Oxidation of methyl fluoride and dimethyl ether by ammonia monooxygenase in Nitrosomonas europaea

Acetylene Tunes Microbial Growth During Aerobic Cometabolism of Trichloroethene

Microbial aerobic cometabolism is a possible treatment approach for large, dilute trichloroethene (TCE) plumes at groundwater contaminated sites. Rapid microbial growth and bioclogging pose a persistent problem in bioremediation schemes. Bioclogging reduces soil porosity and permeability, which negatively affects substrate distribution and contaminant treatment efficacy while also increasing the operation and maintenance costs of bioremediation. In this study, we evaluated the ability of acetylene, an oxygenase enzyme-specific inhibitor, to decrease biomass production while maintaining aerobic TCE cometabolism capacity upon removal of acetylene. We first exposed propane-metabolizing cultures (pure and mixed) to 5% acetylene (v v-1) for 1, 2, 4, and 8 d and we then verified TCE aerobic cometabolic activity. Exposure to acetylene overall decreased biomass production and TCE degradation rates while retaining the TCE degradation capacity. In the mixed culture, exposure to acetylene for 1-8 d showed minimal effects on the composition and relative abundance of TCE cometabolizing bacterial taxa. TCE aerobic cometabolism and incubation conditions exerted more notable effects on microbial ecology than did acetylene. Acetylene appears to be a viable approach to control biomass production that may lessen the likelihood of bioclogging during TCE cometabolism. The findings from this study may lead to advancements in aerobic cometabolism remediation technologies for dilute plumes.

Role of Ammonia Oxidation in Organic Micropollutant Transformation during Wastewater Treatment: Insights from Molecular, Cellular, and Community Level Observations

Organic micropollutants (OMPs) are a threat to aquatic environments, and wastewater treatment plants may act as a source or a barrier of OMPs entering the environment. Understanding the fate of OMPs in wastewater treatment processes is needed to establish efficient OMP removal strategies. Enhanced OMP biotransformation has been documented during biological nitrogen removal and has been attributed to the cometabolic activity of ammonia-oxidizing bacteria (AOB) and, specifically, to the ammonia monooxygenase (AMO) enzyme. Yet, the exact mechanisms of OMP biotransformation are often unknown. This critical review aims to fundamentally and quantitatively evaluate the role of ammonia oxidation in OMP biotransformation during wastewater treatment processes. OMPs can be transformed by AOB via direct and indirect enzymatic reactions: AMO directly transforms OMPs primarily via hydroxylation, while biologically produced reactive nitrogen species (hydroxylamine (NH₂OH), nitrite (NO₂^-), and nitric oxide (NO)) can chemically transform OMPs through nitration, hydroxylation, and deamination and can contribute significantly to the observed OMP transformations. OMPs containing alkyl, aliphatic hydroxyl, ether, and sulfide functional groups as well as substituted aromatic rings and aromatic primary amines can be biotransformed by AMO, while OMPs containing alkyl groups, phenols, secondary amines, and aromatic primary amines can undergo abiotic transformations mediated by reactive nitrogen species. Higher OMP biotransformation efficiencies and rates are obtained in AOB-dominant microbial communities, especially in autotrophic reactors performing nitrification or nitritation, than in non-AOB-dominant microbial communities. The biotransformations of OMPs in wastewater treatment systems can often be linked to ammonium (NH₄⁺) removal following two central lines of evidence: (i) Similar transformation products (i.e., hydroxylated, nitrated, and desaminated TPs) are detected in wastewater treatment systems as in AOB pure cultures. (ii) Consistency in OMP biotransformation (r_bio, μmol/g VSS/d) to NH₄⁺ removal (r_NH4+, mol/g VSS/d) rate ratios (r_bio/r_NH4+) is observed for individual OMPs across different systems with similar r_NH4+ and AOB abundances. In this review, we conclude that AOB are the main drivers of OMP biotransformation during wastewater treatment processes. The importance of biologically driven abiotic OMP transformation is quantitatively assessed, and functional groups susceptible to transformations by AMO and reactive nitrogen species are systematically classified. This critical review will improve the prediction of OMP transformation and facilitate the design of efficient OMP removal strategies during wastewater treatment.

