Manipulation of pyrite colonization and leaching by iron-oxidizing <Emphasis Type="Italic">Acidithiobacillus</Emphasis> species

In this study, the process of pyrite colonization and leaching by three iron-oxidizing Acidithiobacillus species was investigated by fluorescence microscopy, bacterial attachment, and leaching assays. Within the first 4–5 days, only the biofilm subpopulation was responsible for pyrite dissolution. Pyrite-grown cells, in contrast to iron-grown cells, were able to oxidize iron(II) ions or pyrite after 24 h iron starvation and incubation with 1 mM H₂O₂, indicating that these cells were adapted to the presence of enhanced levels of reactive oxygen species (ROS), which are generated on metal sulfide surfaces. Acidithiobacillus ferrivorans SS3 and Acidithiobacillus ferrooxidans R1 showed enhanced pyrite colonization and biofilm formation compared to A. ferrooxidans ^T. A broad range of factors influencing the biofilm formation on pyrite were also identified, some of them were strain-specific. Cultivation at non-optimum growth temperatures or increased ionic strength led to a decreased colonization of pyrite. The presence of iron(III) ions increased pyrite colonization, especially when pyrite-grown cells were used, while the addition of 20 mM copper(II) ions resulted in reduced biofilm formation on pyrite. This observation correlated with a different extracellular polymeric substance (EPS) composition of copper-exposed cells. Interestingly, the addition of 1 mM sodium glucuronate in combination with iron(III) ions led to a 5-fold and 7-fold increased cell attachment after 1 and 8 days of incubation, respectively, in A. ferrooxidans ^T. In addition, sodium glucuronate addition enhanced pyrite dissolution by 25 %.     

Bacterial attachment on optical fibre surfaces

Optical fibres have received considerable attention as high-density sensor arrays suitable for both in vitro and in vivo measurements of biomolecules and biological processes in living organisms and/or nano-environments. The fibre surface was chemically modified by exposure to a selective etchant that preferentially erodes the fibre cores relative to the surrounding cladding material, thus producing a regular pattern of cylindrical wells of approximately 2.5 μm in diameter and 2.5 μm deep. The surface hydrophobicity of the etched and non-etched optical fibres was analysed using the sessile pico-drop method. The surface topography was characterised by atomic force microscopy (AFM), while the surface chemistry was probed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Six taxonomically different bacterial strains showed a consistent preference for attachment to the nano-scale smoother (R _q = 273 nm), non-etched fibre surfaces (water contact angle, θ = 106° ± 4°). In comparison, the surfaces of the etched optical fibres (water contact angle, θ = 96° ± 10°) were not found to be amenable to bacterial attachment. Bacterial attachment on the non-etched optical fibre substrata varied among different strains.     

Mineralogical,Chemical and Biological Characterization of an Anaerobic Biofilm Collected from a Borehole in a Deep Gold Mine in South Africa

A biofilm sample was collected from an anaerobic water and gas-flowing borehole, 1.474 km below land surface in the Evander Au mine, Republic of South Africa. The biofilm was 27 wt% ZnS, which was ～ 2 × 10⁷times more concentrated than the dissolved Zn measured in the borehole water. X-Ray diffraction indicated that the Zn was present in the form of fine grained, 4.7 ± 0.9 nm particles with smaller amounts of pyrite (FeS ₂ ). Scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy confirmed the identity of these minerals in the biofilm. Using transmission electron microscopy, the fine-grained ZnS minerals were found to coat the 1 μ m-diameter rod-shaped bacteria that made up the primary substructure of the biofilm. The FeS ₂ was present as framboids (spherical aggregates of 0.5–1 μ m FeS ₂ crystals) up to 10 μ m in diameter and as large, 2–3 μ m euhedral crystals that were not nucleated on the bacterial surfaces, but were found within the biofilm. Analyses of 16S rDNA utilizing clone libraries and a phylochip indicates that the ZnS rich biofilm is dominated by methanogens with a significant sulfate-reducing bacterial population and minor sulfide and CH ₄ -oxidizing chemolithotrophs. This biofilm community is sustained by sulfate, bicarbonate and H ₂ -bearing paleometeoric water.     

