Summary auto-generated
This study describes a novel bacterium living in obligate coculture with Chondromyces crocatus, a myxobacterium isolated from soil on Madeira. Researchers identified a small, pleomorphic gram-negative rod that consistently accompanied three strains of C. crocatus but could not be maintained in pure culture independently. Through 16S ribosomal DNA sequencing, the companion bacterium was phylogenetically classified within the Cytophaga-Flavobacterium-Bacteroides complex, most closely related to the genus Sphingobacterium. Chemotaxonomic analyses including fatty acid composition, isoprenoid analysis, DNA G+C content (35.9 mol%), and the presence of sphingolipids confirmed this affiliation. The bacterium exhibits different morphologies depending on growth conditions: highly pleomorphic spheroplast-like cells in pure culture versus small, slightly pleomorphic rods in coculture. Because the organism could not survive beyond a few generations on solid media and detailed characterization was hindered by cultivation difficulties, the authors assigned it provisional Candidatus status as "Candidatus comitans." The discovery raises questions about the mutualistic or symbiotic relationship between these organisms, as attempts to eliminate the companion from C. crocatus cultures resulted in the myxobacterium's death.
Key findings
- A small gram-negative bacterium consistently associates with Chondromyces crocatus myxobacteria but cannot be cultured independently, surviving only a few generations in pure culture
- 16S rDNA analysis phylogenetically places this companion organism within the Sphingobacterium genus, with >90% sequence similarity to known Sphingobacterium species
- Chemotaxonomic characteristics including sphingolipids, menaquinone MK-7, fatty acids iso-C15:0 and iso-2-OH-C15:0, and 35.9 mol% G+C content confirm affiliation with Sphingobacterium
- The bacterium shows different cell morphologies depending on culture conditions: pleomorphic spheroplast-like cells in pure culture but slender rods in coculture with C. crocatus
- The organism is assigned provisional Candidatus comitans status due to inability to maintain pure cultures and limited phenotypic characterization
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Abstract
We describe the phylogenetic position and some taxonomically relevant characteristics of a small pleomorphic gram-negative bacterium that was cocultured with some strains of the myxobacterium Chondromyces crocatus that were isolated from the same geographic and ecological habitat. A 16S ribosomal DNA analysis revealed that the companion was a member of the "Cytophaga-Flavobacterium-Bacteroides" complex and was most closely related to members of the genus Sphingobacterium. The results of a fatty acid analysis, an isoprenoid composition analysis, and a DNA G+C content analysis and the presence of sphingolipids confirmed that this bacterium is affiliated with the genus Sphingobacterium. As the companion bacterium survived for only a few generations on solid media and could not be maintained in pure culture, we assign to this novel taxon that lives in close association with the myxobacterium C. crocatus Candidatus status as "Candidatus comitans."