Fast Screening Libraries of Plant Growth Promoting Rhizobacteria (PGPRs) for Insecticidal Activity.

Aims: Plant Growth Promoting Rhizobacteria (PGPR) are ubiquitous among soil bacteria and aid in many growth-related functions for plants. Recent biotechnological advancements involving PGPRs have led to a growing desire to explore and uncover combinatorial or dual use PGPRs. Our study aimed to discover novel insecticidal phenotypes amongst PGPR libraries.

Methods And Results: We screened, through survivorship bioassays, 502 endophytic PGPRs for insecticidal activity against Drosophila melanogaster (fruit flies). Initial bioassay screens were followed by higher (n) testing and subsequent insecticidal assays against 4 key pest species including Drosophila suzukii, Spodoptera frugiperda, Aphis gossypii, and Lygus lineolaris. Of the 502 endophytic PGPRs screened, 39 strains showed statistically significant mortality against insects with three strains killing four pest species and seven killing three pest species. The key insecticidal strains primarily consisted of Serratia marcescens and Bacillus velezensis.

Conclusions: In total, ∼8% of strains tested showed insecticidal phenotypes. The fast screening methodology was successful in uncovering dual use PGPRs. Some bacteria were broad spectrum insect killers and others were more specific to a particular pest.