Desertomycin A

The non-polyenic macrocyclic antibiotic complex 1012 was isolated from the culture broth of a strain Streptomyces spectabilis 1. The complex was found to belong to the desertomycin complex. Three main compounds of complex 1012 were separated and purified by preparative chromatographic methods. The identification was performed by UV, IR, NMR and mass-spectrometric studies. It was proved that two of the compounds with MW. 1191, C61H109NO21 and MW. 1190, C61H106O22 were identical to desertomycin A and D. The other com-pound with MW.1028, C55H96O17 is new macrolactone, named deser-tomycin E. The structures were established by detailed spectroscopic analysis.

Photosynthetic microorganisms including the green algaChlamydomonas reinhardtiiare essential to terrestrial habitats as they start the carbon cycle by conversion of CO2to energy-rich organic carbohydrates. Terrestrial habitats are densely populated, and hence, microbial interactions mediated by natural products are inevitable. We previously discovered such an interaction betweenStreptomyces iranensisreleasing the marginolactone azalomycin F in the presence ofC. reinhardtiiWhether the alga senses and reacts to azalomycin F remained unknown. Here, we report that sublethal concentrations of azalomycin F trigger the formation of a protective multicellular structure byC. reinhardtii, which we named gloeocapsoid. Gloeocapsoids contain several cells which share multiple cell membranes and cell walls and are surrounded by a spacious matrix consisting of acidic polysaccharides. After azalomycin F removal, gloeocapsoid aggregates readily disassemble, and single cells are released. The presence of marginolactone biosynthesis gene clusters in numerous streptomycetes, their ubiquity in soil, and our observation that other marginolactones such as desertomycin A and monazomycin also trigger the formation of gloeocapsoids suggests a cross-kingdom competition with ecological relevance. Furthermore, gloeocapsoids allow for the survival ofC. reinhardtiiat alkaline pH and otherwise lethal concentrations of azalomycin F. Their structure and polysaccharide matrix may be ancestral to the complex mucilage formed by multicellular members of theChlamydomonadalessuch asEudorinaandVolvoxOur finding suggests that multicellularity may have evolved to endure the presence of harmful competing bacteria. Additionally, it underlines the importance of natural products as microbial cues, which initiate interesting ecological scenarios of attack and counter defense.

The kanchanamycins, a group of novel 36-membered polyol macrolide antibiotics were detected in the culture filtrate and mycelium of Streptomyces olivaceus Tü 4018 by HPLC-diode-array and HPLC-electrospray-mass-spectrometry screening. The compounds show antibacterial and antifungal activities, and are especially effective against Pseudomonas fluorescens. Besides the kanchanamycin complex, strain Tü 4018 produces the 42-membered macrolactones, oasomycin A and desertomycin A, as well as tryptophan-dehydrobutyrine diketopiperazine and daidzein.