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J. Bacteriol., 11 1997, 6929-6936, Vol 179, No. 22
MA Fernandez-Moreno, C Vallin and F Malpartida
In a search for strains producing biocides with a wide spectrum of
activity, a new strain was isolated. This strain was taxonomically
characterized as Streptomyces rochei F20, and the chemical structure of the
bioactive product extracted from its fermentation broth was determined to
be a mixture of streptothricins. From a genomic library of the producer
strain prepared in the heterologous host Streptomyces lividans, a 7.2-kb
DNA fragment which conferred resistance to the antibiotic was isolated. DNA
sequencing of 5.2 kb from the cloned fragment revealed five open reading
frames (ORFs) such that ORF1, -2, - 3, and -4 were transcribed in the same
direction while ORF5 was convergently arranged. The deduced product of ORF1
strongly resembled those of genes involved in peptide formation by a
nonribosomal mechanism; the ORF2 product strongly resembled that of mphA
and mphB isolated from Escherichia coli, which determines resistance to
several macrolides by a macrolide 2'-phosphotransferase activity; the ORF3
product had similarities with several hydrolases; and the ORF5 product
strongly resembled streptothricin acetyltransferases from different
gram-positive and gram-negative bacteria. ORF5 was shown to be responsible
for acetyl coenzyme A-dependent streptothricin acetylation. No similarities
in the databases for the ORF4 product were found. Unlike other peptide
synthases, that for streptothricin biosynthesis was arranged as a
multienzymatic system rather than a multifunctional protein. Insertional
inactivation of ORF1 and ORF2 (and to a lesser degree, of ORF3) abolishes
antibiotic biosynthesis, suggesting their involvement in the streptothricin
biosynthetic pathway.
Copyright © 1997, American Society for Microbiology
Streptothricin biosynthesis is catalyzed by enzymes related to nonribosomal peptide bond formation
Centro Nacional de Biotecnologia, CSIC, Campus Universidad Autonoma de Madrid, Canto Blanco, Madrid, Spain.
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