SGER: Molecular Identification of Functionally Significant Nitrogen Fixing Bacteria

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

0084526 Lovell All ecosystems are dependent on nutrient supply and regeneration by microbial communities. These communities are thought to be very sensitive to variations in environmental conditions, changing species diversity and/or activity levels in response to environmental changes. Important environmental functions may be maintained since microbial communities contain a sufficient diversity of species in each major functional group (i.e. functional redundancy) to negate species losses. However, dramatic decreases in function that are correlated with changes in community structure have been observed in some studies. The plasticity of natural microbial communities, particularly in physically structured environments such as vegetated soils and sediments, and the connections between microbial diversity and ecological function are clearly not well understood. A major hurdle impeding progress in this area has been our inability to determine which species within a given functional group (such as the nitrogen fixing bacteria) are actually performing the vital function in question. In this SGER project the investigators will extract messenger RNA encoding the nifH gene product, the nitrogenase iron protein, directly from Spartina root and rhizosphere samples, convert the mRNA sequences to double stranded DNA, and determine the nucleotide sequences of these copy DNA molecules. These sequences will be compared to those recovered directly from existing DNA extracts of nitrogen fixers in a Spartina marsh, to identify which of the many species are actively fixing nitrogen. The responses of the functionally dominant species to experimental manipulations and to seasonal changes in environmental conditions will be determined, to directly assess the importance of functional redundancy to maintenance of the ecologically important process of nitrogen fixation. This study will be among the first to link the environmental function of a key microbial functional group directly to the species responsible for this function. The approach taken here will be broadly applicable to understanding the significance of microbial diversity in a functional context and will provide one of the first direct examinations of the significance of functional redundancy for a natural bacterial assemblage in a complex, natural environment.