Microbial Protein in Soil: Influence of Extraction Method and C Amendment on Extraction and Recovery |
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Authors: | Erin B Taylor Mark A Williams |
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Institution: | (1) Plant and Soil Sciences, Mississippi State University, Starkville, MS, USA; |
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Abstract: | The capacity to study the content and resolve the dynamics of the proteome of diverse microbial communities would help to
revolutionize the way microbiologists study the function and activity of microorganisms in soil. To better understand the
limitations of a proteomic approach to studying soil microbial communities, we characterized extractable soil microbial proteins
using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Two methods were utilized to extract proteins
from microorganisms residing in a Quitman and Benfield soil: (1) direct extraction of bulk protein from soil and (2) separation
of the microorganisms from soil using density gradient centrifugation and subsequent extraction (DGC–EXT) of microbial protein.
In addition, glucose and toluene amendments to soil were used to stimulate the growth of a subset of the microbial community.
A bacterial culture and bovine serum albumin (BSA) were added to the soil to qualitatively assess their recovery following
extraction. Direct extraction and resolution of microbial proteins using SDS-PAGE generally resulted in smeared and unresolved
banding patterns on gels. DGC–EXT of microbial protein from soil followed by separation using SDS-PAGE, however, did resolve
six to 10 bands in the Benfield but not the Quitman soil. DGC–EXT of microbial protein, but not direct extraction following
the addition of glucose and toluene, markedly increased the number of bands (~40) on the gels in both Benfield and Quitman
soils. Low recoveries of added culture and BSA proteins using the direct extraction method suggest that proteins either bind
to soil organic matter and mineral particles or that partial degradation takes place during extraction. Interestingly, DGC
may have been preferentially selected for actively growing cells, as gauged by the 10–100× lower cy19:0/18:1ω7 ratio of the
fatty acid methyl esters in the isolated community compared to that for the whole soil. DGC can be used to isolate soil communities
and provide microbial protein that can be characterized using PAGE. |
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