High nitrogen removal performance at moderately low temperature utilizing anaerobic ammonium oxidation reactions

High rates of nitrogen removal from wastewater have been reported using anammox bacteria at temperatures around 37 degrees C, but not at moderately low temperatures. In this study, nitrogen removal performance of an anaerobic biological filtrated (ABF) reactor, filled with porous polyester nonwoven fabric carriers as a fixed bed for anammox bacteria, was tested at 37 degrees C and at moderately low temperature (20-22 degrees C). To attain higher nitrogen removal performance, effects of influent nitrogen concentrations and hydraulic retention time (HRT) on nitrogen removal rates were investigated. Nitrogen removal rate increased with influent ammonium and nitrite concentrations, resulting in a removal rate of 3.3 kg-N/m(3)/d on day 32 for an HRT of 180 min at 37 degrees C. However, influent nitrite concentrations greater than 280 mg/l inhibited anammox activity. Therefore, the influent nitrite concentration was adjusted to be below 280 mg/l, and high-loading tests were performed for a shorter HRT. As a result, a nitrogen conversion rate of 11.5 kg-N/m(3)/d was achieved. Moreover, to evaluate long-term anammox activity at moderately low temperatures, ABF reactors were operated for 446 d. Anammox activity could be maintained at 20-22 degrees C, and stable nitrogen removal performance was observed. Furthermore, high nitrogen conversion rate of 8.1 kg-N/m(3)/d was attained. These results clearly show that an appropriate nitrite concentration in the influent and a shorter HRT resulted in high nitrogen conversion rates. The nitrogen removal performance we obtained at moderately low temperatures will open the door for application of anammox processes to many types of industrial wastewater treatment.     

Prevalence of anaerobic ammonium-oxidizing bacteria in contaminated groundwater

Anaerobic ammonium-oxidizing (anammox) bacteria perform an important step in the global nitrogen cycle: anaerobic oxidation of ammonium and reduction of nitrite to form dinitrogen gas (N(2)). Anammox organisms appear to be widely distributed in natural and artificial environments. However, their roles in groundwater ammonium attenuation remain unclear and only limited biomarker-based data confirmed their presence prior to this study. We used complementary molecular and isotope-based methods to assess anammox diversity and activity occurring at three ammonium-contaminated groundwater sites: quantitative PCR, denaturing gradient gel electrophoresis, sequencing of 16S rRNA genes, and (15)N-tracer incubations. Here we show that anammox performing organisms were abundant bacterial community members. Although all sites were dominated by Candidatus Brocadia-like sequences, the community at one site was particularly diverse, possessing four of five known genera of anammox bacteria. Isotope data showed that anammox produced up to 18 and 36% of N(2) at these sites. By combining molecular and isotopic results we have demonstrated the diversity, abundance, and activity of these autotrophic bacteria. Our results provide strong evidence for their important biogeochemical role in attenuating groundwater ammonium contamination.     

Cytochrome cd1-containing nitrite reductase encoding gene nirS as a new functional biomarker for detection of anaerobic ammonium oxidizing (Anammox) bacteria

A newly designed primer set (AnnirS), together with a previously published primer set (ScnirS), was used to detect anammox bacterial nirS genes from sediments collected from three marine environments. Phylogenetic analysis demonstrated that all retrieved sequences were clearly different from typical denitrifiers' nirS, but do group together with the known anammox bacterial nirS. Sequences targeted by ScnirS are closely related to Scalindua nirS genes recovered from the Peruvian oxygen minimum zone (OMZ), whereas sequences targeted by AnnirS are more closely affiliated with the nirS of Candidatus 'Kuenenia stuttgartiensis' and even form a new phylogenetic nirS clade, which might be related to other genera of the anammox bacteria. Analysis demonstrated that retrieved sequences had higher sequence identities (>60%) with known anammox bacterial nirS genes than with denitrifiers' nirS, on both nucleotide and amino acid levels. Compared to the 16S rRNA and hydrazine oxidoreductase (hzo) genes, the anammox bacterial nirS not only showed consistent phylogenetic relationships but also demonstrated more reliable quantification of anammox bacteria because of the single copy of the nirS gene in the anammox bacterial genome and the specificity of PCR primers for different genera of anammox bacteria, thus providing a suitable functional biomarker for investigation of anammox bacteria.     

