Blastococcus tunisiensis sp. nov., isolated from limestone collected in Tunisia

A new actinobacterium strain, designated BMG 823^T, was isolated from a limestone sample collected in Tunisia. Its taxonomic position was scrutinized using a polyphasic approach. Colonies of strain BMG 823^T were pink orange-coloured, regular and had a moist surface. Cells are Gram-stain-positive, catalase-negative and oxidase-negative. The strain grew at pH 5.5-9, 10-40 °C and in presence of up to 4 % NaCl (w/v). Chemotaxonomically, strain BMG 823^T was characterized by cell-wall type III containing meso-diaminopimelic acid as diamino acid, glucose, ribose and rhamnose as whole-cell sugars, MK-9(H₄) as predominant menaquinone, and phosphatidylcholine, diphosphadidylglycerol, phosphatidethanolamine, phosphatidylcholine, phosphatidylinositol, unidentified glycolipid, unidentified aminophospholipids and unidentified glycophospholipid as major polar lipids. The fatty acid profile consisted of iso-C_16 : 0 and iso-C_17 : 1  ω9. Phylogenetic trees based on 16S rRNA gene and genome sequences placed strain BMG 823^T within the genus Blastococcus and separated it from all type strains of validly published species. Comparison of 16S rRNA gene sequence similarity, digital DNA-DNA hybridization and average nucleotide identity indicated that strain BMG 823^T was most closely related to Blastococcus litoris DSM 106127^T and Blastococcus colisei BMG 822^T with pairwise values well below the species differentiation thresholds. The distinct phenotypic and genotypic features of strain BMG 823^T (=DSM 46838^T=CECT 8881^T) within the genus Blastococcus warrant its recognition as the type strain for the new species for which we propose the name Blastococcus tunisiensis sp. nov.