Host-symbiont coevolution: Exploring the parasitism-mutualism continuum

Lead Research Organisation: University of Abertay Dundee
Department Name: Sch of Contemporary Sciences

Abstract

Intimate and prolonged associations between different organisms - symbioses - are widespread and important in the natural environment. Symbiotic associations can range from being parasitic, where one organism benefits at the expense of the other, to being mutualistic, where both organisms benefit from the association. Such symbiotic associations underpin the functioning of ecosystems: mutualism can allow pairs of organisms to survive where otherwise neither would and parasitism can limit the growth of host populations. These symbioses are particularly important in microbial communities but little is known about how these associations shape the evolution and diversity of microbial symbionts. Here we want to understand how the evolution of symbiotic organisms is different under conditions that range from parasitic to mutualistic. Our approach is to study the evolution of a bacterial-plasmid symbiosis where the nature of the association ranges from parasitic to mutualistic depending on the environment: in the presence of mercury the association is mutualistic because the plasmid has a gene for mercury resistance; and in the absence of mercury the association is parasitic because carrying the plasmid slows the growth of the bacteria. In nature carrying the plasmid allows bacteria to survive in otherwise toxic mercury contaminated soils. We will exploit the short generation times, and large population sizes of bacteria to observe evolution in action. We will discover and contrast the genetic changes that occur in the genomes of both the bacteria and the plasmid as they co-evolve on a continuum of environments that change the symbiosis from parasitic to mutualistic. - Our study is novel because we will, for the first time, study evolution across a parasitic-mutualistic symbiosis continuum using a single symbiotic association. - Our study is relevant to the natural environment because such bacterial-plasmid associations are widespread, but poorly understood, in microbial communities and are likely to play an important role in maintaining biodiversity and ecosystem function, particularly in response to heavy metal contamination of soils. - Our study is powerful because we will use an experimental approach to study evolution in action. - Our study is timely because we will exploit the latest technologies in DNA sequencing to directly observe evolution of genetic sequences in bacterial and plasmid genomes.
 
Description We sort to better understand why bacteria will retain plasmids - essentially parasitic DNA molecules which often apparently provide no benefit for their host. Our work has shown that bacteria carrying plasmids rapidly co-evolve to minimise the costs of plasmid carriage.
Exploitation Route A key result from this work has been a better understanding of how bacteria can survive in physically and chemically heterogeneous environments (or changing environments) where there are sub-optimal or sub-lethal zones for growth. This is relevant for microbial ecology, but may also inform biotechnology and medical microbiology where the control of bacterial growth and the prevention of mutant development (e.g. resistance and cheaters) is important.
Sectors Agriculture, Food and Drink,Education,Environment

 
Description We have used some aspects of this work, namely the 'evolution in a test-tube', as part of my STEM work with schools in the Dundee area, and with Nuffield Summer Placement Studentships. Secondary school student's imagination has been easily captured by showing how key elements of evolution - adaptive radiation - can be experimentally investigated using simple microcosms. The adaptation to mercury, and the carriage of plasmids (the focus of this grant) have provided additional areas of discussion. We continue to offer Nuffield Placements (as well as host ERASMUS visitors) in our group, investigating other aspects of bacterial adaptation, including biofilm-formation.
First Year Of Impact 2011
Sector Education
Impact Types Societal