The composition of bacterial populations in soil fractions differing in their degree of adherence to barley roots

Soil fractions differing in their degree of adherence to barley roots were sampled, and their microbial populations were cultivated on a nutrient-poor bacterial medium at low temperature. The biomass of each population was harvested and analysed to determine its FAME pattern. The greater the degree of adherence of the soil sample to roots, the higher were the relative proportions of the fatty acids 15 : 0, 15 : 0 Iso, 15 : 0 Iso 3OH, 15 : 1 Iso, 17 : 0 Iso 3OH and 17 : I Iso. This trend was both pronounced and consistent. The opposite relationship was found between relative proportions of the fatty acids 10:0 3OH, 12.0, 12 :0 2OH, 12 : 0 3OH, 16 : 0 and 18 : 1 and degree of root adherend. Differences in the FAME patterns can best be interpreted as differences in the relative proportions of the various types of groups constituting the bacterial populations. Specifically, as the degree of soil adherence to roots increased, there was a shift in favour of bacteria belonging to the Cytophaga-Flavobacterium group and a corresponding decrease in bacteria with FAME patterns similar to that of Pseudomonas. The distribution of the fatty acid 15 : 0 Anteiso indicated that the relative frequencies of certain Gram-positive bacterial strains with a high content of this acid were diminished in habitats close to roots. (C) 1999 Elsevier Science B.V. All rights reserved.