The use of biocides to control sulphate‐reducing bacteria in biofilms on mild steel surfaces

Three different types of biocides, viz. formaldehyde (FM), glutaraldehyde (GA) and isothiozolone (ITZ) were used to control planktonic and sessile populations of two marine isolates of sulphate‐reducing bacteria (SRB). The influence of these biocides on the initial attachment of cells to mild steel surfaces, on subsequent biofilm formation and on the activity of hydrogenase enzymes within developed biofilms was evaluated. In the presence of biocides the rate and degree of colonization of mild steel by SRB depended on incubation time, bacterial isolate and the type of biocide used. Although SRB differed in their susceptibility to biocides, for all isolates the biofilm population was more resistant to the treatment than the planktonic population. GA showed highest efficiency in controlling planktonic and sessile SRB compared with the other two biocides. The activity of the enzyme hydrogenase measured in SRB biofilms varied between isolates and with the biocide treatment. No correlation was found between the number of sessile cells and hydrogenase activity.     

Extracellular polysaccharides from Desulfovibrio desulfuricans and Pseudomonas fluorescens in the presence of mild and stainless steel

Summary This communication reports the presence of polysaccharides in biofilms formed by pure and mixed cultures of Desulfovibrio desulfuricans and Pseudomonas fluorescens on mild and stainless steel surfaces. The results of colorimetric assays, indicating significant differences between the amounts of neutral sugars present in these biofilms, were supported by gas chromatographic (GC)-mass spectrophotometric and GC-flame ionisation detection analyses. Neutral sugars in biofilms grown on mild steel surfaces were identified and quantified, revealing glucose as a major carbohydrate followed by mannose and galactose in all types of biofilm. Extracellular polymeric substances (EPS) precipitated from bacterial cultures grown with and without steel surfaces were also analysed for their carbohydrate content. The influence of the surfaces present in the cultures on the amount and type of sugars released into the bulk phase was established. There was significantly more carbohydrate in EPS harvested from pure and mixed cultures of D. desulfuricans incubated mild and stainless steel coupons than in EPS obtained from coupon-free cultures. No significant difference in sugar quantities was observed in EPS precipitated from cultures of P. fluorescens grown under different conditions (absence or presence of steel surfaces). The main carbohydrates identified in all types of EPS samples were mannose, glucose and galactose in order of prevalence. Offprint requests to: I. B. Beech     

Inhibiting sulfate-reducing bacteria in biofilms on steel with antimicrobial peptides generated in situ

In batch and continuous fermentations, the reduction in corrosion of SAE 1018 mild steel and 304 stainless steel caused by inhibition of the reference sulfate-reducing bacterium (SRB) Desulfovibrio vulgaris by a protective, antimicrobial-producing Bacillus brevis biofilm was investigated. The presence of D. vulgaris produced a thick black precipitate on mild steel and a higher corrosion rate in batch cultures than that seen in a mono-culture of non-antimicrobial-producing Pseudomonas fragi K upon the addition of SRB to the aerobic P. fragi K biofilm. In continuous reactors, the polarization resistance R _p decreased for stainless steel and increased for mild steel upon the addition of SRB to a P. fragi K biofilm. Addition of either 200 μg/ml ampicillin, chloramphenicol, or ammonium molybdate to batch and continuous reactors after SRB had colonized the metal was ineffective in killing SRB, as inferred from the lack of change in both R _p and the impedance spectra. However, when ampicillin was added prior to SRB colonization, the growth of SRB was completely inhibited on stainless steel in continuous reactors. Prior addition of ampicillin was only able to delay the growth of SRB on mild steel in continuous reactors. External addition of the purified peptide antimicrobial agent gramicidin S prior to the addition of SRB also inhibited the growth of SRB on stainless steel in continuous reactors, and the SRB were also inhibited on stainless steel in both batch and continuous reactors by producing gramicidin S in situ in a protective biofilm when the gramicidin-S-overproducing strain Bacillus brevis 18 was used. Received: 29 October 1998 / Received revision: 18 February 1999 / Accepted: 26 February 1999     

The corrosion behaviour of galvanized steel in cooling tower water containing a biocide and a corrosion inhibitor

