Process of Corrosion & How Microbes Indirectly & Directly Corrode Metals | GEO GIRL

In this video, we dive deep into the processes of corrosion! Corrosion is the degradation of metal typically due to oxidation. Metals can be corroded abiotically or biologically. Bacteria and fungi speed up corrosion. But how do microbes contribute to corrosion? Well, the role that microbes play can be either direct or indirect. Indirectly, microbial byproducts may be corrosive and subsequently abiotically corrode any material in contact with the microbial community releasing the byproducts. On the other hand, many microbial enzymes can corrode material directly. Another direct pathway is if microbes produce EPS or biofilms which facilitate electron flow, which facilitate oxidation of the metal, which corrodes the metal. Microbes aren't just accidentally excreting these materials, most of the time they are producing these extracellular substances for the purpose of sequestering important nutrients (like Fe) or for developing a biofilm community that creates their own microenvironmental conditions favorable for growth. Different groups of bacteria corrode different types of material depending on their metabolism. S and N oxidizing bacteria corrode sulfur and nitrogen containing materials. Fe and Mn oxidizing bacteria corrode iron and manganese containing materials. But do bacteria that have reducing metabolisms corrode material if corrosion is oxidation? Yes! In fact, sulfate reducing bacteria (SRB) are some of the most corrosive bacteria because they produce hydrogen sulfide which can then react with water and oxygen to produce sulfuric acid which is highly corrosive. The sulfide can also react with Fe to form Fe sulfides which also corrodes the material. They also can produce protons with their hydrogenase enzymes which corrode material in anoxic environments. Nitrate reducing, methanogenic, Fe reducing bacteria also corrode. Fungi also corrode by producing organic acids and tolerating such extreme conditions.

References: Geomicrobiology: https://amzn.to/2WAloTR
Biology of Microorganisms: https://amzn.to/3kQqIuD

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0:00 Video outline
1:18 What is corrosion?
3:08 O2 is not the only corroding oxidant
3:57 microbial role in corrosion
7:11 S, Fe, N, and Mn corroding bacteria
9:50 Sulfate reducing bacterial corrosion
12:30 Other reducing bacteria (NO3, Fe, CO2)
13:00 Fungal corrosion
14:12 Upcoming videos & references

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