The Dynamic Cultivation System: A new method for the detection of temporal shifts in microbial community structure in clay

Abstract A major problem in the analysis of natural bacterial populations is that probably less than 1% of species were so far cultured and described. In order to overcome this disadvantage, culture independent DNA based methods, such as comparison of PCR-amplified 16S rRNA genes, are used for the description of the bacterial diversity and the identification of various species. Unfortunately, each molecule of DNA, including those of dead organisms and allochthonous genomes, can be detected by PCR-based molecular fingerprint techniques within a sample besides the DNA of native organisms. Hence, an adequate image of the actually active population composition cannot be projected with these methods. An additional challenge is the extraction of DNA from charged particles and the presence of inhibitors for downstream molecular analyses. This study reports the results of a new cultivation approach that allows to overcome these problems and to obtain almost total environmental DNA of microorganisms for subsequent genetic DNA fingerprint techniques. This new approach, the Dynamic Cultivation System (DCS) is characterized by special nutrient availability to simulate the bacterial natural habitat and the cell–cell interaction for various processes, such as collective degradation of compounds. The DCS was applied in combination with the genetic fingerprint technique Denaturing Gradient Gel Electrophoresis (DGGE) to study changes in the population composition during an alteration process of clay. The results indicate a changing bacterial diversity over time which seems to correlate to the changing pH in the clay samples in situ. This effect was most evident after cultivation on the DCS.