Killing two birds with one stone: simultaneous extraction of DNA and RNA from activated sludge biomass

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Abstract
DNA and RNA are usually extracted from activated sludge samples using two separate methods developed for soil and sediment samples. However, activated sludge differs from soil and sediment in at least three aspects: high biomass density, low humic acid content, and the presence of bacterial aggregate flocs. Taking these characteristics into consideration, we developed a simple and rapid method allowing simultaneous DNA and RNA extraction from activated sludge samples. This method combines (i) mini-bead beating, which is most efficient in breaking bacterial aggregate flocs and cells, (ii) protection of RNA with diethyl pyrocarbonate, and (iii) precipitation of impurities with ammonium acetate. Phenol/chloroform extraction and column purification are not necessary. The resulting DNA and RNA are suitable for PCR and reverse transcriptase - PCR, respectively. The efficiencies of cell lysis and nucleic acid recovery were high enough to permit detection by PCR of 102 cells/mL of mixed liquor. By simultaneously extracting both DNA and RNA from a single sample, this method eliminates variability in cell lysis between extraction of DNA and RNA using two different methods. This extraction method is rapid, and within 1 h, one person can process four or more samples. This simple method makes it easier to analyze a large number of activated sludge samples.Key words: activated sludge, DNA, extraction, PCR, RNA.

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