Enzymatic approach in microbial-influenced corrosion: a review based on stainless steels in natural waters.

The electrochemical behavior of stainless steels (SS) in natural waters is characterized by the ennoblement of their free corrosion potential (E(corr)). This phenomenon depends strongly on the settlement of biofilms on SS surfaces. Many hypotheses have been proposed to explain the biofilm action, in particular the enzymatic catalysis plays an important role by shifting the cathodic and/or anodic processes. However, there are still only few studies relating the use of purified enzymes. In contrast with bacteria-associated corrosion, the direct influence of enzymes is still poorly documented. The aim of this review is to show the benefits of the enzymatic approach in the study of biocorrosion. Indeed, enzymatic systems may constitute convenient models to mimic microbial influenced corrosion and to evaluate the behavior of metallic materials in natural waters.

Ennoblement of stainless steel in the presence of glucose oxidase: nature and role of interfacial processes.

The ennoblement of the free corrosion potential (E(corr)) of AISI 316L stainless steel which did not occur in synthetic fresh water (SFW), was observed after introduction of glucose oxidase (Gox) and glucose, or of hydrogen peroxide (H(2)O(2)). The composition of the surface was monitored using AFM and XPS, a detailed XPS analysis being based on the discrimination between oxygen of organic and inorganic nature proposed in a previous study. In H(2)O(2) medium, the main changes regarding the inorganic phase were the increase of the oxygen concentration in the passive film, the increase of the molar concentration ratio of oxidized species Fe(ox)/Cr(ox) and the growth of nanoparticles, presumably made of ferric oxide/hydroxide. In Gox medium, no significant changes were observed in both oxygen concentration and Fe(ox)/Cr(ox) ratio, but the density of colloidal particles decreased, indicating a dissolution of Fe oxide/hydroxide under the influence of gluconate. In contrast with H(2)O(2), in SFW and Gox the amount of organic compounds increased due to the accumulation of polysaccharides and proteins. The influence of glucose oxidase on the ennoblement of stainless steel is not due to indirect effects of H(2)O(2) through the change of surface composition. The E(corr) ennoblement seems to be directly due to the presence of H(2)O(2) and to the electrochemical behavior of H(2)O(2) and related oxygen species. This consideration is important for understanding and controlling microbial influenced corrosion.

Evolution of the passive film and organic constituents at the surface of stainless steel immersed in fresh water.

The evolution of the surface of a conventional stainless steel (AISI 316L) immersed in aqueous medium simulating fresh water (pH approximately 8) was studied using XPS and AFM. A detailed analysis of XPS spectra allowed a distinction to be made between oxygen of organic and inorganic nature. During the first 48 h, the main changes concern the inorganic phase: the oxygen concentration in the passive layer increases, owing both to oxidation of metal elements, including conversion of Fe(II) to Fe(III), and to hydration; the molar ratio of oxidized species Fe(ox)/Cr(ox) decreases slightly; the formation of colloidal particles, presumably made of ferric hydroxide, is observed by AFM. After longer periods of immersion, the Fe(ox)/Cr(ox) is higher, while the coating of colloidal particles reaches a full surface coverage. The amount of organic compounds increases further and the XPS spectra reveal the accumulation of polysaccharides and proteins, which indicate that these organic compounds are of biological origin.

Biodegradation of cyclic amines by a Pseudomonas strain involves an amine mono-oxygenase.

Pseudomonas putida O1G3 catalyzes the degradation of pyrrolidine and piperidine. This strain can use these compounds as the sole source of carbon, nitrogen, and energy. When the cyclic amines were used as the growth substrates, the synthesis of a soluble heme amine mono-oxygenase was induced in this bacteria. This observation was confirmed by spectrophotometric analysis and specific inhibitor. This mono-oxygenase is a NADH-dependent enzyme and catalyzes the cleavage of the C-N bond of the pyrrolidine and piperidine ring by a mechanism similar to a N dealkylation. This reaction could be followed by ring cleavage to form gamma-aminobutyraldehyde oxidized to gamma-aminobutyrate. Further investigations to purify the heme-containing mono-oxygenase are in progress.

Hemoglobin, horseradish peroxidase, and heme-bovine serum albumin as biocatalyst for the oxidation of dibenzothiophene.

Hemoglobin, horseradish peroxidase, and bovine serum albumin incubated heme-catalyzed the oxidation of dibenzothiophene into sulfoxide in the presence of hydrogen peroxide. This reaction was carried out in an aqueous buffer containing 25% of water-miscible organic solvents. The observation of this transient state of hemoproteins during sulfoxidation showed heme degradation. None of the compounds usually involved in a classical peroxidative activity mechanism were detected. Furthermore, this activity did not appear to be based on a Fenton-type reaction. The highest degrees of sulfoxidation were obtained with hemoglobin. Under the best conditions of reaction, 100% of dibenzothiophene were converted into dibenzothiophene sulfoxide by hemoglobin. Heat-denatured hemoproteins did keep their sulfoxidation activity. With hemoglobin, a kcat of 0.22 min-1 was determined. Nearly the same values were obtained with heat-denatured hemoglobin and bovine serum albumin-adsorbed heme. With horseradish peroxidase, only 4% of conversion was attained. This percentage could be slightly increased by using a less pure peroxidase or heat-denatured peroxidase.

Substrate inhibition or activation kinetics of the beta-galactosidase from the extreme thermoacidophile archaebacterium Caldariella acidophila.

The kinetics of the hydrolysis of p-nitrophenyl-beta-D-galactopyranoside (pNPG) by a thermophile, beta-galactosidase, was studied at different temperatures. This enzyme was isolated from the thermophilic microorganism archaebacterium Caldariella acidophila. The hydrolysis of pNPG by beta-galactosidase does not follow Michaelis-Menten law. This enzyme is inhibited by excess substrate at low temperatures and it is activated by excess substrate at high temperatures. A minimum mechanistic model is proposed to explain the behaviour. This model assumes the binding of an additional substrate molecule on the glycosidyl enzyme intermediate. This model is in good agreement with the postulated mechanism for beta-galactosidase from Escherichia coli. The kinetic parameters are calculated at six different temperatures.

Reactivation of the hydrogenase from Desulfovibrio gigas by hydrogen. Influence of redox potential.

The specific activity of the periplasmic hydrogenase from Desulfovibrio gigas is increased approximately 10-fold in the H2 utilization assay with benzyl viologen by several hours of incubation under an atmosphere of H2. After a variable lag phase during which residual traces of O2 are removed, the reversible activation is exponential. The extent of activation is dependent on pH and the redox potential of the incubation medium. A tentative model based on the existence of a monoelectronic redox center is proposed as shown in the following equation: (formula; see text) The potential of this redox couple was determined to be -310 mV (pH = 7; T = 298 K) versus the normal hydrogen electrode.