This suggests that Bdellovibrio species may be effective against other crop pathogenic bacterial species, even if they produce biologically active secreted compounds. This could be followed up with studies of the pure compounds themselves versus B. bacteriovorus. We infrequently isolated Enterobacter species in our experiments from supermarket mushrooms, likely being commensals growing in number after pre-treatment with B. bacteriovorus

HD100, suggesting that these Enterobacter selleckchem isolates are not susceptible to Bdellovibrio predation. A Plant Growth Promoting (PGP) Enterobacter species, Enterobacter cloacae, has been described previously, ALK inhibitor which colonises rice root surfaces and competes with other species in the soil microbiota for nutrients [40]. Enterobacter species have also previously been isolated from spent mushroom compost [41], where they might associate with the mushroom surface in a similar way, competing with other mushroom-indigenous bacteria as commensal species. As Bdellovibrio has previously been shown to prey upon diverse Enterobacter species [42], it was unexpected that numbers seemed unaffected by Bdellovibrio predation; inhibition of predation in this case may be due to a factor such as the presence of a protective S-layer, which may

prevent Bdellovibrio from attaching to and invading Enterobacter prey cells [43], but confirming S-layer presence was beyond the scope of this study. The Enterobacter species in this SPTLC1 study were isolated from Bdellovibrio-treated mushroom tissue, unaffected by any brown blotch disease symptoms; and so the species are unlikely to be pathogenic, and may be commensals. It could therefore be beneficial that Bdellovibrio are unable to prey upon the Enterobacter species isolated in this study, preserving any beneficial commensal effect they might have, while still protecting against P. tolaasii infection. Conclusions Bdellovibrio bacteriovorus HD100 are terrestrial bacteria which show natural control

of Pseudomonas tolaasii, a spoilage pathogen of mushroom crops, on the non-sterile, biotic surface of the mushroom pileus. These terrestrial bacteria therefore have a natural ability to act as “food security guards” against Gram-negative crop pathogens. Methods The bacterial strains and primers used in this study are listed in Tables 1 and 2, respectively. Table 1 Bacterial strains used in this study Strain Description Reference Escherichia coli S17-1 (used as prey to initially culture Bdellovibrio) thi, pro, hsdR − , hsdM + , recA, integrated AR-13324 plasmid RP4-Tc::Mu-Kn::Tn7 [44] Bdellovibrio bacteriovorus HD100 Type strain, genome sequenced [29, 45] Pseudomonas tolaasii 2192T Type strain, NCPPB No.