Researchers isolated two strains of actinomycete bacteria from Japanese soil samples and characterized them as a new subspecies of Catellatospora citrea. The isolates, designated strains 6498-D and 6257-B (type strain), shared most chemotaxonomic and morphological features with the previously described C. citrea, including identical cell wall composition, menaquinone profiles (MK-9(H4) as major component), and carbohydrate utilization patterns. However, the new isolates had a critical distinguishing feature: they required external methionine for growth, a requirement that could not be fulfilled by cysteine or homoserine substitution. This methionine auxotrophy prevented growth on standard synthetic media commonly used for actinomycete cultivation. Based on this nutritional requirement and minor differences in carbon source utilization, the authors designated these isolates as Catellatospora citrea subsp. methionotrophica. The type strain IF0 14553 (6257-B) has a DNA guanine-plus-cytosine content of 70.8±0.5 mol%. This discovery documents a methionine-dependent variant within the C. citrea species complex isolated from distinct geographical locations in Japan.

Key findings

• Two soil-derived isolates sharing morphological and chemotaxonomic characteristics with Catellatospora citrea were designated as a new subspecies, C. citrea subsp. methionotrophica, due to obligate methionine auxotrophy.
• The methionine requirement could not be substituted by cysteine or homoserine, preventing growth on standard synthetic media used for actinomycete isolation.
• The new subspecies shared identical carbohydrate utilization profiles with C. citrea except for inability to utilize melibiose in one strain.
• Menaquinone analysis confirmed MK-9(H4) as the major quinone component, consistent with the genus Catellatospora.
• Type strain IF0 14553 (6257-B) exhibits 70.8±0.5 mol% GC content in DNA, typical for Catellatospora species.