Targeted Transport of Plant Growth Promoting Rhizobacteria by Soil Protists

L.M. Shor, C. Hawxhurst, J.L. Micciulla, D.J. Gage
University of Connecticut,
United States

Keywords: agriculture biotechnology, beneficial bacteria, micromodel, plant growth promoting rhizobacteria (PGPR), protist, reliable carbon sequestration, rhizosphere, soil


Inoculating crops with plant growth promoting rhizobacteria (PGPR) can enhance yield and resilience while reducing fertilizer use and surface water pollution. Examples of PGPR include mucoid strains that protect roots against colonization by pathogens and nitrogen-fixing strains that provide cheap and sustainable fertilization when inoculated on soybean, alfalfa, bean, pea, clover or other legumes. Often, however, PGPR inoculation is ineffective. Various factors may inhibit performance of PGPR including restricted movement of the PGPR, poor water-based transport, and competition with endogenous bacteria. In this talk we demonstrate our patented technology whereby soil protists distribute PGRP along growing roots. Protists are adapted to move rapidly through unsaturated soils and are known to chemotact towards bacterial prey abundant at growing root tips. Filter-feeding soil protists also accumulate bacteria-sized particles from their environment. Here we show the soil protist Colpoda sp. actively transports Sinorhizobium meliloti soil bacteria along growing Medicago truncatula roots. By using a pseudo-2D soil microcosms (termed µ-rhizoslides), we are able to directly observe the presence of fluorescently-labelled S. meliloti along M. truncatula roots and track the displacement of bacteria over time. Two weeks after inoculation, S. meliloti can be detected 30 mm farther along roots in the protist + bacteria treatment versus in the bacteria-only treatment. Protist-facilitated transport may be developed as a sustainable agriculture biotechnology for enhancing the distribution and thereby boosting the efficacy of beneficial bacteria inoculation. Protists also accumulate other “prey-sized” particles (approx. 200 nm – 2 µm), and the technology for scalable micro-encapsulation of agrochemicals is now available. This technology, therefore, may also may act as a mechanism to facilitate transport and target delivery of encapsulated agrochemicals along fully-developed root systems in intact (untilled) soil. This technology may help agriculture double as a means for reliable carbon sequestration; thereby helping to reduce or even reverse the climate effects of food production.