Streptosporangium minutum sp. nov., isolated from garden soil exposed to microwave radiation

The actinobacterium, strain M26^T, was isolated from garden soil that was pre-treated with microwave radiation. The soil sample was collected in Roodepoort, Gauteng Province, South Africa as part of an antibiotic-screening programme. The isolate produced branched vegetative mycelium with sporangiophores bearing small sporangia ranging from 3 to 6 μm in diameter. Rapid genus identification revealed that the isolate belongs to the genus Streptosporangium. To confirm this result, the strain was subjected to polyphasic taxonomic characterisation. Chemotaxonomic characteristics were as follows: meso-DAP in the peptidoglycan, the whole-cell hydrolysate yielded madurose, predominant menaquinones were MK9 (21%), MK9(H₂) (40%), MK9(H₄) (31%) and MK9(H₆) (3%); the polar lipid profile included an aminolipid, phosphoglycolipids, phosphatidylethanolamine, and phosphatidylmonomethylethanolamine. In addition, the fatty acid profile showed the presence of C_16:0 (12.8%), C_17:1ω8c (14.2%), and 10-methyl-C_17:0 (15.8%). Furthermore, 16S rRNA gene sequence phylogenetic analysis showed that the strain is closely related to members of the genus Streptosporangium, which supports its classification within the family Streptosporangiaceae. Strain M26^T exhibited antibiosis against a range of pathogenic bacteria, including, but not limited to Acinetobacter baumannii ATCC 19606^T, Enterobacter cloacae subsp. cloacae ATCC BAA-1143, Enterococcus faecalis ATCC 51299 (vancomycin resistant), Escherichia coli ATCC 25922, Listeria monocytogenes ATCC 19111, Mycobacterium tuberculosis H37Rv^T, Pseudomonas aeruginosa ATCC 27853, Salmonella enterica subsp. arizonae ATCC 13314^T, and the methicillin-resistant Staphylococcus aureus subsp. aureus ATCC 33591 (MRSA). The name Streptosporangium minutum is proposed with the type strain M26^T (=LMG 28850^T =NRRL B-65295^T).