Spore-DNA localization and extraction efficiencies of Bacillus subtilis for accurate results in quantitative real-time polymerase chain reaction.

Mechanical bead disruption is an efficient DNA extraction method from spore cells for subsequent quantification of the spore population by quantitative polymerase chain reaction（qPCR）. In this study, to validate spore DNA localization and extraction efficiencies, the fractionated DNA included the total DNA（tDNA）extracted from spore cells and intracellular（iDNA）and extracellular DNA（eDNA）extracted from fractionated spores through chemical decoating and alkaline lysis buffers, each followed by bead disruption. Furthermore, alkaline lysis buffer-treated spore cells were intensively washed three and five times after each centrifugation to determine how the amount of DNA is affected by repeated centrifugation. This process was achieved through fractionated spore pellet and suspension treatments with propidium monoazide xx（PMAxx）before mechanical bead disruption. Three fractionated and extracted DNAs were assessed with qPCR. The amount of eDNA was higher than that of iDNA, and closer to tDNA levels in the qPCR assay. These results indicted the following: 1）amount of eDNA was more than iDNA and responsible for majority of amount of tDNA through the combination method involving alkaline lysis buffer and bead disruption, 2）lysis buffer partially eliminated the eDNA fragments through multiple washing steps, but it was not largely independent of the number of times centrifugation was performed.