Molecular evidence for association between the sphingobacterium-like organism "Candidatus comitans" and the myxobacterium Chondromyces crocatus

Abstract

Seven strains of the myxobacterium Chondromyces crocatus, isolated from widely separated geographic regions, were investigated for the presence of an associate gram-negative, rod-shaped companion bacterium that is phylogenetically related to the genus Sphingobacterium and has been named "Candidatus comitans" (C. A. Jacobi, E. Stackebrandt, H. Reichenbach, and B. J. Tindall, Int. J. Syst. Bacteriol. 46:119-122, 1996). Five of the Chondromyces strains were found to be associated with a companion bacterium, and one strain lost its companion during the study. A 16S ribosomal DNA (16S rDNA) clone library was generated for each Chondromyces culture. Sequence similarity was > 99.1% for all but one strain of C. crocatus and all but one strain of "Candidatus comitans". The three analyzed 16S rDNA clone sequences of the companion of Cm c7 indicated that this companion strain is slightly less related to the other companion strains. The association between the companion and the myxobacterium including the sporangioles was determined by in situ hybridization with fluorescently labeled rRNA probes and scanning confocal laser microscopy. Based on these results, there are indications that the companion strains may survive environmental stress by inclusion in the aggregates and in the sporangioles of the myxobacterium.