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.
ORIGIN OF LIFE:
POLYMERISATION OF PREBIOTIC MONOMERS
The emergence of biopolymers is one of the key steps that led to the formation of life on Earth. To form functional biopolymers, the preexisting monomers had to be brought into closer proximity and their polymerisation had to be made thermodynamically and kinetically favorable. Most bio-monomers do not polymerize in aqueous solution but the adsorption to mineral surfaces decreases the degrees of freedom, thus increasing the probability of monomer interaction, promoting polymerisation. However, the energetics of nucleotide adsorption on minerals is still not well understood and the proposed mechanisms are questionable.
We used dynamic force spectroscopy (DFS) to explore the bonding relationships between model clay mineral surfaces and model nucleotides, to provide a thermodynamic explanation for differences in nucleotide adsorption on basal and edge clay mineral surfaces.
Our results fills a gap in understanding how polymerisation of nonactivated nucleotides to nucleic acids could have occurred and resulted in the RNA world. This work proves that we can expect different binding energetics between nucleic acids and various minerals. I also view this work as a proof of concept and the methodology introduces a new way of quantifying interactions between polymers and minerals.
The DFS data: