerHA) was deleted and replaced by an erythromycin cassette, which had been amplified from pDG641 (Bacillus Genetic Stock Center), at the gerHA ClaI restriction site with appropriate primers (5'-CCATCGATGGGCGGTGTAGATGTTGATGA-3', 5'-CCATCGATGGACATGCTACACCTCCGGATA-3') (3). The resulting construct was transferred into the gram-positive shuttle vector pKSV7, creating pKSV7:gerHA:Erm, and maintained in E. coli GM272 (Bacillus Genetic Stock Center) (10). Electroporation of B. anthracis Sterne 34F2 was performed with polyethylene glycol-precipitated plasmid DNA (8). Transformants were plated on selective medium, and B. anthracis Sterne gerHA-null strains were obtained via allelic exchange, after curing of the plasmid vector containing wild-type gerHA (8). The identity of the null construct was confirmed by PCR and by Southern blotting.
Germinant surveys with an L-alanine-amino acid combination versus an inosine-amino acid combination. B. anthracis Sterne and gerHA-null endospores were preradiolabeled with 45Ca as described previously but with modified G medium (6, 7). Parental and gerHA-null strains exhibited similar vegetative growth kinetics (data not shown). The percentage of germination was measured as the percentage of 45Ca released from spores relative to the total amount of 45Ca contained in a sample (6, 12). Next, the binary combinations of germinants known to trigger germination in B. anthracis were tested to compare profiles of wild-type and gerHA-null strain phenotypes in MES (morpholineethanesulfonic acid) buffer at pH 8.0 by using 106 endospores/ml of germinant solution. Slight differences between the Sterne germination profiles reported here and those for Sterne (pXO1-, pXO2-) reported previously may result from strain differences or from slight variations in experimental conditions (4, 6). In our studies, MES buffer was used to minimize germination enhancement by monovalent ions. The gerH locus was required for germination with inosine-His, inosine-Met, inosine-Phe, inosine-Tyr, inosine-Val, and Ala-Tyr . The loss of Ala-Tyr-triggered germination in gerHA-null spores indicated that gerH also influenced a non-nucleoside-dependent germination pathway . Therefore, B. anthracis gerH facilitates germination via an inosine-amino acid pathway and, to a lesser extent, via an Ala-aromatic-amino-acid pathway. The presence of an aromatic ring structure is required for gerH-mediated germination, and Tyr cannot substitute for inosine with any amino acids other than Ala (6).
fig.ommittedif7t, 百拇医药
Germination of B. anthracis Sterne 34F2 in inosine plus L-amino acidsif7t, 百拇医药
Germinant studies indicate the testing of purine promiscuity with L-alanine but not with histidine. The degree to which purines could be substituted for each other with an amino acid cogerminant was determined for gerHA-null and Sterne endospores. Purine cogerminants (adenosine, guanosine, ATP, GTP, ITP) were substituted for inosine with 1 mM Ala in parental and gerHA-null strains. Each triggered germination to similar levels, with the sole exception of GTP plus Ala, with which the gerHA-null endospores responded more dramatically than did parental endospores . It is possible that a nonproductive interaction that interferes with GTP-Ala-triggered germination in parental, but not gerHA-null, endospores occurs between GTP and GerH proteins.if7t, 百拇医药
fig.ommittedif7t, 百拇医药
B. anthracis Sterne (parental strain; grey bars) and gerHA-null (black bars) endospore germination responses to a subgerminal concentration of alanine (A) and histidine (B) with purine nucleosides and nucleoside triphosphates. We used a subgerminal concentration of L-alanine (1 mM) (A) and a 10 mM concentration of histidine (B) with a 1 mM concentration of adenosine (ADE), inosine (INO), guanosine (GUA), ATP, ITP, or GTP. Purines and amino acids alone at the concentration used stimulated no endospore germination. Percent germination was calculated at 90 min as described in the text. Experiments were performed at pH 8 with 10 mM MES. Each experiment was performed in triplicate with three independent endospore preparations. Experimental error was calculated as 1 standard deviation from the mean.
