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Applied and Environmental Microbiology, May 1999, p. 2209-2216, Vol. 65, No. 5
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Molecular Phylogenetic and Biogeochemical Studies of Sulfate-Reducing Bacteria in the Rhizosphere of Spartina alterniflora

Mark E. Hines,1,* Robert S. Evans,2 Barbara R. Sharak Genthner,3 Stephanie G. Willis,2 Stephanie Friedman,4 Juliette N. Rooney-Varga,2,dagger and Richard Devereux4

Department of Biological Sciences, University of Alaska Anchorage, Anchorage, Alaska 995081; Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire 038242; Center for Environmental Diagnostics and Bioremediation, University of West Florida, Pensacola, Florida 325143; and National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Gulf Breeze, Florida 325614

Received 22 October 1998/Accepted 1 March 1999

The population composition and biogeochemistry of sulfate-reducing bacteria (SRB) in the rhizosphere of the marsh grass Spartina alterniflora was investigated over two growing seasons by molecular probing, enumerations of culturable SRB, and measurements of SO42- reduction rates and geochemical parameters. SO42- reduction was rapid in marsh sediments with rates up to 3.5 µmol ml-1 day-1. Rates increased greatly when plant growth began in April and decreased again when plants flowered in late July. Results with nucleic acid probes revealed that SRB rRNA accounted for up to 43% of the rRNA from members of the domain Bacteria in marsh sediments, with the highest percentages occurring in bacteria physically associated with root surfaces. The relative abundance (RA) of SRB rRNA in whole-sediment samples compared to that of Bacteria rRNA did not vary greatly throughout the year, despite large temporal changes in SO42- reduction activity. However, the RA of root-associated SRB did increase from <10 to >30% when plants were actively growing. rRNA from members of the family Desulfobacteriaceae comprised the majority of the SRB rRNA at 3 to 34% of Bacteria rRNA, with Desulfobulbus spp. accounting for 1 to 16%. The RA of Desulfovibrio rRNA generally comprised from <1 to 3% of the Bacteria rRNA. The highest Desulfobacteriaceae RA in whole sediments was 26% and was found in the deepest sediment samples (6 to 8 cm). Culturable SRB abundance, determined by most-probable-number analyses, was high at >107 ml-1. Ethanol utilizers were most abundant, followed by acetate utilizers. The high numbers of culturable SRB and the high RA of SRB rRNA compared to that of Bacteria rRNA may be due to the release of SRB substrates in plant root exudates, creating a microbial food web that circumvents fermentation.

* Corresponding author. Mailing address: Department of Biological Sciences, University of Alaska at Anchorage, 3211 Providence Dr., Anchorage, AK 99577. Phone: (907) 786-7762. Fax: (907) 786-4607. E-mail: afmeh{at}uaa.alaska.edu.

dagger Present address: Biological Sciences Department, University of Massachusetts Lowell, Lowell, MA 01854.

Applied and Environmental Microbiology, May 1999, p. 2209-2216, Vol. 65, No. 5
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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Copyright © 1999 by the American Society for Microbiology. All rights reserved.