ABSTRACT
This manuscript is a review of the innovative methodologies that enable more precise evaluations of soil microbial diversity. Highlighting the molecular approach, which does not require the isolation of microorganisms and allows the inclusion of non-culturable genotypes in the analyses, the described methodologies revolutionised the environmental microbiology and opened gateways for an accurate understanding of the ecology and diversity of microorganisms. The application of techniques based on soil total DNA extraction, PCR amplification of genes or gene fragments, and sequence analysis revealed that the microbial universe is far more complex than ever imagined. Examples of applications of the molecular approach to study the diversity of soil diazotrophic bacteria are given.