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Applied and Environmental Microbiology, December 2003, p. 6961-6968, Vol. 69, No. 12
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.12.6961-6968.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Physiological and Community Responses of Established Grassland Bacterial Populations to Water Stress

Robert I. Griffiths,1,2 Andrew S. Whiteley,1* Anthony G. O'Donnell,2 and Mark J. Bailey1

Molecular Microbial Ecology Laboratory, CEH-Oxford, Oxford OX1 3SR,1 Department of Agricultural and Environmental Science, The University of Newcastle Upon Tyne, Newcastle Upon Tyne NE1 7RU, United Kingdom2

Received 19 March 2003/ Accepted 1 September 2003

The effects of water stress upon the diversity and culturable activity of bacterial communities in the rhizosphere of an established upland grassland soil have been investigated. Intact monoliths were subjected to different watering regimens over a 2-month period to study community adaptation to moisture limitation and subsequent response to stress alleviation following rewetting. Genetic diversity was analyzed with 16S-based denaturing gradient gel electrophoresis (DGGE) of total soil-extracted DNA (rRNA genes) and RNA (rRNA transcripts) in an attempt to discriminate between total and active communities. Physiological response was monitored by plate counts, total counts, and BIOLOG-GN2 substrate utilization analyses. Controlled soil drying decreased the total number of CFU on all the media tested and also decreased the substrate utilization response. Following rewetting of dried soil, culture-based analyses indicated physiological recovery of the microbial population by the end of the experiment. In contrast, DGGE analyses of community 16S rRNA genes, rRNA transcripts and cultured communities did not reveal any changes relating to the moisture regimens, despite the observed physiological effects. We conclude that the imposed moisture regimen modulated the physiological status of the bacterial community and that bacterial communities in this soil are resistant to water stress. Further, we highlight the need for a reexamination of rRNA transcript-based molecular profiling techniques as a means of describing the active component of soil bacterial communities.

* Corresponding author. Mailing address: IVEM, CEH-Oxford, Mansfield Rd., Oxford OX1 3SR, United Kingdom. Phone: 44 0 1865 281686. Fax: 44 0 1865 281696. E-mail: whiteley{at}molbiol.ox.ac.uk.

Applied and Environmental Microbiology, December 2003, p. 6961-6968, Vol. 69, No. 12
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.12.6961-6968.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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