The requirement of inosine for purine-His-triggered germination is absolute. Replacing inosine with any other purine in combination with His (10 mM) resulted in a total loss of germination. The ability of the gerHA-null strain to germinate via the purine-alanine pathway shows that gerH is not required for an inosine-based response to a subgerminal concentration of alanine. These data demonstrate, for the first time, differential responses to purines of B. anthracis endospores depending on the amino acid supplied as a cogerminant. The purine-Ala pathway exhibited a higher degree of purine promiscuity than the inosine-His pathway. The purines recognized by the purine-Ala pathway and the amino acids recognized by the inosine-His pathway allow a broad recognition of germinants that likely helps B. anthracis endospores recognize varieties of hospitable environments in which to germinate.);|, http://www.100md.com
Recently, the gerS operon in B. anthracis was characterized and was found to mediate the germination of B. anthracis endospores by germinants containing aromatic ring structures (6). Disruption of the gerS locus results in germinant profiles similar to that of the gerH-null strain. A functional relationship may also exist between gerS and gerH, though that relationship remains undefined. If the two loci are redundant, the loss of one should not abolish germination in response to a pair of cogerminants. Alternatively, it is possible that GerH and GerS are functionally redundant and that together they provide a critical number of germinant sensors required to facilitate germination.
ACKNOWLEDGMENTS+|], http://www.100md.com
We thank T. Dixon, J. Ireland, B. Thomason, S. Cendrowski, B. Heffernan, N. Fisher, and N. Bergman for their useful comments on this work.+|], http://www.100md.com
The sequencing of B. anthracis was supported by the ONR, DOE, NIAID, and DERA. This work was supported in part by the NIH grants AI-08649 and AI-40644 and ONR grants 14-00-1-0422, 14-01-1-1044, and 14-02-1-0061 (P.C.H.).+|], http://www.100md.com
REFERENCES+|], http://www.100md.com
Clements, M. O., and A. Moir. 1998. Role of the gerI operon of Bacillus cereus 569 in the response of spores to germinants. J. Bacteriol. 180:6729-6735.+|], http://www.100md.com
Foster, S. J., and K. Johnstone. 1990. Pulling the trigger: the mechanism of bacterial spore germination. Mol. Microbiol. 4:137-141.+|], http://www.100md.com
Guerot-Fleury, A., K. Shazand, N. Frandson, and P. Straigier. 1995. Antibiotic-resistance cassettes for Bacillus subtilis. Gene 167:335-336.+|], http://www.100md.com
Guidi-Rontani, C., Y. Pereira, S. Ruffie, J. C. Sirard, M. Wever-Levy, and M. Mock. 1999. Identification and characterization of a germination operon on the virulence plasmid pXO1 of Bacillus anthracis. Mol. Microbiol. 33:407-414.
Hachisuka, Y. 1969. Germination of B. anthracis spores in peritoneal cavity of rats and establishment of anthrax. Jpn. J. Microbiol. 13:199-207.}j&3}, 百拇医药
Ireland, J. A. W., and P. Hanna. 2002. Amino acid- and purine ribonucleoside-induced germination of Bacillus anthracis {Delta} Sterne endospores: gerS mediates responses to aromatic ring structures. J. Bacteriol. 184:1296-1303.}j&3}, 百拇医药
Kim, H. U., and J. M. Goepfort. 1974. A sporulation medium for Bacillus anthracis. J. Appl. Bacteriol. 37:265-267.}j&3}, 百拇医药
Koehler, T. M., Z. Dai, and M. Kaufman-Yarbray. 1994. Regulation of the Bacillus anthracis protective antigen gene: CO2 and a trans-activating element activate transcription from one of two promoters. J. Bacteriol. 176:586-595.}j&3}, 百拇医药
Moir, A., E. H. Kemp, C. Robinson, and B. M. Corfe. 1994. The genetic analysis of bacterial spore germination. J. Appl. Bacteriol. 77:9S-16S.}j&3}, 百拇医药
Smith, K., and P. Youngman. 1992. Use of a new integrated vector to investigate compartment specific expression of the Bacillus subtilis spoII gene. Biochimie 74:705-711.}j&3}, 百拇医药
Stewart, G., K. Johnstone, E. Hagelberg, and D. J. Ellar. 1981. Commitment of bacterial spores to germinate. A measure of the trigger reaction. Biochem. J. 198:101-106.}j&3}, 百拇医药
Suzuki, J. B., R. Booth, and N. Grecz. 1971. In vivo and in vitro release of Ca [45] from spores of Clostridium botulinum type A as further evidence for spore germination. Res. Commun. Chem. Pathol. Pharmacol. 2:16-23.(Matthew A. Weiner Timothy D. Read and Philip C. Hanna)