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Applied and Environmental Microbiology, January 2008, p. 495-502, Vol. 74, No. 2
0099-2240/08/$08.00+0     doi:10.1128/AEM.01435-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Prevalence of Lysogeny among Soil Bacteria and Presence of 16S rRNA and trzN Genes in Viral-Community DNA

Dhritiman Ghosh,¹ Krishnakali Roy,¹ Kurt E. Williamson,⁶ David C. White,^2, K. Eric Wommack,^3,4 Kerry L. Sublette,⁵ and Mark Radosevich^1*

Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, Tennessee 37996-4531,¹ Center for Biomarker Analysis, University of Tennessee, Knoxville, Tennessee 37932-2575,² Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware 19716,³ Delaware Biotechnology Institute, University of Delaware, Newark, Delaware 19716,⁴ Chemical Engineering Department, University of Tulsa, Tulsa, Oklahoma 74104-3189,⁵ J. Craig Venter Institute, La Jolla, California 92037⁶

Received 27 June 2007/ Accepted 30 October 2007

Bacteriophages are very abundant in the biosphere, and viral infection is believed to affect the activity and genetic diversity of bacterial communities in aquatic environments. Lysogenic conversion, for example, can improve host fitness and lead to phage-mediated horizontal gene transfer. However, little is known about lysogeny and transduction in the soil environment. In this study we employed atrazine-impregnated Bio-Sep beads (a cell immobilization matrix) to sample active microbiota from soils with prior pesticide exposure history. Once recovered from soil, the bead communities were induced with mitomycin C (MC), and viral and bacterial abundances were determined to evaluate the incidence of inducible prophage in soil bacteria. The inducible fraction calculated within bead communities was high (ca. 85%) relative to other studies in aquatic and sedimentary environments. Moreover, the bacterial genes encoding 16S rRNA and trzN, a chlorohydrolase gene responsible for dehalogenation of atrazine, were detected by PCR in the viral DNA fraction purified from MC-induced bead communities. A diverse collection of actinobacterial 16S rRNA gene sequences occurred within the viral DNA fraction of induced, water-equilibrated beads. Similar results were observed in induced atrazine-equilibrated beads, where 77% of the cloned sequences were derived from actinobacterial lineages. Heterogeneous 16S rRNA gene sequences consisting of fragments from two different taxa were detected in the clone libraries. The results suggest that lysogeny is a prevalent reproductive strategy among soil bacteriophages and that the potential for horizontal gene transfer via transduction is significant in soil microbial communities.

Published ahead of print on 9 November 2007.

Deceased. Please see www.davidcwhite.org/.