The corrosion behaviour of galvanized steel in cooling tower water containing a biocide and a corrosion inhibitor was investigated over a 10-month period in a hotel. Planktonic and sessile numbers of sulphate reducing bacteria (SRB) and heterotrophic bacteria were monitored. The corrosion rate was determined by the weight loss method. The corrosion products were analyzed by energy dispersive X-ray spectroscopy and X-ray diffraction. A mineralized, heterogeneous biofilm was observed on the coupons. Although a biocide and a corrosion inhibitor were regularly added to the cooling water, the results showed that microorganisms, such as SRB in the mixed species biofilm, caused corrosion of galvanized steel. It was observed that Zn layers on the test coupons were completely depleted after 3?months. The Fe concentrations in the biofilm showed significant correlations with the weight loss and carbohydrate concentration (respectively, p?<?0.01 and p?<?0.01).     

Mitigation of the corrosion-causing Desulfovibrio desulfuricans biofilm using an organic silicon quaternary ammonium salt in alkaline media simulated concrete pore solutions

Abstract

Organic silicon quaternary ammonium salt (OSA), an environmentally friendly naturally occurring chemical, was used as a bacteriostatic agent against sulphate-reducing bacteria (SRB) on a 20SiMn steel surface in simulated concrete pore solutions (SCP). Four different media were used: No SRB (NSRB), No SRB and OSA (NSRB?+?OSA), With SRB (WSRB), With SRB and OSA (WSRB?+?OSA). After biofilm growth for 28 days, optimized sessile SRB cells survived at the high pH of 11.35 and as a result these cells caused the breakdown of the passive film due to the metabolic activities of the SRB. Corrosion prevention results showed that the OSA was effective in mitigating the growth of the sessile SRB cells and reduced corrosion in the SCP. These results were further confirmed by scanning electron microscope images, energy dispersive X-ray analysis, confocal-laser scanning microscopy, X-ray photoelectron spectroscopy and corrosion testing using electrochemical analysis.     

Inhibiting mild steel corrosion from sulfate-reducing bacteria using antimicrobial-producing biofilms in Three-Mile-Island process water

Biofilms were used to produce gramicidin S (a cyclic decapeptide) to inhibit corrosion-causing, sulfate-reducing bacteria (SRB). In laboratory studies these biofilms protected mild steel 1010 continuously from corrosion in the aggressive, cooling service water of the AmerGen Three-Mile-Island (TMI) nuclear plant, which was augmented with reference SRB. The growth of both reference SRB (Gram-positive Desulfosporosinus orientis and Gram-negative Desulfovibrio vulgaris) was shown to be inhibited by supernatants of the gramicidin-S-producing bacteria as well as by purified gramicidin S. Electrochemical impedance spectroscopy and mass loss measurements showed that the protective biofilms decreased the corrosion rate of mild steel by 2- to 10-fold when challenged with the natural SRB of the TMI process water supplemented with D. orientis or D. vulgaris. The relative corrosion inhibition efficiency was 50–90% in continuous reactors, compared to a biofilm control which did not produce the antimicrobial gramicidin S. Scanning electron microscope and reactor images also revealed that SRB attack was thwarted by protective biofilms that secrete gramicidin S. A consortium of beneficial bacteria (GGPST consortium, producing gramicidin S and other antimicrobials) also protected the mild steel.     

Extracellular Electron Transfer Is a Bottleneck in the Microbiologically Influenced Corrosion of C1018 Carbon Steel by the Biofilm of Sulfate-Reducing Bacterium Desulfovibrio vulgaris

Carbon steels are widely used in the oil and gas industry from downhole tubing to transport trunk lines. Microbes form biofilms, some of which cause the so-called microbiologically influenced corrosion (MIC) of carbon steels. MIC by sulfate reducing bacteria (SRB) is often a leading cause in MIC failures. Electrogenic SRB sessile cells harvest extracellular electrons from elemental iron oxidation for energy production in their metabolism. A previous study suggested that electron mediators riboflavin and flavin adenine dinucleotide (FAD) both accelerated the MIC of 304 stainless steel by the Desulfovibrio vulgaris biofilm that is a corrosive SRB biofilm. Compared with stainless steels, carbon steels are usually far more prone to SRB attacks because SRB biofilms form much denser biofilms on carbon steel surfaces with a sessile cell density that is two orders of magnitude higher. In this work, C1018 carbon steel coupons were used in tests of MIC by D. vulgaris with and without an electron mediator. Experimental weight loss and pit depth data conclusively confirmed that both riboflavin and FAD were able to accelerate D. vulgaris attack against the carbon steel considerably. It has important implications in MIC failure analysis and MIC mitigation in the oil and gas industry.     

