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United States Department of Agriculture

Agricultural Research Service

Title: Temporal Changes in the Bacterial Communities of Soil, Rhizosphere, and Endoriza Associated with Field Grown Cucumber (Cucumis Sativus L.)

Authors
item Mahaffee, Walter
item Kloepper, J - AUBURN UNIVERSITY

Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 1996
Publication Date: N/A

Interpretive Summary: The manuscript presents information of the mathematical characterization of bacterial communities of three habitats associated with plant tissues (Soil, rhizosphere [root surface and adhering soil], endorhiza [internal tissues of plant roots]. This work established methodology for the objective assessment of shifts in bacterial communities. Field trails of cucumber plants were sampled during 1994 and 1995 growing seasons. More than 6,000 individual bacterial colonies of aerobic heterotroph bacteria were sampled randomly and identified to genus using the Sherlock System (Microbial ID, Inc.) for fatty acid methyl ester analysis. Diversity was assessed using Hill's modifications of Shannon?s index and Simpson?s index (N2 and N1, respectively), while similarity was determined using the coefficient of biotic similarity. Analysis of community structure indicated that the soil was a distinct habitat and remained relatively unchanged throughout the study. Both the rhizosphere and endorhiza were dissimilar from the soil and from each other at particular sampling times. These results indicate that the soil, rhizosphere, and endorhiza communities are structurally distinct, in that the relative abundance of a particular bacterial genera differs among habitats, but share a common membership, where isolates of each bacterial genera are generally isolated from all three habits. Thus when examining bacterial communities both the qualitative (i.e. membership) and quantitative (i.e. abundance) aspects must be examined in order to examine shifts in community structure.

Technical Abstract: The culturable aerobic-heterotroph bacterial communities of three habitats (rhizosphere, endorhiza and soil) associated with field-grown cucumber roots were examined for quantitative and qualitative changes in structure over time. More than 6,000 individual bacterial colonies were sampled randomly and identified to genus using the Sherlock System for fatty acid methyl ester analysis. Diversity was assessed using Hill's modifications of Shannon?s index and Simpson?s index (N2 and N1, respectively), while similarity was determined using the coefficient of biotic similarity. The same general trends were observed for the community structures of each habitat in both years. The soil was the least diverse, and the rhizosphere was most diverse through-out both growing seasons. The endorhiza was less diverse than the rhizosphere because one or two genera tended to be dominant in each sample. Analysis of community similarity indicated that the soil was a distinct habitat and remained relatively unchanged throughout the study. Both the rhizosphere and endorhiza were dissimilar from the soil and from each other at particular sampling times. These results indicate that the soil, rhizosphere, and endorhiza communities are structurally distinct, in that the relative abundance of a particular bacterial genera differs among habitats, but share a common membership, where isolates of each bacterial genera are generally isolated from all three habits. Thus when examining bacterial communities both the qualitative and quantitative

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