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.
BIOMINERALIZATION
-FROM MODEL BIO-MINERAL FORMATION TOWARD BIOGENIC PROCESSES
Biomineralizing organisms are superior in controlling mineral growth. The controls they use are deceptively simple (e.g. ions, polymers, electrons), however, when we seek to mimic such interactions e.g. for bio inspired approaches to materials design and synthesis, we are hindered by the lack of knowledge about the underlying molecular-scale mechanisms these polymer-mineral interactions rely upon. I am particularly interested in obtaining quantitative insight into the underlying mechanistic parameters that essentially control the polymer-mineral interactions.
ANCIENT POLYSACCHARIDE
The production of polymers for controlling calcite growth is a well-known approach in biomineralising organisms. Numerous studies have shown that polymers significantly influenced the growth rate and morphology of CaCO3 but little is known about how the polymers are actually controlled by the organisms. I have made a series of studies showing that an ancient polysaccharide (PS) extracted from 60 Ma chalk still inhibit calcite growth, modeled its complexation strength and that cations can control the effect of the ancient polysaccharides confirming that these processes have been in place for at least 60 million years.
Quantifying cation functionality
Imaging PS and calcite
Imaging cation functionality
POLYMER-CALCITE INTERACTIONS
Calcite-ethanol
-Stabilization of terraces
CaCO3-ethanol
Spherulitic Growth, Polymorph Stabilization,
and Morphology Change
Calcite-polysaccharides
-The role of composition and branching
ACC-polymers
MIMICKING NACRE
Work by Anne Rath Nielsen
-Former PhD student
Peptoid nanosheets
Templated calcite growth
-nucleation thermodynamics
