Strain 12A35 was isolated from a deep-sea sediment collected from the South China Sea and showed promising antibacterial activities. It was identified as Streptomyces sp. by the 16S rDNA sequence analysis. Bioassay-guided fractionation using HP20 adsorption, flash chromatography over silica gel and octadecylsilyl (ODS) and semi-preparative HPLC, led to the isolation and purification of five metabolites from the fermentation culture of 12A35. Two new spirotetronate antibiotics, lobophorins H (1) and I (2), along with three known analogues, O-β-kijanosyl-(1→17)-kijanolide (3), lobophorins B (4) and F (5) were characterized by 1D, 2D-NMR and MS data. These compounds exhibited significant inhibitory activities against Bacillus subtilis. Compounds 1 and 5 exhibited moderate activities against Staphylococcus aureus. In particular, the new compound lobophorin H (1) showed similar antibacterial activities against B. subtilis CMCC63501 to ampicillin.

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Two actinomycete strains isolated from marine sediment samples, designated YIM M11335T (from the Indian Ocean) and 12A09T (from the South China Sea), were obtained and examined by a polyphasic approach. The two Gram-staining-positive, aerobic strains produced branched substrate mycelia and aerial hyphae that were not fragmented, and no diffusible pigment was produced on the media tested. At maturity, spore chains and single spores were formed on aerial hyphae and substrate mycelium, respectively. Whole-organism hydrolysates of both strains contained meso-diaminopimelic acid and the diagnostic sugars glucose and galactose. Their predominant menaquinones were MK-10(H4), MK-10(H6), MK-11(H4), MK-11(H6) and MK-11(H8) for strain YIM 11335T and MK-10(H4), MK-10(H6), MK-11(H4), MK-11(H6) and MK-11(H8) for strain 12A09T. The polar lipids detected in the two strains were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol mannoside, phosphatidylinositol, phosphatidylcholine, an unknown phosphoglycolipid and several unknown glycolipids, phospholipids and polar lipids. The major fatty acids (>10 %) were iso-C16 : 0 and C16 : 0 for strain YIM 11335T and iso-C16 : 0 for strain 12A09T. The G+C contents of the genomic DNA of strains YIM 11335T and 12A09T were 70.7 % and 74.4 %, respectively. DNA–DNA hybridization relatedness values of these two isolates with the type strains Nocardiopsis arabia DSM 45083T and Streptomonospora halophila YIM 91355T supported the hypothesis they are representatives of two different species. Based on phylogenetic analysis, phenotypic and genotypic data, it is concluded that the two isolates belong to the genus Streptomonospora of the family Nocardiopsaceae and that the type strain of N. arabia should be reclassified as a representative of Streptomonospora arabica comb. nov. The names proposed for the two novel species are Streptomonospora sediminis sp. nov. (type strain YIM M11335T = DSM 45723T = CCTCC AB 2012051T) and Streptomonospora nanhaiensis sp. nov. (type strain 12A09T = KCTC 29145T = CCTCC AB 2013140T), respectively. An emended description of the genus Streptomonospora is also proposed in the light of the new data.