Application of the Antibiotic Disk Diffusion Method to Multivariate Profiling of Soil Bacterial Community: Comparing the Power to Discriminate Different Soils and Dimension of the Discrimination with That of the Biolog Method

The antibiotic disk diffution (ADD) method was compared with the Biolog method in terms of power to discriminate soils and dimension of the discrimination. Soils from a forest and a citrus field in Thailand were profiled with these methods. These methods differentiated the soils in the principal component score plots. Then, Wilk’s lambda statistic was determined to estimate power of these methods to discriminate the soils. The ADD method scored Wilk’s lambda of 0.003 (p = 0.144) and 0.000 (p=0.020), for direct and ratio-transformed calculation, respectively. The Biolog method recorded Wilk’s lambda of 0.001 (p=0.067), 0.003 (p=0.144) and 0.035 (p=0.440), at 0.25, 0.50 and 0.75 average well color developments (AWCDs), respectively. The ADD method showed high discrimination power, or at least comparable to that of the Biolog method. Redundancy analysis (RDA) resulted in ordination diagrams, which revealed a difference in dimension of the soil discrimination among the methods and the AWCDs. The soil environmental factors significantly related to the bacterial profiles at p=0.05 were: available phosphorus (ADD method and Biolog 0.25 AWCD), and pH (Biolog 0.50 and 0.75 AWCD). These results indicated that the profiling methods and the AWCDs revealed the multidimensionality of the discrimination. The possibility of the application of the ADD method to extraction of such pieces of information for effective land management was suggested.