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Distribution of Tn551 insertion sites responsible for auxotrophy on the Staphylococcus aureus chromosome.

By P A Pattee


A method was devised to efficiently select isolates of Staphylococcus aureus 8325 in which Tn551, a transposon originating on the pI258 plasmid responsible for erythromycin resistance (Emr), had translocated to the host chromosome. This method consisted of selecting for Emr at 43 degrees C with a strain in which the pI258 plasmid was unable to replicate at 43 degrees C because of a temperature-sensitive plasmid mutation. By selecting isolates that were Emr at 43 degrees C and auxotrophic for nutrients not required by the parent strain. Tn551-induced auxotrophic mutants were readily isolated. The incidence of auxotrophic classes was not random; 80% of the isolates in one experiment were Trp-, whereas only a single example of each of some of the other classes was isolated. Among the Trp- mutants, the distribution of trp genes affected and the frequency of precise excision of Tn551 from individual sites varied. When analyzed by transformation, the Tn551-induced ala, his, ilv, lys, rib, thrA, thrB, and trp mutations were shown to occupy sites previously defined by nitrosoguanidine-induced mutations. Tn551-induced mutagenesis provided three previously unrecognized classes of auxotrophs (tyr, met, and thrC), and the Tn551 integration sites resulting in these mutations have been identified. In addition, a chromosomal region (uraB) was identified by Tn551 mutagenesis that is distinct from uraA (previously defined by chemical mutagenesis). Some Tn551-induced mutations (most notably pur) could not be linked to the known linkage groups of the chromosome by transformation. With the exception of two pur mutations, all of the Tn551-induced auxotrophic mutational sites cotransformed at unity with Tn551 and, in cases in which they were selected, prototrophic transformants were always Ems. Thus, the Tn551 and auxotrophic sites are identical

Topics: Research Article
Year: 1981
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Provided by: PubMed Central
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