Isolation of DNA from saltern soils collected in Taiwan and whole-genome amplification of minute amounts of DNA for construction of metagenomic libraries

Environmental DNAs from 21 samples of saltern soil in Taiwan were isolated by using the SDS-lysis method, resulting in yields ranging from 0.03 ng to 8.06 µg per gram of soil. However, sample 143 collected from saltern soil near a crystallizer had a low yield of 1.2 ng per gram of soil. Comparative analyses of the sequence data of representative clones with other 16S rRNA samples indicated that not all clones for sample 143 were closely related to the soil bacteria. A minute amount of DNA (0.15 ng) was amplified 100,000-times to 15 µg by multiple displacement amplification (MDA). The MDA method was validated by analysis of amplified bacteriorhodopsin (bR) genes. Two clone libraries were constructed from DNA samples before and after amplification and were compared. The result suggests that bR diversity was relatively conserved during whole-genome amplification (WGA). The constructed metagenome fosmid library consists of 1.7 × 10 6 clones with an average insert size of 26.1 kb. Taken together, WGA of metagenomic DNA from very minute microbial sources allows for construction of metagenomic libraries that are previously inaccessible.