Periodic Reporting for period 1 - GMOS-Train (Global Mercury Observation and Training Network in Support to the Minamata Convention)
Reporting period: 2020-01-01 to 2021-12-31
Mercury biogeochemical cycles in environment are dynamic and complex leading to the formation of various mercury species. Gaseous elemental mercury (GEM) is emitted to the atmosphere from both, anthropogenic and natural sources. Hg0 when released into the atmosphere, can lose electrons via redox reactions to form positively charged ions, also known as inorganic mercury (Hg2+). The atmospheric deposition of Hg2+ adds up to global emissions enriched by the cumulative history of anthropogenic emissions. Inorganic mercury (Hg2+) which falls in wet and dry deposition, is transported to the lakes and oceans in runoff and delivered to the bottom of the sea. The inorganic mercury (Hg2+) can convert into toxic methylmercury (MeHg) under anoxic conditions in the deep ocean. Anoxic condition results from high oxygen utilization in the bottom layers of the sea, where the primary production of the ecological pyramid occurs. Inorganic mercury (Hg2+) conversion into MeHg in the ocean environment is mainly driven by anaerobic microorganisms such as sulfate-reducing bacteria (SRB). Biogeochemical cycle of mercury with special relevance to methylmercury is depicted in Figure 1.1. MeHg is formed biotically when sulfate-reducing bacteria (SRBs) add a methyl group to inorganic mercury (Hg2+).
Methylation of Hg2+ requires two genes from the sulfate-reducing bacteria (SRBs). The two genes hgcA and hgcB in Figure 1.2. Indicate various redox states of the corrinoid HgcA enzyme. HgcAB gene is involved in C1 metabolism and the acetyl-CoA pathway. The Acetyl-CoA pathway is a predominant glucose metabolism of sulfate-reducing bacteria [5, 6]. The gene hgcA encodes a coronoid protein that is essential for the biosynthesis of the folate branch of the acetyl-CoA pathway, whereas the gene hgcB encodes a ferredoxin-like protein and is an electron donor to hgcA [6] One-carbon (1C) metabolism comprises a series of interlinking metabolic pathways that include the methionine and folate cycles that are central to cellular function, providing 1C units (methyl group) for the synthesis of DNA, polyamines, amino acids, creatine, and phospholipids.
Health effects of MeHg
MeHg, bioaccumulated and biomagnified via predatory fish reaches the plate of humans. In most developed and third-world countries, fish is the only source of protein for billions of people. MeHg plays a molecular mimicry and disguises itself as methionine after entering the human body. Methionine is the start codon for the so-called “central dogma of life” where DNA transcribed into RNA and RNA translated into proteins. Hence MeHg is a translational inhibitor, which stops the synthesis of all major proteins in the body. Low doses of MeHg can have serious possible harmful effects on the cardiovascular, immune, and reproductive systems. Methylmercury affects the central nervous system, kidneys, and liver and can disturb immune processes; cause tremors, impaired vision and hearing, paralysis, insomnia, and emotional instability. During pregnancy, MeHg crosses the placental barrier and can interfere with the development of the fetus, and cause attention deficit and developmental delays during childhood.
The main objective of ESR 11 is to understand the process of sensor development, which involves interdisciplinary topics and includes some knowledge from material and nanomaterial science, photonics, chemicals, optical indicators, and biology. The main goal of this work is to design a nano-biosensor for MeHg detection.
Methylation of Hg2+ requires two genes from the sulfate-reducing bacteria (SRBs). The two genes hgcA and hgcB in Figure 1.2. Indicate various redox states of the corrinoid HgcA enzyme. HgcAB gene is involved in C1 metabolism and the acetyl-CoA pathway. The Acetyl-CoA pathway is a predominant glucose metabolism of sulfate-reducing bacteria [5, 6]. The gene hgcA encodes a coronoid protein that is essential for the biosynthesis of the folate branch of the acetyl-CoA pathway, whereas the gene hgcB encodes a ferredoxin-like protein and is an electron donor to hgcA [6] One-carbon (1C) metabolism comprises a series of interlinking metabolic pathways that include the methionine and folate cycles that are central to cellular function, providing 1C units (methyl group) for the synthesis of DNA, polyamines, amino acids, creatine, and phospholipids.
Health effects of MeHg
MeHg, bioaccumulated and biomagnified via predatory fish reaches the plate of humans. In most developed and third-world countries, fish is the only source of protein for billions of people. MeHg plays a molecular mimicry and disguises itself as methionine after entering the human body. Methionine is the start codon for the so-called “central dogma of life” where DNA transcribed into RNA and RNA translated into proteins. Hence MeHg is a translational inhibitor, which stops the synthesis of all major proteins in the body. Low doses of MeHg can have serious possible harmful effects on the cardiovascular, immune, and reproductive systems. Methylmercury affects the central nervous system, kidneys, and liver and can disturb immune processes; cause tremors, impaired vision and hearing, paralysis, insomnia, and emotional instability. During pregnancy, MeHg crosses the placental barrier and can interfere with the development of the fetus, and cause attention deficit and developmental delays during childhood.
