Oral Toxicity of Pseudomonas protegens against Muscoid Flies

Abstract

The bioinsecticidal action of Pseudomonas protegens has so far been reported against some target insects, and the mode of action remains unclear. In this study, the pathogenicity potential of a recently isolated strain of this bacterial species against fly larvae of medical and veterinary interest was determined. Preliminary experiments were conducted to determine the biocidal action by ingestion against Musca domestica and Lucilia caesar larvae, which highlighted a concentration-dependent effect, with LC50 values of 3.6 and 2.5 × 108 CFU/mL, respectively. Bacterial septicaemia was observed in the body of insects assuming bacterial cells by ingestion. Such rapid bacterial reproduction in the hemolymph supports a toxin-mediated mechanism of action involving the intestinal barrier overcoming. In order to gain more information on the interaction with the host, the relative time-course expression of selected P. protegens genes associated with virulence and pathogenicity, was determined by qPCR at the gut level during the first infection stage. Among target genes, chitinase D was the most expressed, followed by pesticin and the fluorescent insecticidal toxin fitD. According to our observations and to the diversity of metabolites P. protegens produces, the pathogenic interaction this bacterium can establish with different targets appears to be complex and multifactorial.

Involvement of a novel Pseudomonas protegens strain associated with entomopathogenic nematode infective juveniles in insect pathogenesis

“…The expression of some of these insect virulence factors was recently observed also at the gut level in muscoid fly larvae fed with cells of strain CO1, 12 which aligns with the pathogenic effect on G. mellonella larvae we observed after force‐feeding. However, the slower effectiveness of P. protegens after ingestion compared to injection is a clear consequence of the need to overcome the intestinal barrier, which is a natural obstacle to microorganisms to reach a suitable environment for their proliferation, namely the haemolymph 23 .…”

“…In order to evaluate the actual involvement of P. protegens in the entomopathogenic process, the overtime dynamic of its load in the haemolymph of G. mellonella 3rd instar larvae was monitored by both bacterial colony counts (CFU) and quantitative (q)PCR targeting the 16S rDNA gene with a specifically designed primer pair showing high affinity for P. protegens with respect to other nematode‐associated bacteria including Xenorhabdus spp., 12 as shown in Table 1 . To this end, haemolymph was taken from larvae at different time intervals post‐inoculation with IJ (0, 12, 24, 36, 48, 60 and 72 h).…”

The secret life of plant‐beneficial rhizosphere bacteria: insects as alternative hosts

“…They produce the Fit toxin, an insecticidal protein that is closely related to the Makes caterpillars floppy (Mcf) toxin of Photorhabdus and Xenorhabdus species, both symbionts of entomopathogenic nematodes. Pseudomonas protegens strains kill insect larvae not only when injected into the insect hemocoel (Péchy-Tarr et al, 2008), but also when fed to larvae of several lepidopteran and dipteran species (Olcott et al, 2010;Ruffner et al, 2013;Loper et al, 2016;Rangel et al, 2016;Ruiu and Mura, 2021) (Fig. 1).…”

“…For P. protegens lethal oral infections are mainly observed in experiments with laboratory-reared insect larvae fed on leaves or an artificial diet inoculated with the bacterium. The susceptible insects were either leaffeeding lepidopteran species or dipteran species such as Drosophila melanogaster or Musca domestica, which normally feed on fruits or rotting organic material respectively (Péchy-Tarr et al, 2008, 2013Olcott et al, 2010;Ruffner et al, 2013;Flury et al, 2016;Loper et al, 2016;Rangel et al, 2016;Ruiu and Mura, 2021). However, P. protegens had no or very little effect on the survival of root-feeding dipteran and coleopteran pests (Chiriboga et al, 2018;Flury et al, 2019;Jaffuel et al, 2019).…”

Draft Genome Sequence of Pseudomonas protegens Strain MWU12-2233, Isolated from Wild Cranberry Fruit in Provincetown, Massachusetts

“…Protected wetlands represent an understudied ecosystem that harbors diverse communities of phyllosphere bacteria, including those associated with wild cranberry flowers and fruits ( 1 , 2 ). Some of these bacteria are pseudomonads that produce secondary metabolites with biological activity against fungi and insects ( 3 ), including the plant-growth-promoting and insectivorous bacterium Pseudomonas protegens ( 4 – 7 ), potentially making them a component of the indigenous disease-suppressive microflora. P. protegens MWU12-2233 was isolated in July 2012 from cranberry fruit as part of a culture-dependent survey of bacteria from wild cranberry bogs in the Cape Cod National Seashore, Provincetown, MA (42.070624 N, 70.210548 W).…”