Microalgae community structure analysis based on 18S rDNA amplification from DNA extracted directly from soil as a potential soil bioindicator

Soil algae are photosynthetically active microorganisms showing changeable community structure, depending on the soil type, the agricultural practices and the application of pesticides. To characterise algal community structure, molecular approaches complementary to classical microbiological approaches based on the isolation and the culture of soil algae are required. Our study describes a polymerase chain reaction (PCR) approach targeting algal 18S rDNA sequences of desoxyribonucleic acid (DNA) samples extracted either from unialgal eukaryotic microalgae culture, complex assemblages of microalgae populations or natural soil communities. Our first results showed that microalgae rDNA can be amplified by PCR from soil DNA samples. They also indicated difficulties extracting DNA from diatoms directly from soils, probably because of the presence of robust silicate valves. An 18S rDNA library has been established and preliminary phylogenetic analysis showed the feasibility of applying molecular methods to studying edaphic algae community structure. This is promising for soil algae ecology and for developing soil biological indicators.