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Gene transfer in the Plastisphere

Purpose and background

The spread of antibiotic resistance genes (ARg) is a worldwide health risk (1) and no longer only a clinical issue. Vast reservoirs of ARg are found across natural environments (2), such as soils, sediments and oceans. As such, the geologic perspective and methodological approach can be used to study these environments and inform management strategies for the protection of water resources and ecosystems.

Once in the environment, ARg are surprisingly rapidly propagated- at a rate that is enhanced by the concurrent presence of heavy metals (3). ARg are efficiently distributed between bacteria through horizontal gene transfer (HGT), where one species acquires resistance through gene transfer from other resistant bacteria. Most HGT responsible for the spread of ARg is assumed to be through direct microbe-microbe contact. ARg acquisition by uptake of extracellular DNA shed to the environment is traditionally not considered an effective mode of transfer, simply because extracellular DNA degrades in a matter of days when it is suspended in e.g. seawater (4). However, colleagues and I just showed that sedimentary DNA can be preserved in the environment for geological relevant timescales (at least 2 Ma years) and we have assigned adsorption to minerals as a key for DNA preservation (5)

My group and I found that two environmentally-relevant bacteria can successfully incorporate mineral adsorbed ARg as well as 60bp (fragmented) DNA (6).  Our results show that bacteria acquire and incorporate extracellular DNA adsorbed to mineral surfaces to gain an evolutionary advantage. This pathway of evolution is currently not recognized, although reuse of genetic invention could be an effective means of obtaining evolutionary fitness for microorganisms. In the environment, DNA associated to minerals could be transported and deposited according to sedimentary processes. Bacteria could access and pick up ARg along these transport pathways and at deposition sites, explaining the vast propagation of ARg in the environment.

Expected scientific outcome

Following our results we expect to establish if a) plastic-micro-niches facilitate HGT and if build-up enhance or inhibit gene acquisition, b) which substrate types have the highest and lowest uptake efficiency, and c) if polluted point sources are hotspots for ARg propagation in Kalø Vig.

 

Knowledge of which type of particles inhibit or decrease gene transfer efficiency can be important for mitigation strategies. Importantly, our study can help elucidate the mechanisms behind the rapid ARg propagation in our environment.

 

MERGING OF KNOWLEDGE 

Project partners & expertise:

Funding

Building on expertise funded by:

References

1. Hatosy, S. M. & Martiny, A. C. The Ocean as a Global Reservoir of Antibiotic Resistance Genes. Appl. Environ. Microbiol. 81, 7593–7599 (2015)

2. Martínez, J. L. Antibiotics and Antibiotic Resistance Genes in Natural Environments. Science 321, 365–367 (2008)

3. Hemme, C. L. et al. Lateral Gene Transfer in a Heavy Metal-Contaminated-Groundwater Microbial Community. mBio 7, e02234-15 (2016).

4. Dejean, T. et al. Persistence of Environmental DNA in Freshwater Ecosystems. PLOS ONE 6, e23398 (2011)

5. Kjær, K. H. et al. A 2-million-year-old ecosystem in Greenland uncovered by environmental DNA. Nature 612, 283–291 (2022)

6.Verma, T., Hendiani, S., Andersen, S. B., Burmoelle, M. & Sand, K. K. Sedimentary DNA can influence evolution: Establishing mineral facilitated horizontal gene transfer as a route to bacterial fitness. 2023.01.24.525235 Preprint (2023)

7. Dodhia MS, Rogers KL, Fernández-Juárez V, Carreres-Calabuig, JA, Tisserand AA, Keulen N, Riemann L, Shashoua Y, Posth NR. Microbe-Mineral interactions in the Plastisphere: coastal biogeochemistry and consequences for plastic fate.  Frontiers in Marine Science, 10 (2023)

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