Circular mitochondrial DNA from the avian malarial parasite Plasmodium lophurae.

The avian malarial parasite, Plasmodium lophurae, was liberated from duck erythrocytes with antiduck erythrocyte serum and freed from host cell nuclei by differential centrifugation followed by treatment with trypsin and DNAase. Total as well as mitochondrial DNA isolated from such a preparation of free parasites showed overlapping densities of 1.679 g/ml in CsCl density gradients. To retain the structural integrity of mitochondrial DNA, the treatment of liberated parasites with trypsin and DNAase was eliminated and all steps of isolation of the mitochondrial fraction was performed at ice bath temperature. Under these conditions, mtDNA liberated by osmotic lysis appeared as super coiled molecules. After isolation of DNA from mitochondrial pellets prepared under the above conditions, only a single DNA band was apparent in ethidium bromide/CsCl gradients and open circular molecules with a mean contour length of 10.3 mum were observed.