Fluorescence-Based Quasicontinuous and In Situ Monitoring of Biofilm Formation Dynamics in Natural Marine Environments

Analyzing the dynamics of biofilm formation helps to deepen our understanding of surface colonization in natural environments. While methods for screening biofilm formation in the laboratory are well established, studies in marine environments have so far been based upon destructive analysis of individual samples and provide only discontinuous snapshots of biofilm establishment. In order to explore the development of biofilm over time and under various biotic and abiotic conditions, we applied a recently developed optical biofilm sensor to quasicontinuously analyze marine biofilm dynamics in situ. Using this technique in combination with microscope-assisted imaging, we investigated biofilm formation from its beginning to mature multispecies biofilms. In contrast to laboratory studies on biofilm formation, a smooth transition from initial attachment to colony formation and exponential growth could not be observed in the marine environment. Instead, initial attachment was followed by an adaptation phase of low growth and homogeneously distributed solitary bacterial cells. Moreover, we observed a diurnal variation of biofilm signal intensity, suggesting a transient state of biofilm formation of bacteria. Overall, the biofilm formation dynamics could be modeled by three consecutive development stages attributed to initial bacterial attachment, bacterial growth, and attachment and growth of unicellular eukaryotic microorganisms. Additional experiments showed that the presence of seaweed considerably shortened the adaptation phase in comparison with that on control surfaces but yielded similar growth rates. The outlined examples highlight the advantages of a quasicontinuous in situ detection that enabled, for the first time, the exploration of the initial attachment phase and the diurnal variation during biofilm formation in natural ecosystems.     

Influence of the sulfur species reactivity on biofilm conformation during pyrite colonization by Acidithiobacillus thiooxidans

Massive pyrite (FeS₂) electrodes were potentiostatically modified by means of variable oxidation pulse to induce formation of diverse surface sulfur species (S _n ^2?, S⁰). The evolution of reactivity of the resulting surfaces considers transition from passive (e.g., Fe_1?x S₂) to active sulfur species (e.g., Fe_1?x S_2?y , S⁰). Selected modified pyrite surfaces were incubated with cells of sulfur-oxidizing Acidithiobacillus thiooxidans for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the attached cells density and their exopolysaccharides were analyzed by confocal laser scanning microscopy (CLMS) and atomic force microscopy (AFM) on bio-oxidized surfaces; additionally, S _n ^2?/S⁰ speciation was carried out on bio-oxidized and abiotic pyrite surfaces using Raman spectroscopy. Our results indicate an important correlation between the evolution of S _n ^2?/S⁰ surface species ratio and biofilm formation. Hence, pyrite surfaces with mainly passive-sulfur species were less colonized by A. thiooxidans as compared to surfaces with active sulfur species. These results provide knowledge that may contribute to establishing interfacial conditions that enhance or delay metal sulfide (MS) dissolution, as a function of the biofilm formed by sulfur-oxidizing bacteria.     

Attachment of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum cultured under varying conditions to pyrite, chalcopyrite, low-grade ore and quartz in a packed column reactor

The attachment of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum spp. grown on ferrous medium or adapted to a pyrite mineral concentrate to four mineral substrata, namely, chalcopyrite and pyrite concentrates, a low-grade chalcopyrite ore (0.5 wt%) and quartzite, was investigated. The quartzite represented a typical gangue mineral and served as a control. The attachment studies were carried out in a novel particle-coated column reactor. The saturated reactor containing glass beads, which were coated with fine mineral concentrates, provided a quantifiable surface area of mineral concentrate and maintained good fluid flow. A. ferrooxidans and Leptospirillum spp. had similar attachment characteristics. Enhanced attachment efficiency occurred with bacteria grown on sulphide minerals relative to those grown on ferrous sulphate in an ore-free environment. Selective attachment to sulphide minerals relative to gangue materials occurred, with mineral adapted cultures attaching to the minerals more efficiently than ferrous grown cultures. Mineral-adapted cultures showed highest levels of attachment to pyrite (74% and 79% attachment for A. ferrooxidans and L. ferriphilum, respectively). This was followed by attachment of mineral-adapted cultures to chalcopyrite (63% and 58% for A. ferrooxidans and L. ferriphilum, respectively). A. ferrooxidans and L. ferriphilum exhibited lower levels of attachment to low-grade ore and quartz relative to the sulphide minerals.     

