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Category: Environmental Microbiology
Application of Phylogenetic Techniques in Studies of Soil Microbial Communities, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815882/9781555813796_Chap49-1.gif /docserver/preview/fulltext/10.1128/9781555815882/9781555813796_Chap49-2.gifAbstract:
The author’s goal in writing this chapter is twofold: (i) to persuade the researcher that investigating soil microbial communities by using DNA sequence data is the most appropriate method for making community comparisons or for inferring ecological processes based on community membership, and (ii) to present the best available analytic methods, the steps needed to use those methods, and how to interpret the results. The advent of molecular techniques and cloning allowed microbiology to escape the petri dish and radically changed our understanding of microbial diversity. A section of the chapter presents a brief summary of how to construct phylogenies followed by descriptions of techniques to compare microbial communities and to infer ecological processes. The results suggested that successional changes associated with marked shifts from the wet, cool conditions of winter and spring to the drier and warmer conditions of summer involve the turnover of highly divergent groups rather than shifts in the relative abundance of closely related species. Lineage-per-time plots were introduced by Nee and coworkers, and others as a means of inferring rates of speciation and extinction from phylogenies. Webb developed methods for testing whether sampled phylogenetic lineages comprising ecological communities were more closely related or more distantly related to each other than expected by chance based on the available species pool. Both methods have been applied to the analysis of microbial communities with intriguing results. The best methods require understanding models of DNA sequence evolution, phylogenetic inference, and character evolution, challenging subjects and areas of active research.
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On the left is a typical phylogenetic tree. Branching events closer to the tips of the tree represent more-recent speciation events than branching events deeper in the tree. Closely related species share more life history traits than less related species. On the right is a polytomy—a type of phylogenetic tree in which all species are equally related to one another. If the evolutionary history of a collection of species can accurately be depicted as a polytomy, then species can be used as the unit of comparison.
Flow chart beginning with a collection of DNA sequences and ending with making biological inferences. After DNA sequences are aligned, the alignment can be sent to descriptive statistics or transformed into a distance matrix, or phylogenetic relationships can be inferred. After the second step, outputs can be analyzed in a variety of programs to make biological inferences.
The effect of incorporating phylogenetic and character state mapping uncertainty into the Phylo-test when comparing nirK DNA sequences (from reference 28 ). This demonstrates the perils of using a single evolutionary relationship when performing the Phylo-test. (A) When a single NJ tree is used (NJ-Parsimony) the two communities are significantly different. However, incorporating phylogenetic uncertainty through a bootstrap analysis (NJ Bootstrap-Parsimony) or using Bayesian trees (Bayesian-Parsimony) reverses the inference. (B) Incorporating character state mapping uncertainty causes a nearly complete overlap of the observed (Bayesian-Stochastic) and null (Null-Stochastic) distributions. Reprinted from Microbial Ecology ( 16 ) with permission from the publisher.
Lineage-per-time plots demonstrating an excess of highly divergent lineages (top) or an excess of closely related lineages (bottom right). Constant birth and extinction rates would yield an exponential lineage-per-time plot (indicated by the straight line). Note the logarithmic scale of the y axis. Reprinted from Applied and Environmental Microbiology ( 22 ) with permission from the publisher.
Lineage-per-time plots of Costa Rican AOB communities (16S) and alpine tundra fungal communities (18S). In the AOB comparison, the forest community has significantly more lineages at each time point. The convex lineage-per-time plots of the pasture and plantation communities demonstrate an excess of closely related community members. In the fungal community comparison, the spring community has significantly more lineages at time 0.25 and the summer community has significantly fewer lineages at time 0.9.
∫-LIBSHUFF comparisons of Costa Rican soil bacterial 16S rRNA gene libraries a