Entomopathogenic potential of bacteria associated with soil-borne nematodes and insect immune responses to their infection

Abstract

Soil-borne nematodes establish close associations with several bacterial species. Whether they confer benefits to their hosts has been investigated in only a few nematode-bacteria systems. Their ecological function, therefore, remains poorly understood. In this study, we isolated several bacterial species from rhabditid nematodes, molecularly identified them, evaluated their entomopathogenic potential on Galleria mellonella larvae, and measured immune responses of G. mellonella larvae to their infection. Bacteria were isolated from Acrobeloides sp., A. bodenheimeri, Heterorhabditis bacteriophora, Oscheius tipulae, and Pristionchus maupasi nematodes. They were identified as Acinetobacter sp., Alcaligenes sp., Bacillus cereus, Enterobacter sp., Kaistia sp., Lysinibacillus fusiformis, Morganella morganii subsp. morganii, Klebsiella quasipneumoniae subsp. quasipneumoniae, and Pseudomonas aeruginosa. All bacterial strains were found to be highly entomopathogenic as they killed at least 53.33% G. mellonella larvae within 72h post-infection, at a dose of 106 CFU/larvae. Among them, Lysinibacillus fusiformis, Enterobacter sp., Acinetobacter sp., and K. quasipneumoniae subsp. quasipneumoniae were the most entomopathogenic bacteria. Insects strongly responded to bacterial infection. However, their responses were apparently little effective to counteract bacterial infection. Our study, therefore, shows that bacteria associated with soil-borne nematodes have entomopathogenic capacities. From an applied perspective, our study motivates more research to determine the potential of these bacterial strains as biocontrol agents in environmentally friendly and sustainable agriculture.

Ecology, Adaptation, and Parasitism of Entomopathogenic Nematodes

“…Pathogenic soil bacteria can attach to the surface of the EPN, FLN, and plant parasitic nematodes (PPN) [29]. Main bacteria attacking these nematodes are Pasteuria sp., Kaistia sp., Lysinibacillus fusiformis, Enterobacter sp., Bacillus cereus, Klebsiella quasipneumoniae, and Pseudomonas aeruginosa [30]. Endospore-forming bacteria have been related to the reduction of virulence in EPNs.…”

“…This detection triggers both cell-autonomous and non-autonomous responses. Understanding how EPNs identify and respond to various pathogens may give important insights about target markers that might improve EPN survival in soil [30].…”

A Comprehensive Review on the Roles of Metals Mediating Insect–Microbial Pathogen Interactions

“…Another trace metal, such as Cu, is also essential for the immune response of insects against microbial infections [ 177 ]. Insects can produce Cu-binding proteins and transporters to remove Cu from the environment and limit its availability to invading pathogens.…”

Microbial Community Changes in Silkworms Suspected of Septicemia and Identification of Serratia sp.

“…In the growing insect industry, entomopathogenic bacteria can quickly and easily infect and multiply, resulting in the reduced production of industrial insects and subsequent economic losses [16]. Sepsis, a common bacterial disease in insects, is associated with entomopathogenic bacteria that attach to specific tissue surfaces and multiply, producing various immunosuppressive factors, toxin proteins, and specialized metabolites that cause rapid death of the host [17].…”

“…Therefore, entomopathogenic bacteria are often used as biological control agents to suppress pests in plant cultivation. Representative entomopathogenic bacteria include Bacillaceae, Pseudomonadaceae, Enterobacteriaceae, Streptococcaceae, Micrococcaceae, and Paeni-bacillaceae; additionally, S. marcescens and S. entomophila are attracting attention for use as biological control agents owing to their strong pathogenicity [16,17]. S. marcescens and S. entomophila infect lepidopteran insects, impairing their feeding and growth, and rapidly proliferate and secrete large amounts of proteolytic enzymes such as β-hemolysins, elastases, and chitinases.…”