Phenol removal from aqueous solutions by peroxidase extracted from horseradish

Horseradish peroxidase (HRP) is one of the most recently used enzymes in the process of enzymatic phenol removal. It has a catalytic ability over a broad range of pH, temperature and contaminant concentrations. In this study we revealed the possibility of successful use the crude peroxidase obtained from horseradish roots for the phenol removal from aqueous solutions in the presence of the low molecular polyethylene glycol (PEG 300) at room temperature (20°C) and pH 7.2. Reaction was monitored by direct measuring of the absorbance changes in a samples taken at certain time intervals from the reaction mixture. At the first time PEG 300 was shown to be a more stabilizing effect on crude HRP and provided a higher phenol removal in comparison with PEG 3350. Crude HRP used in these study demonstrated a greater resistance on phenol and hydrogen peroxide inactivation that allowed a higher phenol removal. The highest phenol removal was achieved when the concentration of PEG 300, phenol and hydrogen peroxide were 300 mg/L, 2.0 and 2.5 mM, respectively.     

Susceptibility of Fusobacterium nucleatum to killing by peroxidase-iodide-hydrogen peroxide combination in buffer solution and in human whole saliva

Some Gram-negative anaerobic bacteria have been associated with the infection of tooth supporting tissues, i.e. periodontitis. Of these bacteria, Fusobacterium nucleatum is sensitive to lactoperoxidase/myeloperoxidase-iodide-hydrogen peroxide system in vitro, but salivary concentrations of thiocyanate abolishes the bactericidality. These bacteria are located in periodontal pockets, on oral mucosa and in saliva. Although F. nucleatum most probably does not belong to the group of main periodontal pathogens, it sustains its proportion in the periodontal flora when gingivitis progresses to periodontitis. In this study, the sensitivity of F. nucleatum to different horseradish peroxidase-iodide-hydrogen peroxide combinations was tested both in buffer and in sterilized human whole saliva. Horseradish peroxidase was chosen because it does not bind thiocyanate at pH > or = 6. After 1h incubation at 37 degrees C, the cell viability was estimated by plate count and with flow cytometer using LIVE/DEAD BacLight kit (Molecular Probes, USA). In saliva, the horseradish peroxidase (50 microg/mL)-iodide (2.5 mM)-hydrogen peroxide (2.5 mM) combination decreased the amount of viable bacteria to 37% compared to 85% in the control without any of the components when measured with flow cytometer. Replacement of buffer by saliva decreased the bactericidality of the peroxidase system. However, in buffer less iodide and hydrogen peroxide was needed to produce significant decrease in the number of viable bacteria when measured by plate count than with flow cytometer. Our study shows that horseradish peroxidase-iodide-hydrogen peroxide combination is able to kill F. nucleatum cells in saliva. Horseradish peroxidase-iodide-hydrogen peroxide combination may be useful to diminish the degree of re-colonization of periodontitis-associated bacteria after periodontal therapy and to inhibit the transmission of these bacteria via saliva.     

Colorimetric paper bioassay by horseradish peroxidase for the detection of catechol and resorcinol in aqueous samples

Abstract

Phenolic compounds such as catechol and resorcinol are toxic and persistent pollutants in the aqueous environment. Detection procedures such as chromatographic and spectrophotometric methods are time-consuming and require sophisticated instruments with skilled manpower. Development of a simple, cost effective, portable and disposable paper based biosensor could be a better alternative to the conventional methods. The present study attempted to develop a paper based biosensor by immobilizing horseradish peroxidase enzyme to detect catechol and resorcinol in aqueous samples. Horseradish peroxidase catalyzes the oxidation of phenolic compounds to semiquinones, which on reaction with a chromogen, 3-methyl 2-benzothiazolinone hydrazine (MBTH) gives faint pink to red color depending on the compound and its concentration in the sample is the basis for biosensing application. Different methods of enzyme immobilization on filter paper like physical adsorption, covalent coupling, and polysaccharide entrapment were executed. The performance of the various enzyme immobilization methods was evaluated by analyzing the developed color intensity using ImageJ software. Entrapment technique is the most effective method of immobilizing enzyme on the filter paper that produces the highest color intensity with better stability. The visible limit of detection (LoD) was observed as 0.45?mM (50?mg/L) for catechol and 0.09?mM (10?mg/L) for resorcinol in aqueous samples.     

