Are nematodes a missing link in the confounded ecology of the entomopathogen Bacillus thuringiensis?

Specificity determinants for Cry insecticidal proteins: Insights from their mode of action

“…The poor ability of Bt to colonize various habitats including plant surfaces (Maduell et al, 2008), would also seem to limit the extent to which insects in those environments are exposed to Bt, unless transmission is primarily through insect-to-insect interactions (Milutinovic et al, 2015). Various interactions between Bt and nematodes have also been proposed as a mechanism by which the bacterium and its Cry toxins can be delivered to a susceptible host (Ruan et al, 2015). The specificity of certain Cry toxins (parasporins) towards human cancer cells (Mizuki et al, 2000) is particularly difficult to explain in evolutionary terms.…”

Infection of Tribolium castaneum with Bacillus thuringiensis: Quantification of Bacterial Replication within Cadavers, Transmission via Cannibalism, and Inhibition of Spore Germination

“…Although B. thuringiensis efficiently kills various insects, little is known about its role in the environment and natural modes of transmission (11,19). An important aspect is whether direct transmission from host to host is efficient.…”

“…In the spore stage, Bt can endure unfavorable conditions for many years (18). When nutrients become available again, for example in the insect gut, spores can germinate instantly and colonize the host (11,16).Numerous successful infections and disease phenotypes have been reported in laboratory experiments and in field applications; however, the ecology of Bt and its role in the environment still remain rather puzzling (11,19). Despite its obvious adaptations to insect hosts, Bt spores are found abundantly in diverse environments, such as soil, freshwater, the rhizosphere, and the phylloplane, where its hosts are not always present (11).…”

Anthropogenic action shapes the evolutionary ecology of Bacillus thuringiensis: response to Ruan et al

“…Despite the vast knowledge about mechanisms of insecticidal action and specificity of Bt, its largely unresolved ecology has been a matter of hot debate due to its occurrence in an astounding variety of niches. Ruan et al [2] have proposed an interesting view of nematodes as a possible 'missing link' between the pathogenic role and the cosmopolitan occurrence of Bt in a wide range of soilrelated environments. Here, we expand this viewpoint, arguing that a yet broader view of Bt as a multihost environmental pathogen can encompass both insects and nematodes as important parts of a bigger picture in Bt's ecology.…”

“…The main argument of Ruan et al is indeed relevant: the role of nematodes as a significant host type could explain such an array of niches attributed to Bt because nematodes (i) are as widely distributed as insects, (ii) can also be found in the same soil environments as Bt, and (iii) can aid in dispersion and occurrence of the bacterium through phoresy, necromeny, and pathogenesis [2]. In our view, though, various pieces of evidence point to a larger repertoire of genetic and physiologic possibilities that can explain Bt's ability to thrive everywhere ( Figure 1).…”