Bacteria as Transporters of Phosphorus through Soil: Quantification by Real Time PCR.

Quantification of the transport of total bacteria through soil is of interest in the transport of nutrients from agricultural soils to groundwater and surface waters via drainage. Our hypothesis is that bacteria accounts for a significant part of the organic phosphorus being transported from agricultural fields to aquatic environments which could lead to potential eutrophication of aquatic environments.

We wish to quantify total bacterial biomass to get a deeper understanding of the role of bacteria in transport of phosphorus. Until now, the available techniques (CFU and DAPI and etc.) are either very unreliable or impossible in soil. Molecular techniques such as real time PCR is a quantitative and precise method for detection of bacteria in soil without relying on cultivation. We have tested a primer set at a universal bacteria specific 16S DNA region to quantify total bacterial biomass by real time PCR on a bacterial library extracted from soil. We found 19 clones to amplify DNA equally with the universal primers. We have furthermore compared real time PCR with a bacterial count (DAPI) on a 10% soil extract using a bacterial extraction gradient (Nycodenz) and found equivalent bacterial numbers with the two methods.

We are further using these primers to quantify total bacterial biomass in leachates from intact soil columns of three soil textures with and without application of manure. We compare the results with measurements of phosphorus in the leachates to elucidate the mechanisms involved in the transport of phosphorus through soil.