Characterization of two sulfate-reducing bacteria from the gut of the soil-feeding termite,Cubitermes speciosus

Two sulfate-reducing bacteria (SRB) were isolated from a mixed culture enriched with benzoate obtained from gut homogenate of the soil-feeding higher termite, Cubitermes speciosus. The organisms were vibrioid rods, staining Gram-negative, which performed incomplete substrate oxidation. They differed in several features. The smaller one, strain STp, was motile with a single polar flagellum. This strain differed from Desulfovibrio desulfuricans only by its inability to oxidize malate and pentanol. The bigger one, strain STg, differed from Desulfovibrio giganteus only by its nonmotility and a lower length. It is the first evidence of the presence of SRB in termite gut.     

Population Dynamics of a Single-Stage Sulfidogenic Bioreactor Treating Synthetic Zinc-Containing Waste Streams

Waste streams from industrial processes such as metal smelting or mining contain high concentrations of sulfate and metals with low pH. Dissimilatory sulfate reduction carried out by sulfate-reducing bacteria (SRB) at low pH can combine sulfate reduction with metal-sulfide precipitation and thus open possibilities for selective metal recovery. This study investigates the microbial diversity and population changes of a single-stage sulfidogenic gas-lift bioreactor treating synthetic zinc-rich waste water at pH 5.5 by denaturing gradient gel electrophoresis of 16S rRNA gene fragments and quantitative polymerase chain reaction. The results indicate the presence of a diverse range of phylogenetic groups with the predominant microbial populations belonging to the Desulfovibrionaceae from δ-Proteobacteria. Desulfovibrio desulfuricans-like populations were the most abundant among the SRB during the three stable phases of varying sulfide and zinc concentrations and increased from 13% to 54% of the total bacterial populations over time. The second largest group was Desulfovibrio marrakechensis-like SRB that increased from 1% to about 10% with decreasing sulfide concentrations. Desulfovibrio aminophilus-like populations were the only SRB to decrease in numbers with decreasing sulfide concentrations. However, their population was <1% of the total bacterial population in the reactor at all analyzed time points. The number of dissimilatory sulfate reductase (DsrA) gene copies per number of SRB cells decreased from 3.5 to 2 DsrA copies when the sulfide concentration was reduced, suggesting that the cells' sulfate-reducing capacity was also lowered. This study has identified the species present in a single-stage sulfidogenic bioreactor treating zinc-rich wastewater at low pH and provides insights into the microbial ecology of this biotechnological process.     

Mercury Methylation Independent of the Acetyl-Coenzyme A Pathway in Sulfate-Reducing Bacteria

Sulfate-reducing bacteria (SRB) in anoxic waters and sediments are the major producers of methylmercury in aquatic systems. Although a considerable amount of work has addressed the environmental factors that control methylmercury formation and the conditions that control bioavailability of inorganic mercury to SRB, little work has been undertaken analyzing the biochemical mechanism of methylmercury production. The acetyl-coenzyme A (CoA) pathway has been implicated as being key to mercury methylation in one SRB strain, Desulfovibrio desulfuricans LS, but this result has not been extended to other SRB species. To probe whether the acetyl-CoA pathway is the controlling biochemical process for methylmercury production in SRB, five incomplete-oxidizing SRB strains and two Desulfobacter strains that do not use the acetyl-CoA pathway for major carbon metabolism were assayed for methylmercury formation and acetyl-CoA pathway enzyme activities. Three of the SRB strains were also incubated with chloroform to inhibit the acetyl-CoA pathway. So far, all species that have been found to have acetyl-CoA activity are complete oxidizers that require the acetyl-CoA pathway for basic metabolism, as well as methylate mercury. Chloroform inhibits Hg methylation in these species either by blocking the methylating enzyme or by indirect effects on metabolism and growth. However, we have identified four incomplete-oxidizing strains that clearly do not utilize the acetyl-CoA pathway either for metabolism or mercury methylation (as confirmed by the absence of chloroform inhibition). Hg methylation is thus independent of the acetyl-CoA pathway and may not require vitamin B₁₂ in some and perhaps many incomplete-oxidizing SRB strains.     