A peroxidase/phenolics/ascorbate system can scavenge hydrogen peroxide in plant cells

The function of a peroxidase/phenolics/ascorbic acid system in plant vacuoles has not yet been well elucidated. We wished to study the redox reactions among hydrogen peroxide, phenolics and ascorbic acid (AA) in the presence of horseradish peroxidase. Horseradish peroxidase oxidized rutin and chlorogenic acid (CGA), compounds present in many kinds of plant. The oxidation was inhibited by AA. As a result of the inhibition. AA was oxidized and when almost all of it had been oxidized, oxidation of the phenolics commenced. Monodehydroascorbic acid (MDA) radical was detected during the oxidation of AA, suggesting that the inhibition of oxidation of rutin and CGA was due to reduction of phenoxyl radicals by AA. By comparison of time courses of changes in levels of AA and MDA radicals, and by kinetic calculation, it is suggested that in addition to AA, MDA radicals may also reduce phenoxyl radicals. It is proposed that the peroxidase/phenolics/AA system can function as a hydrogen peroxide scavenging system.     

An environmental nuisance: odor concentrated and transported by dust

Intensive swine production generates odorous emissions which flow from the buildings housing the animals. High ventilation rates bring in fresh air, remove heat and moisture and enhance pork productivity. Numerous compounds contribute to the uniquely offensive odors from swine facilities, including fatty acids, amines, aromatics and sulfur compounds. Dust particles, which originate predominantly from feces and feed, can adsorb and concentrate odorants in swine facilities. In addition, organic particles can decay and generate odorous compounds. Odorants can exist in much higher concentrations in the dust particles than in equivalent volumes of air. Thus, inhalation of odorous dust and deposition of the dust particles in the mucus overlying the olfactory mucosa are likely responsible for some odor-related complaints by swine farm neighbors. Accurate prediction of odor transport and dispersion downwind from swine farms may require models of dust dispersion and correlation between dust and odorant levels. Unfortunately, many approaches to estimating odor impact currently incorporate filtering of air to remove particulate matter before sensing by humans or electronic sensors. Accelerated progress in understanding this and other 'real world' odor control problems will require methodological innovations that allow quantification of odor in response to air streams containing vapor and particulate phases.     

Role of Calcium on Phenolic Compounds and Enzymes Related to Lignification in Soybean (Glycine max L.) Root Growth

Changes in soluble and cell wall bound peroxidases activities, phenylalanine ammonia-lyase activity and phenolic compounds and lignin contents in roots of calcium-treated soybean (Glycine max (L.) Merr.) seedlings and their relationships with root growth were investigated. Three-day-old soybean seedlings were cultivated in nutrient solution with or without 0.025–5.0 mM calcium for 24 h. In general, length and fresh and dry weights of roots increased, while activities of enzymes (soluble and cell-wall peroxidases and phenylalanine ammonia-lyase) and phenolic compounds and lignin contents decreased against calcium concentrations. In the absence of calcium, phenylalanine ammonia-lyase and peroxidases activities increased by accumulating phenolic compounds and lignin due to restricted growth of roots. Enhanced calcium supply reduced the production of phenolic compounds and lignification due to low phenylalanine ammonia-lyase and peroxidases activities, reinforcing the essential role of calcium to improve the soybean root growth.     

Enzymatic transformations of morphinane alkaloids

Horseradish peroxidase transforms morphinane alkaloids into N-oxides and morphine to pseudomorphine in the presence of hydrogen peroxide. The crude poppy enzyme fraction shows the same activities. The rates of reactions were influenced by phenolic compounds and their relation controlled by the concentration of hydrogen peroxide and the presence of ascorbic acid.     

Carvacrol and Thymol Reduce Swine Waste Odor and Pathogens: Stability of Oils

An incomplete anoxic fermentation of livestock waste results in offensive odor emissions. Antimicrobial additives may be useful in controlling odor emissions and pathogens. Natural antimicrobial compounds, carvacrol or thymol at 16.75 mM (2.5 g/l) completely inhibited the production of the offensive odor compounds, isobutyrate, valerate, isovalerate, and cresol, and significantly reduced other short-chain volatile fatty acids and gas emissions from swine waste. Fecal coliforms were reduced from 6.3 × 10⁶ to 1.0 × 10³ cells per ml 2 days after treatment with carvacrol (13.3 mM) and were not detectable within 14 days. Total culturable anaerobic bacteria were reduced from 12.4 × 10¹⁰ to 7.2 × 10⁸ cells per ml after 2 days and were suppressed below this level for 28 days. Lactate production was not prevalent in untreated swine waste indicating that the microbial populations differ from those in cattle waste. Carvacrol and thymol were stable in swine waste under anoxic conditions for 62 days with 90 to 95% of the additive being recovered in the waste solids. In conclusion, carvacrol and thymol are not metabolized in anoxic swine waste and they are potentially useful in controlling odor emissions and pathogens in swine waste. Received: 22 March 2001 / Accepted: 14 May 2001     

Controlled layer-by-layer immobilization of horseradish peroxidase.

