The parasporal crystals of Bacillus pumilus strain 15.1: a potential virulence factor?

Abstract

Summary Bacillus pumilus strain 15.1 was previously found to cause larval mortality in the Med‐fly Ceratitis capitata and was shown to produce crystals in association with the spore. As parasporal crystals are well‐known as invertebrate‐active toxins in entomopathogenic bacteria such as Bacillus thuringiensis (Cry and Cyt toxins) and Lysinibacillus sphaericus (Bin and Cry toxins), the B. pumilus crystals were characterized. The crystals were composed of a 45 kDa protein that was identified as an oxalate decarboxylase by peptide mass fingerprinting, N‐terminal sequencing and by comparison with the genome sequence of strain 15.1. Synthesis of crystals by a plasmid‐cured derivative of strain 15.1 (produced using a novel curing strategy), demonstrated that the oxalate decarboxylase was encoded chromosomally. Crystals spontaneously solubilized when kept at low temperatures, and the protein produced was resistant to trypsin treatment. The insoluble crystals produced by B. pumilus 15.1 did not show significant toxicity when bioassayed against C. capitata larvae, but once the OxdD protein was solubilized, an increase of toxicity was observed. We also demonstrate that the OxdD present in the crystals has oxalate decarboxylate activity as the formation of formate was detected, which suggests a possible mechanism for B. pumilus 15.1 activity. To our knowledge, the characterization of the B. pumilus crystals as oxalate decarboxylase is the first report of the natural production of parasporal inclusions of an enzyme.

Bacillus pumilus 15.1, a Strain Active against Ceratitis capitata, Contains a Novel Phage and a Phage-Related Particle with Bacteriocin Activity

“…Several strains were susceptible to Bp15.1PLP particles ( Table 7 ), showing a clear halo when a drop of a suspension of Bp15.1PLP (and Bp15.1Hope) was placed over the strain in a spot test. All of the susceptible strains were B. pumilus strains, including B. pumilus 15.1C, an extra-chromosomal DNA cured strain obtained from B. pumilus 15.1 and previously described by our group [ 5 ]. Bp15.1Hope was not able to form plaques in any of the strains tested in lawn assays (data not shown), so the halos observed seem to indicate that Bp15.1PLP has a strong bacteriocin-like activity.…”

“…The enzyme can catalyse the transformation of oxalate to formate, a previously recognised neurotoxic compound. It has been proposed that oxalate decarboxylase could be a potential virulence factor [ 5 ], although the mechanism of toxicity is still under study.…”

Scientific Opinion on the update of the list of QPS‐recommended biological agents intentionally added to food or feed as notified to EFSA (2017–2019)

“…Sixteen papers were analysed in depth. Eleven had methodological problems with regard to the identification procedures (Danilova et al., ; Garcia‐Ramon et al., ; Osman et al., ; Joshi et al., ; Shah et al., ,b; Li et al., ; Tsonis et al., ), source attribution (Allam et al., ; Joshi et al., , Shah et al., ,b) or were not food related (Aydin et al., ).…”

A model industrial workhorse: Bacillus subtilis strain 168 and its genome after a quarter of a century

“…The gene belongs to the phage 6 region and has been recruited by the sporulation process with its expression dependent on sigma(K). OxD is a spore coat inner layers constituent (Costa et al, 2004 ), identified in crystalline form in B. pumilus (Garcia‐Ramon et al, 2018 ).…”