Assessing the impact of synthetic estrogen on the microbiome of aerated submerged fixed-film reactors simulating tertiary sewage treatment and isolation of estrogen-degrading consortium

17α-ethinylestradiol (EE2) is a synthetic estrogen that can cause harmful effects on animals, such as male feminization and infertility. However, the impact of the EE2 contamination on microbial communities and the potential role of bacterial strains as bioremediation agents are underexplored. The aim of this work was to evaluate the impact of EE2 on the microbial community dynamics of aerated submerged fixed-film reactors (ASFFR) simulating a polishing step downstream of a secondary sewage treatment. For this purpose, the reactors were fed with a synthetic medium with low COD content (around 50 mg l^-1), supplemented (reactor H) or not (reactor C) with 1 μg l^-1 of EE2. Sludge samples were periodically collected during the bioreactors operation to assess the bacterial profile over time by 16S rRNA gene amplicon sequencing or by bacterial isolation using culture-dependent approach. The results revealed that the most abundant phyla in both reactors were Proteobacteria and Bacteroidetes. At genus level, Chitinophagaceae, Nitrosomonas and Bdellovibrio predominated. Significant effects caused by EE2 treatment and bioreactors operating time were observed by non-metric multidimensional scaling. Therefore, even at low concentrations as 1 μg l^-1, EE2 is capable of influencing the bioreactor microbiome. Culture-dependent methods showed that six bacterial isolates, closely related to Pseudomonas and Acinetobacter genera, could grow on EE2 as the sole carbon source under aerobic conditions. These organisms may potentially be used for the assembly of an EE2-degrading bacterial consortium and further exploited for bioremediation applications, including tertiary sewage treatment to remove hormone-related compounds not metabolized in secondary depuration stages.

Impact of microbial physiology and microbial community structure on pharmaceutical fate driven by dissolved oxygen concentration in nitrifying bioreactors

Operation at low dissolved oxygen (DO) concentrations (<1 mg/L) in wastewater treatment could save utilities significantly by reducing aeration energy costs. However, few studies have evaluated the impact of low DO on pharmaceutical biotransformations during treatment. DO concentration can impact pharmaceutical biotransformation rates during wastewater treatment both directly and indirectly: directly by acting as a limiting substrate that slows the activity of the microorganisms involved in biotransformation; and indirectly by shaping the microbial community and selecting for a community that performs pharmaceutical biotransformation faster (or slower). In this study, nitrifying bioreactors were operated at low (∼0.3 mg/L) and high (>4 mg/L) DO concentrations to understand how DO growth conditions impacted microbial community structure. Short-term batch experiments using the biomass from the parent reactors were performed under low and high DO conditions to understand how DO concentration impacts microbial physiology. Although the low DO parent biomass had a lower specific activity with respect to ammonia oxidation than the high DO parent reactor biomass, it had faster biotransformation rates of ibuprofen, sulfamethoxazole, 17α-ethinylestradiol, acetaminophen, and atenolol in high DO batch conditions. This was likely because the low DO reactor had a 2x higher biomass concentration, was enriched for ammonia oxidizers (4x higher concentration), and harbored a more diverse microbial community (3x more unique taxa) as compared to the high DO parent reactor. Overall, the results show that there can be indirect benefits from low DO operation over high DO operation that support pharmaceutical biotransformation during wastewater treatment.

Activity-Based Protein Profiling of Ammonia Monooxygenase in Nitrosomonas europaea

