Soil protists can actively redistribute beneficial bacteria along Medicago truncatula roots
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Abstract
The rhizosphere is the region of soil directly influenced by plant roots. The microbial community in the rhizosphere includes fungi, protists, and bacteria, all of which play a significant role in plant health. The beneficial bacterium Sinorhizobium meliloti infects growing root hairs on nitrogen-starved leguminous plants. Infection leads to the formation of a root nodule, where S. meliloti converts atmospheric nitrogen to ammonia, a usable form of nitrogen for plants. S. meliloti is often found in biofilms and travels slowly along the roots, leaving developing root hairs at the growing root tips uninfected. Soil protists are an important component of the rhizosphere system who prey on soil bacteria and have been known to egest undigested phagosomes. We show that the soil protist, Colpoda sp ., can transport S. meliloti down Medicago truncatula roots. By using pseudo-3D soil microcosms, we directly observed the presence of fluorescently labelled S. meliloti along M. truncatula roots and tracked the displacement of the fluorescence signal over time. Two weeks after co-inoculation, this signal was detected 52 mm, on average, farther down the roots when Colpoda sp . was also present compared with the experimental treatment that contained bacteria but not protists. Direct counts also showed that protists are required for viable bacteria to reach the deeper sections of root systems in our microcosms. Facilitating bacterial transport may be an important mechanism whereby soil protists promote plant health. As a sustainable agriculture biotechnology, protist-facilitated transport has the potential to boost efficacy of bacterial inoculants, thereby helping growers avoid overuse of nitrogen fertilizers and enhance performance of climate-smart, no-till farming practices.
Importance
Soil protists are an important part of the microbial community in the rhizosphere. Plants grown with protists fare better than plants grown without protists. Mechanisms through which protists support plant health include nutrient cycling, alteration of the bacterial community through selective feeding, and consumption of plant pathogens. Here we provide data in support of an additional mechanism: protists act as transport vehicles for bacteria in soil. We show that protist-facilitated transport can deliver plant-beneficial bacteria to the growing tips of roots that may otherwise be sparsely inhabited with bacteria originating from a seed-associated inoculum. By co-inoculating Medicago truncatula roots with both S. meliloti , a nitrogen fixing legume symbiont, and Colpoda sp ., a ciliated protist, we show substantial and statistically significant transport with depth and breadth of bacteria-associated fluorescence as well as transport of viable bacteria. Co-inoculation with shelf-stable encysted soil protists may be employed as a sustainable agriculture biotechnology to better distribute beneficial bacteria and enhance the performance of inoculants.
Article activity feed
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replicates distinguished by color
Very cool way to look at the results.
Would be super interested in why the blue replicate is an outlier in terms of curve shape. It makes me wonder whether there is anything fundamentally different about the associated roots (growth rate, morphology).
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Selected composite brightfield (at last imaging date) and fluorescence (false-colored by week as indicated) images of soil channels for:
This was such an important figure for helping you understand all downstream analyses. It would have been great to have a normal light photo or cartoon schematic to the side to help orient me on what I was looking at.
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actively
It was a cool paper that presented a newly developed system that can be used to longitudinally track microbes along growing roots of a plant. There are going to be a lot of cool applications from this, and I would expect that this platform sets up all sorts of cool projects from this group and others in the future. I'm excited to see what develops!
It took me a few reads though to fully appreciate how cool it was because the title led me to expect a slightly different set of questions/conclusions. Namely, I think two things on this point: 1) it wasn't clear at the outset that they were engineering a new tool. 2) the word "actively" made me think that they were going to provide very direct evidence of active transport of some kind. However, it was largely focused on microscopy-based tracking and interesting correlations that …
actively
It was a cool paper that presented a newly developed system that can be used to longitudinally track microbes along growing roots of a plant. There are going to be a lot of cool applications from this, and I would expect that this platform sets up all sorts of cool projects from this group and others in the future. I'm excited to see what develops!
It took me a few reads though to fully appreciate how cool it was because the title led me to expect a slightly different set of questions/conclusions. Namely, I think two things on this point: 1) it wasn't clear at the outset that they were engineering a new tool. 2) the word "actively" made me think that they were going to provide very direct evidence of active transport of some kind. However, it was largely focused on microscopy-based tracking and interesting correlations that point to some kind of co-distribution of protist/bacteria in a protist-dependent way. But it didn't necessarily shed light on whether this was truly direct and "active" in the classic sense of the word (ATP). It also didn't necessarily conclude on directionality (i.e. protists driving bacteria rather than the other way around), although the dependency on protists and other lines of evidence in literature would certainly strongly suggest this!
And to be totally clear, I LOVE tool/platform papers, including this one! It just took a little effort to work align my expectations with the title.
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replicates distinguished by color
Very cool way to look at the results.
Would be super interested in why the blue replicate is an outlier in terms of curve shape. It makes me wonder whether there is anything fundamentally different about the associated roots (growth rate, morphology).
-
actively
It was a cool paper that presented a newly developed system that can be used to longitudinally track microbes along growing roots of a plant. There are going to be a lot of cool applications from this, and I would expect that this platform sets up all sorts of cool projects from this group and others in the future. I'm excited to see what develops!
It took me a few reads though to fully appreciate how cool it was because the title led me to expect a slightly different set of questions/conclusions. Namely, I think two things on this point: 1) it wasn't clear at the outset that they were engineering a new tool. 2) the word "actively" made me think that they were going to provide very direct evidence of active transport of some kind. However, it was largely focused on microscopy-based tracking and interesting correlations that …
actively
It was a cool paper that presented a newly developed system that can be used to longitudinally track microbes along growing roots of a plant. There are going to be a lot of cool applications from this, and I would expect that this platform sets up all sorts of cool projects from this group and others in the future. I'm excited to see what develops!
It took me a few reads though to fully appreciate how cool it was because the title led me to expect a slightly different set of questions/conclusions. Namely, I think two things on this point: 1) it wasn't clear at the outset that they were engineering a new tool. 2) the word "actively" made me think that they were going to provide very direct evidence of active transport of some kind. However, it was largely focused on microscopy-based tracking and interesting correlations that point to some kind of co-distribution of protist/bacteria in a protist-dependent way. But it didn't necessarily shed light on whether this was truly direct and "active" in the classic sense of the word (ATP). It also didn't necessarily conclude on directionality (i.e. protists driving bacteria rather than the other way around), although the dependency on protists and other lines of evidence in literature would certainly strongly suggest this!
And to be totally clear, I LOVE tool/platform papers, including this one! It just took a little effort to work align my expectations with the title.
-
Selected composite brightfield (at last imaging date) and fluorescence (false-colored by week as indicated) images of soil channels for:
This was such an important figure for helping you understand all downstream analyses. It would have been great to have a normal light photo or cartoon schematic to the side to help orient me on what I was looking at.
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