There is a great need to understand the global carbon cycle; with specific interest in the cycling of soil carbon. This need is two-fold and interconnected. The global climate change is in-part due to the loss of soil organic carbon and the reduced ability of soils to sequester carbon. Also, to maintain sustainable, high yielding agriculture, carbon loss from soil must be mitigated and in turn this can restore the ability of soils to sequester carbon. A specific group of bacteria, the Cytophaga-Flavobacterium (CF), are of interest in these contexts because evidence suggests that they have the potential to exacerbate the loss of organic carbon from soil. The CF are globally distributed, often detected as organisms responsible for degradation or organic compounds. Other research has demonstrated their active presence in soil, especially the zone around plant roots. Most importantly, these bacteria produce a large assortment of hydrolytic enzymes that can degrade complex carbohydrates. The first studies in this dissertation were intended to investigate the phylogenic diversity and distribution of CF in soil. CF specific clone libraries were generated to investigate a possible link between the CF and soils under different land management and use history, and thus different carbon contents. Also in this dissertation, we tested the hypothesis that Flavobacterium soil isolates would weaken, or degrade, remolded aggregates generated with xylan, a complex carbohydrate, in an effort to describe how Flavobacterium can be responsible for the loss of organic carbon from soil. While the initial studies were exploratory in design, some specific comparisons were made. The CF community from the agricultural soil was determined to be a subset of the communities found in the non-agricultural soils. When the CF communities from deciduous forest soil and fertilized deciduous forest soil were compared, no differences in phylogenetic diversity or distribution were identified. A significant difference in the phylogenetic distribution was detected when the CF community from conventionally tilled agricultural soils was compared to the community from a no-till agricultural management. The diversity of the community from the tilled soil was greater than the community from the no-till soil. Remolded aggregates composed with xylan were challenged with nine Flavobacterium spp. isolated from soil to test the hypothesis that they would degrade the xylan causing a reduction in the erosive strength of the remolded aggregates. In natural soils, increased breakage can lead to a loss of carbon from the soil. The erosive strength is a measure of how readily aggregates will break apart. These values are determined by eroding the aggregates in precision-machined soil aggregate erosion chambers and recording the length of time and amount of force required to remove layers of the aggregate. Using two measures of erosive strength, the highest recorded value, or peak erosive strength, and the total erosive strength for all layers of the aggregate, the aggregates treated with Flavobacterium spp. were compared to uninoculated controls. It was determined that six of the nine species significantly reduced the peak erosive strength and four species also reduced the total erosive strength. These data support the hypothesis that Flavobacterium spp. contribute to a loss of organic carbon from soil. These works can now be extended, using the same techniques, by investigating the role of Flavobacterium as part of the whole bacterial community, as well as investigating the influence of temperature on their degradation activity.
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