Ennoblement of Stainless Steel by the Manganese-Depositing Bacterium Leptothrix discophora

Abstract

The noble shift in open-circuit potential exhibited by microbially colonized stainless steel (ennoblement) was investigated by examining the relationship among surface colonization, manganese deposition, and opencircuit potential for stainless steel coupons exposed to batch cultures of the manganese-depositing bacterium Leptothrix discophora. Open-circuit potential shifted from ؊100 to ؉330 mV SCE as a biofilm containing 75 nmol of MnO x cm ؊2 formed on the coupon surface but changed little further with continued MnO x deposition up to 270 nmol cm ؊2. Increased open-circuit potential corresponded to decreasing Mn(II) concentration in solution and to increased MnO x accumulation and attached cell density on the coupon surfaces. MnO x deposition was attributable to biological activity, and Mn(II) was observed to enhance cell attachment. The experimental results support a mechanism of ennoblement in which open-circuit potential is fixed near ؉350 mV SCE by the cathodic activity of biomineralized MnO x .

Occurrence of manganese-oxidizing microorganisms and manganese deposition during biofilm formation on stainless steel in a brackish surface water

“…In our experiments, manganese concentrations were 10-fold higher : manganese concentrations up to 30 Wg Mn cm 32 were retrieved after a total exposure time to fresh £owing water of about 4 weeks (Table 5). In the case of Dickinson et al [44], however, this open-circuit potential changed little further with continued MnO x biodeposition up to 15 Wg Mn cm 32 . The fact that Dickinson et al [44] investigated the mineral deposition of a pure culture made it more probable that these manganese oxides were deposited in direct contact with the steel.…”

“…In the case of Dickinson et al [44], however, this open-circuit potential changed little further with continued MnO x biodeposition up to 15 Wg Mn cm 32 . The fact that Dickinson et al [44] investigated the mineral deposition of a pure culture made it more probable that these manganese oxides were deposited in direct contact with the steel. In our case also other microorganisms can initially adhere to the steel surface or other organic/inorganic deposits may be formed preventing a direct contact between the manganese oxide and the steel.…”

“…Linhardt [47] stated that even minute amounts of MnO 2 at the surface might have considerable in£uence on the E corr of the stainless steel. In their experiments, Dickinson et al [44] found the open-circuit potential to shift from 390 to +340 mV AgaAgCl as a bio¢lm containing 75 nmol of MnO x cm 32 (comparable to 4.1 Wg Mn cm 32 ) formed on the coupon surface. In our experiments, manganese concentrations were 10-fold higher : manganese concentrations up to 30 Wg Mn cm 32 were retrieved after a total exposure time to fresh £owing water of about 4 weeks (Table 5).…”

Induction of pitting corrosion on stainless steel (grades 304 and 316) used in dairy industry by biofilms of common sporeformers

“…A complete absence of chromium and nickel, which are the major alloy elements in austenitic steel, was noticed. Such corrosion could have been caused by any one or combination of the cathodic and anodic activity, leading to changes in metal surface electrochemistry, by changed surface film resistivity or by localised acidic conditions (Dickinson et al 1997). Other modes of action could have been the formation of a live galvanic cell that had redox reactions occurring on the surface of the SS coupon, or due to the production of metabolic products such as enzymes, organic acids and hydrogen sulphide on the surface.…”

Relationship between the ennoblement of passive metals and microbe adsorption kinetics in seawater

“…Microbial colonization of passive metals can shift the corrosion potential in the noble direction. The phenomena, known as ennoblement, have been variously ascribed to depolarization of the oxygen reduction reaction [4], manganese-depositing bacteria [5,6], enzymes mechanisms [7], H 2 O 2 produced by marine microorganisms in native biofilms [8] etc. All the work confirms that attached biofilm is the reason for the ennoblement of passive metals.…”