Bacterial Chemotaxis in Beneficial Plant-Microbe Associations

A significant increase in agricultural production is needed to meet the demand for food to feed the expected ~10 billion people by 2050. This increased agricultural output will also require sustainable and environmentally friendly practices including reducing or eliminating reliance on chemical fertilizers, which are also source of environmental pollution. One of the potential solutions to this global challenge is to inoculate plants with beneficial microorganisms that are able to promote plant growth by a variety of mechanisms. Plant growth promoting rhizobacteria or PGPR are a diverse group of beneficial soil bacteria that are currently used as bio-inoculants and/or bio-fertilizers when inoculated to crops. A prerequisite to promoting plant growth is the ability to colonize the root surfaces. The root surfaces and the zone around the roots under the influence of plant secretion, a.k.a. the rhizosphere, is a spatially and chemically heterogenous environment and bacteria must be able to successfully navigate in the rhizosphere to colonize root surfaces. Bacterial motility and chemotaxis have been repeatedly shown in experiments to be required for a successful colonization of plant root surfaces by rhizosphere bacteria, including PGPR. The chemotaxis function is also enriched in soil and root bacterial metagenomes compared to the human gut or the oceans metagenomes. The presentation will compare and contrast recent approaches and improved tools to study bacterial chemotaxis in real time in the rhizosphere using model PGPR. The insight gained from the recent studies regarding the role of chemotaxis and root surface colonization in some of the PGPR will also be discussed.

Learning Objectives: 

1. Describe roles that plant growth promoting rhizobacteria (PGPR) have in sustainable agricultural practices.

2. Explain the role of bacterial chemotaxis in navigating the rhizosphere and in plant root surface colonization.

3. Cite examples of spatial and temporal gradient chemotaxis assays.

4. Compare and contrast the sensitivity of the different assays for studying bacterial chemotaxis in PGPR.

5. Cite examples of evidence for chemotaxis in supporting plant root colonization in PGPR.