Mercury-methylating bacteria are associated with copepods: A proof-of-principle survey in the Baltic Sea

• Published in: PloS one Vol. 15; no. 3; p. e0230310
• Main Authors: Gorokhova, Elena, Soerensen, Anne L, Motwani, Nisha H
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 16-03-2020; Public Library of Science (PLoS)
• Subjects: Archaea; Bacteria; Bacterial genetics; Baltic and East European studies; Bioaccumulation; Biology and Life Sciences; Copepoda; Copepods; Deoxyribonucleic acid; Detritus; Dimethylmercury; DNA; DNA methylation; Earth sciences; Ecology and Environmental Sciences; Environmental science; Firmicutes; Fishes; Food chains; Food contamination & poisoning; Food webs; Genes; Genetic research; Heterotrophic bacteria; Intestinal microflora; Mercury; Mercury (metal); Metagenomics; Methylation; Methylmercury; Methylmercury compounds; Microbiomes; Microbiota; Microbiota (Symbiotic organisms); Microorganisms; Neurotoxins; Physical Sciences; Plankton; Seasonal variability; Seawater; Sediments (Geology); Surveys; Toxins; Water circulation; Water column; Zooplankton; Östersjö- och Östeuropaforskning; Baltic Sea; Sweden
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0230310

Methylmercury (MeHg) is a potent neurotoxin that biomagnifies in marine food webs. Inorganic mercury (Hg) methylation is conducted by heterotrophic bacteria inhabiting sediment or settling detritus, but endogenous methylation by the gut microbiome of animals in the lower food webs is another possible source. We examined the occurrence of the bacterial gene (hgcA), required for Hg methylation, in the guts of dominant zooplankters in the Northern Baltic Sea. A qPCR assay targeting the hgcA sequence in three main clades (Deltaproteobacteria, Firmicutes and Archaea) was used in the field-collected specimens of copepods (Acartia bifilosa, Eurytemora affinis, Pseudocalanus acuspes and Limnocalanus macrurus) and cladocerans (Bosmina coregoni maritima and Cercopagis pengoi). All copepods were found to carry hgcA genes in their gut microbiome, whereas no amplification was recorded in the cladocerans. In the copepods, hgcA genes belonging to only Deltaproteobacteria and Firmicutes were detected. These findings suggest a possibility that endogenous Hg methylation occurs in zooplankton and may contribute to seasonal, spatial and vertical MeHg variability in the water column and food webs. Additional molecular and metagenomics studies are needed to identify bacteria carrying hgcA genes and improve their quantification in microbiota.