DISTRIBUTION OF ANTIBIOTIC RESISTANCE GENES IN THE ENVIRONMENT:
THE ROLE OF MINERAL FACILITATED HORIZONTAL GENE TRANSFER
Combining recent research across disciplines, I see evidence that minerals hold a high and unrecognized potential for enhancing the distribution of the ARg in the environment. Adsorption of ARg to minerals significantly increases the ARg’s lifetime and facilitates their distribution by sedimentary transport processes. In addition, minerals also serve as a) sites for horizontal gene transfer (HGT), b) platforms for microbial growth and, hence 3) act as hot spots for propagation of adsorbed ARg to other microbes. However, some minerals and ARg are bound more strongly than others and various bacteria have different affinities toward various minerals. Those variations in affinity are poorly quantified but vital for predicting the distribution of ARg in the environment.
Bacterial colony formation.
Image by Lisselotte Jauffred (collaborator from NBI)
The spread of antibiotic resistance genes (ARg) is a worldwide health risk1 and is no longer only a clinical issue. Vast reservoirs of ARg are found in natural environments2–4 such as soils, sediments and oceans. The emergence and release of ARg to the environment is in particular caused by extended use of antibiotics in farming, e.g. where the genes dissipate from the manure.5 Once in the environment, the ARg are surprisingly rapidly propagated. It is well known that the ARg are distributed to neighbour bacteria through processes of both cell sharing or through horizontal gene transfer (HGT) where one species acquirer resistance from another.6,7 Most HGT responsible for the spread of ARg are assumed to be through direct microbe-microbe contact. However, I find that the outcome of non-contact transfer is grossly underestimated. In the HGT mechanism called “Transformation”, free ARg in suspension or adsorbed to a mineral can be picked up and incorporated into non-related organisms. Considering that free DNA only can survive for a few weeks in sea- and freshwater environments,8–10 any HGT from free DNA can rightly be assumed to be local, but if the DNA gets adsorbed to a mineral, it can survive for several hundred thousands of years.11–14 If this also holds for ARg, then minerals offer a potent mechanism for distributing ARg through our environments my means of sedimentary processes.
MINERAL FACILITATED HORIZONTAL GENE TRANSFER.
A NEW PRINCIPLE FOR EVOLUTION OF LIFE?
Traditionally, we think of life principally evolving following the phylogenetic tree of life through vertical modification of existing genetic information. However, the genetic information can be passed on by horizontal exchange of DNA between non-related species i.e. the genetic material is transferred between organisms that are not closely genetically related: horizontal gene transfer (HGT). HGT has become a hot topic in science and an increasing amount of studies show that passing on new traits horizontally can significantly facilitate exchange of genetic material and blur the evolutionary phylogenetic relationship between species.
For HGT to occur, DNA has to be available in the environment. DNA released into the aqueous environment or soil is subjected to degradation by dynamic biological, physical, and chemical factors which are working against the success of HGT. However, findings of ancient DNA in sediments as well as degradation experiments show that minerals can protect the DNA allowing it to survive over time and in conditions that would otherwise be unfavorable for the stability of DNA. Minerals that are able to preserve DNA across timescales would function as selectors for transfer of genetic material between distant organisms, hence the availability and whereabouts of those minerals through time would impact the evolution of life.
APPROACH
Currently we are combining top down and bottom up approaches to address this hypothesis.
We are using atomic force microscopy to study stabilization of DNA on mineral surfaces and we are setting up microbial work to address the uptake rate into soil relevant microbes.
Stay tuned for updates
In the meantime:
https://doi.org/10.3389/fmicb.2018.02217
The idea and potential impact is illustrated in the schematics below.
SIMPLIFIED FRAMEWORK ILLUSTRATING MINERAL FACILITATED HGT
AND PROPOSED IMPACT FOR THE EVOLUTION OF EARLY LIFE
STUDENT PROJECTS
Calling students with interest in
geology, chemistry or (geo)microbiology
Visualization of DNA-mineral interaction dynamics
Biofilm formation on mineral surfaces
Enzymatic DNA degradation
The studies will include and a range of spectroscopy and microscopic tools, and potentially genomics and fieldwork.
No knowledge of those is required beforehand.
Send an informal email for for more info: kks@sund.ku.dk
FUNDING
Moving on to the next stage with this research Program is funded by the Carlsberg Foundation through a Young Researcher Fellowship.
Implication for propagation of antibiotic resistance genes are funded through a VILLUM Young Investigator grant
Proof of concept studies are funded by the Danish Research Counsel on their DFF-ERC initiative.
Idea and hypothesis development was under funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 663830 and the Welsh Government and Higher Education Funding Council for Wales through the Sêr Cymru National Research Network for Low Carbon, Energy and Environment.
