Hopanoid-free Methylobacterium extorquens DM4 overproduces carotenoids and has widespread growth impairment.
Hopanoids are sterol-like membrane lipids widely used as geochemical proxies for bacteria. Currently, the physiological role of hopanoids is not well understood, and this represents one of the major limitations in interpreting the significance of their presence in ancient or contemporary sediments. Previous analyses of mutants lacking hopanoids in a range of bacteria have revealed a range of phenotypes under normal growth conditions, but with most having at least an increased sensitivity to toxins and osmotic stress. We employed hopanoid-free strains of Methylobacterium extorquens DM4, uncovering severe growth defects relative to the wild-type under many tested conditions, including normal growth conditions without additional stressors. Mutants overproduce carotenoids-the other major isoprenoid product of this strain-and show an altered fatty acid profile, pronounced flocculation in liquid media, and lower growth yields than for the wild-type strain. The flocculation phenotype can be mitigated by addition of cellulase to the medium, suggesting a link between the function of hopanoids and the secretion of cellulose in M. extorquens DM4. On solid media, colonies of the hopanoid-free mutant strain were smaller than wild-type, and were more sensitive to osmotic or pH stress, as well as to a variety of toxins. The results for M. extorquens DM4 are consistent with the hypothesis that hopanoids are important for membrane fluidity and lipid packing, but also indicate that the specific physiological processes that require hopanoids vary across bacterial lineages. Our work provides further support to emerging observations that the role of hopanoids in membrane robustness and barrier function may be important across lineages, possibly mediated through an interaction with lipid A in the outer membrane.
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, United States of America.|Department of Earth and Planetary Sciences, Washington University in St Louis, St Louis, MO, United States of America.
Alexander S
http://orcid.org/0000-0002-4044-2802
AS
Bradley
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, United States of America.
Paige K
PK
Swanson
Equipe Adaptations et interactions microbiennes, Université de Strasbourg, UMR 7156 UNISTRA-CNRS Génétique Moléculaire, Génomique, Microbiologie, Strasbourg, France.
Emilie E L
EE
Muller
Equipe Adaptations et interactions microbiennes, Université de Strasbourg, UMR 7156 UNISTRA-CNRS Génétique Moléculaire, Génomique, Microbiologie, Strasbourg, France.
Françoise
F
Bringel
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, United States of America.
Sean M
SM
Caroll
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, United States of America.
Ann
A
Pearson
Equipe Adaptations et interactions microbiennes, Université de Strasbourg, UMR 7156 UNISTRA-CNRS Génétique Moléculaire, Génomique, Microbiologie, Strasbourg, France.
Stéphane
S
Vuilleumier
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, United States of America.|Department of Biological Sciences, University of Idaho, Moscow, ID, United States of America.|Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID, United States of America.|Center for Modeling Complex Interactions, University of Idaho, Moscow, ID, United States of America.
Christopher J
CJ
Marx
D002338:Carotenoids / Q000096:biosynthesis* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002480:Cellulase / Q000378:metabolism; D003470:Culture Media; D005227:Fatty Acids / Q000378:metabolism; D005427:Flocculation; D006863:Hydrogen-Ion Concentration; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000502:physiology*; D020601:Methylobacterium extorquens / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D009154:Mutation; D009994:Osmolar Concentration; D013312:Stress, Physiological
D003470:Culture Media; D005227:Fatty Acids; D008563:Membrane Lipids; D002338:Carotenoids; D002480:Cellulase