Variation in the ability of Pseudomonas sp. strain B13 cultures to utilize meta-chlorobenzoate is associated with tandem amplification and deamplification of DNA.

Single-colony isolates of Pseudomonas sp. strain B13 were examined for their ability to utilize benzoate (Ben) and meta-chlorobenzoate (3CB) as the sole carbon source. Scoring of B13 cultures by the replica-plating technique revealed that under nonselective conditions, B13 spontaneously formed four different types of colonies: 3CB+ Ben+, 3CB+ Ben-, 3CB- Ben-, 3CB- Ben+. Successive testing of each of the four colony types showed that each produced the same four different types of single-colony isolates. Colonies of each class had characteristic phenotypic properties with respect to the accumulation of Ben or 3CB pathway intermediate products. The physical abundance of a 4.3-kilobase DNA encoding the first three enzymes of the chlorocatechol pathway correlated with the 3CB+ phenotype. Increased abundance of the 4.3-kilobase DNA fragment was the result of tandem amplification.