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 Gundlapally S. N. Reddy, Ruth M. Potrafka and Ferran Garcia-Pichel Correspondence Ferran Garcia-Pichel ferran@asu.edu School of Life Sciences, Arizona State University, Main Campus, Tempe, AZ 85287-4501, USA 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 6C 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 T , 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 (5ATCC BAA-1040 T 5DSM 16678 T ) is the type strain of M. versicolor. The description of microbial diversity in arid soils has received relatively little attention compared with that in mesic or agricultural soils, even though arid and semi-arid lands comprise around 30 % of the Earth’s terrestrial surface. Biological soil crusts (BSCs) that develop in the topmost layers of otherwise bare soils are one of the most conspicuous and widespread microbial communities of the arid zone. BSCs are important components of the soil system as they not only stabilize the soil against erosion (Belnap & Gardner, 1993), but also import nutrients such as carbon and nitrogen (Belnap, 2002; Belnap & Lange, 2001; Johnson et al., 2005). Their community composition always includes some oxygenic phototrophs (often cyano- bacteria, but also eukaryotic green algae), which are commonly free-living, but also often occur as lichen symbionts. An array of heterotrophic bacteria, archaea and fungi accompanies the primary producers (Garcia- Pichel, 2002). Recent cultivation-independent surveys have revealed that actinobacteria are one of the most important groups of heterotrophs in soil crusts (Reddy & Garcia- Pichel, 2006; Nagy et al., 2005). North American BSCs have been surveyed using molecular cultivation-independent methods (Garcia-Pichel et al., 2001; Smith et al., 2004; Nagy et al., 2005; Reddy & Garcia-Pichel, 2006) and novel bacteria and fungi have been isolated (Reddy & Garcia- Pichel, 2005; Reddy et al., 2006; Reddy & Garcia-Pichel, 2007; Bates et al., 2006). Many isolates from these crusts are pigmented and it would seem that pigment synthesis is a common strategy among many crust inhabitants, and not Abbreviations: BSC, biological soil crust; m-DAP, meso-diaminopimelic acid; OPA, o-phthalaldehyde. The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain CP153-2 T is AJ871304. International Journal of Systematic and Evolutionary Microbiology (2007), 57, 2014–2020 DOI 10.1099/ijs.0.64932-0 2014 64932 G 2007 IUMS Printed in Great Britain