Bacterial diversity and community structure shapes pederin polymorphism but lacks association with host genotype specificity in the rove beetle, Paederus fuscipes.

Paederus beetles are notorious for their irritant haemolymph toxin pederin, which is synthesised by an unculturable bacterial symbiont, causing dermatitis when in contact with human skin. Pederin polymorphism is observed when (+) females carrying the toxin pederin and (-) females lacking this co-occur in natural populations. Despite reports detecting pederin polymorphism in several Paederina beetles, symbiont infection frequencies in their natural populations and the bacterial diversity differences underlying the polymorphism between these female types are understudied. Herein we report a high prevalence (>80%) of female Paederus fuscipes carrying bacterial ped genes in all six study populations. This finding suggests that selection pressure favouring pederin-producing females is crucial for survival in the natural environment. 16S rRNA metabarcoding analysis revealed significant dominance of the unculturable pederin-producing Pseudomonas-like bacterium (Gammaproteobacteria) in (+) females, consistent with previous studies. The microbial diversity of the (-) females revealed a significant abundance of Apibacter (Bacteroidia), previously undocumented, suggesting its importance in the functionality of (-) females. Predicted functions related to metabolisms are enriched in (-) females, suggesting fitness advantage possibilities in sustaining the population in the absence of predation. Further investigations on the possible genetic basis of the host genotype revealed no association of host mtDNA and pederin polymorphism in Pa. fuscipes.

Multifaceted interactions between the pseudomonads and insects: mechanisms and prospects.

Insects and bacteria are the most widespread groups of organisms found in nearly all habitats on earth, establishing diverse interactions that encompass the entire range of possible symbiotic associations from strict parasitism to obligate mutualism. The complexity of their interactions is instrumental in shaping the roles of insects in the environment, meanwhile ensuring the survival and persistence of the associated bacteria. This review aims to provide detailed insight on the multifaceted symbiosis between one of the most versatile bacterial genera, Pseudomonas (Gammaproteobacteria: Pseudomonadaceae) and a diverse group of insect species. The Pseudomonas engages with varied interactions with insects, being either a pathogen or beneficial endosymbiont, as well as using insects as vectors. In addition, this review also provides updates on existing and potential applications of Pseudomonas and their numerous insecticidal metabolites as biocontrol agents against pest insects for the improvement of integrated pest management strategies. Here, we have summarized several known modes of action and the virulence factors of entomopathogenic Pseudomonas strains essential for their pathogenicity against insects. Meanwhile, the beneficial interactions between pseudomonads and insects are currently limited to a few known insect taxa, despite numerous studies reporting identification of pseudomonads in the guts and haemocoel of various insect species. The vector-symbiont association between pseudomonads and insects can be diverse from strict phoresy to a role switch from commensalism to parasitism following a dose-dependent response. Overall, the pseudomonads appeared to have evolved independently to be either exclusively pathogenic or beneficial towards insects.