A rapid and simple respirometric biosensor with immobilized cells of Nitrosomonas europaea for detecting inhibitors of ammonia oxidation

Simultaneous algae-polluted water treatment and electricity generation using a biocathode-coupled electrocoagulation cell (bio-ECC)

How to utilize electrocoagulation (EC) technology for algae-polluted water treatment in an energy-efficient manner remains a critical challenge for its widespread application. Herein, a novel biocathode-coupled electrocoagulation cell (bio-ECC) with sacrificial iron anode and nitrifying biocathode was developed. Under different solution conductivities (2.33±0.25mScm^-1 and 4.94±0.55mScm^-1), the bio-ECC achieved almost complete removal of algae cells. The maximum power densities of 8.41 and 11.33Wm^-3 at corresponding current densities of 48.03Am^-3 and 66.26Am^-3 were obtained, with the positive energy balance of 4.52 and 7.44Wm^-3. In addition, the bio-ECC exhibited excellent NH₄⁺-N removal performance with the nitrogen removal rates of 7.28mgL^-1h^-1 and 6.77mgL^-1h^-1 in cathode chamber, indicating the superiority of bio-ECC in NH₄⁺-N removal. Pyrosequencing revealed that nitrifiers including Nitrospira, Nitrobacter, Nitrosococcus, and Nitrosomonas were enriched in biocathode. The removal mechanisms of algae in anode chamber were also explored by AFM and SEM-EDX tests. These results provide a proof-of-concept study of transferring energy-intensive EC process into an energy-neutral process with high-efficiency algae removal and electricity recovery.

Rheology and Microbiology of Sludge from a Thermophilic Aerobic Membrane Reactor

A thermophilic aerobic membrane reactor (TAMR) treating high-strength COD liquid wastes was submitted to an integrated investigation, with the aim of characterizing the biomass and its rheological behaviour. These processes are still scarcely adopted, also because the knowledge of their biology as well as of the physical-chemical properties of the sludge needs to be improved. In this paper, samples of mixed liquor were taken from a TAMR and submitted to fluorescent in situ hybridization for the identification and quantification of main bacterial groups. Measurements were also targeted at flocs features, filamentous bacteria, and microfauna, in order to characterize the sludge. The studied rheological properties were selected as they influence significantly the performances of membrane bioreactors (MBR) and, in particular, of the TAMR systems that operate under thermophilic conditions (i.e., around 50°C) with high MLSS concentrations (up to 200 gTS L−1). The proper description of the rheological behaviour of sludge represents a useful and fundamental aspect that allows characterizing the hydrodynamics of sludge suspension devoted to the optimization of the related processes. Therefore, in this study, the effects on the sludge rheology produced by the biomass concentration, pH, temperature, and aeration were analysed.

A potentiometric flow biosensor based on ammonia-oxidizing bacteria for the detection of toxicity in water

A flow biosensor for the detection of toxicity in water using the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea as a bioreceptor and a polymeric membrane ammonium-selective electrode as a transducer is described. The system is based on the inhibition effects of toxicants on the activity of AOB, which can be evaluated by measuring the ammonium consumption rates with the ammonium-selective membrane electrode. The AOB cells are immobilized on polyethersulfone membranes packed in a holder, while the membrane electrode is placed downstream in the flow cell. Two specific inhibitors of the ammonia oxidation—allylthiourea and thioacetamide—have been tested. The IC₅₀ values defined as the concentration of an inhibitor causing a 50% reduction in the ammonia oxidation activity have been measured as 0.17 μM and 0.46 μM for allylthiourea and thioacetamide, respectively. The proposed sensor offers advantages of simplicity, speed and high sensitivity for measuring toxicity in water.

Application of an integrated statistical design for optimization of culture condition for ammonium removal by Nitrosomonas europaea

Statistical methodology was applied to the optimization of the ammonium oxidation by Nitrosomonas europaea for biomass concentration (C_B), nitrite yield (Y_N) and ammonium removal (R_A). Initial screening by Plackett-Burman design was performed to select major variables out of nineteen factors, among which NH₄Cl concentration (C_N), trace element solution (TES), agitation speed (AS), and fermentation time (T) were found to have significant effects. Path of steepest ascent and response surface methodology was applied to optimize the levels of the selected factors. Finally, multi-objective optimization was used to obtain optimal condition by compromise of the three desirable objectives through a combination of weighted coefficient method coupled with entropy measurement methodology. These models enabled us to identify the optimum operation conditions (C_N = 84.1 mM; TES = 0.74 ml; AS = 100 rpm and T = 78 h), under which C_B = 3.386×10⁸ cells/ml; Y_N = 1.98 mg/mg and R_A = 97.76% were simultaneously obtained. The optimized conditions were shown to be feasible through verification tests.

