Oligotrophic PYGV medium, inoculated with soils from Linnaeus Terrace (1600 m, Antarctica), yielded four aerobic actinomycetes with short rods, multiple and irregular septa and often motile buds. Cells were 1.0-2.8 x 1.0-3.0 microm and colonies were beige to pink. The isolates were nearly identical in physiological and biochemical tests. Three strains grew from 0 degrees C to 25-28 degrees C, but one was psychrophilic with a maximum growth temperature of 20 degrees C. Carbon sources utilized were D-glucose, D-galactose, lactose, sucrose or mannitol; malate, succinate, fumarate, pyruvate or glutarate were decarboxylated aerobically. Peptone and yeast extract were the preferred nitrogen sources. Nitrate was reduced aerobically or anaerobically. Cell walls contained meso-diaminopimelic acid, glutamate, alanine, glycine, galactose, glucose and ribose. Major fatty acids of strains AA-802, -824, -825 and -826T were n18:1, i16:0 and ai17:0. Major respiratory quinones were MK-9(H4) and MK-8(H4). Polar lipids were diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol. Phosphatidylglycerol was found in most strains. The DNA G+C contents were 68-70 mol%. In 16S rDNA analyses, similarity values obtained for 500 nucleotides from the 5' terminus were > 99.5%. Almost complete sequences from AA-826T and -825 were 99.9% similar. Strain AA-826T belonged to a novel cluster of desert soil and rock isolates within the Geodermatophilaceae and was equidistantly related to members of Geodermatophilus and to a Blastococcus lineage. The four isolates represent a new genus, Modestobacter gen. nov., with Modestobacter multiseptatus sp. nov. as the type species. The type strain, Modestobacter multiseptatus AA-826T, was deposited in the DSMZ as DSM 44406T.


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