Macrophage-Mediated Germination of
            <i>Bacillus anthracis</i>
            Endospores Requires the
            <i>gerH</i>
            Operon

Weiner, Matthew A.; Hanna, Philip C.

doi:10.1128/iai.71.7.3954-3959.2003

Cited by 47 publications

(44 citation statements)

References 31 publications

(69 reference statements)

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“…Therefore, we next asked whether BA spores, like LPS, could directly induce IL-1b mRNA and caspase-1 activity that processed pro-IL-1b gene product to the mature cytokine. To ensure that we were examining the initial interaction between macrophages and BA spores rather than vegetative bacilli, we used a congenic mutant of the Sterne 34F2 strain, DgerH, that germinates poorly within macrophages [14,16]. Thus, during macrophage cell culture there is limited expression of either LT or edema toxin (ET).…”

Section: Ba Spore-induced Il-1b Requires Myd88 and Caspase-1 Activationmentioning

confidence: 99%

Bacillus anthracis spores and lethal toxin induce IL‐1β via functionally distinct signaling pathways

et al. 2008

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Previous reports suggested that lethal toxin (LT)-induced caspase-1 activity and/or IL-1b accounted for Bacillus anthracis (BA) infection lethality. In contrast, we now report that caspase-1-mediated IL-1b expression in response to BA spores is required for anti-BA host defenses. Caspase-1 -/-and IL-1b -/-mice are more susceptible than wild-type (WT) mice to lethal BA infection, are less able to kill BA both in vivo and in vitro, and addition of rIL-1b to macrophages from these mice restored killing in vitro. Non-germinating BA spores induced caspase-1 activity, IL-1b and nitric oxide, by which BA are killed in WT but not in caspase-1 -/-mice, suggesting that the spore itself stimulated inflammatory responses.While spores induced IL-1b in LT-susceptible and -resistant macrophages, LT induced IL-1b only in LT-susceptible macrophages. Cooperation between MyD88-dependent and -independent signaling pathways was required for spore-induced, but not LT-induced, IL-1b. While both spores and LT induced caspase-1 activity and IL-1b, LT did not induce IL-1b mRNA, and spores did not induce cell death. Thus different components of the same bacterium each induce IL-1b by distinct signaling pathways. Whereas the spore-induced IL-1b limits BA infection, LT-induced IL-1b enables BA to escape host defenses.

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Section: Ba Spore-induced Il-1b Requires Myd88 and Caspase-1 Activationmentioning

confidence: 99%

Bacillus anthracis spores and lethal toxin induce IL‐1β via functionally distinct signaling pathways

et al. 2008

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“…Realtime PCR allowed an evaluation of cytokine mRNA 1 h after addition of spores to M. Second, we used the ⌬gerH mutant of Sterne 34F2, which germinates poorly in the presence of M (43,44). We measured levels of IL-1␤, TNF-␣, IFN-␤, RANTES, and IL-6 because of their importance in stimulating different components of the immune response, such as phagocytes (TNF-␣, IL-1␤), B cells, and antibody formation (IL-6).…”

Section: Bmentioning

confidence: 99%

“…First, we used the germination-proficient B. anthracis Sterne strain 34F2 (pXO1 ϩ pXO2 Ϫ ) and examined the spore M interaction at 1 h, prior to the spore germination and cytokine production, by employing quantitative PCR to study cytokine gene expression. Second, we measured cytokine protein responses by M by using the congenic germination-deficient ⌬gerH (gerH-null) strain spores (43,44). The tri-cistronic gerHABC operon encodes germinant sensors in the presence of M and M-conditioned media and is required for endospore germination within the M environment (43).…”

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confidence: 99%

“…Second, we measured cytokine protein responses by M by using the congenic germination-deficient ⌬gerH (gerH-null) strain spores (43,44). The tri-cistronic gerHABC operon encodes germinant sensors in the presence of M and M-conditioned media and is required for endospore germination within the M environment (43). Since the germination-deficient (⌬gerH) mutant does not form vegetative bacilli in M cultures, it is a useful tool for dissecting the M response to the B. anthracis spore in the absence of germination and allows us to distinguish the response elicited to the spore form of B. anthracis that does not express toxins or capsule from that elicited to the vegetative form.…”

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confidence: 99%

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Role ofBacillus anthracis Spore Structures in Macrophage Cytokine Responses