Influence of the surface speciation on biofilm attachment to chalcopyrite by Acidithiobacillus thiooxidans

Surfaces of massive chalcopyrite (CuFeS₂) electrodes were modified by applying variable oxidation potential pulses under growth media in order to induce the formation of different secondary phases (e.g., copper-rich polysulfides, S _n ^2?; elemental sulfur, S⁰; and covellite, CuS). The evolution of reactivity (oxidation capacity) of the resulting chalcopyrite surfaces considers a transition from passive or inactive (containing CuS and S _n ^2?) to active (containing increasing amounts of S⁰) phases. Modified surfaces were incubated with cells of sulfur-oxidizing bacteria (Acidithiobacillus thiooxidans) for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the density of cells attached to chalcopyrite surfaces, the structure of the formed biofilm, and their exopolysaccharides and nucleic acids were analyzed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy coupled to dispersive X-ray analysis (SEM-EDS). Additionally, CuS and S _n ^2?/S⁰ speciation, as well as secondary phase evolution, was carried out on biooxidized and abiotic chalcopyrite surfaces using Raman spectroscopy and SEM-EDS. Our results indicate that oxidized chalcopyrite surfaces initially containing inactive S _n ^2? and S _n ^2?/CuS phases were less colonized by A. thiooxidans as compared with surfaces containing active phases (mainly S⁰). Furthermore, it was observed that cells were partially covered by CuS and S⁰ phases during biooxidation, especially at highly oxidized chalcopyrite surfaces, suggesting the innocuous effect of CuS phases during A. thiooxidans performance. These results may contribute to understanding the effect of the concomitant formation of refractory secondary phases (as CuS and inactive S _n ^2?) during the biooxidation of chalcopyrite by sulfur-oxidizing microorganisms in bioleaching systems.     

The attachment of Enteromorpha zoospores to a bacterial biofilm assemblage

This study has investigated the relationship between bacterial biofilms and the attachment of zoospores of the green macroalga Enteromorpha. Zoospore attachment to glass slides was enhanced in the presence of a bacterial biofilm assemblage, and the number attaching increased with the number of bacteria present. Zoospores also attached to control surfaces, but at lower numbers; glass surfaces conditioned in autoclaved seawater had the same number of zoospores attached as new glass surfaces. The spatial relationship between bacterial cells and attached zoospores was quantified by image analysis. The hypothesis tested was that zoospores attached preferentially to, or in the very close vicinity of, bacterial cells. Spatial microscopic analysis showed that more bacteria were covered by zoospores than would be expected if zoospore attachment was a random process and zoospores appeared to attach to bacterial clusters. The most likely explanation is that zoospores are attracted to bacterial cells growing on surfaces and the presence of a bacterial biofilm enhances their settlement. The possibility is discussed that Enteromorpha zoospores respond to a chemical signal produced by bacteria, i.e. that there may be prokaryote‐eukaryote cell signalling.     

Selective Adhesion of Thiobacillus ferrooxidans to Pyrite

Bacterial adhesion to mineral surfaces plays an important role not only in bacterial survival in natural ecosystems, but also in mining industry applications. Selective adhesion was investigated with Thiobacillus ferrooxidans by using four minerals, pyrite, quartz, chalcopyrite, and galena. Escherichia coli was used as a control bacterium. Contact angles were used as indicators of hydrophobicity, which was an important factor in the interaction between minerals and bacteria. The contact angle of E. coli in a 0.5% sodium chloride solution was 31°, and the contact angle of T. ferrooxidans in a pH 2.0 sulfuric acid solution was 23°. E. coli tended to adhere to more hydrophobic minerals by hydrophobic interaction, while T. ferrooxidans selectively adhered to iron-containing minerals, such as pyrite and chalcopyrite. Ferrous ion inhibited the selective adhesion of T. ferrooxidans to pyrite competitively, while ferric ion scarcely inhibited such adhesion. When selective adhesion was quenched by ferrous ion completely, adhesion of T. ferrooxidans was controlled by hydrophilic interactions. Adhesion of E. coli to pyrite exhibited a liner relationship on langmuir isotherm plots, but adhesion of T. ferrooxidans did not. T. ferrooxidans recognized the reduced iron in minerals and selectively adhered to pyrite and chalcopyrite by a strong interaction other than the physical interaction.     