Effects of selected pharmaceutically active compounds on the ammonia oxidizing bacterium Nitrosomonas europaea

Pharmaceutically active compounds (PhACs) are commonly found in wastewater influent. However, little research has focused on determining their impact on fundamental processes in wastewater treatment such as nitrogen removal. In this study, focus was placed on 4 commonly occurring PhACs (ketoprofen, naproxen, carbamazepine and gemfibrozil). Their effect was ascertained in the ammonia oxidizing bacterium (AOB), Nitrosomonas europaea in terms of membrane integrity and nitrite production. These PhACs were shown to inhibit nitrite production at concentrations of 1 and 10 μM while no effect was observed at 0.1 μM. The maximum observed nitrification inhibition was 25%, 29%, 22% and 26% for ketoprofen, naproxen, carbamazepine and gemfibrozil, respectively. A decrease in the live/dead ratio ranging from 10% to 16% suggests that these PhACs affect membrane integrity in N.europaea. The difference in nitrite production between PhACs treated cells and non PhAC treated controls was still significant following washing suggesting that inhibition is irreversible. Finally, nitrite production when adjusted to the live fraction of cells was also found to decrease suggesting that PhACs inhibited the activity of surviving cells. These results suggest that the presence of PhACs may affect AOB activity and may impact nitrogen removal, a key function in wastewater treatment. Follow up studies with additional AOB and in mixed culture are needed to further confirm these results.

Automatic biodetector of water toxicity (ABTOW) as a tool for examination of phenol and cyanide contaminated water

We describe an automatic biodetector for continuous monitoring of water toxicity (ABTOW). Construction of the ABTOW is based on natural ability of the biofilm formation to immobilize consortia of nitrifying bacteria (the sensing element) on the open cellular polyurethane foam as the support. Change of rates of oxygen consumption is used as an indicator of biocatalytic activity (nitrification) of the bacteria in response to xenobiotics. Owing to this design the ABTOW features stability long-term use, is inexpensive and simple in operation. The dynamics of ABTOW response is studied in details for phenol and cyanide as model toxins. These data indicate that the sensitivity was 3.5 μM for phenol and 0.19 μM for cyanide, respectively. The magnitudes of toxic effect were proportional to concentration whereas kinetics of the response is an indicator for the mechanism of toxicity. Similar methodology is applied to quantify toxicity of a range of heavy metals, herbicides and oxidative chain inhibitors. One may conclude that the presented biodetector provides a good sensitivity for continuous on-line monitoring of toxicity in water.

Nitrification and degradation of halogenated hydrocarbons--a tenuous balance for ammonia-oxidizing bacteria

The process of nitrification has the potential for the in situ bioremediation of halogenated compounds provided a number of challenges can be overcome. In nitrification, the microbial process where ammonia is oxidized to nitrate, ammonia-oxidizing bacteria (AOB) are key players and are capable of carrying out the biodegradation of recalcitrant halogenated compounds. Through industrial uses, halogenated compounds often find their way into wastewater, contaminating the environment and bodies of water that supply drinking water. In the reclamation of wastewater, halogenated compounds can be degraded by AOB but can also be detrimental to the process of nitrification. This minireview considers the ability of AOB to carry out cometabolism of halogenated compounds and the consequent inhibition of nitrification. Possible cometabolism monitoring methods that were derived from current information about AOB genomes are also discussed. AOB expression microarrays have detected mRNA of genes that are expressed at higher levels during stress and are deemed "sentinel" genes. Promoters of selected "sentinel" genes have been cloned and used to drive the expression of gene-reporter constructs. The latter are being tested as early warning biosensors of cometabolism-induced damage in Nitrosomonas europaea with promising results. These and other biosensors may help to preserve the tenuous balance that exists when nitrification occurs in waste streams containing alternative AOB substrates such as halogenated hydrocarbons.

