Aquaculture drives spread of antibiotic resistance in the ocean

PD Dr. Jörn Petersen

Petri dish with red, white and brown marine bacteria from the Roseobacter group. Growth on the antibiotic chloramphenicol is made possible by the natural 57 kb RepC_soli plasmid pP72_e, which was exchanged between the bacteria across the species boundary.

Researchers led by assistant professor Dr. Jörn Petersen of the Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures GmbH have for the first time investigated the relevance of antibiotic resistance in the group of marine Roseobacter bacteria. The scientists were able to demonstrate that a plasmid acquired by horizontal gene transfer confers a 50-fold increased tolerance to the broad-spectrum antibiotic chloramphenicol. The team published their findings in the renowned journal Environmental Microbiology (doi: 10.1111/1462-2920.15380).

Roseobacter already part of the oceans’ resistome
Roseobacter account for up to a quarter of the oceans’ bacteria. Jörn Petersen’s working group has been investigating these alphaproteobacteria for several years as part of the collaborative research centre “Roseobacter (TRR51)” at the Leibniz Institute DSMZ. The bacteria play a key role in the global carbon and sulphur cycles, and their versatile metabolism offers great potential for biotechnological usage. In the present study, the researchers examined a hitherto uncharacterised group of plasmids, i.e. circular DNA molecules that reproduce independently of the bacterial chromosome in the bacterial cell. Plasmids allow bacteria to swiftly and easily exchange genetic material amongst each other, which is a key mechanism for the development of multi-resistant hospital pathogens. The plasmid investigated in depth in the present study is called RepC_soli pP72_e. It contains genetic information for a 50-fold increased tolerance to the broad spectrum antibiotic chloramphenicol and was easily transferred to other marine bacteria using a sophisticated molecular machinery reminiscent of pneumatic dispatch systems. On the basis of their findings, the authors assume that the investigated Roseobacter strains from Spanish aquacultures adopted their antibiotic resistance fairly recently via horizontal gene transfer from evolutionary distant Gammaproteobacteria. This hypothesis is supported by the fact that this resistance gene has never been found in any other species of investigated marine roseobacters, yet it frequently occurs on plasmids of pathogens such as Salmonella enterica or Vibrio cholerae, both of which are harmful to humans and animals.

“As the bacteria we investigated were isolated from mussels from Spanish aquaculture farms, it seems reasonable to assume that the acquired tolerance to chloramphenicol is a genetic legacy from earlier antibiotic use”, explains Lukas Birmes, the study’s lead author. Antibiotics were in the past frequently used in aquacultures to prevent diseases or to promote growth. However, due to the consequences for humans and nature in general, many countries have decided to significantly reduce the use of these drugs. In addition, it is remarkable that the gene for chloramphenicol-tolerance is not present in more than a dozen other closely related Phaeobacter strains with completely sequenced genomes, isolated in the seas of Denmark, France, Germany and Australia. The researchers stress that it is far from them to apportion blame. “But results like ours on the interconnectivity between public health, livestock breeding and marine aquaculture do emphasise how closely the modern world is connected from a biological point of view. People should be aware of the footprint they leave in the Anthropocene”, summarizes Jörn Petersen.

Original publication
Birmes, L., Freese, H. M., Petersen, J. (2021) RepC_soli: A novel promiscuous plasmid type of Rhodobacteraceae mediates horizontal transfer of antibiotic resistances in the ocean. Environ Microbiol. 2021 Jan 3. doi: 10.1111/1462-2920.15380. Online ahead of print.

Press contact:
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Phone: ++49 (0)531/2616-300
Mail: press(at)dsmz.de

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