ARS | Publication request: Taxonomic diversity of predominant bacteria associated with microaggregates from two different agroecosystems and their ability to aggregate soil in vitro

Submitted to: Microbial Ecology International Symposium
Publication Type: Abstract Only
Publication Acceptance Date: June 20, 2006
Publication Date: N/A

Technical Abstract: Contrary to soil macroaggregates (>250 µm) which are easily disrupted when wetted quickly, microaggregates (50- to 250 µm) are highly stable. There is little knowledge of functional groups of bacteria from microaggregates that can stabilize soil and their diversity. We isolated the predominant bacteria from microaggregates of a site cropped to barley (40 years with tillage) and to alfalfa (9 years with no tillage) to study their potential function in aggregating soil. Soil suspensions from physically disrupted microaggregates were spiral-plated and bacterial colonies were isolated from the most dilute portion of the spiral then purified. Fatty acid methyl ester (FAME) profiles, substrate utilization patterns (BIOLOG gram - and gram + microplates), and DNA sequence analysis using 16s rRNA amplification region were performed for bacterial identification. Principal component analysis of FAME profiles and BIOLOG patterns was performed to distinguish patterns of bacterial species within each habitat and between the two habitats in relation to aggregating ability. Artificial aggregates were generated by amending soil with species of different genera identified from microaggregates of both soils and tested for their water stability and their strength. This study demonstrated that microaggregates harbor functional groups of bacterial species capable of aggregating soil particles, and there were more efficient soil aggregating species identified in microaggregates of non disturbed soil (alfalfa, 9 years) than in disturbed, yearly tilled soil (barley, 40 years). This study additionally provides a baseline for monitoring the community structure and dynamics of soil aggregating bacteria in various habitats and environmental conditions.