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Applied and Environmental Microbiology, April 2000, p. 1328-1333, Vol. 66, No. 4
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

rRNA Operon Copy Number Reflects Ecological Strategies of Bacteria

Joel A. Klappenbach, John M. Dunbar,dagger and Thomas M. Schmidt*

Department of Microbiology and Center for Microbial Ecology, Michigan State University, East Lansing, Michigan 48824-1101

Received 29 October 1999/Accepted 21 January 2000

Although natural selection appears to favor the elimination of gene redundancy in prokaryotes, multiple copies of each rRNA-encoding gene are common on bacterial chromosomes. Despite this conspicuous deviation from single-copy genes, no phenotype has been consistently associated with rRNA gene copy number. We found that the number of rRNA genes correlates with the rate at which phylogenetically diverse bacteria respond to resource availability. Soil bacteria that formed colonies rapidly upon exposure to a nutritionally complex medium contained an average of 5.5 copies of the small subunit rRNA gene, whereas bacteria that responded slowly contained an average of 1.4 copies. In soil microcosms pulsed with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), indigenous populations of 2,4-D-degrading bacteria with multiple rRNA genes (<A><AC>x</AC><AC>&cjs1171;</AC></A> = 5.4) became dominant, whereas populations with fewer rRNA genes (<A><AC>x</AC><AC>&cjs1171;</AC></A> = 2.7) were favored in unamended controls. These findings demonstrate phenotypic effects associated with rRNA gene copy number that are indicative of ecological strategies influencing the structure of natural microbial communities.

* Corresponding author. Mailing address: Department of Microbiology and Center for Microbial Ecology, Michigan State University, 202 Giltner Hall, East Lansing, MI 48824-1101. Phone: (517) 353-1796. Fax: (517) 353-8957. E-mail: tschmidt{at}pilot.msu.edu.

dagger Present address: Life Sciences Division, Los Alamos National Laboratories, Los Alamos, NM 87545.

Applied and Environmental Microbiology, April 2000, p. 1328-1333, Vol. 66, No. 4
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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