The detection of picoplankton 16S rDNA in cases of drowning

Picoplankton belonging to the Synechococcus genus in cyanobacteria (approximately 1 micron in size) are found ubiquitously in Lake Biwa, Japan. However, they could not be morphologically discriminated from other bacteria by microscopy. In this study we attempted to use picoplankton for the diagnosis of drowning by PCR analysis of the 16S ribosomal DNA (rDNA). We designed primers complementary to the variable regions of 16S rDNA of the picoplankton we had sequenced. A comparison was made of the PCR products from the three picoplanktons, five other cyanobacteria, Melosira (diatom), Staurdstrum (green alga), bacteria from Lake Baikal, and humans. The picogram order of template DNA from picoplankton was specifically amplified by the primers. When the template of picoplankton was mixed with human lung tissue, at least 10 ng of template DNA was needed to obtain a PCR product. The isolation of the picoplankton from human lung tissue increased the sensitivity of PCR more than a hundred-fold. The specific PCR products of the picoplankton were obtained from formalin-fixed drowning tissue. Molecular biological diagnosis of drowning was successful using picoplankton 16S rDNA.