This study describes Actinoplanes caeruleus, a new antibiotic-producing bacterial species isolated from soil in California. The organism produces irregular to globose sporangia that release motile, polarly flagellated spores. It is distinguished by striking blue vegetative mycelial pigments and whole-cell sugars of arabinose and xylose, consistent with the genus Actinoplanes. Chemical analysis revealed lysine as the major dibasic amino acid but absence of diaminopimelic acid in the cell wall. Strain SCC 1014T differs from other Actinoplanes species by its ability to hydrolyze adenine and hypoxanthine, resistance to lysozyme and salicylate, inability to utilize L-arabinose, D-xylose, and succinate as sole carbon sources, and production of a heptaene antifungal antibiotic. Comparative physiological testing with previously described Actinoplanes species confirmed this represents a distinct new species, named A. caeruleus after its characteristic blue pigmentation. The type strain was deposited in the American Type Culture Collection as ATCC 33937.

Key findings

• Actinoplanes caeruleus produces striking blue vegetative mycelial pigments and irregular to globose sporangia with polarly flagellated motile spores (1.3-2.0 μm diameter)
• The organism lacks diaminopimelic acid in its cell wall but contains arabinose and xylose as whole-cell sugars, confirming placement in genus Actinoplanes
• A. caeruleus uniquely combines blue pigmentation, absence of cell wall DAP, positive adenine and hypoxanthine hydrolysis, lysozyme resistance, and inability to utilize L-arabinose, D-xylose, and succinate
• The species produces a novel heptaene antifungal antibiotic with broad activity against pathogenic fungi, the first polyene antibiotic reported from an actinoplanete
• Comparative testing with all established Actinoplanes species confirmed A. caeruleus represents a distinct new species with no other strain sharing its complete phenotypic profile