The main objective of ESR 11 is to understand the process of sensor development, which involves interdisciplinary topics and includes some knowledge from material and nanomaterial science, photonics, chemicals, optical indicators, and biology. The main goal of this work is to design a nano-biosensor for MeHg detection.
ESR 11 have taken up additional deliverable of developing nanomaterials for adsorption of Hg2+ and MeHg. ESR has completed the deliverable. One research article titled “Removal of Pb2+, Cr3+ and Hg2+ ions from aqueous solutions using SiO2 and amino-functionalized SiO2 particles” is submitted Sol-gel science and technology Journal, and the article is under review. (Figure 2)
Another article titled removal of Pb2+, Cr6+, Co2+ and Hg2+ ions from aqueous solutions using amino-functionalized magnetic nanoparticles is also completed. ESR 11 is a co-author, and we plan to submit it in the Separation and purification technology Journal.
Fig 2
The next deliverable is to develop a nano-biosensor for detecting MeHg in various environmental matrices; we have decided our receptor of the biosensor to be Mer B protein (Organomercurial lyase) that are generally present in bacteria such as desulfovibrio desulfuricans that reduces methylmercury (MeHg) to Hg2+ in the aquatic environment. We will clone, express, purify, and characterize Mer B and Mer A protein for this approach. The Mer B and Mer A gene's source gene will be from MerB Rluc plasmid and R100 plasmid in Dr Aleš Lapenje laboratory. The MerBRluc plasmid and R100 plasmid in their respective E.coli strains will be used as a source for the Mer B gene and Mer A gene, respectively.
Structure of the plasmid pmerBRBSluc. Abbreviations used: amp, gene-encoding ampicillin resistance; Plac, lac promoter; merB, organomercurial lyase gene; merR, gene-encoding repressor/activator of the mer promoter; PmerR, merR promoter; Pmer, promoter of mer operon; lucFF, gene-encoding firefly luciferase Fig 3.
Fig 4
Fig 5. a, 5. b
Fig 6
Another article titled removal of Pb2+, Cr6+, Co2+ and Hg2+ ions from aqueous solutions using amino-functionalized magnetic nanoparticles is also completed. ESR 11 is a co-author, and we plan to submit it in the Separation and purification technology Journal.
Fig 2
The next deliverable is to develop a nano-biosensor for detecting MeHg in various environmental matrices; we have decided our receptor of the biosensor to be Mer B protein (Organomercurial lyase) that are generally present in bacteria such as desulfovibrio desulfuricans that reduces methylmercury (MeHg) to Hg2+ in the aquatic environment. We will clone, express, purify, and characterize Mer B and Mer A protein for this approach. The Mer B and Mer A gene's source gene will be from MerB Rluc plasmid and R100 plasmid in Dr Aleš Lapenje laboratory. The MerBRluc plasmid and R100 plasmid in their respective E.coli strains will be used as a source for the Mer B gene and Mer A gene, respectively.
Structure of the plasmid pmerBRBSluc. Abbreviations used: amp, gene-encoding ampicillin resistance; Plac, lac promoter; merB, organomercurial lyase gene; merR, gene-encoding repressor/activator of the mer promoter; PmerR, merR promoter; Pmer, promoter of mer operon; lucFF, gene-encoding firefly luciferase Fig 3.
Fig 4
Fig 5. a, 5. b
Fig 6
The nanobiosensor should be very sensitive to detect picogram/per liter of MeHg in the presence of nanogram/liter of total mercury concentration with predominant interference from Hg2+. The sensor should overcome interference of various minerals and salts and trace amount of other metals. The sample will be collected on the cruise campaign in various locations in the sea which makes the seawater sample different in pH, temperature, conductivity, salinity, turbidity and MeHg concentration. To the best of our knowledge there is no sensor that can real-time detect the MeHg in seawater. A lot of validation and customization has to be done for successful development of the portable nano biosensor. Given all the above scenarios we have challenging task ahead of us to develop nanobiosensor for MeHg detection.
At IOS, we have developed functionalized silica, cobalt ferrite and iron oxide nanoparticles that can adsorb or mask the interferences from other metals and Hg2+, enabling more efficient detection of MeHg. The adsorption of MeHg, Hg2+ using the functionalized nanoparticles is under investigation
We are planning to collaborate with the materials research group or an electrical engineering research group that have a custom made instrument that can very precisely and specifically measure electrical voltage difference in the MerB protein functionalized nanomaterial matrix that we will built.
ESR 11 have presented a lecture on state of the art sensors to detect MeHg in various environmental matrices to the Master's graduate students to the Department of Human Biology, Madurai Kamaraj University, Madurai, India.
At IOS, we have developed functionalized silica, cobalt ferrite and iron oxide nanoparticles that can adsorb or mask the interferences from other metals and Hg2+, enabling more efficient detection of MeHg. The adsorption of MeHg, Hg2+ using the functionalized nanoparticles is under investigation
We are planning to collaborate with the materials research group or an electrical engineering research group that have a custom made instrument that can very precisely and specifically measure electrical voltage difference in the MerB protein functionalized nanomaterial matrix that we will built.
ESR 11 have presented a lecture on state of the art sensors to detect MeHg in various environmental matrices to the Master's graduate students to the Department of Human Biology, Madurai Kamaraj University, Madurai, India.