Characterisation of bacteria in soils under barley monoculture and crop rotation

Rhizobacterial populations on barley roots, originating from experimental fields with barley monoculture (MC) and crop rotation (CR), were analyzed for their fatty profiles. In the first part of the study, the profiles of 1188 isolates were statistically analyzed to identify clusters of bacteria with a possible high prevalence in MC or CR soil. One such cluster was found, termed Ps4-C4, with characteristically high contents of C12:1 3OH (9.8%) and an unidentified fatty acid with the equivalent chain length (ECL) of 12.35, which was provisionally named ECL12.35 (4.5%). Bacteria in Ps4-C4 were also rich in C10:0 3OH (8.3%) and C12:0 3OH (8.1%). The cluster consisted of 109 isolates, 86 from MC populations and 23 from CR, none of which could be identified by means of fatty acid analysis. In the second part of the study, fatty acid profiles of 240 microbial populations from the same fields were analyzed. Results showed higher relative contents of C12:1 3OH, ECL12.35, C10:0 3OH and C12:0 3OH in MC populations, which also had a high proportion of C12:0 2OH and C16:0. A detailed statistical analysis of the correlations between the fatty acids indicated that Ps4-C4 alone explained the higher portions of C12:1 3OH and ECL12.35 in populations from MC soil, while other bacterial groups are seem to have contributed to the elevated contents of C10:0 3OH and C12:0 3OH. Some common functional characteristics of bacteria in the Ps4-C4 cluster are also described. (C) 2000 Elsevier Science Ltd. All rights reserved.