Nitrosomonas europaea is an aerobic nitrifying bacterium that oxidizes ammonia (NH3) to nitrite (NO2 (-)) through the sequential activities of ammonia monooxygenase (AMO) and hydroxylamine dehydrogenase (HAO). Many alkynes are mechanism-based inactivators of AMO, and here we describe an activity-based protein profiling method for this enzyme using 1,7-octadiyne (17OD) as a probe. Inactivation of NH4 (+)-dependent O2 uptake by N. europaea by 17OD was time- and concentration-dependent. The effects of 17OD were specific for ammonia-oxidizing activity, andde novoprotein synthesis was required to reestablish this activity after cells were exposed to 17OD. Cells were reacted with Alexa Fluor 647 azide using a copper-catalyzed azide-alkyne cycloaddition (CuAAC) (click) reaction, solubilized, and analyzed by SDS-PAGE and infrared (IR) scanning. A fluorescent 28-kDa polypeptide was observed for cells previously exposed to 17OD but not for cells treated with either allylthiourea or acetylene prior to exposure to 17OD or for cells not previously exposed to 17OD. The fluorescent polypeptide was membrane associated and aggregated when heated with β-mercaptoethanol and SDS. The fluorescent polypeptide was also detected in cells pretreated with other diynes, but not in cells pretreated with structural homologs containing a single ethynyl functional group. The membrane fraction from 17OD-treated cells was conjugated with biotin-azide and solubilized in SDS. Streptavidin affinity-purified polypeptides were on-bead trypsin-digested, and amino acid sequences of the peptide fragments were determined by liquid chromatography-mass spectrometry (LC-MS) analysis. Peptide fragments from AmoA were the predominant peptides detected in 17OD-treated samples. In-gel digestion and matrix-assisted laser desorption ionization-tandem time of flight (MALDI-TOF/TOF) analyses also confirmed that the fluorescent 28-kDa polypeptide was AmoA.

Inhibition of nitrification by low oxygen concentrations in an aerated treatment pond system with biofilm promoting mats

Inhibition of nitrification in the presence of low oxygen concentrations (below 1.2 mg/L) and temperature dependency at oxygen saturation levels were observed in an aerated treatment pond system with biofilm promoting mats in two parallel ponds for remediation of ammonium, methyl tertiary butyl ether (MTBE), and benzene-contaminated groundwater. Within the first 18 months, at an average oxygen concentration of 0.7 +/- 0.5 mg/L along the ponds, no significant decrease of ammonium or significant formation of nitrification products were observed. After increasing the aeration to oxygen saturation levels, the ammonium removal increased up to a maximum of 27%, with concomitant formation of nitrite and nitrate (up to 26 and 0.6 mM). The subsequent reduction of aeration in one pond to the previous level resulted in a definitive stop of nitrification, while, in the other pond, nitrification was well-correlated with the water temperature, reaching up to 45% ammonium removal.

Effects of Soil on Ammonia, Ethylene, Chloroethane, and 1,1,1-Trichloroethane Oxidation by Nitrosomonas europaea

Ammonia monooxygenase (AMO) from Nitrosomonas europaea catalyzes the oxidation of ammonia to hydroxylamine and has been shown to oxidize a variety of halogenated and nonhalogenated hydrocarbons. As part of a program focused upon extending these observations to natural systems, a study was conducted to examine the influence of soil upon the cooxidative abilities of N. europaea. Small quantities of Willamette silt loam (organic carbon content, 1.8%; cation-exchange capacity, 15 cmol/kg of soil) were suspended with N. europaea cells in a soil-slurry-type reaction mixture. The oxidations of ammonia and three different hydrocarbons (ethylene, chloroethane, and 1,1,1-trichloroethane) were compared to results for controls in which no soil was added. The soil significantly inhibited nitrite production from 10 mM ammonium by N. europaea. Inhibition resulted from a combination of ammonium adsorption onto soil colloids and the exchangeable acidity of the soil lowering the pH of the reaction mixture. These phenomena resulted in a substantial drop in the concentration of NH(4) in solution (10 to 4.5 mM) and, depending upon the pH, in a reduction in the amount of available NH(3) to concentrations (8 to 80 muM) similar to the K(s) value of AMO for NH(3) ( approximately 29 muM). At a fixed initial pH (7.8), the presence of soil also modified the rates of oxidation of ethylene and chloroethane and changed the concentrations at which their maximal rates of oxidation occurred. The modifying effects of soil on nitrite production and on the cooxidation of ethylene and chloroethane could be circumvented by raising the ammonium concentration in the reaction mixture from 10 to 50 mM. Soil had virtually no effect on the oxidation of 1,1,1-trichloroethane.