A critical stage in the formation of acid mine drainage: Colonization of pyrite by Acidithiobacillus ferrooxidans under pH-neutral conditions

A dominant Acidithiobacillus ferrooxidans ssp. was isolated from the supergene copper deposit in Morenci, Arizona, USA. Washed bacterial suspensions (10⁸ MPN per treatment), in pH‐neutral buffer, were inoculated onto pyrite cubes for 24 h. Heterogeneous bacterial absorption onto the pyrite removed approximately 90% of the viable bacteria from the inoculum. At T = 0, the bacteria were observed primarily in regions enriched in phosphorus. Over 30 days, the bacterial population on the pyrite cubes increased from 1.3 × 10⁷ to 2.9 × 10⁸ bacteria cm^?2. During this growth stage, low levels of thiobacilli (228 ± 167 MPN mL^?1) were also recovered from the fluid phase; however, this population decreased to zero within 30 days. Growth on pyrite occurred as micrometre‐scale planar microcolonies, a biofilm, coating the mineral surfaces. These microcolonies possessed viable thiobacilli, even after 4 months at ‘circumneutral pH’. Imaging the pyrite cubes using SEM‐EDS and scanning force microscopy demonstrated that the thiobacilli grew as iron oxy‐hydroxide‐cemented cells, leading to the formation of mineralized microcolonies. Removing the iron oxy‐hydroxides with oxalic acid did not dislodge the bacteria, demonstrating that the secondary minerals were not responsible for ‘gluing’ the bacteria to the pyrite surface. Removing organic material, i.e. the cells, by an oxygen plasma treatment revealed the presence of corrosion pits the size and shape of bacteria. Because of the inherent geochemical constraints on pyrite oxidation at neutral pH, the colonization of pyrite under circumneutral pH conditions must be facilitated by the development of an acidic nanoenvironment between the bacteria and the pyrite mineral surface.     

Listeria monocytogenes Behaviour in Presence of Non-UV-Irradiated Titanium Dioxide Nanoparticles

Listeria monocytogenes is the agent of listeriosis, a food-borne disease. It represents a serious problem for the food industry because of its environmental persistence mainly due to its ability to form biofilm on a variety of surfaces. Microrganisms attached on the surfaces are a potential source of contamination for environment and animals and humans. Titanium dioxide nanoparticles (TiO₂ NPs) are used in food industry in a variety of products and it was reported that daily exposure to these nanomaterials is very high. Anti-listerial activity of TiO₂ NPs was investigated only with UV-irradiated nanomaterials, based on generation of reactive oxigen species (ROS) with antibacterial effect after UV exposure. Since both Listeria monocytogenes and TiO₂ NPs are veicolated with foods, this study explores the interaction between Listeria monocytogenes and non UV-irradiated TiO₂ NPs, with special focus on biofilm formation and intestinal cell interaction. Scanning electron microscopy and quantitative measurements of biofilm mass indicate that NPs influence both production and structural architecture of listerial biofilm. Moreover, TiO₂ NPs show to interfere with bacterial interaction to intestinal cells. Increased biofilm production due to TiO₂ NPs exposure may favour bacterial survival in environment and its transmission to animal and human hosts.     

Alumina surfaces with nanoscale topography reduce attachment and biofilm formation by Escherichia coli and Listeria spp.

This work reports on a simple, robust and scientifically sound method to develop surfaces able to reduce microbial attachment and biofilm development, with possible applications in medicine, dentistry, food processing, or water treatment. Anodic surfaces with cylindrical nanopores 15 to 100 nm in diameter were manufactured and incubated with Escherichia coli ATCC 25922 and Listeria innocua. Surfaces with 15 and 25 nm pore diameters significantly repressed attachment and biofilm formation. Surface–bacteria interaction forces calculated using the extended Derjaguin Landau Verwey-Overbeek (XDLVO) theory indicate that reduction in attachment and biofilm formation is due to a synergy between electrostatic repulsion and surface effective free energy. An attachment study using E. coli K12 strains unable to express appendages also suggests that the small-pore surfaces may inhibit flagella-dependent attachment. These results can have immediate, far-reaching implications and commercial applications, with substantial benefits for human health and life.     

