Specific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>

ABSTRACT A better understanding of how bacteria resist stresses encountered during the progression of plant-microbe symbioses will advance our ability to stimulate plant growth. Here, we show that the symbiotic system comprising the nitrogen-fixing bacterium Bradyrhizobium diazoefficiens and the leg...

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Autores principales:	Gargi Kulkarni, Nicolas Busset, Antonio Molinaro, Daniel Gargani, Clemence Chaintreuil, Alba Silipo, Eric Giraud, Dianne K. Newman
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Lenguaje:	EN
Publicado:	American Society for Microbiology 2015
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/d03666ec65034f98991e9ed164c0f799
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spelling	oai:doaj.org-article:d03666ec65034f98991e9ed164c0f7992021-11-15T15:41:30ZSpecific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>10.1128/mBio.01251-152150-7511https://doaj.org/article/d03666ec65034f98991e9ed164c0f7992015-10-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01251-15https://doaj.org/toc/2150-7511ABSTRACT A better understanding of how bacteria resist stresses encountered during the progression of plant-microbe symbioses will advance our ability to stimulate plant growth. Here, we show that the symbiotic system comprising the nitrogen-fixing bacterium Bradyrhizobium diazoefficiens and the legume Aeschynomene afraspera requires hopanoid production for optimal fitness. While methylated (2Me) hopanoids contribute to growth under plant-cell-like microaerobic and acidic conditions in the free-living state, they are dispensable during symbiosis. In contrast, synthesis of extended (C35) hopanoids is required for growth microaerobically and under various stress conditions (high temperature, low pH, high osmolarity, bile salts, oxidative stress, and antimicrobial peptides) in the free-living state and also during symbiosis. These defects might be due to a less rigid membrane resulting from the absence of free or lipidA-bound C35 hopanoids or the accumulation of the C30 hopanoid diploptene. Our results also show that C35 hopanoids are necessary for symbiosis only with the host Aeschynomene afraspera but not with soybean. This difference is likely related to the presence of cysteine-rich antimicrobial peptides in Aeschynomene nodules that induce drastic modification in bacterial morphology and physiology. The study of hopanoid mutants in plant symbionts thus provides an opportunity to gain insight into host-microbe interactions during later stages of symbiotic progression, as well as the microenvironmental conditions for which hopanoids provide a fitness advantage. IMPORTANCE Because bradyrhizobia provide fixed nitrogen to plants, this work has potential agronomical implications. An understanding of how hopanoids facilitate bacterial survival in soils and plant hosts may aid the engineering of more robust agronomic strains, especially relevant in regions that are becoming warmer and saline due to climate change. Moreover, this work has geobiological relevance: hopanes, molecular fossils of hopanoids, are enriched in ancient sedimentary rocks at discrete intervals in Earth history. This is the first study to uncover roles for 2Me- and C35 hopanoids in the context of an ecological niche that captures many of the stressful environmental conditions thought to be important during (2Me)-hopane deposition. Though much remains to be done to determine whether the conditions present within the plant host are shared with niches of relevance to the rock record, our findings represent an important step toward identifying conserved mechanisms whereby hopanoids contribute to fitness.Gargi KulkarniNicolas BussetAntonio MolinaroDaniel GarganiClemence ChaintreuilAlba SilipoEric GiraudDianne K. NewmanAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 6, Iss 5 (2015)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Gargi Kulkarni Nicolas Busset Antonio Molinaro Daniel Gargani Clemence Chaintreuil Alba Silipo Eric Giraud Dianne K. Newman Specific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>
description	ABSTRACT A better understanding of how bacteria resist stresses encountered during the progression of plant-microbe symbioses will advance our ability to stimulate plant growth. Here, we show that the symbiotic system comprising the nitrogen-fixing bacterium Bradyrhizobium diazoefficiens and the legume Aeschynomene afraspera requires hopanoid production for optimal fitness. While methylated (2Me) hopanoids contribute to growth under plant-cell-like microaerobic and acidic conditions in the free-living state, they are dispensable during symbiosis. In contrast, synthesis of extended (C35) hopanoids is required for growth microaerobically and under various stress conditions (high temperature, low pH, high osmolarity, bile salts, oxidative stress, and antimicrobial peptides) in the free-living state and also during symbiosis. These defects might be due to a less rigid membrane resulting from the absence of free or lipidA-bound C35 hopanoids or the accumulation of the C30 hopanoid diploptene. Our results also show that C35 hopanoids are necessary for symbiosis only with the host Aeschynomene afraspera but not with soybean. This difference is likely related to the presence of cysteine-rich antimicrobial peptides in Aeschynomene nodules that induce drastic modification in bacterial morphology and physiology. The study of hopanoid mutants in plant symbionts thus provides an opportunity to gain insight into host-microbe interactions during later stages of symbiotic progression, as well as the microenvironmental conditions for which hopanoids provide a fitness advantage. IMPORTANCE Because bradyrhizobia provide fixed nitrogen to plants, this work has potential agronomical implications. An understanding of how hopanoids facilitate bacterial survival in soils and plant hosts may aid the engineering of more robust agronomic strains, especially relevant in regions that are becoming warmer and saline due to climate change. Moreover, this work has geobiological relevance: hopanes, molecular fossils of hopanoids, are enriched in ancient sedimentary rocks at discrete intervals in Earth history. This is the first study to uncover roles for 2Me- and C35 hopanoids in the context of an ecological niche that captures many of the stressful environmental conditions thought to be important during (2Me)-hopane deposition. Though much remains to be done to determine whether the conditions present within the plant host are shared with niches of relevance to the rock record, our findings represent an important step toward identifying conserved mechanisms whereby hopanoids contribute to fitness.
format	article
author	Gargi Kulkarni Nicolas Busset Antonio Molinaro Daniel Gargani Clemence Chaintreuil Alba Silipo Eric Giraud Dianne K. Newman
author_facet	Gargi Kulkarni Nicolas Busset Antonio Molinaro Daniel Gargani Clemence Chaintreuil Alba Silipo Eric Giraud Dianne K. Newman
author_sort	Gargi Kulkarni
title	Specific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>
title_short	Specific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>
title_full	Specific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>
title_fullStr	Specific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>
title_full_unstemmed	Specific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>
title_sort	specific hopanoid classes differentially affect free-living and symbiotic states of <italic toggle="yes">bradyrhizobium diazoefficiens</italic>
publisher	American Society for Microbiology
publishDate	2015
url	https://doaj.org/article/d03666ec65034f98991e9ed164c0f799
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Specific Hopanoid Classes Differentially Affect Free-Living and Symbiotic States of <italic toggle="yes">Bradyrhizobium diazoefficiens</italic>

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