Metabolism of Inorganic N Compounds by Ammonia-Oxidizing Bacteria

Ammonia oxidizing bacteria extract energy for growth from the oxidation of ammonia to nitrite. Ammonia monooxygenase, which initiates ammonia oxidation, remains enigmatic given the lack of purified preparations. Genetic and biochemical studies support a model for the enzyme consisting of three subunits and metal centers of copper and iron. Knowledge of hydroxylamine oxidoreductase, which oxidizes hydroxylamine formed by ammonia monooxygenase to nitrite, is informed by a crystal structure and detailed spectroscopic and catalytic studies. Other inorganic nitrogen compounds, including NO, N2O, NO2, and N2 can be consumed and/or produced by ammonia-oxidizing bacteria. NO and N2O can be produced as byproducts of hydroxylamine oxidation or through nitrite reduction. NO2 can serve as an alternative oxidant in place of O2 in some ammonia-oxidizing strains. Our knowledge of the diversity of inorganic N metabolism by ammonia-oxidizing bacteria continues to grow. Nonetheless, many questions remain regarding the enzymes and genes involved in these processes and the role of these pathways in ammonia oxidizers.

Biodegradation of perfluorinated compounds

The information available in the literature provides evidence for the biodegradation of some poly- and per-fluorinated compounds, but such biodegradation is incomplete and may not result in mineralization. Recent publications have demonstrated that 8:2 fluorotelomer alcohol, for example, can be degraded by bacteria from soil and wastewater treatment plants to perfluorooctanoic acid. Similarly, 2-N-ethyl(perfluorooctane sulfonamido)ethanol can be degraded by wastewater treatment sludge to perfluorooctanesulfonate. It is presently unclear whether these two products are degraded further. Therefore, the question remains as to whether there is a potential for defluorination and biodegradation of PFCs that contributes significantly to their environmental fate. The lack of mineralization observed is probably caused by the stability of the C-F bond, although there are examples of microbially catalyzed defluorination reactions. As is the case with reductive dechlorination or debromination, reductive defluorination is energetically favorable under anaerobic conditions and releases more energy than that available from sulfate reduction or methanogenesis. Consequently, we should consider the possibility that bacteria will adapt to utilize this source of energy, although evolving mechanisms to overcome the kinetic barriers to degradation of these compounds may take some time. The fact that such reactions are absent for some PFCs, to date, may be because too little time has passed for microorganisms to adapt to these potential substrates. Hence, the situation may be comparable to that of chlorinated organic compounds several decades ago. For many years, organochlorine compounds were considered to be catabolically recalcitrant; today, reductive chlorination reactions of many organochlorines, including PCBs and dioxins, are regularly observed in anaerobic environments. Hence, it is opportune and important to continue studying the potential degradation of perfluorinated compounds in carefully designed experiments with either microbial populations from contaminated sites or cultures of bacteria known to dehalogenate chlorinated compounds.

Transient accumulation of γ-butyrolactone during degradation of bis(4-chloro-n-butyl) ether by diethylether-grown Rhodococcus sp. strain DTB

Rhodococcus sp. strain DTB (DSM 44534) grows aerobically on diethylether as sole source of carbon and energy. Dense cell suspension experiments showed that the induced ether-cleaving enzyme system attacks a broad range of ethers like tetrahydrofuran, phenetole and chlorinated alkylethers including Calpha-substituted alkylethers. Identification of metabolites revealed that degradation of the ethers started by an initial attack of the ether bond. Diethylether-grown cells degraded bis(4-chloro-n-butyl) ether via an initial ether scission followed by the transient accumulation of gamma-butyrolactone as intermediate at nearly stoichiometric concentrations.

Improved methods for the cultivation of the chemolithoautotrophic bacterium Nitrosomonas europaea

The chemolithoautotrophic nitrifier Nitrosomonas europaea is useful for biotechnological processes such as bioremediation of toxic chemicals, as well as playing an essential role in the global nitrogen cycle. To successfully apply this bacterium in biotechnology, large quantities of active cells need to be produced. In this paper we demonstrate improved methods for mass cultivation of N. europaea. A doubling in the final cell density to 30 mg dry wt l(-1) was achieved with a fed-batch culture technique using ammonium bicarbonate or sodium bicarbonate for pH control. The cells displayed high ammonia oxidizing activity in excess of 20 mmol g(-1) dry wt h(-1). Continuous culture under energy limited growth conditions (<0.1 mM residual ammonium) in a bench scale bioreactor using a microfiltration membrane for high cell recycle produced final culture densities greater than 350 mg dry wt l(-1). This system allowed operator controlled culturing of cells under excess substrate as well as energy limited growth conditions with a maximum ammonium oxidation potential in excess of 250 mmol g(-1) dry wt h(-1).

