SCREENING MARINE FUNGI FOR PLASMIDS AND CHARACTERIZATION OF A LINEAR MITOCHONDRIAL PLASMID IN A LULWORTHIA SP

Twenty-one marine filamentous fungi, including 18 isolates capable of growth on hexadecane, were screened for plasmids. Twenty of the isolat es screened did not have plasmids, indicating that neither the ability to grow on hydrocarbons nor the lack of this ability can be correlate d with the presence of plasmids. One organism, Lulworthia sp. 046, tha t grows on hydrocarbons, contained a plasmid approximately 14kb in siz e. The plasmid, designated pQB, is linear, as shown by the results of both UV-nicking experiments and digestion with exonuclease III and lam bda exonuclease. The plasmid was present in DNA extracted from mitocho ndria, and it banded with mitochondrial DNA when nuclear and mitochond rial DNA were separated on a cesium chloride gradient. These results s uggest that the plasmid is mitochondrial in origin. Southern analysis showed that the plasmid is not homologous with nuclear or mitochondria l genomic DNA, and therefore replicates autonomously.