Methods for assessing the composition and diversity of soil microbial communities

Soil microorganisms play important roles in soil quality and plant producti vity. The development of effective methods for studying the diversity, dist ribution, and behavior of microorganisms in soil habitats is essential for a broader understanding of soil health. Traditionally, the analysis of soil microbial communities has relied on culturing techniques using a variety o f culture media designed to maximize the recovery of diverse microbial popu lations. However, only a small fraction (<0.1%) of the soil microbial commu nity has been accessible with this approach. To overcome these problems, ot her methods such as the analysis of phospholipid fatty acids and community- level physiological profiles have been utilized in an attempt to access a g reater proportion of the soil microbial community. in recent years, molecul ar methods for soil microbial community analysis have provided a new unders tanding of the phylogenetic diversity of microbial communities in soil. Amo ng the most useful of these methods are those in which small subunit rRNA g enes are amplified from soil-extracted nucleic acids. Using these technique s, it is possible to characterize and study soil microbes that currently ca nnot be cultured. Microbial rRNA genes can be detected directly from soil s amples and sequenced. These sequences can then be compared with those from other known microorganisms. Additionally, group- and taxon-specific oligonu cleotide probes can be developed from these sequences making direct visuali zation of microorganisms in soil habitats possible. The use of these techni ques provides new ways of assessing soil microbial diversity and ultimately , a more complete understanding of the potential impacts of environmental p rocesses and human activities on responses of soil microorganisms. Informat ion gained from such studies will have direct impacts on our understanding of the role of microbial processes in soil health. (C) 2000 Published by El sevier Science B.V.