How energy landscapes shape biological communities
Sometimes what we think of as obvious relationships in natural systems portray an unintuitive complexity upon more thorough investigation. The relationship between energy availability and distribution of functional groups of organisms might be considered as an example of this.
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In late 2014 CGB scientists (Dahle et al.) published an article in ISME examining the intricate relationships between energy availability in the unusual environment of hydrothermal systems on the Arctic Mid-Ocean Ridge and the microbial groups that reside there.
Little biological knowledge is required to understand that plants - requiring light as an energy source - are abundant on Earth’s surface and absent in environments in perpetual darkness. The same reasoning holds true for organisms feeding on energy from chemical reactions: in an environment where the oxidation of sugars represents an ample energy source, one could expect sugar oxidizers to be present in high numbers. However, the potential chemical energy in most natural systems does not come from one or two sources, but in the form of tens, hundreds or even thousands of different chemical disequilibria involving a variety of both organic and inorganic compounds. Obviously, the emerging energy landscapes will somehow constrain the distribution of functional groups of organisms in the environment. But exactly how? Answering this question might improve our ability to predict the biological effects of shifting environments in the past and future.
Yet, a rigorous investigation of how chemical energy landscapes shape microbial communities is by no means straightforward. First of all it requires detailed chemical analyses of the environment. This is not limited to measuring concentrations of the chemical compounds present in a system, but also involves evaluating fluxes, the relevance of non-biogenic chemical reactions as well as the modulation of the energy landscapes by biological activity. Complicating things further, the term 'potential chemical energy' can be understood in fundamentally different ways such as the instantaneous energy release per reaction (e.g. Joules per mole electrons transferred in redox reactions) or as energy density (e.g. Joules per kg of fluids).
Using hydrothermal systems on the Arctic Mid Ocean Ridge as natural laboratories, researchers at CGB explored the link between energy availability and composition of chemotrophic microbial communities by (i) modeling energy landscapes based on available chemical data, (ii) constructing models of the distribution of functional groups of microbial communities that were entirely based on modeled energy availabilities, and (iii) comparing models with observed communities. The results of the study revealed a fit between observed communities and energy-density based models. Although the models can be developed further (for example by incorporating kinetics) the study provides a framework of how biological communities are shaped by chemical energy landscapes. An understanding of microbial relationships to energy is important in answering the larger ecological question of why organisms are distributed as they are on our planet.
Read the article in ISME: Multidisciplinary Journal of Microbial Ecology
