We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization.
Bibliographical noteFunding Information:
This study was funded by the Agouron Institute, the University of Minnesota Department of Geology and Geophysics, the Max Planck Society, and the National Science Foundation (OCE-0826254 and OCE 09-39557). Parts of this work were carried out in the Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network (http:// www.mrfn.org) via the MRSEC program with assistance from Chris Frethem and Fang Zhou. Scanning electron microscopy was performed in the University of Minnesota, Twin Cities, Limnological Research Center with the support of Amy Myrbo. Furthermore, we thank Tony Rathburn, Shana Goffredi, Anders Waren, Danwei Huang, Anne Dekas, Olivia Mason, Ben Harrison, the crew of the R/V Atlantis and pilots of the DSV Alvin (15–44 and 15–59) for assistance at sea, and Ben Grupe for providing live gastropods from Hydrate Ridge. We thank the reviewers of this manuscript for valuable comments that helped improve the manuscript.