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Journal of Bacteriology, October 2009, p. 6145-6156, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.00460-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Hopanoids Play a Role in Membrane Integrity and pH Homeostasis in Rhodopseudomonas palustris TIE-1{triangledown} ,{dagger}

Paula V. Welander,1 Ryan C. Hunter,1 Lichun Zhang,2 Alex L. Sessions,2 Roger E. Summons,3 and Dianne K. Newman1,3,4*

Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 68-380, Cambridge, Massachusetts 02139,1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, MC100-23, 1200 E. California Boulevard, Pasadena, California 91125,2 Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, E25-633, Cambridge, Massachusetts 02139,3 Howard Hughes Medical Institute, 77 Massachusetts Avenue, 68-171, Cambridge, Massachusetts 021394

Received 3 April 2009/ Accepted 6 July 2009

Sedimentary hopanes are pentacyclic triterpenoids that serve as biomarker proxies for bacteria and certain bacterial metabolisms, such as oxygenic photosynthesis and aerobic methanotrophy. Their parent molecules, the bacteriohopanepolyols (BHPs), have been hypothesized to be the bacterial equivalent of sterols. However, the actual function of BHPs in bacterial cells is poorly understood. Here, we report the physiological study of a mutant in Rhodopseudomonas palustris TIE-1 that is unable to produce any hopanoids. The deletion of the gene encoding the squalene-hopene cyclase protein (Shc), which cyclizes squalene to the basic hopene structure, resulted in a strain that no longer produced any polycyclic triterpenoids. This strain was able to grow chemoheterotrophically, photoheterotrophically, and photoautotrophically, demonstrating that hopanoids are not required for growth under normal conditions. A severe growth defect, as well as significant morphological damage, was observed when cells were grown under acidic and alkaline conditions. Although minimal changes in shc transcript expression were observed under certain conditions of pH shock, the total amount of hopanoid production was unaffected; however, the abundance of methylated hopanoids significantly increased. This suggests that hopanoids may play an indirect role in pH homeostasis, with certain hopanoid derivatives being of particular importance.

* Corresponding author. Mailing address: Department of Biology, 77 Massachusetts Ave., 68-380, Cambridge, MA 02139. Phone: (617) 324-2770. Fax: (617) 324-3972. E-mail: dkn{at}mit.edu

{triangledown} Published ahead of print on 10 July 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, October 2009, p. 6145-6156, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.00460-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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