Improvement in the RFLP procedure for studying the diversity of nifH genesin communities of nitrogen fixers in soil

Several specific primers for the nifH gene were tested with different pure telluric Nz-fixing strains. A PolF/PolR primer set provided successful ampl ification of 19 representative N-2-fixing strains. Three restriction enzyme s, HaeIII, NdeII and MnlI, chosen for restriction fragment length polymorph ism (RFLP) analyses, were the most discriminating for the study of nifH gen e diversity as they resulted in differences between strains at the species level. Amplification by selected primers and RFLP were applied to assess th e genetic diversity of the nifH gene pool in soil. Pair soils, one under cu ltivation, the second under permanent pasture, were found to harbor a contr asting diversity of nifH genes. Pure strain profiles could not be recognize d in the nifH soil patterns. Using the simple procedure described, it was s hown that the structure of nitrogen fixers in soil was influenced by soil f unctioning. (C) 2001 Editions scientifiques et medicales Elsevier SAS.