Marco Krämer

Caboxamycin, a new antibiotic of the benzoxazole family produced by the deep-sea strain Streptomyces sp. NTK 937*

Caboxamycin, a new benzoxazole antibiotic, was detected by HPLC-diode array screening in extracts of the marine strain Streptomyces sp. NTK 937, which was isolated from deep-sea sediment collected in the Canary Basin. The structure of caboxamycin was determined by mass spectrometry, NMR experiments and X-ray analysis. It showed inhibitory activity against Gram-positive bacteria, selected human tumor cell lines and the enzyme phosphodiesterase.

Albidopyrone, a new α-pyrone-containing metabolite from marine-derived Streptomyces sp. NTK 227

Albidopyrone, a new α-pyrone-containing secondary metabolite, was produced by Streptomyces sp. NTK 227, a strain isolated from Atlantic Ocean sediment and found to be a member of the Streptomyces albidoflavus 16S rRNA gene clade. The structure of the compound was determined by MS and NMR spectroscopy, and found to have a moderate inhibitory activity against protein-tyrosin phosphatase B.

Sulfate assimilation in Rhodopseudomonas sulfidophila

The mechanism of sulfate assimilation was investigated in Rhodopseudomonas sulfidophila, a bacterium able to grow either photoautotrophically, with sulfide as electron donor, or photoheterotrophically with sulfate as sole sulfur source. ATP sulfurylase, adenosine-5′-phosphosulfate kinase, 3′-phosphoadenosine-5′-phosphosulfate sulfotransferase, thiosulfonate reductase and cysteine synthase were present. Reduced sulfur compounds, especially sulfide and sulfite repressed all steps of sulfate activation and reduction including sulfate uptake. Adenosine-5′-phosphosulfate kinase activity in contrast to the other activities was high in the presence of cysteine or reduced glutathione in the growth medium. Sulfur was incorporated into the cellular sulfolipid from sulfate and also from reduced sulfur compounds like cysteine and thiosulfate. The activity of 3′-phosphoadenosine-5′-phosphosulfate sulfotransferase was rapidly lost during gel filtration or dialysis. From comparison with other sulfotransferases and from the specific cofactor requirement for the enzyme of R. sulfidophila it is concluded that two different low molecular weight cofactors are required in this system. A reaction sequence is proposed involving thioredoxin as the reductant of another dialysable low molecular weight cofactor, that binds to the protein.