Inhibition of diethyl ether degradation in Rhodococcus sp. strain DEE5151 by glutaraldehyde and ethyl vinyl ether

Alkyl ether-degrading Rhodococcus sp. strain DEE5151, isolated from activated sewage sludge, has an activity for the oxidation of a variety of alkyl ethers, aralkyl ethers and dibenzyl ether. The whole cell activity for diethyl ether oxidation was effectively inhibited by 2,3-dihydrofurane, ethyl vinyl ether and glutaraldehyde. Glutaraldehyde of less than 30 μM inhibited the activity by a competitive manner with the inhibition constant, KI of 7.07 ± 1.36 μM. The inhibition type became mixed at higher glutaraldehyde concentrations &gt;30 μM, probably due to the inactivation of the cell activity by the Schiff-base formation. Structurally analogous ethyl vinyl ether inhibited the diethyl ether oxidation activity in a mixed manner with decreasing the apparent maximum oxidation rate, , and icreasing the apparent Michaelis–Menten constant, . The mixed type inhibition by ethyl vinyl ether seemed to be introduced not only by the structure similarity with diethyl ether, but also by the reactivity of the vinyl ether with cellular components in the whole cell system.

Degradation of alkyl ethers, aralkyl ethers, and dibenzyl ether by Rhodococcus sp. strain DEE5151, isolated from diethyl ether-containing enrichment cultures

Twenty strains isolated from sewage sludge were found to degrade various ethers, including alkyl ethers, aralkyl ethers, and dibenzyl ether. In Rhodococcus strain DEE5151, induction of ether degradation needed substrates exhibiting at least one unsubstituted Calpha-methylene moiety as the main structural prerequisite. The cleavage reaction observed with anisole, phenetole, and dibenzyl ether indicates that the initial oxidation occurs at such respective Calpha positions. Diethyl ether-induced strain DEE5151 degraded dibenzyl ether via intermediately accumulated benzoic acid. Phenetole seems to be subject also to another ether-cleaving enzyme. Other strains of this group showed different enzymatic activities towards the substrate classes investigated.

Biodegradation of bis(1-chloro-2-propyl) ether via initial ether scission and subsequent dehalogenation by Rhodococcus sp. strain DTB

Rhodococcus sp. strain DTB (DSM 44534) grows on bis(1-chloro-2-propyl) ether (DDE) as sole source of carbon and energy. The non-chlorinated diisopropyl ether and bis(1-hydroxy-2-propyl) ether, however, did not serve as substrates. In ether degradation experiments with dense cell suspensions, 1-chloro-2-propanol and chloroacetone were formed, which indicated that scission of the ether bond is the first step while dehalogenation of the chlorinated C(3)-compounds occurs at a later stage of the degradation pathway. Inhibition of ether scission by methimazole suggested that the first step in degradation is catalyzed by a flavin-dependent enzyme activity. The non-chlorinated compounds 1,2-propanediol, hydroxyacetone, lactate, pyruvate, 1-propanol, propanal, and propionate also supported growth, which suggested that the intermediates 1,2-propanediol and hydroxyacetone are converted to pyruvate or to propionate, which can be channeled into the citric acid cycle by a number of routes. Total release of chloride and growth-yield experiments with DDE and non-chlorinated C(3)-compounds suggested complete biodegradation of the chlorinated ether.

Ammonia oxidation by Nitrosomonas eutropha with NO(2) as oxidant is not inhibited by acetylene

The effect of acetylene ((14)C(2)H(2)) on aerobic and anaerobic ammonia oxidation by Nitrosomonas eutropha was investigated. Ammonia monooxygenase (AMO) was inhibited and a 27 kDa polypeptide (AmoA) was labelled during aerobic ammonia oxidation. In contrast, anaerobic, NO(2)-dependent ammonia oxidation (NO(2)/N(2)O(4) as oxidant) was not affected by acetylene. Further studies gave evidence that the inhibition as well as the labelling reaction were O(2)-dependent. Cells pretreated with acetylene under oxic conditions were unable to oxidize ammonia with O(2) as oxidant. After these cell suspensions were supplemented with gaseous NO(2), ammonia oxidation activity of about 140 micromol NH(4)(+) (g protein)(-1) h(-1) was detectable under both oxic and anoxic conditions. A significantly reduced acetylene inhibition of the ammonia oxidation activity was observed for cells incubated in the presence of NO. This suggests that NO and acetylene compete for the same binding site on AMO. On the basis of these results a new hypothetical model of ammonia oxidation by N. eutropha was developed.

