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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 and Newman, Dianne K. (2022) Hopanoids Confer Robustness to Physicochemical Variability in the Niche of the Plant Symbiont Bradyrhizobium diazoefficiens. Journal of Bacteriology, 204 (7). Art. No. jb.00442-21. ISSN 0021-9193. doi:10.1128/jb.00442-21.

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Rhizobia are a group of bacteria that increase soil nitrogen content through symbiosis with legume plants. The soil and symbiotic host are potentially stressful environments, and the soil will likely become even more stressful as the climate changes. Many rhizobia within the Bradyrhizobium 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 symbioses with success similar to that of the wild type, despite being delayed in root nodule initiation. Here, we show that in B. diazoefficiens, the 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 of lipid packing and membrane permeability, we show that extended hopanoids confer robustness to environmental variability. These results help explain the discrepancy between previous in-culture 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 environments within root nodules. To improve the legume-rhizobium symbiosis through either bioengineering or strain selection, it will be important to consider the full life cycle of rhizobia, from soil to symbiosis.

Item Type:Article
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URLURL TypeDescription Material Paper
Tookmanian, Elise0000-0003-3114-2354
Ledermann, Raphael0000-0003-4612-1708
Saenz, James0000-0001-8901-4377
Newman, Dianne K.0000-0003-1647-1918
Additional Information:© 2022 American Society for Microbiology. Received 30 August 2021; Accepted 3 May 2022. We thank members of the Newman lab for their helpful comments and insights, especially Brittany Belin and all past members of Team Hopanoid. We are grateful to Hans Martin-Fischer for his encouragement and support of our work. This research was enabled by an 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). The authors declare no conflict of interest.
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Bundesministerium für Bildung und Forschung (BMBF)03Z22EN12
Volkswagen Foundation93090
Subject Keywords:bradyrhizobia, climate change, hopanoids, osmotic stress, robustness, soil microbiology
Issue or Number:7
Record Number:CaltechAUTHORS:20210902-193802546
Persistent URL:
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:03 Aug 2022 17:20

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