BROAD-SCALE ANALYSIS OF SOIL MICROBIAL COMMUNITY DNA FROM UPLAND GRASSLANDS

We have applied a broad-scale approach to the analysis of DNA extracte d from soils which support characteristic grasslands at an upland site in the UK. To test for the degree of coherence between microbial and vascular communities, grasslands were characterised as 'improved', 'se mi-improved', or 'unimproved', according to the degree of management t hey had received and consequent botanical composition. Microbial DNA w as extracted directly from the grassland soils and analysed by three t echniques: (i) thermal denaturation, which profiles the guanine and cy tosine (G+C) base distribution within the community; (ii) cross hybrid isation of the DNA which measures the degree of similarity between the samples. (iii) measurement of reassociation kinetics of denatured DNA , which provides a measure of the complexity of the DNA. Thermal denat uration revealed significant differences in the %G+C composition of th e communities. DNA from the improved soil had the highest median %G+C value, whilst that from the unimproved soil had the lowest. The relati ve distribution of G+C bases also differed significantly between the s amples from the three grasslands. Cross hybridisation of DNA from the different soils also indicated significant differences in the degree o f similarity between the DNA from the grasslands, with unimproved show ing 59% similarity to improved. Indices from the cross hybridisation a ssay suggested that, in terms of complexity, the samples ranked unimpr oved > semi-improved > improved. Reassociation kinetics supported this conclusion, but the rates of reassociation were such that less than 4 0% reassociation occurred over a 31-day period, thus preventing calcul ation of C(o)t(1/2).