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Applied and Environmental Microbiology, March 2003, p. 1482-1487, Vol. 69, No. 3
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.3.1482-1487.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Ecologie Microbienne, UMR-CNRS 5557 and INRA,2 Laboratoire de Biométrie et Biologie Evolutive, UMR-CNRS 5558, Université Claude Bernard-Lyon I, 69622 Villeurbanne Cedex, France,3 Sugar Association Experiment Station, Mount Edgecombe 4300, South Africa1
Received 20 November 2002/ Accepted 10 December 2002
The spatial and genetic unit of bacterial population structure is the clone. Surprisingly, very little is known about the spread of a clone (spatial distance between clonally related bacteria) and the relationship between spatial distance and genetic distance, especially at very short scale (microhabitat scale), where cell division takes place. Agrobacterium spp. Biovar 1 was chosen because it is a soil bacterial taxon easy to isolate. A total of 865 microsamples 500 µm in diameter were sampled with spatial coordinates in 1 cm3 of undisturbed soil. The 55 isolates obtained yielded 42 ribotypes, covering three genomic species based on amplified ribosomal DNA restriction analysis (ARDRA) of the intergenic spacer 16S-23S, seven of which contained two to six isolates. These clonemates (identical ARDRA patterns) could be found in the same microsample or 1 cm apart. The genetic diversity did not change with distance, indicating the same habitat variability across the cube. The mixing of ribotypes, as assessed by the spatial position of clonemates, corresponded to an overlapping of clones. Although the population probably was in a recession stage in the cube (103 agrobacteria g-1), a high genetic diversity was maintained. In two independent microsamples (500 µm in diameter) at the invasion stage, the average genetic diversity was at the same level as in the cube. Quantification of the microdiversity landscape will help to estimate the probability of encounter between bacteria under realistic natural conditions and to set appropriate sampling strategies for population genetic analysis.
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