Revealing Functional Traits of Insect Pest Suppressive Rhizobacterial Strains Through Comparative Genomics.

Root inoculation with rhizobacteria is an emerging strategy to enhance plant resistance to aphid herbivory, yet the microbial functional traits underpinning these responses remain poorly characterised. Here, we present a comparative genomic analysis of five rhizobacteria (Acidovorax radicis N35, Bacillus subtilis B171, Bacillus velezensis FZB42, Rhizobium radiobacter F4 and Pseudomonas simiae WCS417r) that suppress aphids when inoculated onto barley. As expected, functional variation largely reflected phylogenetic relatedness; however, candidate traits implicated in modulation of plant immune defences were conserved across all strains, including biosynthesis of 2,3-butanediol, riboflavin and salicylic acid. Additional shared functions, linked to plant defence signalling, included phytoene and squalene biosynthesis (absent in P. simiae) and N-acyl homoserine lactone quorum sensing (absent in Bacillus spp.). Strain-specific traits were also identified, including surfactin production in Bacillus spp. and hydrogen cyanide biosynthesis in A. radicis and P. simiae. Comparison with a broader collection of rhizobacteria revealed that many putative plant-beneficial functions identified were widely conserved, including among closely related phytopathogens. This extensive functional overlap suggests aphid suppression cannot be explained solely by presence or absence of broad functional traits, but rather by specific trait combinations, regulatory differences, or context-dependent expression. This highlights the need for genome-informed approaches for bioinoculant discovery.