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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 theirOMproteins 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. [ABSTRACT FROM AUTHOR]

Myxobacteria are predatory and are prolific producers of secondary metabolites. Here, we tested a hypothesized role that secondary metabolite antibiotics function as weapons in predation. To test this, a Myxococcus xanthus Δta1 mutant, blocked in antibiotic TA (myxovirescin) production, was constructed. This TA- mutant was defective in producing a zone of inhibition (ZOI) against Escherichia coli. This shows that TA is the major M. xanthus-diffusible antibacterial agent against E. coli. Correspondingly, the TA- mutant was defective in E. coli killing. Separately, an engineered E. coil strain resistant to TA was shown to be resistant toward predation. Exogenous addition of spectinomycin, a bacteriostatic antibiotic, rescued the predation defect of the TA- mutant. In contrast, against Micrococcus luteus the TA- mutant exhibited no defect in ZOI or killing. Thus, TA plays a selective role on prey species. To extend these studies to other myxobacteria, the role of antibiotic corallupyronin production in predation was tested and also found to be required for Corallococcus coralloides killing on E. coli. Next, a role of TA production in myxobacterial fitness was assessed by measuring swarm expansion. Here, the TA- mutant had a specific swarm rate reduction on prey lawns, and thus reduced fitness, compared to an isogenic TA+ strain. Based on these observations, we conclude that myxobacterial antibiotic production can function as a predatory weapon. To our knowledge, this is the first report to directly show a link between secondary metabolite production and predation. [ABSTRACT FROM AUTHOR]