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Applied and Environmental Microbiology, October 2009, p. 6047-6054, Vol. 75, No. 19
0099-2240/09/$08.00+0     doi:10.1128/AEM.00063-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Evolution of Diversity in Spatially Structured Escherichia coli Populations{triangledown}

José Miguel Ponciano,1,2,4,{dagger} Hyun-Joon La,3 Paul Joyce,1,2,4 and Larry J. Forney3,4*

Departments of Mathematics,1 Statistics,2 Biological Sciences,3 the Initiative for Bioinformatics and Evolutionary Studies (IBEST), University of Idaho, Moscow, Idaho 83844-30514

Received 11 January 2009/ Accepted 26 July 2009

The stochastic Ricker population model was used to investigate the generation and maintenance of genetic diversity in a bacterial population grown in a spatially structured environment. In particular, we showed that Escherichia coli undergoes dramatic genetic diversification when grown as a biofilm. Using a novel biofilm entrapment method, we retrieved 64 clones from each of six different depths of a mature biofilm, and after subculturing for ~30 generations, we measured their growth kinetics in three different media. We fit a stochastic Ricker population growth model to the recorded growth curves. The growth kinetics of clonal lineages descendant from cells sampled at different biofilm depths varied as a function of both the depth in the biofilm and the growth medium used. We concluded that differences in the growth dynamics of clones were heritable and arose during adaptive evolution under local conditions in a spatially heterogeneous environment. We postulate that under nutrient-limited conditions, selective sweeps would be protracted and would be insufficient to purge less-fit variants, a phenomenon that would allow the coexistence of genetically distinct clones. These findings contribute to the current understanding of biofilm ecology and complement current hypotheses for the maintenance and generation of microbial diversity in spatially structured environments.

* Corresponding author. Mailing address: Department of Biological Sciences, Life Sciences South, Rm. 455, University of Idaho, Moscow, ID 83844-3051. Phone: (208) 885-6011. Fax: (208) 885-7905. E-mail: lforney{at}uidaho.edu

{triangledown} Published ahead of print on 31 July 2009.

{dagger} Present address: Centro de Investigación en Matemáticas, CIMAT A.C. Calle Jalisco s/n, Col. Valenciana, C.P. 36240 Guanajuato, Guanajuato, México.

Applied and Environmental Microbiology, October 2009, p. 6047-6054, Vol. 75, No. 19
0099-2240/09/$08.00+0     doi:10.1128/AEM.00063-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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