Horseradish peroxidase (HRP) was biotinylated with biotinamidocaproate N-hydroxysuccinimide ester (BcapNHS) in a controlled manner to obtain biotinylated horseradish peroxidase (Bcap-HRP) with two biotin moieties per enzyme molecule. Avidin-mediated immobilization of HRP was achieved by first coupling avidin on carboxy-derivatized polystyrene beads using a carbodiimide, followed by the attachment of the disubstituted biotinylated horseradish peroxidase from one of the two biotin moieties through the avidin-biotin interaction (controlled immobilization). Another layer of avidin can be attached to the second biotin on Bcap-HRP, which can serve as a protein linker with additional Bcap-HRP, leading to a layer-by-layer protein assembly of the enzyme. Horseradish peroxidase was also immobilized directly on carboxy-derivatized polystyrene beads by carbodiimide chemistry (conventional method). The reaction kinetics of the native horseradish peroxidase, immobilized horseradish peroxidase (conventional method), controlled immobilized biotinylated horseradish peroxidase on avidin-coated beads, and biotinylated horseradish peroxidase crosslinked to avidin-coated polystyrene beads were all compared. It was observed that in solution the biotinylated horseradish peroxidase retained 81% of the unconjugated enzyme's activity. Also, in solution, horseradish peroxidase and Bcap-HRP were inhibited by high concentrations of the substrate hydrogen peroxide. The controlled immobilized horseradish peroxidase could tolerate much higher concentrations of hydrogen peroxide and, thus, it demonstrates reduced substrate inhibition. Because of this, the activity of controlled immobilized horseradish peroxidase was higher than the activity of Bcap-HRP in solution. It is shown that a layer-by-layer assembly of the immobilized enzyme yields HRP of higher activity per unit surface area of the immobilization support compared to conventionally immobilized enzyme.     

Olfactory detectability of L-amino acids in the European honeybee (Apis mellifera)

The honeybee is one of several insect model systems for the study of olfaction, yet our knowledge regarding the spectrum of odorants detectable by Apis mellifera is limited. One class of odorants that has never been tested so far are the amino acids, which are important constituents of floral nectar. Using the proboscis extension response paradigm, we assessed whether the odor of amino acids is detectable for honeybees and determined olfactory detection thresholds for those amino acids that were detectable. We found that honeybees are able to detect the odor of 5 of the 20 proteinogenic amino acids when presented at a concentration of 50 or 100 mM. Median olfactory detection thresholds for these 5 amino acids were 12.5 mM with L-tyrosine and L-cysteine, 50 mM with L-tryptophan and L-asparagine, and 100 mM with L-proline. All detection thresholds were much higher than reported concentrations of amino acids in floral nectars. We conclude that in the foraging and feeding context, honeybees are likely to detect amino acids through taste rather than olfaction. Across-species comparisons of the detectability of and sensitivity to amino acids suggest that the number of functional genes coding for olfactory receptors may affect both a species' sensitivity for odorants and the breadth of its spectrum of detectable odorants.     

Spatial and temporal changes in the microbial community in an anaerobic swine waste treatment lagoon

Microorganisms are central to both the beneficial (organic degradation, nutrient removal, biogas production) and detrimental (odor production, pathogen contamination) effects of swine waste storage systems. In this study, both quantitative (real-time polymerase chain reaction) and qualitative (denaturing gradient gel electrophoresis, cloning, sequence analysis) molecular analyses were used to track spatial and temporal changes in the microbial community of swine slurry from a 0.4 ha anaerobic lagoon. The lagoon, located in a region of western Kentucky which has a humid, subtropical environment, was sampled on a monthly basis (n = 10) over a period of one year at four different depths (top, 51 cm from the top, 152 cm from the top, and bottom >198 cm). The concentration and diversity of Bacteroides sp. was seasonal (up to 90% decrease between March and June). Hespellia sp. and other clostridial species, on the other hand, were endemic in the slurry (concentrations up to 1.0 × 10⁷ cells mL^?1 slurry) regardless of time of the year or lagoon depth. Results suggest that there were seasonal effects on the microbial community in the swine lagoon, while the effect of depth was not as pronounced. Seasonal changes in the microbial community in stored wastes may be (directly or indirectly) correlated with changes in malodor emissions from lagoons.     

