Affiliation:
1. Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada
2. Département de Génie Biologique, Université de Technologie de Compiègne, Compiègne, France
Abstract
ABSTRACT
Root-associated microorganisms play an important role in plant health, such as plant growth-promoting rhizobacteria (PGPR) from the
Bacillus
and
Pseudomonas
genera. Although bacterial consortia including these two genera would represent a promising avenue to efficient biofertilizer formulation, we observed that
Bacillus subtilis
root colonization is decreased by the presence of
Pseudomonas fluorescens
and
Pseudomonas protegens
. To determine if
B. subtilis
can adapt to the inhibitory effect of
Pseudomonas
on roots, we conducted adaptative laboratory evolution experiments with
B. subtilis
in mono-association or co-cultured with
P. fluorescens
on tomato plant roots. Evolved isolates with various colony morphology and stronger colonization capacity of both tomato plant and
Arabidopsis thaliana
roots emerged rapidly from the two evolution experiments. Certain evolved isolates also had better fitness on the root in the presence of other
Pseudomonas
species. In all independent lineages, whole-genome resequencing revealed non-synonymous mutations in genes
ywcC
or
sinR
encoding regulators involved in repressing biofilm development, suggesting their involvement in enhanced root colonization. These findings provide insights into the molecular mechanisms underlying
B. subtilis
adaptation to root colonization and highlight the potential of directed evolution to enhance the beneficial traits of PGPR.
IMPORTANCE
In this study, we aimed to enhance the abilities of the plant-beneficial bacterium
Bacillus subtilis
to colonize plant roots in the presence of competing
Pseudomonas
bacteria. To achieve this, we conducted adaptive laboratory experiments, allowing
Bacillus
to evolve in a defined environment. We successfully obtained strains of
Bacillus
that were more effective at colonizing plant roots than the ancestor strain. To identify the genetic changes driving this improvement, we sequenced the genomes of these evolved strains. Interestingly, mutations that facilitated the formation of robust biofilms on roots were predominant. Many of these evolved
Bacillus
isolates also displayed the remarkable ability to outcompete
Pseudomonas
species. Our research sheds light on the mutational paths selected in
Bacillus subtilis
to thrive in root environments and offers exciting prospects for improving beneficial traits in plant growth-promoting microorganisms. Ultimately, this could pave the way for the development of more effective biofertilizers and sustainable agricultural practices.
Funder
Natural Sciences and Engineering Research Council of Canada
Publisher
American Society for Microbiology
Subject
Computer Science Applications,Genetics,Molecular Biology,Modeling and Simulation,Ecology, Evolution, Behavior and Systematics,Biochemistry,Physiology,Microbiology