Investigating microbial community structure in soils by physiological, biochemical and molecular fingerprinting methods

Several biochemical and molecular methods are used to investigate the microbial diversity and changes in microbial community structure in rhizospheres and bulk soils resulting from changes in management. We have compared the effects of plants on the microbial community, using several methods, in three different types of soils. Pots containing soil from three contrasting sites were planted with Lolium perenne (rye grass). Physiological (Biolog), biochemical (PLFA) and molecular (DGGE and TRFLP) fingerprinting methods were employed to study the change in soil microbial communities caused by the growth of rye grass. Different methods of DNA extraction and nested PCR on TRFLP profiles were examined to investigate whether they gave different views of community structure. Molecular methods were used for both fungal and bacterial diversity. Principal component analysis of Biolog data suggested a significant effect of the plants on the microbial community structure. We found significant effects of both soil type and plants on microbial communities in PLFA data. Data from TRFLP of soil bacterial communities showed large effects of soil type and smaller but significant effects of plants. Effects of plant growth on soil fungal communities were measured by TRFLP and DGGE. Multiple Procrustes analysis suggested that both methods gave similar results, with only soil types having a significant effect on fungal communities. However, TRFLP was more discriminatory as it generated more ribotype fragments for each sample than the number of bands detected by DGGE. Neither methods of DNA extraction nor the nested PCR had any effect on the evaluation of soil microbial community structure. In conclusion, the different methods of microbial fingerprinting gave qualitatively similar results when samples were processed consistently and compatible statistical methods used. However, the molecular methods were more discriminatory than the physiological and biochemical approaches. We believe results obtained from this experiment will have a major impact on soil microbial ecology in general and rhizosphere–microbial interaction studies in particular, as we showed that the different fingerprinting methods for microbial communities gave qualitatively similar results.