Microbial conversion of lonophorous antibiotic nigericin by the ciliate Tetrahymena pyriformis.

The ionophorous antibiotic nigericin is toxic towards the ciliate Tetrahymena pyriformis GL. At the high concentration of 30 mg/l (sublethal dose), it is bioconverted into several products. The yield of one of these (N1) is appreciably improved with pretreated cells, higher concentrations of nigericin (50 or 100 mg/1), and the presence of a larger ciliate biomass. A structural study of N1 by FAB mass spectrometry combined with tandem mass spectrometry and nuclear magnetic resonance shows it to be an epimer, epinigericin, about half as toxic as nigericin. Bioconversion of nigericin by T. pyriformis may be regarded as a detoxication process.

Microbial conversion of grisorixin, a monovalent cation ionophorous antibiotic.

The isolation and identification of a bioconversion product of grisorixin from a strain of Streptomyces rimosus is reported. The structure of this product was elucidated from physicochemical data, in particular 13C NMR spectra. Its ionophorous and antibiotic properties are markedly different from those of grisorixin.

Biosynthetic study on the polyether carboxylic antibiotic, nigericin production and biohydroxylation of grisorixin by nigericin-producing Streptomyces hygroscopicus NRRL B-1865.

With addition of methyl oleate, the increased yield of antibiotic production by nigericin-producing Streptomyces hygroscopicus NRRL B-1865 also resulted in the isolation of three additional polyether antibiotics. Two of these are abierixin and epinigericin, as new antibiotics. The third antibiotic is grisorixin. The production of both abierixin (opened ring A and 30-CH2OH) and grisorixin (ring A and 30-CH3) poses the problem of the identity of the last pathway precursor of the major metabolite, nigericin (ring A and 30-CH2OH). Transformation experiments of abierixin by S. hygroscopicus gave negative results. Hydroxylation of grisorixin to nigericin by S. hygroscopicus represents the final step in nigericin biosynthesis.

Degradation products of a phenylurea herbicide, diuron: synthesis, ecotoxicity, and biotransformation.

The degradation products of diuron (photoproducts and metabolites), already described in the literature, were synthesized in order to carry out further investigations. Their ecotoxicity was determined using the standardized Microtox test, and most of the derivatives presented a nontarget toxicity higher than that of diuron. Therefore, the biotransformation of these compounds was tested with four fungal strains and a bacterial strain, which were known to be efficient for diuron transformation. With the exception of the 3,4-dichlorophenylurea, all the degradation products underwent other transformations with most of the strains tested, but no mineralization was observed. For many of them, the biodegradation compound for which the toxicity was important was 3,4-dichlorophenylurea. This study underlines the importance of knowing the nature of the degradation products, which has to be kept in mind while analyzing natural water samples or soil samples.

Production of S-Methylthioacetate by Brevibacterium linens.

Volatile sulfur compounds production by eight strains of Brevibacterium linens isolated from cheeses was demonstrated: methanethiol, dimethyldisulfide, and 2,3,4-trithiapentane. Four of these strains also produced S-methylthioacetate, an important aroma component of smear-coated cheeses. It is the first demonstrated microbiological production of a thioester.