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Hopanoids confer robustness to physicochemical variability in the niche of the plant symbiont Bradyrhizobium diazoefficiens

Tookmanian, Elise and Junghans, Lisa and Kulkarni, Gargi and Ledermann, Raphael and Saenz, James Peter and Newman, Dianne K. (2021) Hopanoids confer robustness to physicochemical variability in the niche of the plant symbiont Bradyrhizobium diazoefficiens. . (Unpublished)

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Climate change poses a threat to soil health and agriculture, but the potential effects of climate change on soil bacteria that can help maintain soil health are understudied. Rhizobia are a group of bacteria that increase soil nitrogen content through a symbiosis with legume plants. The soil and symbiosis are potentially stressful environments, and the soil will likely become even more stressful as the climate changes. Many rhizobia within the bradyrhizobia clade, like Bradyrhizobium diazoefficiens, possess the genetic capacity to synthesize hopanoids, steroid-like lipids similar in structure and function to cholesterol. Hopanoids are known to protect against stresses relevant to the niche of B. diazoefficiens. Paradoxically, mutants unable to synthesize the extended class of hopanoids participate in similarly successful symbioses compared to the wild type, despite being delayed in root nodule initiation. Here, we show that in B. diazoefficiens, the in vitro growth defects of extended hopanoid deficient mutants can be at least partially compensated for by the physicochemical environment, specifically by optimal osmotic and divalent cation concentrations. Through biophysical measurements, we show that extended hopanoids confer robustness to environmental variability. These results help explain the discrepancy between previous in vitro and in planta results and indicate that hopanoids may provide a greater fitness advantage to rhizobia in the variable soil environment than the more controlled environment within root nodules. To improve the legume-rhizobia symbiosis through either bioengineering or strain selection, it will be important to consider the full lifecycle of rhizobia, from the soil to the symbiosis.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Ledermann, Raphael0000-0003-4612-1708
Saenz, James Peter0000-0001-8901-4377
Newman, Dianne K.0000-0003-1647-1918
Additional Information:The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license. This version posted September 1, 2021. We thank members of the Newman lab for their helpful comments and insights, especially Brittany Belin and all past members of Team Hopanoid. Thank you to Hans Martin-Fischer for his constant support of our work. This research was enabled by a NSF graduate research fellowship Foundation (E.T.), NASA (NNX16AL96G to D.K.N.), a German Federal Ministry of Education and Research BMBF grant (to J.S., project 03Z22EN12), and a VW Foundation ‘"Life" grant (to J.S., project 93090).
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Bundesministerium für Bildung und Forschung (BMBF)03Z22EN12
Volkswagen Foundation93090
Record Number:CaltechAUTHORS:20210902-193802546
Persistent URL:
Official Citation:Hopanoids confer robustness to physicochemical variability in the niche of the plant symbiont Bradyrhizobium diazoefficiens. Elise M Tookmanian, Lisa Junghans, Gargi Kulkarni, Raphael Ledermann, James Peter Saenz, Dianne K. Newman. bioRxiv 2021.08.31.458470; doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110699
Deposited By: Tony Diaz
Deposited On:02 Sep 2021 20:28
Last Modified:16 Nov 2021 19:42

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