Reduction of molybdate by sulfate-reducing bacteria

Molybdate is an essential trace element required by biological systems including the anaerobic sulfate-reducing bacteria (SRB); however, detrimental consequences may occur if molybdate is present in high concentrations in the environment. While molybdate is a structural analog of sulfate and inhibits sulfate respiration of SRB, little information is available concerning the effect of molybdate on pure cultures. We followed the growth of Desulfovibrio gigas ATCC 19364, Desulfovibrio vulgaris Hildenborough, Desulfovibrio desulfuricans DSM 642, and D. desulfuricans DSM 27774 in media containing sub-lethal levels of molybdate and observed a red-brown color in the culture fluid. Spectral analysis of the culture fluid revealed absorption peaks at 467, 395 and 314 nm and this color is proposed to be a molybdate–sulfide complex. Reduction of molybdate with the formation of molybdate disulfide occurs in the periplasm D. gigas and D. desulfuricans DSM 642. From these results we suggest that the occurrence of poorly crystalline Mo-sulfides in black shale may be a result from SRB reduction and selective enrichment of Mo in paleo-seawater.     

Dibenzothiophene sulfur can serve as the sole electron acceptor during growth by sulfate-reducing bacteria

Summary Three species of Sulfate-Reducing Bacteria (SRB) were able to grow using dibenzothiophene (DBT) as their sole source of sulfur and sole electron acceptor. Desulfotomaculum orientis and Desulfovibrio desulfuricans were grown at 30°C while Thermodesulfobacterium commune was grown at 60°C, in media containing lactate and citrate. Hydrogen sulfide was the product of dissimilatory sulfur reduction.Research supported by the Office of Oil and Gas Processing of Fossil Energy, U.S. Department of Energy under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems Inc.     

Activity of an isothiazolone biocide against Hormoconis resinae in pure and mixed biofilms

Biofilms containing single or mixed cultures of the fungus Hormoconis resinae and anaerobic sulphate-reducing bacteria (SRB) on stainless steel were incubated with an isothiazolone biocide (Kathon FP) at 28°C for 24 h. H. resinae within the biofilm was enumerated by immunofluorescence microscopy using specific antiserum, and SRB were assayed by culture. Fungal numbers in mixed biofilms were considerably reduced in comparison with those in pure biofilms. The biocide was shown to be effective against H. resinae in pure biofilms at 50 and 100 ppm, but in mixed biofilms only at the higher concentration. This concentration also reduced the sessile SRB numbers by 99%.P.S. Guiamet is with the Sección Biolectroquimica, INIFTA, Suc. 4, C.C. 16, 1900 La Plata, Argentina. C.C Gaylarde is with the Departamento de Solos, Fac. de Agronomia, UFRGS, Av. Bento Gonçalves, 7712, 91540-000 Porto Alegre, RS, Brazil     

Mutual Influences of Pseudomonas aeruginosa and Desulfovibrio desulfuricans on their Adhesion to Stainless Steel

The mutual influences of Pseudomonas aeruginosa PAO1 and Desulfovibrio desulfuricans subsp. desulfuricans (ATCC 29577) on their adhesion to stainless steel were investigated in batch and column experiments. It was found that P. aeruginosa promoted the adhesion of D. desulfuricans under conditions of turbulence, but not under quiescent conditions. The enhancement involved the alignment of most D. desulfuricans along P. aeruginosa cells and was attributed to the additional interaction surface area provided by adhered P. aeruginosa to aligning D. desulfuricans cells. A slightly positive effect of pre-adhered D. desulfuricans on the adhesion of P. aeruginosa was found. Under condition of laminar flow, substantially better adhesion of D. desulfuricans to confluent P. aeruginosa biofilms than to steel was observed. The mutual influences are discussed in terms of more favorable adhesion energies and the influence of changed hydraulic conditions due to the roughness of P. aeruginosa biofilms.     

