Exploring the endospore coat of Pasteuria penetrans, the bacterial hyperparasite of plant-parasitic nematodes, using Bacillus spp.

Pasteuria penetrans, previously named as Bacillus penetrans, belong to a group of Gram positive endospore forming bacteria (phylum: Firmicutes; family: Pasteuriaceae) that are hyperparasites of plant-parasitic nematodes. These bacteria could provide an environmentally benign and sustainable control strategy for economically important plant-parasitic nematodes as an alternative to nematicides. Earlier studies based on 16S rRNA, spoOA and other housekeeping genes suggest a close relatedness of Pasteuria to Bacillus. They are obligate parasites, but recently they have been mass produced by proprietary fermentation technology owned by Syngenta. The attachment of Pasteuria endospores to the cuticle of their host nematode is a crucial step in the infection process. The molecular structure of the Pasteuria endospore is little studied, although collagen-like fibres present on the spore surface are thought to be involved in spore attachment to its host. Some 4000+ genome survey sequences of Pasteuria are available in public databases, but there is not as yet a complete annotated genome. In the current study, we utilize well characterized endospore forming Bacillus spp. as comparative tools to investigate the surface of Pasteuria endospore.

Sequenced genomes of animal pathogenic and non-pathogenic Bacillus spp. were used to identify selected genes related to endospore and exosporium formation and function. Synteny across the selected genes was explored using a web-based synteny explorer software SyntTax (Oberto, 2013). The genome survey sequences (GSS database, NCBI) of Pasteuria were interrogated for the presence of sequences homologous to selected Bacillus genes. In silico studies identified the presence of at least 10 collagen-like coding genes in the Pasteuria genome. Antibodies raised against Pasteuria endospores show cross-reactivity to proteins extracted from endospores of Bacillus thuringiensis following Western blot analyses. This indicates similarities in the endospore protein profile of Bacillus and Pasteuria. Likewise, subsequent immunofluorescence microscopic comparisons of Pasteuria and Bacillus thuringiensis endospores coats showed similarities in their antigenic determinants and further characterisation of these determinants suggested the involvement of carbohydrate moieties.