Proteus mirabilis is a human pathogen able to form biofilms on the surface of urinary catheters. Little is known about P. mirabilis biofilms on natural or industrial surfaces and the potential consequences for these settings. The main aim of this work was to assess and compare the adhesion and biofilm formation of P. mirabilis strains from different origins on chitin and stainless steel surfaces within 4 to 96 h. Using environmental scanning electron microscopy, the biofilms of a clinical strain grown on chitin at 4 h showed greater adhesion, aggregation, thickness, and extracellular matrix production than those grown on stainless steel, whereas biofilms of an environmental strain had less aggregation on both surfaces. Biofilms of both P. mirabilis strains developed different structures on chitin, such as pillars, mushrooms, channels, and crystalline-like precipitates between 24 and 96 h, in contrast with flat-layer biofilms produced on stainless steel. Significant differences (p < 0.05) were found in the frequency of pillars and channels. Images of transmission electron microscopy demonstrated abundant fimbriae in 100 % of cells from both strains, which could be related to surface adherence and biofilm formation. This represents the first study of P. mirabilis showing adhesion, biofilm formation, and development of different structures on surfaces found outside the human host.

This study was undertaken to evaluate cathodic depolarization as the action mechanism triggered by sulfate-reducing bacteria (SRB) in microbiologically induced corrosion (MIC), using an inert substrate such as a 1-mm thick Pd foil with and without cathodic polarization, a H 0 permeation conventional Devanathan-type cell, and the bacteria Desulfovibrio desulfuricans subsp. desulfuricans ATCC 7757. The permeation tests were run using a deaerated sterile culture medium inoculated or not with 10% D. desulfuricans at 10 8 cell/mL. Serial dilution was used to evaluate the bacterial growth, and scanning electron microscopy (SEM) was used to analyze the characteristics of the biofilm and products formed on the Pd foil. Results indicated bacterial growth on the order of 4 ¥ 10 10 CFU/mL at 24 h in both polarization and nonpolarization tests, and hydrogen permeation tests without cathodic polarization determined that there were no conditions for the reduction of the H + generated by hydrogen sulfide (H 2 S) dissociation. These results show that these bacteria develop similarly, whether or not they are on a polarized surface as a source of H 0 , generating H 2 S as a product of sulfate-dissimilating activity. Furthermore, hydrogen permeation tests with cathodic polarization determined an increase in the permeation current, which was associated with the maximum enzymatic activity phase of the bacteria. This good SRB development with cathodic polarization could be an indication that cathodic protection does not control MIC problems.

Alloy Cu-10% Ni (ASTM B-111, UNS C70600) has been used extensively for condenser and heat exchanger tubes in power stations. However, there have been cases of severe localized corrosion in this alloy. This paper presents the evaluation of Cu-10% Ni in a dynamic online monitoring system with oneway circulation using alkaline (pH 7.2 to pH 8.8) brackish water with and without chlorination for 3-, 8-, and 12-month exposure periods. Electrochemical laboratory tests-opencircuit potential (OCP), linear polarization resistance (LPR), and cyclic polarization (CP)-also were run. Before chlorination, the microbiological water analysis indicated microbial development with planktonic and sessile sulfate-reducing bacteria (SRB) on the order of 10 7 cells/mL and 10 5 cells/mL, respectively, with sessile SRB at 10 cells/mL after chlorina- tion. Prechlorination scanning electron microscopy (SEM)/ energy dispersive x-ray (EDX) analysis/x-ray diffraction (XRD) analysis after 3 months revealed very few cuprite (Cu 2 O) crystals and bacterial cells, whereas dense cell populations associated with hemispheric holes typical of microbiologically influenced corrosion (MIC) were found after 8 months. Postchlorination SEM/EDX/XRD analysis helped establish a definition of how chlorine increases the Cu-10%Ni corrosion rate. Initially, a dense layer of star-shaped Cu 2 O crystals was observed. It later was removed partly because it quickly oxidized into nonprotective, nonadherent secondary corrosion products, which again exposed the material to the hypochlorite ions in the corrosive medium, consequently forming a new layer of Cu 2 O. The formation of different corrosion products and redeposited copper with severe localized corrosion below the deposits and severe general corrosion finally were shown by the analysis of a tube that was in service for 3 years in the same chlorinated, brackish water. CP curves indicated that chlorine content increased the corrosion current from 2.5 µA/cm 2 per 0.0 ppm Cl 2 to 5.0 µA/cm 2 per 0.3 ppm Cl 2 , and that Cu-10% Ni is not passivated in this brackish water. All these results suggest that this alloy is not corrosion resistant in brackish water, and chlorine treatment accelerates corrosion even more.

The mechanism of microbiologically infl uenced corrosion (MIC) on carbon steel (CS) by the bacteria Desulfovibrio desulfuricans subs. desulfuricans was studied using hydrogen permeation, open-circuit potential, and cathodic polarization techniques, in a concentrated culture medium containing bacteria cells (10 7 cell/mL) and ferrous ions (300 mg/L) designed to simulate a condition common in systems for the secondary recovery of crude oil, characterized by highly contaminated microenvironments that severely corrode iron alloys in a short time period. This research project was carried out using several 24-h experiments to defi ne initial stages of the corrosive process under the conditions indicated. The results evidenced a hydrogen permeation current peak of about 12 µA correlated with a minimum open-circuit potential of -780 mV vs saturated calomel electrode (SCE), 400 min after inoculation. Next, the permeation current decreased abruptly to its base line and the potential increased, stabilizing at -585 mV SCE at 24 h, a condition that is associated with high, similar bacterial activity both with and without cathodic polarization (10 8 CFU/mL and 10 9 CFU/mL), typical hydrogen sulfi de (H 2 S) attack morphology, and a weak iron sulfi de fi lm. These results using CS as the corrodible material, together with those obtained using a palladium strip as previously reported, show defi nitely that the cathodic depolarization theory does not represent the chief mechanism used by D. desulfuricans in the MIC process, whereas sulfi de corrosion together with iron sulfi de products seem to better explain the mechanism of this severe bacterial corrosion problem.KEY WORDS: biofi lms, carbon steel, cathodic depolarization, Desulfovibrio desulfuricans, hydrogen permeation, microbiologically infl uenced corrosion, sulfate-reducing bacteria, sulfi de corrosion

The microbiologically influenced corrosion (MIC) of water injection systems by sulphate‐reducing prokaryotes (SRP) has caused many problems in the oil industry. These prokaryotes produce H2S, which reacts aggressively with steel and is thus widely considered to be the main cause of bacterial corrosion of industrial oil equipment. However, current microbiological treatments and controls have not taken into account other groups of sulphidogenic prokaryotes, which also produce H2S or its derivatives and with the same adverse effects of MIC. In the present work, sulphidogenic prokaryotes were isolated from water injection systems and identified by DNA sequencing. The identified species included sulphate‐reducing Desulfovibrio termitidis and non‐sulphate‐reducing Escherichia coli. Biocorrosion tests were carried out on API 5L grade X65 carbon steel. Electrochemical impedance spectroscopy, polarisation resistance, open circuit potential and weight loss were carried out. Steel corrosion resulting from the production of the metabolite H2S by SRP and non‐SRP was observed, with sulphide generation by SRP much greater than that by non‐SRP. These results confirm the need to investigate and consider the role of not only SRP but also non‐SRP in order to improve the control over bacterial corrosion of oil‐industry equipment.