Inhibiting sulfate-reducing bacteria in biofilms by expressing the antimicrobial peptides indolicidin and bactenecin

To identify novel, less-toxic compounds capable of inhibiting sulfate-reducing bacteria (SRB), Desulfovibrio vulgaris and Desulfovibrio gigas in suspension cultures were exposed to several antimicrobial peptides. The bacterial peptide antimicrobials gramicidin S, gramicidin D, and polymyxin B as well as the cationic peptides indolicidin and bactenecin from bovine neutrophils decreased the viability of both SRB by 90% after a 1-h exposure at concentrations of 25–100 μg ml⁻¹. To reduce corrosion by inhibiting SRB in biofilms, the genes for indolicidin and bactenecin were expressed in Bacillus subtilisBE1500 and B. subtilis WB600 under the control of the constitutive alkaline protease (apr) promoter, and the antimicrobials were secreted into the culture medium using the apr signal sequence. Bactenecin was also synthesized and expressed as a fusion to the pro-region of barnase from Bacillus amyloliquefaciens. Concentrated culture supernatants of B. subtilis BE1500 expressing bactenecin at 3 μg ml⁻¹ decreased the viability of Escherichia coli BK6 by 90% and the reference SRB D. vulgaris by 83% in suspension cultures. B. subtilis BE1500 and B. subtilis WB600 expressing bactenecin in biofilms also inhibited the SRB-induced corrosion of 304 stainless steel six to 12-fold in continuous reactors as evidenced by the lack of change in the impedance spectra (resistance polarization) upon addition of SRB and by the reduction in hydrogen sulfide and iron sulfide in batch fermentations with mild steel. A 36-fold decrease in the population of D. vulgaris in a B. subtilis BE1500 biofilm expressing bactenecin was also observed. This is the first report of an antimicrobial produced in a biofilm for in vivo applications and represents the first application of a beneficial, genetically-engineered biofilm for combating corrosion. Received 27 October 1998/ Accepted in revised form 21 February 1999     

A green biocide enhancer for the treatment of sulfate-reducing bacteria (SRB) biofilms on carbon steel surfaces using glutaraldehyde

Generally speaking, a much higher concentration of biocide is needed to treat biofilms compared to the dosage used to for planktonic bacteria. With increasing restrictions of environmental regulations and safety concerns on large-scale biocide uses such as oil field applications, it is highly desirable to make more effective use of biocides. In this paper a green biocide enhancer ethylenediaminedisuccinate (EDDS) that is a biodegradable chelator, was found to enhance the efficacy of glutaraldehyde in its treatment of sulfate-reducing bacteria (SRB) biofilms. Experiments were carried out in 100 ml anaerobic vials with carbon steel coupons. The ATCC 14563 strain of Desulfovibrio desulfuricans was used. Biofilms on coupon surfaces were visualized using scanning electron microscopy (SEM). Experimental results showed that EDDS reduced the glutaraldehyde dosages considerably in the inhibition of SRB biofilm establishment and the treatment of established biofilms on carbon steel coupon surfaces.     

Chelators enhanced biocide inhibition of planktonic sulfate-reducing bacterial growth

Biocides are currently the primary mitigation method to control sulfate-reducing bacteria (SRB) in biofouling, reservoir souring and microbiologically influenced corrosion. Increasingly restrictive environmental regulations and safety concerns on biocide uses demand more efficient dosing of biocides. Chelators have been known to enhance antibiotics because of their properties such as increasing the permeability of the outer cell membrane of Gram-negative bacteria. Two readily biodegradable chelators, ethylenediaminedisuccinate (EDDS) and N-(2-hydroxyethyl)iminodiacetic acid (HEIDA) disodium salts that are touted as potential replacements of ethylenediaminetetraacetic acid (EDTA), were evaluated as potential biocide enhancers for glutaraldehyde and tetrakis hydroxymethyl phosphonium sulfate (THPS) in their inhibition of planktonic SRB growth. Desulfovibrio vulgaris ATCC 7757 and Desulfovibrio desulfuricans ATCC 14563 were grown in modified ATCC 1249 medium and in enriched artificial seawater, respectively. Laboratory tests in 100 ml anaerobic vials showed that EDDS or HEIDA alone did not inhibit SRB growth. However, when EDDS or HEIDA was combined with glutaraldehyde or THPS, each of them enhanced the biocide inhibition of planktonic SRB growth.     

