Iron corrosion by methanogenic archaea characterized by stable isotope effects and crust mineralogy

Carbon and hydrogen stable isotope effects associated with methane formation by the corrosive archaeon Methanobacterium strain IM1 were determined during growth with hydrogen and iron. Isotope analyses were complemented by structural, elemental and molecular composition analyses of corrosion crusts. During growth with H-2, strain IM1 formed methane with average delta C-13 of -43.5 parts per thousand and delta H-2 of -370 parts per thousand. Corrosive growth led to methane more depleted in C-13, with average delta C-13 ranging from -56 parts per thousand to -64 parts per thousand during the early and the late growth phase respectively. The corresponding delta H-2 were less impacted by the growth phase, with average values ranging from -316 to -329 parts per thousand. The stable isotope fractionation factors, alpha 13CCO2/CH4, were 1.026 and 1.042 for hydrogenotrophic and corrosive growth respectively. Corrosion crusts formed by strain IM1 have a domed structure, appeared electrically conductive and were composed of siderite, calcite and iron sulfide, the latter formed by precipitation of sulfide (from culture medium) with ferrous iron generated during corrosion. Strain IM1 cells were found attached to crust surfaces and encrusted deep inside crust domes. Our results may assist to diagnose methanogens-induced corrosion in the field and suggest that intrusion of sulfide in anoxic settings may stimulate corrosion by methanogenic archaea via formation of semiconductive crusts.

Automated summary

The research focused on the stable carbon and hydrogen isotope effects associated with methane formation by the corrosive archaeon Methanobacterium strain IM1 during growth with hydrogen and iron. The growth resulted in methane with depleted C-13 values, while H-2 values were less impacted by growth phase. The corrosion crusts formed were composed of siderite, calcite, and iron sulfide, with attached cells found on crust surfaces and deep inside crust domes.