Oligomycins A and E, major bioactive secondary metabolites produced by Streptomyces sp. strain HG29 isolated from a Saharan soil.

An actinobacterial strain, HG29, with potent activity against pathogenic, toxigenic and phytopathogenic fungi was isolated from a Saharan soil sample of Algeria. On the basis of morphological and chemotaxonomic characteristics, the strain was classified in the genus Streptomyces. Analysis of the 16S rRNA gene sequence showed a similarity level of 99.3% with Streptomyces gancidicus NBRC 15412T. The comparison of its cultural and physiological characteristics with this species revealed significant differences. Moreover, the phylogenetic tree showed that strain HG29 forms a distinct phyletic line within the genus Streptomyces. Production of antifungal activity was investigated by following kinetics in shake broth. The highest antifungal activity was obtained after five days of fermentation, and in the dichloromethane extract. Two active compounds, NK1 and NK2, were purified by HPLC using a C18 column. Their chemical structures were identified through nuclear magnetic resonance experiments and mass spectrometry as oligomycins E and A, respectively, which have not been reported to be produced by S. gancidicus. The two bioactive compounds exhibited significant antifungal activity in vitro, showing minimal inhibitory concentrations (MICs) values between 2 and 75µg/mL.

Isolation and partial characterization of pigment-like antibiotics produced by a new strain of Streptosporangium isolated from an Algerian soil.

AIMS: Identification of a new actinomycete strain Sg3, belonging to the genus Streptosporangium and partial characterization of the produced antibacterial activities. METHODS AND RESULTS: The strain Sg3 was isolated from an Algerian Saharan soil and identified by morphological, chemotaxonomic and phylogenetic analyses to the genus Streptosporangium. The comparison of its physiological characteristics with those of known species of Streptosporangium showed significant differences with the nearest species Streptosporangium carneum. Analysis of the 16S rDNA sequence of strain Sg3 showed a similarity level ranging between 97% and 98.8% within Streptosporangium species, with S. carneum the most closely related. Strain Sg3 showed a red coloured antibacterial activity against gram-positive bacteria on several culture media. The purification of the red pigment by chromatographic methods led to the isolation of three active products. The (1)H nuclear magnetic resonance (NMR), mass, infrared (IR) and ultraviolet-visible (UV-VIS) data of these molecules strongly suggested that they belonged to the quinone-anthracycline group with three or more rings. CONCLUSIONS: Strain Sg3 represents a distinct phyletic line suggesting a new genomic species. It produces antibacterial activities identified as quinone-anthracycline aromatics. SIGNIFICANCE AND IMPACT OF THE STUDY: The quinone-anthracycline antibiotics are known for their antimicrobial and antineoplastic activities and are used in chemotherapy for the treatment of many cancer diseases. The present work constitutes the first stage of a whole series of studies to be realized on these antibiotics before arriving at a possible application.

Saccharothrix algeriensis sp. nov., isolated from Saharan soil.

The taxonomic position of a soil isolate, strain SA 233T, recovered from Saharan soil from Algeria was established using a polyphasic approach. This isolate has been previously reported to produce three novel dithiolopyrrolone antibiotics, and preliminary chemotaxonomic and morphological characteristics suggested that it was representative of a member of the genus Saccharothrix. Phylogenetic analysis of the strain from 16S rDNA sequences, along with a detailed analysis of morphological, chemotaxonomic and physiological characteristics, indicates that it belongs to the genus Saccharothrix and represents a novel species that is readily distinguished from all recognized Saccharothrix species. The name Saccharothrix algeriensis sp. nov. is proposed for the isolate, with type strain SA 233T (=NRRL B-24137T=DSM 44581T).