Pseudomonas fluorescens NZI7 repels grazing by C. elegans, a natural predator

Abstract

The bacteriovorous nematode Caenorhabditis elegans has been used to investigate many aspects of animal biology, including interactions with pathogenic bacteria. However, studies examining C. elegans interactions with bacteria isolated from environments in which it is found naturally are relatively scarce. C. elegans is frequently associated with cultivation of the edible mushroom Agaricus bisporus, and has been reported to increase the severity of bacterial blotch of mushrooms, a disease caused by bacteria from the Pseudomonas fluorescens complex. We observed that pseudomonads isolated from mushroom farms showed differential resistance to nematode predation. Under nutrient poor conditions, in which most pseudomonads were consumed, the mushroom pathogenic isolate P. fluorescens NZI7 was able to repel C. elegans without causing nematode death. A draft genome sequence of NZI7 showed it to be related to the biocontrol strain P. protegens Pf-5. To identify the genetic basis of nematode repellence in NZI7, we developed a grid-based screen for mutants that lacked the ability to repel C. elegans. The mutants isolated in this screen included strains with insertions in the global regulator GacS and in a previously undescribed GacS-regulated gene cluster, 'EDB' ('edible'). Our results suggest that the product of the EDB cluster is a poorly diffusible or cell-associated factor that acts together with other features of NZI7 to provide a novel mechanism to deter nematode grazing. As nematodes interact with NZI7 colonies before being repelled, the EDB factor may enable NZI7 to come into contact with and be disseminated by C. elegans without being subject to intensive predation.

To settle or to move? The interplay between two classes of cyclic lipopeptides in the biocontrol strain Pseudomonas CMR12a

“…It would be worthwhile to investigate whether tolaasin‐producing mushroom pathogens such as P. tolaasii and P. fluorescens NZI7 also produce a second CLP and whether they have biocontrol activities when applied to plant roots. In this context, it is noteworthy that the genome of P. fluorescens NZI7 is very similar to that of the biocontrol agent P. protegens Pf‐5 (Burlinson et al ., ).…”

Commensals, probiotics and pathogens in theCaenorhabditis elegansmodel

“…Nematodes exhibit preference for one food source over another under laboratory conditions: C. elegans has been shown to seek out 'edible' mutants of an otherwise repellent bacterium from numerous patches on an agar plate (Burlinson et al, 2013). There are numerous examples of binary choice assays in which C. elegans exhibits a consistent preference for one bacterial strain over another, and the neural pathways by which this occurs have been partially characterized (Zhang et al, 2005;Shtonda and Avery, 2006;Abada et al, 2009).…”

“…The genetic basis for bacterial repulsion of C. elegans grazing has been investigated using Pseudomonas fluorescens (Burlinson et al, 2013). The bacterial global regulator GacS was identified as an important factor in repulsion, as was a previously uncharacterized locus in the GacS regulon known as EDB (edible).…”

Indole‐associated predator–prey interactions between the nematode Caenorhabditis elegans and bacteria

“…Caenorhabditis elegans is a bacterivorous nematode found in soil and decaying plants where many microbes reside (Burlinson et al, 2013;Choi et al, 2016). It also provides a useful model host for the study of host-bacteria interactions, bacterial pathogenesis and drug development, because it has simple growth requirements, a short generation time and well-established genetic tools (Niu et al, 2010).…”