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Abstract Title: Proof of Concept for Aerobic Mercury Methylation by Sulfate Reducing Bacteria
Presenter Name: Dmitrii Deev
Company/Institution: Jožef Stefan Institute
Session: Special Session - Meta-omic and geochemical approaches to linking microbial activity to biogeochemical mercury cycling
Day and Session: Friday 29th July - Session Two
Start Time: 09:30 UTC
Co-Authors: Dmitrii Deev

Abstract Information :

Microorganisms such as sulfate-reducing bacteria (SRB) are the main contributors to methylmercury (MeHg) synthesis in ocean ecosystems. Until recently, microbial methylation was assumed to be an anaerobic process and restricted to the anoxic niches in sediments.
However, some studies showed MeHg formation in aerated conditions such as open oceans. According to the microbiological niche hypothesis, interaction of microorganisms in multicellular structures might result in the formation of anaerobic conditions due to the oxygen depletion by aerobic or facultative anaerobic bacteria, we can expect that SRBs might form stable multicellular structures. Studying these structures will improve our knowledge of mercury methylation in aerobic environments.
To prove the concept, we have developed a synthetic approach for constructing aggregates containing two-species by the method developed in the colloid biology laboratory. Here we prepared specific aggregates consisting of cells of the Desulfovibrio africanus and the common marine representative Cobetia marina. The anaerobic activity in the aggregates was tested qualitatively by culturing in specific media. Structural changes in aggregates over time were studied using fluorescent and confocal microscopy. MeHg production was determined by spiking 50ml of nutrient medium with 500pg of HgCl2 and cultivation for 24 h. Samples were digested in 4? HNO3, mercury species were ethylated with sodium tetraethylborate and the amount of MeHg produced was determined by the cold vapor atomic fluorescence spectroscopy.
The results showed that the aggregates in batch reactors retained their activity for up to ten days. The microscopic analysis also showed the self-organization of structures, where D. africanus occupying an anaerobic niche in the core, while C. marina is present superficially. According to our predictions, we observed the methylating activity in aerobic conditions. The conversion rate from the initial concentration of added inorganic mercury was 0.9ñ0.2%, which is 67.4% less than the values strict anaerobiotic conditions.

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