Flow system for the automatic screening of the effect of phenolic compounds on the luminol–hydrogen peroxide–peroxidase chemiluminescence system

In this work, an automated flow‐based procedure for the screening of the effect of the different phenolic compounds on the chemiluminescence (CL) luminol–hydrogen peroxide–horseradish peroxidase (HRP) system is presented. This procedure involves the combination of multisyringe flow injection analysis (MFSIA) and sequential injection analysis (SIA) techniques and exploits the ability of the different subgroups of phenols, such as cholorophenols, nitrophenols, methylphenols and polyphenols, to enhance or inhibit the described CL system. The implementation of this reaction in the SIA–MSFIA system enabled favourable and precise conditions to evaluate the effect of phenolic compounds, as it involves an in‐line reaction between the phenolic derivative, hydrogen peroxide and peroxidase and subsequent oxidized HRP intermediates generation prior to the fast reaction with the chemiluminogenic reagent. Several studies were then performed with the aim of establishing the appropriate flow system configuration and reaction conditions. It was shown that phenol and chlorophenols produce an enhanced CL response and nitrophenols, methylphenols and polyphenols are inhibitors within the range of concentrations studied (1–100 mg/L). Based on these studies, the developed method was applied to the determination of total polyphenol and phenol content in wine/grape seeds and water samples, respectively, and the results obtained showed good agreement with those furnished by the corresponding Folin–Ciocalteu and 4‐aminoantipyrine reference methods. The developed approach is further pursued by designing an automated generic tool for performing studies of peroxidase‐catalysed CL reactions of luminol focused on the detection of compounds that will affect the rate of those reactions. Copyright © 2011 John Wiley & Sons, Ltd.     

Odor-active constituents in fresh pineapple (Ananas comosus [L.] Merr.) by quantitative and sensory evaluation

By application of aroma extract dilution analysis (AEDA) to an aroma distillate prepared from fresh pineapple using solvent-assisted flavor evaporation (SAFE), 29 odor-active compounds were detected in the flavor dilution (FD) factor range of 2 to 4,096. Quantitative measurements performed by stable isotope dilution assays (SIDA) and a calculation of odor activity values (OAVs) of 12 selected odorants revealed the following compounds as key odorants in fresh pineapple flavor: 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDF; sweet, pineapple-like, caramel-like), ethyl 2-methylpropanoate (fruity), ethyl 2-methylbutanoate (fruity) followed by methyl 2-methylbutanoate (fruity, apple-like) and 1-(E,Z)-3,5-undecatriene (fresh, pineapple-like). A mixture of these 12 odorants in concentrations equal to those in the fresh pineapple resulted in an odor profile similar to that of the fresh juice. Furthermore, the results of omission tests using the model mixture showed that HDF and ethyl 2-methylbutanoate are character impact odorants in fresh pineapple.     

Construction of a Quantitative Three-dimensional Model for Odor Quality using Comparative Molecular Field Analysis (CoMFA)

A quantitative structure-activity relationship (QSAR) studyof odorants was performed taking an odor as an activity. Asan example, we took the ‘green odor of pyrazine derivatives’as an activity. Conformational analysis of the pyrazine derivativeswas performed, and conformers were selected using the longestside-length of a circumscribed box (LLCB) as a criterion. Comparativemolecular field analysis (CoMFA) was used to elucidate the three-dimensional(3D) structural features of the derivatives. As a result, itwas found that the steric and electrostatic features of thederivatives were correlated with human olfactory detection thresholdvalues. We constructed a quantitative 3D model using the graphicviews of CoMFA and partial structures of the derivatives. Theprediction of human olfactory detection threshold values ofother pyrazine derivatives with green odor was possible by usingthe 3D model. As another example, we took the ‘sweet odorof compounds with various structures’ as an activity.A quantitative 3D model for sweet odor was constructed in thesame manner. Analysing the structural features of odorants byCoMFA and constructing 3D models for several important odorqualities would help to (i) explain or predict human olfactorydetection threshold values of interesting odorants, (ii) designnew odorants by suggesting the steric and electrostatic requirements,and (iii) elucidate the mechanism of odorant-receptor interaction.Chem Senses 21: 201–210, 1996.     

