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Kumar, Chandan
(2025).
DOI: https://doi.org/10.21954/ou.ro.00103214
Abstract
Over the past decade, it has become evident that the plant microbiome consists of a complex multispecies community. Plant growth-promoting bacteria (PGPB) found within the microbiome enhance plant growth and health through nutrient acquisition, hormone regulation, pathogen protection, and biocontrol. PGPB provide microbiome-based solutions for improving crop resilience and productivity.
This thesis presents an introduction providing literature background, three experimental chapters and a general discussion. The first experimental chapter (Chapter 2) focused on analyzing the rhizobacteriome of sorghum using 16S rRNA amplicon community profiling from sorghum plants grown across various genotypes and different geographical areas. This analysis identified key bacteriome members and consequently isolated representative strains and created three multi-strain bacterial synthetic consortia. Subsequently, their effectiveness in promoting sorghum plant growth was tested in growth chambers as well as in open field experiments, demonstrating their potential in promoting plant health.
The second experimental chapter (Chapter III) involves studies of cell-cell contact-independent quorum sensing (QS) signaling in the plant growth-promoting (PGP) endophyte Enterobacter asburiae AG129. This strain, which has PGP traits, was shown to possess a canonical N-acyl homoserine lactone (AHL) QS system, comprising of the genetically adjacent easI and easR genes which are responsible for synthesizing and responding to AHLs. Studies revealed that this AHL QS system positively regulates T6SS as well as the production of several volatile compounds however it negatively regulates rice root colonization, thus providing novel insights into the role of AHL QS in bacterial endophytes.
The third experimental chapter (Chapter IV) focuses on Alcaligenes faecalis strain SC1, demonstrating its biocontrol potential against the rice sheath-rot pathogen Pseudomonas fuscovaginae. This strain was isolated from healthy rice in a sheath-rot infested area in Burundi and was shown to possess strong anti-bacterial activity against P. fuscovaginae. Genome sequencing and analysis revealed potential biosynthetic gene clusters encoding anti-bacterial compounds. Initial purification of bioactive compounds evidenced the feasibility of purifying the compound(s) which exhibit anti-bacterial activity.
In summary, this thesis contributes to enhance the knowledge on how to use bacteriome data and PGPB in order to develop practical applications for crop resilience and productivity. It also increases knowledge of the role of QS in PGP bacterial endophytes and in the biocontrol of a rice pathogen.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)
