Orthologues of Bacillus subtilis Spore Crust Proteins Have a Structural Role in the Bacillus megaterium QM B1551 Spore Exosporium

Abstract

The exosporium ofBacillus megateriumQM B1551 spores is morphologically distinct from exosporia observed for the spores of many other species. Previous work has demonstrated that unidentified genes carried on one of the large indigenous plasmids are required for the assembly of theBacillus megateriumexosporium. Here, we provide evidence that pBM600-encoded orthologues of theBacillus subtilisCotW and CotX proteins, which form the crust layer in spores of that species, are structural components of theBacillus megateriumQM B1551 spore exosporium. The introduction of plasmid-bornecotWand orthologouscotXgenes to the PV361 strain, which lacks all indigenous plasmids and produces spores that are devoid of an exosporium, results in the development of spores with a rudimentary exosporium-type structure. Additionally, purified recombinant CotW protein is shown to assemble at the air-water interface to form thin sheets of material, which is consistent with the idea that this protein may form a basal layer in theBacillus megateriumQM B1551 exosporium.IMPORTANCEWhen starved of nutrients, some bacterial species develop metabolically dormant spores that can persist in a viable state in the environment for several years. The outermost layers of spores are of particular interest since (i) these represent the primary site for interaction with the environment and (ii) the protein constituents may have biotechnological applications. The outermost layer, or exosporium, inBacillus megateriumQM B1551 spores is of interest, as it is morphologically distinct from the exosporia of spores of the pathogenicBacillus cereusfamily. In this work, we provide evidence that structurally important protein constituents of theBacillus megateriumexosporium are different from those in theBacillus cereusfamily. We also show that one of these proteins, when purified, can assemble to form sheets of exosporium-like material. This is significant, as it indicates that spore-forming bacteria employ different proteins and mechanisms of assembly to construct their external layers.

Contributions of crust proteins to spore surface properties in Bacillus subtilis

“…It should be noted that these proteins are absent or have diverged greatly in strains of the B. cereus group that have exosporia instead of crusts. On the other hand, CotX is required, along with CotW, for exosporium formation in B. megaterium QMB 1551, which does not have orthologs of CotY and CotZ (Manetsberger et al ., ). CotO is conserved in Bacillus species that also have orthologs of CotY and CotZ.…”

Diversity and evolutionary dynamics of spore-coat proteins in spore-forming species of Bacillales

“…Thus, the crust may be absent in both groups or possibly it is composed of different proteins, as the case of Bacillus megaterium that possesses an exosporium as the outermost layer of the coat [17]. However, the strain B. megaterium QM B1551 has an exosporium composed of plasmid-borne orthologues of B. subtilis cotW and cotX genes [65]. Further studies are needed to clarify these possibilities.…”

The “beauty in the beast”—the multiple uses of Priestia megaterium in biotechnology

“…The plasmid-less DSM319 and its variant MS941, which lacks the gene coding for the major extracellular protease NprM (Wittchen and Meinhardt 1995), are best suited candidates for plasmid-based genetic applications, including the generation of mutants and the recombinant production of proteins (Biedendieck et al 2011). Strain QM B1551 is used in basic research, especially within the context of sporulation genetics (Manetsberger et al 2018;Riyami et al 2019). Strain WSH-002 has been used for co-cultivation with Ketogulonicigenium vulgare (Zhang et al 2010) or Gluconobacter oxydans (Lü et al 2003) to produce vitamin C (Liu et al 2011).…”