Streptomyces lunaelactis sp. nov., a novel ferroverdin A-producing Streptomyces species isolated from a moonmilk speleothem.

A novel actinobacterium, designated MM109(T), was isolated from a moonmilk deposit collected from the cave 'Grotte des Collemboles' located in Comblain-au-Pont, Belgium. Based on a polyphasic taxonomic approach comprising chemotaxonomic, phylogenetic, morphological, and physiological characterization, the isolate has been affiliated to the genus Streptomyces. Multilocus sequence analysis based on the 16S rRNA gene and five other house-keeping genes (atpD, gyrB, rpoB, recA and trpB) showed that the MM109(T) isolate is sufficiently distinct from its closest relative, Streptomyces peucetius strain AS 4.1799(T), as to represent a novel species. The phylogenetic distinctiveness of the taxon represented by isolate MM109(T) was supported by the isolation and identification of additional twelve moonmilk-derived isolates, which according to multilocus sequence analysis were clustered along with MM109(T). Scanning electron microscopy observations revealed complex and diversified structures within a MM109(T) colony, made from branching vegetative mycelia. The spore chains of the MM109(T) isolate undergo complete septation at the late stages of the morphological differentiation process, leading to the formation of packs of smooth cylindrical-shaped spores. Isolate MM109(T) produces several intracellular and diffusible pigments, particularly an intracellular green-pigmented secondary metabolite, which was identified through UPLC-ESI-MS analysis as ferroverdin A, an iron-chelating molecule formerly extracted and characterized from Streptomyces sp. strain WK-5344. The isolate MM109(T) is thus considered to represent a novel species of Streptomyces, for which the name Streptomyces lunaelactis sp. nov. is proposed with the type strain MM109(T) (=DSM 42149(T) = BCCM/LMG 28326(T)).