8.3 Microbial Physiology and Engineering: Phenazine-mediated extracellular electron transfer and microbial community organization
Abstract
Microorganisms can be found in densely packed aggregates, or ÒbiofilmsÓ, attached to each other and/or a surface just about everywhere we look: from engineered systems (wastewater treatment plants), to animal hosts (within our guts, on our teeth, attached to implanted medical devices), to agricultural settings (plant root communities) to methane-?oxidizing microbial assemblages at the bottom of the ocean. The composition of these biofilms ranges from populations of single species to communities of many phyla. Regardless of their context, the rules underpinning biofilm structure and function are poorly understood. The central tenant of this proposal is that in order to design synthetic biofilms to perform specific tasks, we need to understand the rules governing natural biofilms. What makes a biofilm robust is a multifaceted problem, but here we propose a focused set of experiments that will help us answer important questions relevant to this larger topic: how do electron shuttles mediate extracellular electron transfer (EET) within biofilms? How is the metabolic activity of an electron shuttle-?producing organism affected by the presence of other organisms that respond to that electron shuttle in different ways? These questions address a core challenge biofilm cells face-maintaining metabolic activity in the face of oxidant limitation. This problem interests researchers in diverse fields, yet only a small number of model systems have been used to study it, with different experimental limitations. Here, we propose to use a simple biofilm system comprising Pseudomonas aeruginosa (a model extracellular electron shuttle (i.e. phenazine) producer) and a small number of other organisms that do not produce phenazines but respond to them in different ways (positively, neutrally, or negatively). Our hope is that this "bottom up" experimental system will allow us to identify a set of principles that can be abstracted to diverse microbial communities that are oxidant?limited. An attractive aspect of to our system is that it is highly tractable with respect to being able to control both phenazine production and consumption using well-validated mutant strains, as well as the trafficking of these shuttles through specific components of the biofilm matrix. We propose two specific aims: Aim 1. Understand how phenazines mediate EET through P. aeruginosa biofilms. We will characterize phenazine-mediated EET in the biofilm matrix using electrochemical approaches, to distinguish between EET mediated by diffusion vs. electron hopping within the biofilm matrix. We will test the hypotheses that phenazines impact the metabolic activity of P. aeruginosa in anoxic regions of the biofilm, and that phenazine intercalation into extracellular DNA, an important component of the biofilm matrix, is necessary for optimal EET. Aim 2: Identify how the spatiometabolic organization of P. aeruginosa in multispecies biofilms is influenced by other organisms that are differentially affected by phenazines. Using a representative set of organisms that respond positively, neutrally or negatively to phenazines, we will study how varying oxygen levels impact the distribution of different species within the biofilm, and how these interactions, in turn, impact the spatiometabolic organization of P. aeruginosa within multispecies biofilms. More broadly, lessons learned from these studies will shed light on how microbial communities that rely on EET self-?assemble as a function of the presence of an electron shuttle.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 07, 2018
- Source ID
- W911NF1710024
Entities
People
- Dianne Newman
Organizations
- Army Contracting Command
- California Institute of Technology
- United States Army