Antibiotic R2, a new angucyclinone compound from Streptosporangium sp. Sg3

Antibiotic R2, a new angucyclinone compound from Streptosporangium sp. Sg

Saccharothrix sp. PAL54, a new chloramphenicol-producing strain isolated from a Saharan soil

An actinomycete strain designated PAL54, producing an antibacterial substance, was isolated from a Saharan soil in Ghardaïa, Algeria. Morphological and chemical studies indicated that this strain belonged to the genus Saccharothrix. Analysis of the 16S rDNA sequence showed a similarity level ranging between 96.9 and 99.2% within Saccharothrix species, with S. longispora DSM 43749T, the most closely related. DNA–DNA hybridization confirmed that strain PAL54 belonged to Saccharothrix longispora. It showed very strong activity against pathogenic Gram-positive and Gram-negative bacteria responsible for nosocomial infections and resistant to multiple antibiotics. Strain PAL54 secreted the antibiotic optimally during mid-stationary and decline phases of growth. One antibacterial compound was isolated from the culture broth and purified by HPLC. The active compound was elucidated by uv-visible and NMR spectroscopy and by mass spectrometry. The results showed that this compound was a D(-)-threo chloramphenicol. This is the first report of chloramphenicol production by a Saccharothrix species

The Interaction of Solar Radiation with Earth’s Atmosphere: Modeling the Total Atmospheric Transmittance by a Regression Function

Springer Proceedings in EnergyInternational audienceIn this investigation, a numerical simulation has been performed based on the SMARTS2 model to study the influence of the zenith angle on the variation of the total atmospheric transmittances. This calculation has been made for ultraviolet and visible light in the range of [0.2, 0.39 µm] and [0.4, 0.75 µm], respectively by taking into account the absorption and the scattering of radiation by the atmospheric gas molecules as well as aerosols. In order to determine the direct dependence of the total atmospheric transmittance on the light wavelength, a regression approach has been used for four values of zenith angles [0°, 25°, 35°, 57°]. The result shows that total atmospheric transmittance can be modeled by a polynomial function of sixth order which describes fairly the atmospheric transmittance as a function of wave length and zenith angle. More importantly, the comparison between our present results and Modtran’s results shows a good agreement with relative reduction ratio of transmission equals approximately to 1

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

International audienceAn 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