title: Myxobacteria produce outer membrane-enclosed tubes in unstructured environments.
abstract: Myxobacteria are social microbes that exhibit complex multicellular behaviors. By use of fluorescent reporters, we show that Myxococcus xanthus isolates produce long narrow filaments that are enclosed by the outer membrane (OM) and contain proteins. We show that these OM tube (OMT) structures are produced at surprisingly high levels when cells are placed in liquid medium or buffer without agitation. OMTs can be long and easily exceed multiple cell lengths. When viewed by transmission electron microscopy, their morphology varies between tubes and chain-like structures. Intermediate-like structures are also found, suggesting that OMTs may transition between these two morphotypes. In support of this, video epifluorescence microscopy found that OMTs in solution dynamically twist and jiggle. On hard surfaces, myxobacteria glide, and upon cell-cell contact, they can efficiently exchange their OM proteins and lipids by a TraAB-dependent mechanism. Although the structure of OMTs hints at a possible role as conduits for exchange, evidence is presented to the contrary. For example, abundant OMT production occurs in traA or traB mutants and when cells are grown in liquid medium, yet transfer cannot occur under these conditions. Thus, genetic and environmental conditions that promote OMT production are incongruent with OM exchange.
authors.affiliation: Department of Molecular Biology, University of Wyoming, Laramie, Wyoming, USA.
authors.forename: Xueming
authors.initials: X
authors.lastname: Wei
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Vassallo
authors.forename: Darshankumar T
authors.initials: DT
authors.lastname: Pathak
authors.forename: Daniel
authors.initials: D
authors.lastname: Wall
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000502:physiology*; D001431:Bacteriological Techniques; D002462:Cell Membrane / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D008164:Luminescent Proteins; D056265:Microbial Interactions; D016941:Myxococcus xanthus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013194:Staining and Labeling; D000097573:Red Fluorescent Protein
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D008164:Luminescent Proteins; D000097573:Red Fluorescent Protein