Solids,organic load and nutrient concentration reductions in swine waste slurry using a polyacrylamide (PAM)-aided solids flocculation treatment

Increased swine production results in concentration of wastes generated within a limited geographical area, which may lead to land application rates exceeding the local or regional assimilatory capacity. This may result in pollutant transfer through surface water or soil-groundwater systems, environmental degradation, and/or odor concerns. Existing swine waste pit storage and lagoon treatment technologies may be inadequate to store or treat waste prior to land application without these concerns resulting. Efficient swine waste solids separation may reduce environmental health concerns and generate a value-added bioresource (solids). This study evaluated the efficiency of a polyacrylamide (PAM) flocculant-aided solids separation treatment to reduce pollution indicator concentrations in raw (untreated) swine waste slurry. Swine waste slurry solids separation efficiency through gravity settling (sedimentation) was evaluated before and after the addition of a proprietary polymeric (PAM) flocculant. Results indicated that polymer amendments at concentrations of 62.5-750 mg/l improved slurry solids separation efficiency and significantly reduced concentrations of other associated aquatic pollution indicators in a majority of analyses conducted (33 of 50 total analyses conducted). Results also suggested that PAM-aided solids separation from swine waste slurry might facilitate further treatment and/or disposal and therefore reduce associated environmental degradation potential.     

Silylating reagents: a powerful tool for the construction of isosteric analogs of highly branched odorants

We have discovered that alpha-[dimethyl(thexyl)silyl]acetaldehyde (= [dimethyl(1,1,2-trimethylpropyl)silyl]acetaldehyde; 31) has a strong, woody odor. Structural analysis has shown resemblance to known odorants with similar organoleptic properties. On the basis of structure-odor relationships, new and more-powerful woody and ambery sila odorants were prepared. Further derivatization led to a set of compounds with very interesting organoleptic properties. Selected chiral compounds were also prepared stereoselectively. The influence of the absolute configuration on the olfactory properties was in agreement with theoretical assumptions. We also designed other groups of organosilicon odorants. The compounds discovered can be obtained in a few simple steps from commercially available reagents, and may find application in the fragrance and flavor industry. Their structures provide interesting data for further research on structure-odor relationships.     

Peroxidase-catalyzed color removal from bleach plant effluent

Effluent from the caustic extraction stage of a bleach plant is highly colored due to the presence of dissolved products from lignin chlorination and oxidation. Color removal from the effluent by hydrogen peroxide at neutral pH was catalyzed by addition of horseradish peroxidase. The catalysis with peroxidase (20 mg/L) was observed over a wide range of peroxide concentrations (0.1mM-500mM), but the largest effect was between 1mM and 100mM. The pH optimum for catalysis was around 5.0, while the basal rate of noncatalyzed peroxide color removal simply increased with pH within the range tested (3-10). Peroxidase catalysis at pH 7.6 reached a maximum at 40 degrees C in 4 h assays with 10mM peroxide, and disappeared above 60 degrees C. Compared with mycelial color removal by Coriolus versicolor, the rate of color removal by peroxide plus peroxidase was initially faster (first 4 h), but the extent of color removal after 48 h was higher with the fungal treatment. Further addition of peroxidase to the enzyme-treated effluent did not produce additional catalysis. Thus, the peroxide/peroxidase system did not fully represent the metabolic route used by the fungus.     

Olfactory discrimination ability for aromatic odorants as a function of oxygen moiety.

To assess the significance of the type of oxygen moiety on odor quality of aromatic compounds, I tested the ability of human subjects to distinguish between odorants sharing a benzene ring and the same total number of carbon atoms but differing in their functional groups. Phenyl ethanol, phenyl acetaldehyde, phenyl methyl ketone, methyl benzoate and phenyl acetic acid, were employed. In a forced-choice triangular test procedure 20 subjects were repeatedly presented with all possible binary combinations of the five odorants, and asked to identify the bottle containing the odd stimulus. I found (i) that as a group, the subjects performed significantly above chance level in six of the tasks whereas they failed to do so with the four other tasks; (ii) marked interindividual differences in discrimination performance, ranging from subjects who were able to significantly distinguish between all 10 odor pairs to subjects who failed to do so with the majority of the tasks; and (iii) that odor pairs that involved methyl benzoate or phenyl methyl ketone were significantly easier to discriminate than those that involved phenyl acetaldehyde or phenyl ethanol, and thus there was a clear dependence of discriminability on type of functional group. Additional tests of the degree of trigeminality of the five aromatic substances indicated that the discriminability of the odor pairs is indeed due to differences in odor quality. A comparison of the present results with those of an earlier study that employed aliphatic odorants suggests that functional oxygen-containing groups may generally be an important determinant of the interaction between the stimulus molecule and the olfactory receptor, and thus may generally be a molecular property affecting odor quality in a substance class-specific manner. The poorer discriminatory performance of the subjects with aromatic odorants compared with corresponding aliphatic substances suggests that the structure of the alkyl rest attached to a functional group may also play a crucial role for recognition of ligands at the olfactory receptor and thus for odor quality.     

