Project

Discipline

Co-evolution; Microbial communities; Range expansion; Metabolic specialization; Evolutionary ecology; Microbial ecology; Mutualism; Microbial diversity; Tradeoffs; Denitrification

Lead
Mikrobielle Gemeinschaften beeinflussen die biologischen und chemischen Prozesse nahezu jedes Habitats auf der Erde und bestehen typischerweise aus tausenden verschiedenen Arten. Dieser extrem hohe Grad an Diversität wirft einige der fundamentalsten und herausforderndsten Fragen der mikrobiellen Ökologie auf. Warum bestehen mikrobielle Gemeinschaften aus so vielen Arten? Wie können all diese Arten koexistieren?
Lay summary
Dieses Projekt schlägt drei allgemeingültige Mechanismen vor die Erklären können wie verschiedene Spezies koexistieren: 1) Sie können koexistieren wenn sie verschiedene metabolische Prozesse durchführen, die biochemisch nicht miteinander vereinbar sind. 2) Sie können koexistieren, wenn sie gegenseitig voneinander abhängig sind. 3) Sie können koexistieren wenn sie zusammen koevolviert sind (d.h. wenn evolutionäre Veränderungen in einer Spezies die direkte Antwort auf evolutionäre Veränderungen in einer anderen Spezies sind). Obwohl alle drei Mechanismen durch theoretische Überlegungen gestützt werden, wurde bis jetzt noch keiner experimentell in mikrobiellen Gemeinschaften geprüft. Dieses Projekt schlägt konkrete Experimente vor, um diese Mechanismen zu testen. Das Testen dieser Mechanismen wird unser grundlegendes Verständnis darüber erweitern, wieso und wie Diversität in mikrobiellen Gemeinschaften entsteht und aufrechterhalten wird. Das Verständnis dieser Prozesse kann wiederum konkrete Anwendungen haben. Man könnte damit zum Beispiel vorhersagen wie metabolische Prozesse auf verschiedene Spezies verteilt werden müssen, um einen gewünschten Biotransformationsprozess optimal ablaufen zu lassen. Somit wird es auch dazu beitragen die Grundlagen für ein neues wissenschaftliches Feld, der synthetischen Ökologie, zu schaffen.

Direct link to Lay Summary

Last update: 14.10.2013

Active participation

Number	Title	Start	Funding scheme

Microbial communities impact the biological and chemical processes occurring in nearly every habitat on earth. They are also increasingly called upon to solve some of the most pressing problems facing our society, including the removal of environmental pollutants and the conversion of renewable resources into valuable products. These communities are often tremendously diverse, with a single liter of sea water estimated to contain many thousands of different microbial taxa. These levels of diversity raise some of the most basic and challenging questions in microbial ecology. Why do microbial communities contain so many different cell types? What are the mechanisms that prevent a few cell types from evolving that outcompete the other cell types? Metabolic specialization provides a plausible explanation for how diversity could be promoted and maintained. Consider a microbial cell residing in the human gut. This cell encounters myriad different substrates that could be metabolized to support its growth. Yet, even if this cell were near starvation, it would only metabolize a subset of the available substrates. What is the advantage of metabolizing subsets of the available substrates rather than all of them? What are the underlying causes of metabolic specialization? Can we predict which substrates are likely metabolized by the same cell type and which are likely metabolized by different cell types? We currently lack a deep understanding of the underlying mechanisms causing metabolic specialization, which hinders us from addressing these questions and elucidating the general rules and principles governing the assembly and diversity of microbial communities.In this proposal, I postulate three general mechanisms that could promote and maintain diversity in microbial communities. The first is that incompatibilities between different metabolic processes cause the processes to segregate into different specialized cell types over evolutionary time, thus promoting diversity. Metabolic incompatibilities have often been used to explain the emergence of metabolic specialization, but empirical measures of incompatibilities are limited to a few well-investigated metabolic processes. This hinders us from obtaining a more holistic perspective on metabolic incompatibilities that could reveal the general rules and principles governing the cellular fates of different metabolic processes. To reveal these general rules and principles, I propose specific experiments that address the following critical questions. •Can incompatibilities between hundreds of different pairs of metabolic processes be experimentally measured in parallel, thus generating a more holistic perspective on metabolic incompatibilities?•Are incompatible metabolic processes more likely than compatible metabolic processes to segregate into different specialized cell types, thus promoting diversity?•What are the underlying genetic changes and physiological tradeoffs that cause metabolic specialization and diversification? I also postulate two general mechanisms whereby mutualistic interactions between different metabolically specialized cell types could maintain and promote further diversification in spatially structured environments. The first is that mass transfer limitations of exchanged metabolites constrain the maximum permissible distance between different mutualist cell types, thus maintaining diversity during range expansion. The second is that mutualistic interactions cause co-evolutionary changes between metabolically specialized cell types that promote and maintain diversity during prolonged periods of spatial separation. Although both mechanisms are supported by theoretical considerations, neither has been experimentally tested with microbial communities. To address this knowledge gap, I propose specific experiments that address the following critical questions.•Do mass transfer limitations of exchanged metabolites constrain the maximum permissible distance between different mutualist cell types?•Does this constraint maintain diversity during range expansion?•Do mutualistic interactions cause co-evolutionary changes between metabolically specialized cell types that promote and maintain diversity during prolonged periods of spatial separation?Testing these general mechanisms would significantly advance our basic understanding about why and how diversity is promoted and maintained in microbial communities. Ultimately, the insights gained could be useful for predicting the assembly and diversity of natural microbial communities. The insights also have applied implications. They could be used to predict the optimal distribution of different metabolic processes across different cell types to maximize a desired biotransformation, thus contributing towards establishing a field of synthetic ecology.