Researchers describe a novel gram-negative bacterium isolated from Australian freshwaters exhibiting a unique dimorphic life cycle. The organism, named Conglomeromonas largomobilis, exists in two distinct phases: motile unicellular rods with mixed flagellation (one polar and 1-10 lateral flagella of different dimensions) and multicellular conglomerates formed through multiplanar centripetal cell wall septation. Conglomerate formation is specifically enhanced by sodium ions but not other metal ions or osmotic stress. The conglomerates dissociate into motile cells under appropriate conditions, producing water-clear colonies with sparse cells in clear fluid. Ultrastructural analysis reveals that conglomerate units are bound by laminated acidic polysaccharide layers and contain poly-β-hydroxybutyrate inclusions. The organism is gram-negative, facultatively anaerobic, and produces catalase, oxidase, and urease. It grows optimally at 28°C and shows fermentative carbohydrate metabolism. DNA G+C content ranges from 67.2 to 70.0 mol%, distinguishing it from related organisms like Geodermatophilus and Dermatophilus. Three strains were isolated, leading to the designation of a new genus and species with two proposed subspecies.

Key findings

• Conglomeromonas largomobilis exhibits unique dimorphic growth with motile unicellular and immotile multicellular conglomerate phases, reversibly interconvertible under different environmental conditions
• The organism possesses distinctive mixed flagellation with a single polar flagellum and 1-10 lateral flagella of different thickness and wavelength, differentiating it from morphologically similar gram-positive bacteria
• Conglomerate formation is specifically enhanced by sodium ions (at 0.35 M concentration) but not by other metal ions or osmotic stress, representing a unique sodium-dependent developmental response
• The organism is gram-negative (confirmed by cell wall chemistry, aminopeptidase presence, and sodium lauryl sulfate sensitivity), distinguishing it from morphologically similar gram-positive genera like Geodermatophilus and Dermatophilus