Binary culture biofilm formation by Stenotrophomonas maltophilia and Fusarium oxysporum

Binary culture biofilm formation by Stenotrophomonas maltophilia and Fusarium oxysporum was investigated using the recirculating modified Robbins device batch culture system. Sequential attachment studies were carried out in the Robbins device on PVC and glass surfaces, with each species as either the first or the second colonizer. Different surfaces had no significant effect on total numbers of S. maltophilia and F. oxysporum in the binary population biofilm. The attachment of the second colonizer was not influenced significantly by the previous attachment of the first colonizer. These results were confirmed using scanning electron micrographs. Journal of Industrial Microbiology & Biotechnology (2001) 26, 178–183. Received 06 July 1999/ Accepted in revised form 02 November 2000     

Monitoring of microbial adhesion and biofilm growth using electrochemical impedancemetry

Electrochemical impedance spectroscopy was tested to monitor the cell attachment and the biofilm proliferation in order to identify characteristic events induced on the metal surface by Gram-negative (Pseudomonas aeruginosa PAO1) and Gram-positive (Bacillus subtilis) bacteria strains. Electrochemical impedance spectra of AISI 304 electrodes during cell attachment and initial biofilm growth for both strains were obtained. It can be observed that the resistance increases gradually with the culture time and decreases with the biofilm detachment. So, the applicability of electric cell-substrate impedance sensing (ECIS) for studying the attachment and spreading of cells on a metal surface has been demonstrated. The biofilm formation was also characterized by the use of scanning electron microscopy and confocal laser scanning microscopy and COMSTAT image analysis. The electrochemical results roughly agree with the microscope image observations. The ECIS technique used in this study was used for continuous real-time monitoring of the initial bacterial adhesion and the biofilm growth. It provides a simple and non-expensive electrochemical method for in vitro assessment of the presence of biofilms on metal surfaces.     

Effects of phenol and natural phenolic compounds on biofilm formation by Pseudomonas aeruginosa

A biofilm is formed as a result of adhesion of microorganisms to various surfaces with the production of extracellular polymers (polysaccharides and proteins). Biofilms cause serious problems in the chemical, medical and pharmaceutical industries. Recent findings indicate that some natural phenolic compounds found in plants have an anti-biofouling effect on biofilm formation by Gram-negative bacteria. The anti-biofouling activities of 14 selected phenol and natural phenolic compounds were tested against Pseudomonas aeruginosa, using a microtiter-plate. A modified microtiter-plate assay was used because it enabled indirect measurement of bacterial cells attached to the surface of the wells. This assay involved fixing the bacterial film with methanol, staining with crystal violet dye and then releasing the bound dye with 33% glacial acetic acid. The optical density (OD) of the solution was measured at 570 nm by using an automated ICN Flow Titertek Multiscan Plus reader. Phenol and natural phenolic compounds except ethyl linoleate and tocopherol showed a significant reduction in biofilm formation by P. aeruginosa.     

Short communication: Adverse effect of surface-active reagents on the bioleaching of pyrite and chalcopyrite by Thiobacillus ferrooxidans

Oxidation of Fe(II) iron and bioleaching of pyrite and chalcopyrite by Thiobacillus ferrooxidans was adversely affected by isopropylxanthate, a flotation agent, and by LIX 984, a solvent-extraction agent, each at 1 g/l. The reagents/l were adsorbed on the bacterial surface, decreasing the bacteria's development and preventing biooxidation. Both reagents inhibited the bioleaching of pyrite and LIX 984 also inhibited the bioleaching of chalcopyrite.     

Salmonella enterica isolates from layer farm environments are able to form biofilm on eggshell surfaces

This study examined the eggshell biofilm forming ability of Salmonella enterica isolates recovered from egg farms. Multicellular behaviour and biofilm production were examined at 22 and 37°C by Congo red morphology and the crystal violet staining assay. The results indicated that the biofilm forming behaviour of Salmonella isolates was dependent on temperature and associated with serovars. Significantly greater biofilm production was observed at 22°C compared with 37°C. The number of viable biofilm cells attached to eggshells after incubation for 48 h at 22°C was significantly influenced by serovar. Scanning electron microscopic examination revealed firm attachment of bacterial cells to the eggshell surface. The relative expression of csgD and adrA gene was significantly higher in eggshell biofilm cells of S. Mbandaka and S. Oranienburg. These findings demonstrate that Salmonella isolates are capable of forming biofilm on the eggshell surface and that this behaviour is influenced by temperature and serovar.     

