Using global marine metagenomics to understand MERcury microbial associated processes: finding a CURE for mercury contaminated environments

Periodic Reporting for period 1 - MER-CURE (Using global marine metagenomics to understand MERcury microbial associated processes: finding a CURE for mercury contaminated environments)

Berichtszeitraum: 2018-09-01 bis 2020-09-30

Anthropogenic perturbations have alarmingly tripled the mercury content of surface Earth reservoirs (atmosphere, ocean, or terrestrial) compared to pre-anthropogenic conditions. Nowadays, millions of people are exposed to harmful levels of this potent neurotoxin, concretely to the organic form methylmercury that bio-accumulates in organisms and biomagnifies in marine food webs. Understanding mercury transformations within the oceanic water column remains a critical issue because fish harvested for commercial use originates largely from marine ecosystems, and are a primary source of methylmercury to humans globally. The overall aim of MER-cURE in to describe microbial populations involved in Hg processes in the marine environments at a global ocean scale. The specific objectives are:
1. To identify key microbial prokaryotic populations involved in Hg processes (containing hgcAB and/or merAB genes) in the marine environments at a global ocean scale.
2. To provide quantitative data of the amount of MeHg and Hg that can be degraded/eliminated in the sea, thus revealing ocean hot-spots for Hg detoxification and helping to complete global oceanic Hg models.
3. To quantify Hg detoxification rates in bacterial cultures and marine contaminated sediments to develop a pilot-system for Hg removal.
4. To engage stakeholders in the management process, to develop and implement a communication strategy based on formative purposes to effectively translate and share research achievements from objectives 1 to 3.

WP-1: Project organization, management and career development of the candidate (Figure 1). Both Andrea García Bravo and Josep M Gasol verified together in monthly basis the progress of the Project. At the beginning of the Project, they developed a succesful CDP as the cadidate just obtained a highly competitive 5-y position at the Institute of Marine Sciences. In the CDP plan, Andrea García Bravo and Josep M Gasol planned the application to different competitive calls. The fellow applied as PI to the Plan Estatal de Investigación Científica y Técnica y de Innovación Programa Estatal de I+D+i Orientada a los Retos de la Sociedad (Jóvenes Invetigadores), which is a spanish 3-y grant for young researchers that includes the salary and the research at the Institute of Marine Sciences (CSIC). The fellow also applied to a tenure track Ramón y Cajal competitive Spanish National call. The CDP was succesful and the fellow is current running the project for young researchers and got the tenure track Ramón y Cajal. The Marie Curie and the CDP built the bridge between an unstable post-doc position to a tenure track position.
WP-2: Genomic reconstruction of mer and hgcAB metagenomes and metatranscriptomes.
The fellow started the project writing a review: Biotic formation of methylmercury: A bio–physico–chemical conundrum. Bravo and Cosio (Limnology & Oceanography, 65, 1010–1027). This review gives an overview of recent knowledge and approaches used to understand HgII‐methylation, microbial biodiversity and activity involved in this process, and highlights the current limits for predicting MMHg concentrations in the environment (Figure 2). Deeper knowledge on the hgcA genes were provided in Capo et al., (2020) and Xu et al (2021). In Capo et al (2020), we used the metagenomics data analyzed in Alneberg et al. (2018) and compiled in BalticMicrobeDB1 to search for hgcAB genes and we observed that hgcAB were predominantly detected in anoxic water, but some hgcAB genes were also detected in hypoxic and normoxic waters. Higher relative quantities of hgcAB genes were found in metagenomes from marine particles compared to free-living communities in anoxic water, suggesting that such particles are hotspot habitats for Hg methylators in oxygen-depleted seawater (Figure 3; Capo et al 2020). In Xu et al., we showed that local physicochemical conditions, such as pH, nutrient concentrations, water content and prevailing redox states, are important for shaping the hgcA+microbial community structure. Furthermore, we observed a significant correlation between HgII methylation rate constants and the structure of the hgcA+microbial community. Our findings expand the current knowledge on the hgcA+microbial community composition and the physicochemical factors underpinning spatial heterogeneity in such communities (Figure 4).
We have also increased current knowledge on the distribution of Hg-related genes in the deep ocean. By analysing the global deep ocean metagenomes and metatranscriptomes of the Malapasina 2010 circumnavigation, we have unveiled the biogeography and expression patterns of genes related to the Hg volatilization and MeHg degradation, merA and merB, respectively. Our results reveal that the abundance patterns of merAB are controlled by the life-style of the organisms carrying the genes. Localized effects however seem to control the merAB transcript expression (Figure 5). These results represent the first global deep ocean analysis of the merAB genes and transcripts in the marine biogeochemical Hg. This MS should be submitted before June 2021.
WP3- The activities of this WP were delayed due to the COVID-19. The experiments were carried out but not the measurements of Hg (which have to be done in France). The candidate will do measurements in the following year and will acknowledge the MC MER-CURE in the publicaiton.
WP-4- Active dissemination plan:
A (i) webpage for the Project (ii a talk in the participation in the European Night Science, at Lycée Francais (17-18 years old); (iii) a talk at the young plenary of Barcelona Sustainable Energy Days (13-14 yers old; European Commission), organised by the Government of Catalonia and the municipalities of Barcelona, (iv) a workshop at the Voramar School (9 years old children) and (v) at the Voramón school (15-16 years old children) for the International Day of Women and Girls in Science (2020) were performed within the context of MER-CURE. The fellow participated as invited talk at the workshop MISTRALS (Marseille 2018), Venecia (VENEZIA2021, November 2019), MERCLUB (Bilbao, December 2019) and at different scientific meetings such as the ICMGP2019 (Krakow, September 2019), the Canadien Ecotoxicity Workshop (invited talk, October 2019), ASLO (plenary talk at Puerto Rico, February 2019) and SEM (Málaga, July 2019). The impact of the fellow's research has been dissemiated in two radio programs: i) Las Dones de Mar, El Far (https://cutt.ly/Tx3GTA0) and ii) at the national radio (RN) “A hombros de gigantes” (https://cutt.ly/Ax3GQBW)

This project improves current knowledge about the mechanisms controlling mercury transformations in the ocean. This is particularly important as human exposure to Hg mainly occurs through marine fish consumption. This makes MER-CURE the perfect platform to position the current knowledge about the risk of mercury closer to citizens and increase its impact on society.
MERCURE searched for hgcAB, merA and merB genes in the Malaspina Deep-SeaGene Collection (MDSGC) metagenomes of the deep Sea. However, as the the Malaspina Deep-SeaGene Collection also includes samples collected at different depths of the ocean water column, Andrea G Bravo, during her new contract at the ICM-CSIC, will search for hgcAB, merA and merB genes in 17 vertical profiles of the ocean water column distributed across the globe.

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Periodic Reporting for period 1 - MER-CURE (Using global marine metagenomics to understand MERcury microbial associated processes: finding a CURE for mercury contaminated environments)

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