et al. 2007

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The innate immune response of macrophages (M) to spores, the environmentally acquired form of Bacillus anthracis, is poorly characterized. We therefore examined the early M cytokine response to B. anthracis spores, before germination. M were exposed to bacilli and spores of Sterne strain 34F2 and its congenic nongerminating mutant (⌬gerH), and cytokine expression was measured by real-time PCR and an enzymelinked immunosorbent assay. The exosporium spore layer was retained (exo ؉ ) or removed by sonication (exo ؊ ). Spores consistently induced a strong cytokine response, with the exo ؊ spores eliciting a two-to threefold-higher response than exo ؉ spores. The threshold for interleukin-1␤ (IL-1␤) production by wild-type M was significantly lower than that required for tumor necrosis factor alpha expression. Cytokine production was largely dependent on MyD88, suggesting Toll-like receptor involvement; however, the expression of beta interferon in MyD88 ؊/؊ M suggests involvement of a MyD88-independent pathway. We conclude that (i) the B. anthracis spore is not immunologically inert, (ii) the exosporium masks epitopes recognized by the M, (iii) the M cytokine response to B. anthracis involves multiple pattern recognition receptors and signaling pathways, and (iv) compared to other cytokines, IL-1␤ is expressed at a lower spore concentration.Bacillus anthracis, the causative agent of anthrax, is a highly virulent gram-positive, spore-forming bacterium that is typically acquired through exposure to spores from anthrax sporeinfected animals or animal products or atypically through intentional exposure as a biological weapon (7, 13). Virulent strains of B. anthracis carry two large plasmids, pXO1 and pXO2, which carry the genes encoding anthrax toxin production and capsule formation, respectively, each of which is critical to the pathogenesis of anthrax infection.B. anthracis exists in the environment as dormant spores capable of resisting adverse conditions. Upon uptake by macrophages (M), B. anthracis spores, the form initially encountered by M, rapidly germinate, with the outgrowth of vegetative bacilli constituting the first stage of anthrax spore infection (14). Spore germination enables the bacteria to actively proliferate, synthesize their virulence factors (lethal and edema toxins, capsule), and disseminate within the host, leading to massive septicemia (7). Thus, the recognition and elimination of B. anthracis by M (6, 7, 28, 29, 45, 46) represent critical early events in anthrax pathogenesis.Since a successful innate immune response to B. anthracis might prevent the replication and dissemination of the vegetative form, we examined the M cytokine response to B. anthracis spores. Little is known about the ability of B. anthracis spores to induce M cytokine responses, which might be expected to activate macrophagicidal activity, thereby lowering the replication and dissemination of bacilli. To address this question, we used two approaches. First, we used the germination-proficient B. anthracis Sterne strain 34F2 ...

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“…This did not reveal any GerT function but demonstrated that GerN is important in any circumstances where the GerI receptor is implicated in germination. In B. anthracis, the GerH germinant receptor has been implicated in virulence (26). Apart from sequence differences in the long repeat region near the N termini of GerHA and GerIA, the GerH proteins are almost identical in amino acid sequence to the GerI proteins of B. cereus ATCC 10876.…”

Section: Discussionmentioning

confidence: 87%

The Bacillus cereus GerN and GerT Protein Homologs Have Distinct Roles in Spore Germination and Outgrowth, Respectively

Senior

Moir

2008

J Bacteriol

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The GerT protein of Bacillus cereus shares 74% amino acid identity with its homolog GerN. The latter is a Na ؉ /H ؉ -K ؉ antiporter that is required for normal spore germination in inosine. The germination properties of single and double mutants of B. cereus ATCC 10876 reveal that unlike GerN, which is required for all germination responses that involve the GerI germinant receptor, the GerT protein does not have a significant role in germination, although it is required for the residual GerI-mediated inosine germination response of a gerN mutant. In contrast, GerT has a significant role in outgrowth; gerT mutant spores do not outgrow efficiently under alkaline conditions and outgrow more slowly than the wild type in the presence of high NaCl concentrations. The GerT protein in B. cereus therefore contributes to the success of spore outgrowth from the germinated state during alkaline or Na ؉ stress.Bacillus cereus ATCC 10876 spores germinate in inosine or in L-alanine as sole germinants (5). They require both GerI and GerQ germinant receptors for germination in inosine as the sole germinant, whereas the GerL receptor is responsible for most of the response to L-alanine as the sole germinant, with a smaller contribution from the GerI receptor (3). The GerN protein is needed for successful inosine germination, as spores of a gerN mutant of B. cereus ATCC 10876 demonstrate a slow and abnormally ordered germination response in inosine as the sole germinant (24). The residual germination was very asynchronous, and some spores appeared to become phase dark before losing heat resistance (24). This GerN protein is a homolog of a widely distributed family of cation transporters (9) and has been demonstrated to mediate Na ϩ /H ϩ and Na ϩ / H ϩ -K ϩ antiport activity when expressed at a low level in Escherichia coli (21). Such GerN-mediated antiport activity is therefore apparently required for the germination response mediated by the GerI germinant receptor in B. cereus. The role of such an ion transport protein in germination remains unclear, especially as other germinant receptors in the same strain do not require a functional GerN protein; for example, the gerL-dependent alanine response is almost identical to that of the wild type in a gerN mutant (24). Both GerN and a closely related homolog are encoded in B. cereus ATCC 14579 (13) and in other members of the family, including Bacillus anthracis (17) and Bacillus thuringiensis (16). Both genes appear to be monocistronic, and their coding sequences are widely separated on the genome. We have called this second gerN-like gene gerT (19). An entirely different (spore coat) protein in B. subtilis has recently been called gerT (7), but that gene does not have a homolog in B. cereus, and as B subtilis does not carry an equivalent homolog of the B. cereus gerN or gerT gene, the nomenclature will not overlap. We describe here the spore germination and outgrowth phenotypes of mutants of B. cereus ATCC 10876 carrying an insertionally inactivated gerT gene. Resulting phenotypes s...

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Macrophage-Mediated Germination of Bacillus anthracis Endospores Requires the gerH Operon

Cited by 47 publications

References 31 publications

Bacillus anthracis spores and lethal toxin induce IL‐1β via functionally distinct signaling pathways

Bacillus anthracis spores and lethal toxin induce IL‐1β via functionally distinct signaling pathways

Role ofBacillus anthracis Spore Structures in Macrophage Cytokine Responses

The Bacillus cereus GerN and GerT Protein Homologs Have Distinct Roles in Spore Germination and Outgrowth, Respectively

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