Revealing Sulfate-Reducing Microorganisms in Oilfield Waters (Flysch Carpathians,South-eastern Poland)

Sulphidogenous microorganism communities were isolated from selected oilfield waters in the Flysch Carpathians of south-eastern Poland. Organisms were incubated using the microcosms method with application of two media: minimal medium and modified Postgate C medium with yeast extract or trisodium citrate or monocyclic hydrocarbons from the BTEX group (benzene, toluene, ethylbenzene, and xylene) as the sole carbon source. Activity of sulphidogenic, autochthonous microorganism communities was noted only on the Postgate medium. Beside active sulphate reduction – max. 70%, ca. 74% biodegradation of organic compounds was also observed in the cultures. The highest content of sulphate-reducing bacteria (SRB) in the COD (ca. 83%) was noted in cultures, in which trisodium citrate and yeast extract were applied as the sole carbon source. Molecular analysis indicated not only the presence of SRB such as Desulfobacterium autothrophicum, Desulfovibrio desulfuricans, but also other microorganisms, e.g., Geobacter metallireducens. All these taxa are obligatory or facultative anaerobes, with metabolism linked mostly with elemental sulphur and/or its oxidized forms, as well as iron. Analysis of the mineral composition of the residues confirmed the presence of elemental sulphur, testifying for the active reduction of sulphates by incompletely oxidizing sulphate reducers assigned to the SRB group. Based on the obtained results, it is concluded that the physical and chemical properties of the oilfield waters are favorable for the growth and development of sulphidogenic microorganism assemblages and mineral-forming processes conducted by them.     

Phylogenetic Identification and Substrate Uptake Patterns of Sulfate-Reducing Bacteria Inhabiting an Oxic-Anoxic Sewer Biofilm Determined by Combining Microautoradiography and Fluorescent In Situ Hybridization

We simultaneously determined the phylogenetic identification and substrate uptake patterns of sulfate-reducing bacteria (SRB) inhabiting a sewer biofilm with oxygen, nitrate, or sulfate as an electron acceptor by combining microautoradiography and fluorescent in situ hybridization (MAR-FISH) with family- and genus-specific 16S rRNA probes. The MAR-FISH analysis revealed that Desulfobulbus hybridized with probe 660 was a dominant SRB subgroup in this sewer biofilm, accounting for 23% of the total SRB. Approximately 9 and 27% of Desulfobulbus cells detected with probe 660 could take up [¹⁴C]propionate with oxygen and nitrate, respectively, as an electron acceptor, which might explain the high abundance of this species in various oxic environments. Furthermore, more than 40% of Desulfobulbus cells incorporated acetate under anoxic conditions. SRB were also numerically important members of H₂-utilizing and ¹⁴CO₂-fixing microbial populations in this sewer biofilm, accounting for roughly 42% of total H₂-utilizing bacteria hybridized with probe EUB338. A comparative 16S ribosomal DNA analysis revealed that two SRB populations, related to the Desulfomicrobium hypogeium and the Desulfovibrio desulfuricans MB lineages, were found to be important H₂ utilizers in this biofilm. The substrate uptake characteristics of different phylogenetic SRB subgroups were compared with the characteristics described to date. These results provide further insight into the correlation between the 16S rRNA phylogenetic diversity and the physiological diversity of SRB populations inhabiting sewer biofilms.     

Microbially influenced corrosion of galvanized steel pipes in aerobic water systems

Aims: To investigate the role of heterotrophic bacteria in the corrosion of galvanized steel in the presence of water. Methods and Results: Samples were taken from corroding galvanized steel pipes conveying water for specialist applications, and heterotrophic bacteria were isolated and cultured. The majority of bacteria were Gram‐negative aerobes and included Pseudomonas sp., Bacillus pumilus, Afipia spp. and Blastobacter denitrificans/Bradyrhizobium japonicum. Zinc tolerance was assessed through growth and zinc disc diffusion experiments. In general, zinc negatively influenced growth rates. An unidentified yeast also isolated from the system demonstrated a high tolerance to zinc at concentrations up to 4 g l^?1. Coupon experiments were performed to assess corrosion by the bacteria on galvanized steel and steel coupons. The majority of isolates as pure culture biofilms (69%) accelerated corrosion of galvanized coupons, assessed as zinc release, relative to sterile control coupons (P < 0·05). Pure culture biofilms did not increase the corrosion of steel, with four isolates demonstrating protective effects. Conclusions: Pure culture biofilms of heterotrophic bacteria isolated from a corroding galvanized pipe system were found to accelerate the corrosion of galvanized steel coupons. Significance and Impact of the Study: Microbially influenced corrosion is a potential contributor to sporadically occurring failures in galvanized steel systems containing water. Management strategies should consider microbial control as a means for corrosion prevention in these systems.