Differences in colonisation of five marine bacteria on two types of glass surfaces

The retention patterns of five taxonomically different marine bacteria after attachment on two types of glass surfaces, as-received and chemically etched, have been investigated. Contact angle measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectrometry (XPS) were employed to investigate the impact of nanometer scale surface roughness on bacterial attachment. Chemical modification of glass surfaces resulted in a ～1 nm decrease in the average surface roughness (R _a) and the root-mean-squared roughness (R_q ) and in a ～8 nm decrease in the surface height and the peak-to-peak (R _max) and the 10-point average roughness (R_z ). The study revealed amplified bacterial attachment on the chemically etched, nano-smoother glass surfaces. This was a consistent response, notwithstanding the taxonomic affiliation of the selected bacteria. Enhanced bacterial attachment was accompanied by elevated levels of secreted extracellular polymeric substances (EPS). An expected correlation between cell surface wettability and the density of the bacterial attachment on both types of glass surfaces was also reported, while no correlation could be established between cell surface charge and the bacterial retention pattern.     

XPS and ab initio calculation of surface states of sulfide minerals: pyrite,chalcopyrite and molybdenite

Sulfide minerals contain sulphur in a large variety of coordination environments. Consequently, the S 2p XPS of various mineral surface states undergo different shifts in binding energy (BE) relative to the bulk, depending on the charge distribution on the surface. This in turn depends on the number, type and position of the atoms on the fracture surface, which is determined by the fracture mechanism.

We have investigated three sulfide minerals: pyrite (tetrahedrally-coordinated S), chalcopyrite (tetrahedrally-coordinated S) and molybdenite (layered structure with trigonally-coordinated S). Comparison of conventional with surface sensitive synchrotron XPS shows that the S 2p spectrum displays two additional doublets at lower BE than the bulk signal for pyrite, and one doublet each at lower and at higher BE for chalcopyrite. Each of these signals is derived from surface states. Molybdenite shows no additional states. A BE shift to lower (higher) BE suggests a charge increase (decrease) on the S atoms relative to those in the bulk because of higher (lower) charge screening.

We have used ab initio density functional calculations to validate this interpretation of the experimental evidence, obtaining Mulliken population analyses for the possible fracture surfaces and comparing their charge distribution with the corresponding bulk charge distribution. Our calculations support the assignments of S 2p surface contributions as follows: the lower BE peak of chalcopyrite (160.84 eV) as under-coordinated surface S states, the higher BE peak of chalcopyrite (161.88 eV) as surface S polymers, the lowest BE peak of pyrite (161.3 eV) as surface S monomers, and the next lowest BE peak of pyrite (162.0 eV) as under-coordinated surface S dimers. The absence of any surface states in molybdenite is also confirmed by the models.     

Effect of curli expression and hydrophobicity of Escherichia coli O157:H7 on attachment to fresh produce surfaces

Aim: To investigate the effect of curli expression on cell hydrophobicity, biofilm formation and attachment to cut and intact fresh produce surfaces. Methods and Results: Five Escherichia coli O157:H7 strains were evaluated for curli expression, hydrophobicity, biofilm formation and attachment to intact and cut fresh produce (cabbage, iceberg lettuce and Romaine lettuce) leaves. Biofilm formation was stronger when E. coli O157:H7 were grown in diluted tryptic soy broth (1 : 10). In general, strong curli‐expressing E. coli O157:H7 strains 4406 and 4407 were more hydrophobic and attached to cabbage and iceberg lettuce surfaces at significantly higher numbers than other weak curli‐expressing strains. Overall, E. coli O157:H7 populations attached to cabbage and lettuce (iceberg and Romaine) surfaces were similar (P > 0·05), indicating produce surfaces did not affect (P < 0·05) bacterial attachment. All E. coli O157:H7 strains attached rapidly on intact and cut produce surfaces. Escherichia coli O157:H7 attached preferentially to cut surfaces of all produce types; however, the difference between E. coli O157:H7 populations attached to intact and cut surfaces was not significant (P > 0·05) in most cases. Escherichia coli O157:H7 attachment and attachment strength (S_R) to intact and cut produce surfaces increased with time. Conclusions: Curli‐producing E. coli O157:H7 strains attach at higher numbers to produce surfaces. Increased attachment of E. coli O157:H7 on cut surfaces emphasizes the need for an effective produce wash to kill E. coli O157:H7 on produce. Significance and Impact of the Study: Understanding the attachment mechanisms of E. coli O157:H7 to produce surfaces will aid in developing new intervention strategies to prevent produce outbreaks.