Scialog: Collaborative Teams - 2016
Boston University, Physics,
What constrains microbial diversity? Deriving new ecological principles for the microbial world
Microbes often live in richly diverse communities that may include thousands of different species. Even communities where nutrients are scarce and conditions are harsh can harbor exceedingly large varieties of micro-organisms.
“Classical results in community ecology suggest that the number of species in a community cannot exceed the number of resources,” noted researchers Alvaro Sanchez (Yale) and Pankaj Mehta (Boston U). However, recent experiments in Sanchez’s lab revealed that complex microbial communities with more 15 species can co-exist on a single carbon source such as glucose. “This seems to directly contradict the competitive exclusion principle,” they claim.
Now, Sanchez and Mehta have each received a $50,000 Scialog Award to determine, through a combination of theorizing and new experiments, the physical and chemical constraints on microbial diversity. “In particular, we seek to identify the basic ecological principles that govern community assembly in microbial ecosystems,” they said.
The researchers starting point is that when microbes metabolize a rich substrate, such as glucose, they produce a number of metabolic byproducts. Many of these are then excreted to the immediate environment, where they can be absorbed and metabolized by other species, producing yet another layer of molecules of lower value that are in turn secreted to the environment.
“We propose that this process of serial metabolism bootstraps microbial diversity,” Sanchez and Mehta said. “This prompts the question -- what limits this bootstraping process? In addition to this process, some of the secondary metabolites act as antibiotics that kill neighboring cells. In turn, cell lysis also releases new metabolites and resources into the environment. We hypothesize that the fundamental difference between microbial ecology and some macroscopic ecological systems is that most microbes within an ecosystem exist on the same trophic level while constructing their own ‘niches’, and hence there exist strong interdependencies the organisms and their environment.”
They will test these hypotheses by developing new theoretical models of microbial community ecology. In particular, they will revisit classical models of community assembly and adapt them to the microbial setting by accounting for the ubiquitous production and consumption of small metabolic molecules by microbes and include the release of small molecule resources from cell death in a population.
Sanchezwill then test the models experimentally by growing complex communities in a variety of carbon sources. Hewill vary parameters such as the energy per substrate molecule, number of carbons per molecule, total amount of carbon in the medium, as well as population dynamic effects (death rate).
This combination of theory and experiment will allow Sanchez and Mehtato uncover the fundamental principle underlying community ecology in microbes.
Sanchez and Mehta are among more than 60 early career scientists participating in Scialog: Molecules Come to Life, a three-year program jointly sponsored by Research Corporation for Science Advancement (RCSA) and the Gordon and Betty Moore Foundation. Additional funding has been provided by the Simons Foundation. Scialog supports research, intensive dialog and community building to address scientific challenges of global significance. Within each multi-year initiative, Scialog Fellows collaborate in high-risk discovery research on untested ideas and communicate their progress and form new collaborations in annual conferences.
Molecules Come to Life focuses on such questions as, what are the fundamental principles that make a collection of molecules within a cell produce behaviors that we associate with life? How do molecules combine and dynamically interact to form functional units in cells, and how do cells themselves interact to form more complex lifeforms?
The researchers formed their collaboration at a Scialog conference held earlier this year in Tucson, Arizona. There scientists from diverse fields of biology, physics and chemistry engaged in intensive discussions designed to produce creative ideas for innovative research.
“Scialog aims to encourage collaborations between theorists and experimentalists,” said RCSA Program Director Richard Wiener. “And, we encourage approaches that are driven by theory and coarse-grained modeling, that are testable by experiments.”