Degradation of ethinyl estradiol by nitrifying activated sludge

Degradation of ethinyl estradiol (EE2) by nitrifying activated sludge was studied with micro-organisms grown in a reactor with feedback of sludge fed with only a mineral salts medium containing ammonium as the sole energy source. Ammonium was oxidised by this sludge at a rate of 50 mg NH4+ g(-1) DW h(-1). This activated sludge was also capable of degrading EE2 at a maximum rate of 1 microg g(-1) DW h(-1). Using sludge with an insignificant nitrifying capacity of 1 mg NH4+ g(-1) DW h(-1), no degradation of EE2 was detected. Oxidation of EE2 by nitrifying sludge resulted in the formation of hydrophilic compounds, which were not further identified. Most probably degradation by nitrifying sludge results in a loss of estrogenic activity, as hydroxylated derivatives of EE2 are known to have a substantially lower pharmacological activity than EE2.

New insights into methyl bromide cooxidation by Nitrosomonas europaea obtained by experimenting with moderately low density cell suspensions

We examined the rates and sustainability of methyl bromide (MeBr) oxidation in moderately low density cell suspensions ( approximately 6 x 10(7) cells ml(-1)) of the NH(3)-oxidizing bacterium Nitrosomonas europaea. In the presence of 10 mM NH(4)(+) and 0.44, 0. 22, and 0.11 mM MeBr, the initial rates of MeBr oxidation were sustained for 12, 12, and 24 h, respectively, despite the fact that only 10% of the NH(4)(+), 18% of the NH(4)(+), and 35% of the NH(4)(+), respectively, were consumed. Although the duration of active MeBr oxidation generally decreased as the MeBr concentration increased, similar amounts of MeBr were oxidized with a large number of the NH(4)(+)-MeBr combinations examined (10 to 20 micromol mg [dry weight] of cells(-1)). Approximately 90% of the NH(3)-dependent O(2) uptake activity and the NO(2)(-)-producing activity were lost after N. europaea was exposed to 0.44 mM MeBr for 24 h. After MeBr was removed and the cells were resuspended in fresh growth medium, NO(2)(-) production increased exponentially, and 48 to 60 h was required to reach the level of activity observed initially in control cells that were not exposed to MeBr. It is not clear what percentage of the cells were capable of cell division after MeBr oxidation because NO(2)(-) accumulated more slowly in the exposed cells than in the unexposed cells despite the fact that the latter were diluted 10-fold to create inocula which exhibited equal initial activities. The decreases in NO(2)(-)-producing and MeBr-oxidizing activities could not be attributed directly to NH(4)(+) or NH(3) limitation, to a decrease in the pH, to the composition of the incubation medium, or to toxic effects caused by accumulation of the end products of oxidation (NO(2)(-) and formaldehyde) in the medium. Additional cooxidation-related studies of N. europaea are needed to identify the mechanism(s) responsible for the MeBr-induced loss of cell activity and/or viability, to determine what percentages of cells damaged by cooxidative activities are culturable, and to determine if cooxidative activity interferes with the regulation of NH(3)-oxidizing activity.

