Plant growth-promoting bacteria in lettuce for resilience against enteropathogens

Abstract

Introduction: Observe the role of Plant Growth Promoting Bacteria (PGPB) obtained from the phyllosphere, rhizoplane, and roots of Bok choy for antagonistic responses and resilience to biotic stressors, Salmonella Typhimurium and E. coli 2705C in vitro and in lettuce.

Purpose: Unravel the potential of PGPB root colonization for resilience to enteric pathogens in Romaine lettuce. understanding the responses of PGPB to enteric pathogens for the enhancement of plant growth and contributions to food safety

Methods: Rhizobacteria (n=35) were isolated from the roots of bok choy (Brassica rapa subsp. chinensis) grown at the University of Maryland TerpFarm. Bacterial isolates were taxonomically classified using full-length 16S rRNA gene sequencing. Lettuce seed (Rogue d’Hiver) was inoculated 3- and 6- days post germination with single strain suspensions of 7 log CFU/plant. All the isolates were further screened for their potential to enhance food safety, utilizing both in vitro and vivo assay. Leaf populations of Salmonella Typhimurium were enumerated by direct plate counting on Tryptic Soy Agar 24 h after leaf inoculation with 5 log CFU. An antagonistic assay was conducted by inoculating PGPB onto TSA plates and applying a drop of E. coli 2705C and Salmonella Typhimurium to observe potential inhibitory effects.

Results: From the Bok choy leaves and rhizoplane a total of 7 and 4 unique genera were classified, respectively. Intriguingly, all eight endophytes from the root tissue exclusively belonged to the genus Pseudomonas, indicating its dominance, and suggesting influence over other symbiotic microorganisms in plant roots. Through in vitro assay, 3 phyllosphere endophytes created a zone of inhibition around E. coli 2705C and Salmonella Typhimurium, indicating their antimicrobial activity. The reduction in Salmonella populations on lettuce treated with three rhizoplane isolates (Pseudomonas fluorescens, Priestia magaterium, Lysinibacillus xylanilyticus) and two root endophytes (Pseudomonas spp.), was slightly greater compared to uninoculated plants.

Significance: Our research highlights the prospect of leveraging microbial interactions to achieve sustainable and safe crop production during environmental challenges.