Deodorization study of the swine manure with two yeast strains

With the transition of livestock production from the traditional small household farming to large-scale centralized breeding, the odor pollution caused by livestock manure has become pressing in China. In this study, two yeast strains Y1 and Y2 with high deodorization efficiency were isolated from the sample collected from an outlet in a swine farm in Shuangliu County, Sichuan Province. The scale-up deodorization experiments were carried out for strains Y1, Y2, and their mixture Y1+Y2. The results showed that the reduction rate of treatments on NH₃ was in the sequence of Y1+Y2 (35.6 ～ 68.7%) >Y1 (20.3 ～ 63.7%) >Y2 (?11.7 ～ 53.8%). The reduction rate of treatments on H₂S was in the sequence of Y1+Y2 (47.2 ～ 70.1%) > Y2 (36.6 ～ 60.8%) > Y1 (27.6 ～ 42.0%). The reduction rate of treatments on total volatile organic compounds (TVOC) was in the sequence of Y1+Y2 (49.1 ～ 68.3%) > Y1 (36.2 ～ 54.6%) >Y2 (20.8 ～ 48.6%). The reduction rate of treatments on odor intensity was in the sequence of Y1+Y2 (27.2–60.3%) > Y1 (16.3 ～ 38.5%) >Y2 (?0.4 ～ 35.2%). Furthermore, the concentrations of VFAs, indole, skatole, total nitrogen (TN), organic nitrogen (ON), total sulfur (TS), and ammonium nitrogen (AN) in swine manure during deodorization by yeast strains Y1, Y2, and their mixture Y1+Y2 were assayed. The results showed the concentrations of VFAs, indole, and skatole in the manure with Y1, Y2, and Y1+Y2 treatments were all lower than those of the control group. The concentrations of TN, ON, and TS in treatments were all higher than that of the control group. The concentrations of AN in the treatment groups were all lower than those of the control group.     

Dissimilatory iron reduction and odor indicator abatement by biofilm communities in swine manure microcosms

Animal waste odors arising from products of anaerobic microbial metabolism create community relations problems for livestock producers. We investigated a novel approach to swine waste odor reduction: the addition of FeCl(3), a commonly used coagulant in municipal wastewater treatment, to stimulate degradation of odorous compounds by dissimilatory iron-reducing bacteria (DIRB). Two hypotheses were tested: (i) FeCl(3) is an effective source of redox-active ferric iron (Fe(3+)) for dissimilatory reduction by bacteria indigenous to swine manure, and (ii) dissimilatory iron reduction results in significant degradation of odorous compounds within 7 days. Our results demonstrated that Fe(3+) from FeCl(3) was reduced biologically as well as chemically in laboratory microcosms prepared with prefiltered swine manure slurry and limestone gravel, which provided pH buffering and a substrate for microbial biofilm development. Addition of a 1-g liter(-1) equivalent concentration of Fe(3+) from FeCl(3), but not from presynthesized ferrihydrite, caused initial, rapid solids flocculation, chemical Fe(3+) reduction, and E(h) increase, followed by a 2-day lag period. Between 2 and 6 days of incubation, increases in Fe(2+) concentrations were accompanied by significant reductions in concentrations of volatile fatty acids used as odor indicators. Increases in Fe(2+) concentrations between 2 and 6 days did not occur in FeCl(3)-treated microcosms that were sterilized by gamma irradiation or amended with NaN(3), a respiratory inhibitor. DNA sequences obtained from rRNA gene amplicons of bacterial communities in FeCl(3)-treated microcosms were closely related to Desulfitobacterium spp., which are known representatives of DIRB. Use of iron respiration to abate wastewater odors warrants further investigation.