Modestobacter versicolor sp nov., an actinobacterium from biological soil crusts that produces melanins under oligotrophy, with emended descriptions of the genus Modestobacter and Modestobacter multiseptatus Mevs et al. 2000

A novel isolate, CP153-2(T), was obtained from topsoil biological crusts in the Colorado Plateau (USA). Colonies were black in colour due to melanin-like pigments when grown on oligotrophic medium, but not when grown on copiotrophic medium. Induction of melanogenesis was independent of growth phase or illumination conditions, including exposure to UVB and UVA radiation, but exposure to UVB could enhance total pigment production and growth under low nitrogen prevented its synthesis. This mode of regulation was previously unknown among melanin-producing bacteria. Polyphasic characterization of the strain revealed that cells were short, straight to curved or irregular rods that developed into pairs and formed multiseptate short filaments, with rare bud-like cells. Short rods were typically motile by means of flagella; multicellular structures tended to be sessile. Cells stained Gram-positive, grew at 4-30 degrees C and had a narrow range of pH tolerance (pH 5-9). The major fatty acids were iso-C-15:0 iso-C-16:0, anteiso-C-15:0 and C-18:1; MK-9(H-4) was the major respiratory quinone. Its peptidoglycan contained meso-diaminopimelic acid. Based on 16S rRNA gene sequence similarity data, its closest relative (98.1% similarity) was Modestobacter multiseptatus DSM 44406, which is similar morphologically. Based on the above characteristics, strain CP153-2(T) was also assigned to the genus Modestobacter. However, CP153-2(T) had a relatedness of only 49.9% in whole-genome reassociation comparisons with the type strain of M. multiseptatus and thus formally represents a novel species, for which the name Modestobacter versicolor sp. nov. is proposed. Additional evidence in support of a novel species comes from phenotypic and chemotaxonomic characteristics. Strain CP153-2(T) (=ATCC BAA-1040(T) = DSM 16678(T)) is the type strain of M. versicolor.