Guest Seminar: In situ monitoring of exopolymer-dependent Mn mineralization on bacterial surfaces

You are invited to join us for a seminar from Dr. Thaïs Couasnon titled: “In situ monitoring of exopolymer-dependent Mn mineralization on bacterial surfaces”


Bacterial biomineralization is a widespread process that largely impacts and has impacted the cycling of metals in present and past environments. Functionalized bacterial cell surfaces and exopolymers secreted by bacteria are suspected to play a key role as nucleation template initiating mineral formation. However, direct evidence of these mechanisms is hampered by technical challenges. Here, we present breakthrough in the use of liquid-cell scanning transmission electron microscopy to directly observe mineral growth onto bacteria and the exopolymers they secrete. Two Escherichia coli mutants are investigated, that form either proteinaceous conjugative F pili at the cell surface, or overexpress extracellular cellulose formation. We use the incident electron beam to provoke and observe the precipitation of Mn-bearing minerals without any additional contrasting agent. Differences in precipitate morphology and distribution likely reflect differences in nucleation site density and accessibility between the two strains, with the dense extracellular cellulose layer partly inhibiting nucleation at the cell surfaces. Direct observation in liquid conditions highlights the critical role of cell surface charges and exopolymers types in metal mineralization. This has strong environmental implications since biofilms structured by exopolymers are widespread and constitute the main form of microbial life on Earth.


Dr. Thais Couasnon is a Postdoctoral researcher in Interface Geochemistry, at GeoForshungZentrum. 2015 - 2019 - Ph.D. in Earth and Environmental Science: "Role of reactive oxygen species and substances exopolymeric bacteria in the process of biomineralization of manganese". Studied at Institut de Physique du Globe de Paris (IPGP), Paris, France. Advisors: Alexandre Gélabert and Bénédicte Ménez. Received an award of International mobility funding 2017, Université Sorbone Paris Cité. 


Couasnon, T., Gélabert, A., Ona-Nguema, G., Zanna, S., Ménez, B., Guyot, F. (2019): Experimental assessment of occurrences and stability of lead-bearing minerals in bacterial biofilms. - Chemical Geology, 505, pp. 23-35.