The InhA1 metalloprotease allows spores of the B. cereus group to escape macrophages

Abstract

SummaryBacteria of the Bacillus cereus group are resistant to the immune systems of various hosts and establish potent infections, implying that bacteria circumvent the bactericidal activity of host phagocytic cells. We investigated the fate of Bacillus spores after their internalization by macrophages. We found that these spores survive and escape from macrophages, and that the bacterial metalloprotease InhA1, the major component of the exosporium, is essential for efficient spore release from macrophages. InhA1 from Bacillus thuringiensis also enables Bacillus subtilis to escape from macrophages. Analysis of membrane permeability showed that the bacteria cause alterations in the macrophage membranes and that InhA1 is involved in these processes. Thus, InhA1 contributes to protect the bacteria against the host immune system. These findings provide further insight into the pathogenicity of B. cereus group members.

The InhA Metalloproteases ofBacillus cereusContribute Concomitantly to Virulence

“…We have previously shown that spores of the ⌬inhA1 mutant were retained inside macrophages, whereas spores of the wildtype B. thuringiensis strain 407 were capable of escaping from the cells (50). However, spores of the 407 ⌬inhA2 and 407 ⌬inhA3 mutants are still capable of escaping from macrophages (data not shown), implying that only InhA1 is involved in this process.…”

“…Spore release infection experiments and cytotoxicity assays on J774 murine macrophage-like cells were performed as previously described (49,50 Infection by injection into the hemolymph of Galleria mellonella or Bombyx mori larvae was performed as described previously (17,52). For groups of 15 last-instar larvae, the base of the last proleg was injected with a 10-l suspension containing 7.5 ϫ 10 3 vegetative bacteria or spores for G. mellonella, or 50 vegetative bacteria for B. mori.…”

“…Another putative role of InhA1 is suggested by the fact that InhA1 is both secreted throughout the growth cycle of B. cereus and associated with the spore exosporium (8). The spores are internalized by macrophages but are able to survive and escape from this hostile environment; InhA1 is a key effector involved in this process (50). Previous studies have characterized a gene encoding another putative metalloprotease that has 66% identity to InhA1 and also harbors a zinc-binding domain.…”

Identification and characterization of a novel spore-associated subtilase from Thermoactinomyces sp. CDF

“…Although the spores are known as the dormant form of bacteria, many spore-associated enzyme activities have been identified, especially those of Bacillus species, where proteases are crucial for spore germination (Hilbert & Piggot, 2004). In addition, some sporeassociated proteases contribute to the virulence of bacteria (Ramarao & Lereclus, 2005). With regard to Thermoactinomyces species, esterase activity has been detected in the spores of Thermoactinomyces vulgaris by using fluorogenic substrates (Gazenko et al, 1998).…”

The role of a purine-specific nucleoside hydrolase in spore germination of Bacillus thuringiensis

“…Dozens of proteins, including a putative NH, were identified from the exosporia of B. cereus and B. anthracis spores (Redmond et al, 2004;Steichen et al, 2003;Todd et al, 2003). Although the role of some proteins has been studied, most functions remain to be elucidated (Boydston et al, 2006;Ramarao & Lereclus, 2005;Steichen et al, 2005;Yan et al, 2007).…”