Fluidity of Plasmid DNA Fragments Involved in Biodegradation of Aromatic Hydrocarbons by pseudomonas putida Strain R5-3

Abstract

Pseudomonas putida strain R5-3 isolated from sewage sludge contained two plasmids 100 and 80 kb in size after growth on media containing 4-methylbenzoate (4-MB) as sole carbon source. When transferred to toluene (Tol) or 3-xylene (3-Xyl) as the sole carbon source, the plasmid profile changed with loss of the 80-kb plasmid and the appearance of two plasmids 50 and 60 kb in size. When R5-3 was transferred back to 4-MB from either Tol or 3-Xyl, the original 100- and 80-kb plasmids were present and the 50- and 60-kb plasmids were lost. Restriction enzyme analysis of total plasmid DNA indicated rearrangements and loss of DNA restriction fragments in the strains maintained on Tol and 3-Xyl when compared to the original R5-3 maintained on 4-MB. In the isolate which “retrieved” the original plasmid profile, the restriction enzyme fragment pattern was identical to the original R5-3, in that the fragments which were missing after prolonged growth on Tol or 3-Xyl were again present. The possibility that selected fragments are sequestered in the chromosome is presently under investigation.