A. Koeppel

The central questions of bacterial ecology and evolution require a method to consistently demarcate, from the vast and diverse set of bacterial cells within a natural community, the groups playing ecologically distinct roles (ecotypes). Because of a lack of theory-based guidelines, current methods in bacterial systematics fail to divide the bacterial domain of life into meaningful units of ecology and evolution. We introduce a sequence-based approach ("ecotype simulation") to model the evolutionary dynamics of bacterial populations and to identify ecotypes within a natural community, focusing here on two Bacillus clades surveyed from the "Evolution Canyons" of Israel. This approach has identified multiple ecotypes within traditional species, with each predicted to be an ecologically distinct lineage; many such ecotypes were confirmed to be ecologically distinct, with specialization to different canyon slopes with different solar exposures. Ecotype simulation prov...

We have investigated microbial mats of alkaline siliceous hot springs in Yellowstone National Park as natural model communities to learn how microbial populations group into species-like fundamental units. Here, we bring together empirical patterns of the distribution of molecular variation in predominant mat cyanobacterial populations, theory-based modelling of how to demarcate phylogenetic clusters that correspond to ecological species and the dynamic patterns of the physical and chemical microenvironments these populations inhabit and towards which they have evolved adaptations. We show that putative ecotypes predicted by the theory-based model correspond well with distribution patterns, suggesting populations with distinct ecologies, as expected of ecological species. Further, we show that increased molecular resolution enhances our ability to detect ecotypes in this way, though yet higher molecular resolution is probably needed to detect all ecotypes in this microbial community.

Hot spring microbial mats are highly organized with both photosynthetic and non-photosynthetic organisms present. Cyanobacteria, often the dominant primary producers within this ecosystem, Live in the top 1-2 mm and at survive temperatures of over 70 degrees C. The genomes of two Synechococcus isolates (ecotypes) that are present in overlapping thermal environments were sequenced. The two Synechococcus genomes have similar

Bacterial systematics currently lacks a theory-based approach to identify the fundamental units of ecology and evolution. Consequently, a single bacterial species typically contains multiple phylogenetically and ecologically distinct lineages. Thus, the species of bacterial systematics are too broadly conceived to help the microbial ecologist who seeks to behold the full ecological diversity within a community, and to determine the interactions and functions of its ecologically distinct populations. Here, we review some of our recent work aiming to discover the ecologically distinct populations of a clade through analysis of DNA sequence diversity. We have developed an algorithm to compare simulations of bacterial sequence evolution with observed sequence diversity patterns within a clade. By finding the set of parameters that give a maximum likelihood fit between evolutionary simulations and actual sequence data, we are able to estimate lineage-specific rates of evolution and to make predictions about sequence clusters that correspond to ecologically distinct populations (ecotypes). We applied this approach to bacterial isolates of "Evolution Canyon" III in the southern Negev Desert. Within the Bacillus subtilis-B. licheniformis clade, our simulation identified numerous putative ecotypes, some of which were shown to be strongly associated with different microhabitats, confirming their ecological distinctness. Also, several confirmed ecotypes were found to be grouped within a single named species, demonstrating the power of the algorithm to discern ecologically significant variation that is beyond the current focus of bacterial systematics. These findings highlight the promise of a theory-driven approach to identify fundamental units of bacterial diversity.