Monitoring structure and activity of nitrifying bacterial biofilm in an automatic biodetector of water toxicity

Automatic biodetector of water toxicity is a biosensor based on monitoring of catalytic activity of the nitrifying bacteria. To create a standardized biosensing system, development of the biofilm must be characterized to determine the prerequisites for its biological (biocatalytic) stability. In this paper, growth of biofilm comprising ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in the open cellular polyurethane material polyurethane sponge bioreactor has been investigated. Dynamics of the biofilm formation was estimated using AOB and NOB metabolic activity and the volume occupied by these two types of bacteria in the biofilm. Spectrophotometry liquid ion chromatography and image cytometry were used, respectively, for these measurements. A mathematical model of the dynamics of biofilm formation was established. These data indicate that open cellular polyurethane material is a good basis for the immobilization of nitrifying bacteria. Moreover, growth of the biofilm leads to its stable structural form, whose biocatalytic activity (12.29 for AOB and 6.84 micromol min(-1) for NOB) is constant in the long term.

Applications of microbial cell sensors

Since the first microbial cell sensor was studied by Karube et al. in 1977, many types of microbial cell sensors have been developed as analytical tools. The microbial cell sensor utilizes microbes as a sensing element and a transducer. The characteristics of microbial cell sensors as sensing devices are a complete contrast to those of enzyme sensors or immunosensors, which are highly specific for the substrates of interest, although the specificity of the microbial cell sensor has been improved by genetic modification of the microbe used as the sensing element. Microbial cell sensors have the advantages of tolerance to measuring conditions, a long lifetime, and good cost performance, and have the disadvantage of a long response time. In this review, applications of microbial cell sensors are summarized.

Physiological and transcriptional responses of Nitrosomonas europaea to toluene and benzene inhibition

Ammonia oxidizing bacteria (AOB) are inhibited by many compounds found in wastewater treatment plant (WWTP) influent, including aromatic hydrocarbons. The detection of "sentinel genes" to identify the presence of aromatic hydrocarbons could be useful to WWTP operators. In this study, the transcriptomic responses of Nitrosomonas europaea during the cometabolism of benzene to phenol and toluene to benzyl alcohol and benzaldehyde were evaluated using whole genome Affymetrix microarrays and qRT-PCR. Benzyl alcohol and benzaldehyde were found not to inhibit N. europaea. However, phenol concentrations as low as 5 microM directly inhibited ammonia oxidation. Surprisingly, there were no significant up- or down-regulation of genes in N. europaea cells exposed to 20 microM toluene, which caused 50% inhibition of ammonia oxidation. Exposing N. europaea to 40 microM benzene, which caused a similar degree of inhibition, resulted in the up-regulation of seven adjacent genes, including NE 1545 (a putative pirin protein) and NE 1546 (a putative membrane protein), that appear to be involved with fatty-acid metabolism, lipid biosynthesis, and membrane protein synthesis. qRT-PCR analysis revealed that NE 1545 and NE 1546 were significantly up-regulated upon exposure to benzene and phenol, but not upon exposure to toluene. Transmission electron microscope images revealed a shift in outer cell structure in response to benzene exposure.

Development of microbial sensors and their application

Many types of microbial sensors have been developed as analytical tools since the first microbial sensor was studied by Karube et al. in 1977. The microbial sensor consists of a transducer and microbe as a sensing element. The characteristics of the microbial sensors are a complete contrast to those of enzyme sensors or immunosensors, which are highly specific for the substrates of interest, although the specificity of the microbial sensor has been improved by genetic modification of the microbe used as the sensing element. Microbial sensors have the advantages of tolerance to measuring conditions, a long lifetime, and cost performance, and also have the disadvantage of a long response time. In this review, the long history of microbial sensor development is summarized.

Detecting oxygen consumption in the proximity ofSaccharomyces cerevisiae cells using self-assembled fluorescent nanosensors

We describe a strategy for the preparation and self-assembly of fluorescent nanosensors onto Saccharomyces cerevisiae cell surfaces for dynamically measuring oxygen concentration in the proximity of living cells. Amine functionalized polystyrene nanobeads were impregnated with an oxygen-sensitive ruthenium(II) complex and the beads' surface was coated with polyethylenimine. The resulting nanosensors were assembled on individual S. cerevisiae cells in a controlled manner at physiological pH for continuously monitoring oxygen consumption. This approach exemplifies a general scheme for assembling fluorescent nanosensors on cells for the non-invasive, reversible, and real-time measurement of other physiologically relevant processes, such as the efflux of protons and carbon dioxide, or the influx of glucose.