Molecular Analysis of the In Situ Growth Rates of Subsurface Geobacter Species |
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| Authors: | Dawn E. Holmes Ludovic Giloteaux Melissa Barlett Milind A. Chavan Jessica A. Smith Kenneth H. Williams Michael Wilkins Philip Long Derek R. Lovley |
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| Affiliation: | aDepartment of Physical and Biological Sciences, Western New England University, Springfield, Massachusetts, USA;bDepartment of Microbiology, University of Massachusetts, Amherst, Massachusetts, USA;cDepartment of Environmental Science, Policy and Management, University of California Berkeley, Berkeley, California, USA;dPacific Northwest National Laboratory, Richland, Washington, USA |
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| Abstract: | Molecular tools that can provide an estimate of the in situ growth rate of Geobacter species could improve understanding of dissimilatory metal reduction in a diversity of environments. Whole-genome microarray analyses of a subsurface isolate of Geobacter uraniireducens, grown under a variety of conditions, identified a number of genes that are differentially expressed at different specific growth rates. Expression of two genes encoding ribosomal proteins, rpsC and rplL, was further evaluated with quantitative reverse transcription-PCR (qRT-PCR) in cells with doubling times ranging from 6.56 h to 89.28 h. Transcript abundance of rpsC correlated best (r2 = 0.90) with specific growth rates. Therefore, expression patterns of rpsC were used to estimate specific growth rates of Geobacter species during an in situ uranium bioremediation field experiment in which acetate was added to the groundwater to promote dissimilatory metal reduction. Initially, increased availability of acetate in the groundwater resulted in higher expression of Geobacter rpsC, and the increase in the number of Geobacter cells estimated with fluorescent in situ hybridization compared well with specific growth rates estimated from levels of in situ rpsC expression. However, in later phases, cell number increases were substantially lower than predicted from rpsC transcript abundance. This change coincided with a bloom of protozoa and increased attachment of Geobacter species to solid phases. These results suggest that monitoring rpsC expression may better reflect the actual rate that Geobacter species are metabolizing and growing during in situ uranium bioremediation than changes in cell abundance. |
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