Contribution of methanotrophic and nitrifying bacteria to CH4 and NH4+ oxidation in the rhizosphere of rice plants as determined by new methods of discrimination

Methanotrophic and nitrifying bacteria are both able to oxidize CH4 as well as NH4+. To date it is not possible to estimate the relative contribution of methanotrophs to nitrification and that of nitrifiers to CH4 oxidation and thus to assess their roles in N and C cycling in soils and sediments. This study presents new options for discrimination between the activities of methanotrophs and nitrifiers, based on the competitive inhibitor CH3F and on recovery after inhibition with C2H2. By using rice plant soil as a model system, it was possible to selectively inactivate methanotrophs in soil slurries at a CH4/CH3F/NH4+ molar ratio of 0.1:1:18. This ratio of CH3F to NH4+ did not affect ammonia oxidation, but methane oxidation was inhibited completely. By using the same model system, it could be shown that after 24 h of exposure to C2H2 (1,000 parts per million volume), methanotrophs recovered within 24 h while nitrifiers stayed inactive for at least 3 days. This gave an "assay window" of 48 h when only methanotrophs were active. Applying both assays to model microcosms planted with rice plants demonstrated a major contribution of methanotrophs to nitrification in the rhizosphere, while the contribution of nitrifiers to CH4 oxidation was insignificant.

Toluene 2-Monooxygenase-Dependent Growth of Burkholderia cepacia G4/PR1 on Diethyl Ether

Aerobic bacterial growth on aromatic hydrocarbons typically requires oxygenase enzymes, which are known to fortuitously oxidize nongrowth substrates. In this study, we found that oxidation of diethyl ether by toluene 2-monooxygenase supported more rapid growth of Burkholderia cepacia G4/PR1 than did the aromatic substrates n-propylbenzene and o-xylene. The wild-type Burkholderia cepacia G4 failed to grow on diethyl ether. Purified toluene 2-monooxygenase protein components oxidized diethyl ether stoichiometrically to ethanol and acetaldehyde. Butyl methyl ether, diethyl sulfide, and 2-chloroethyl ethyl ether were oxidized by B. cepacia G4/PR1.

Biodegradability of fluorinated surfactants under aerobic and anaerobic conditions

The "ready biodegradability" of three fluorinated surfactants was determined under aerobic and anaerobic conditions. Surfactant 1, a solution of a fluorinated surfactant in water, was easily degradable under both aerobic and anaerobic conditions during the incubation periods of 28 and 60 days, respectively. Surfactant 2, a nonionic fluorinated surfactant, was degraded under aerobic conditions in a range of 35-77% during 28 days depending on the source of activated sludge. Aerobic degradation was inhibited by the nitrification-inhibitor dicyandiamide indicating that ammonium oxidizing bacteria may play a role in degradation of surfactant 2. Under anaerobic conditions surfactant 2 was not degraded. Surfactant 3, an anionic fluorinated surfactant, was degraded neither under aerobic nor under anaerobic conditions. Under anaerobic conditions, surfactant 3 inhibited the methane production rate of sludge from a digester. The EC50, i.e. the concentration of surfactant 3 that inhibited 50% of methanogenesis, was determined at 160 mg/l.

Effects of ammonia on the de novo synthesis of polypeptides in cells of Nitrosomonas europaea denied ammonia as an energy source

The effects of ammonium on the de novo synthesis of polypeptides in the soil-nitrifying bacterium Nitrosomonas europaea have been investigated. Cells were incubated in the presence of both acetylene and NH4+. Under these conditions, the cells were unable to utilize NH4+ as an energy source. Energy to support protein synthesis was supplied by the oxidation of hydroxylamine or other alternative substrates for hydroxylamine oxidoreductase. De novo protein synthesis was detected by 14C incorporation from 14CO2 into polypeptides by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. In the presence of NH4+, acetylene-treated cells synthesized the 27-kDa polypeptide of ammonia monoxygenase (AMO) and two other major polypeptides (with sizes of 55 and 65 kDa). The synthesis of these polypeptides was completely inhibited by chloramphenicol and attenuated by rifampin. The optimal concentration of hydroxylamine for the in vivo 14C-labeling reaction was found to be 2 mM. The effect of NH4+ concentration was also examined. It was shown to cause a saturable response with a Ks of approximately 2.0 mM NH4+. Labeling studies conducted at different pH values suggest cells respond to NH3 rather than NH4+. No other compounds tested were able to influence the synthesis of the 27-kDa component of AMO, although we have also demonstrated that this polypeptide can be synthesized under anaerobic conditions in cells utilizing pyruvate- or hydrazine-dependent nitrite reduction as an energy source. We conclude that ammonia has a regulatory effect on the synthesis of a subunit of AMO in addition to providing nitrogen for protein synthesis.