Combined nitritation-anammox: advances in understanding process stability

Efficient nitrogen removal from wastewater containing high concentrations of ammonium but little organic substrate has recently been demonstrated by several full-scale applications of the combined nitritation-anammox process. While the process efficiency is in most cases very good, process instabilities have been observed to result in temporary process failures. In the current study, conditions resulting in instability and strategies to regain efficient operation were evaluated. First, data from full-scale operation is presented, showing a sudden partial loss of activity followed by recovery within less than 1 month. Results from laboratory-scale experiments indicate that these dynamics observed in full scale can be caused by partial inhibition of the ammonia oxidizing bacteria (AOB), while anammox inhibition is a secondary effect due to temporarily reduced O(2) depletion. Complete anammox inhibition is observed at 0.2 mg O(2) · L(-1), resulting in NO(2)(-) accumulation. However, this inhibition of anammox is reversible within minutes after O(2) depletion. Thus, variable AOB activity was identified as the key to reactor stability. With appropriate interpretation of the online NH(4)(+) signal, accumulation of NO(2)(-) can be detected indirectly and used to signal an imbalance of O(2) supply and AOB activity (no suitable online NO(2)(-) electrode is currently available). Second, increased abundance of nitrite-oxidizing bacteria (NOB; competing with anammox for NO(2)(-)) is known as another cause of instability. Based on a comparison of parallel full-scale reactors, it is suggested that an infrequent and short-term increased O(2) supply (e.g., for maintenance of aerators) that exceeds prompt depletion of oxygen by AOB may have caused increased NOB abundance. The volumetric air supply as a proxy for O(2) supply thus needs to be linked to AOB activity. Further, NOB can be washed out of the system during regular operation if the system is operated at a sludge age in the range of 45 days and by controlling the air supply according to the NO(3)(-) concentration in the treated effluent. Early detection of growing NOB abundance while the population is still low can help guide process operation and it is suggested that molecular methods of quantifying NOB abundance should be tested.     

Another multiheme protein, hydroxylamine oxidoreductase, abundantly produced in an anammox bacterium besides the hydrazine-oxidizing enzyme

A hydroxylamine oxidoreductase (HAO) was purified from anammox sludge in which an anammox bacterium, strain KSU-1, was dominant. The enzyme was a 118-kDa homodimer composed of a 53-kDa subunit. With phenazine methosulfate and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide as electron acceptors, the V(max) and K(m) for hydroxylamine were determined as 9.6+/-0.2 micromol/min x mg and 33+/-2 microM, while those for hydrazine were 0.54+/-0.0 micromol/min x mg and 25+/-2 microM, respectively. The HAO had a P468 chromophore. These enzymatic properties were different from those of the hydrazine-oxidizing enzyme (HZO), a multiheme protein abundantly produced by the KSU-1 strain, but were similar to those of the HAO purified from Candidatus Brocadia anammoxidans. The hao gene exists upstream of the hzoB gene, which codes for the HZO. The sequence deduced from the hao gene indicated eight c-type heme binding motifs and showed 87% identity with a polypeptide encoded by an open reading frame (kustc1061) in the genome of an anammox bacterium Candidatus Kuenenia stuttgartiensis. These suggested that the HAO is an indispensable enzyme and well conserved in anammox bacteria, similar to the HZO. This enzyme might therefore be a specific hydroxylamine oxidoreductase for anammox bacteria.     

Anammox bacterial abundance, biodiversity and activity in a constructed wetland

An integrated approach to document high anammox activity and biodiversity in a constructed wetland (CW) was performed and showed that substantial anammox activity could mitigate undesirable N(2)O emission. The enhanced anammox bacterial abundance, biodiversity and activity were achieved by supplementing activated sludge to the CW. Up to 3.38 × 10(7) gene copies g(-1) dry soil of anammox bacteria were enriched in the CW. The activity measured by isotope pairing technique increased from 1.6 nmol N g(-1) sludge h(-1) in the original activated sludge to 18 nmol N g(-1) soil h(-1) in the CW, with the specific cellular activity increased from 5.1 to 12.8 fmol cell(-1) d(-1). Up to 33% of produced N(2) could be attributed to anammox process in the CW, with the remainder being due to denitrification. Phylogenetic analysis of anammox bacterial 16S rRNA genes indicated a shift of community from single Candidatus "Brocadia fulgida" in sludge to multiple "Jettenia", "Brocadia", and "Anammoxoglobus" species in the CW. With static chambers and control experiments, the CW with supplemented sludge had a 30% reduced N(2)O emission flux compared with the tests without adding biomass during an 8 month testing period.     

Nitrogen removal from wastewater using simultaneous nitrate reduction and anaerobic ammonium oxidation in single reactor

The effects of C/N ratio and total organic carbon (TOC) loading on nitrogen removal through simultaneous nitrate reduction and anaerobic ammonium oxidation in a single reactor were examined. Granular sludge taken from a methane fermentation reactor was placed in an upflow reactor and supplied with synthetic wastewater containing nitrate at a C/N ratio of 1 to grow heterotrophic denitrifying bacteria. When nitrogen removal ratio reached 30%, anammox sludge attached to nonwoven-carrier was added into the same reactor and then ammonia was added to the synthetic wastewater. Nitrogen removal ratio was markedly increased to 80-94%. In this system, nitrogen removal ratio was affected by C/N ratio and TOC loading, not by the amount of granular sludge. A stable isotopic analysis using 15N-labeled nitrate showed that N2 gas was formed by anammox reaction.     

Lighted upflow anaerobic sludge blanket

The upflow anaerobic sludge blanket (UASB) method has been developed as an efficient anaerobic wastewater treatment process; however, the performance of this process in the removal nitrogenous compounds and phosphate is not high. Here, we present the water treatment performance of a lighted upflow anaerobic sludge blanket (LUASB) reactor and propose a novel LUASB concept. A population of phototrophic bacteria was induced from UASB granules under light conditions (100 microE x m(-2) x s(-1)). The ammonium and phosphate ion removal efficiencies of the LUASB reactor were higher than those of a UASB reactor. The difference in the results from runs under light and dark conditions suggests that the efficiencies of ammonium and phosphate ion removal were improved by an increase in the phototrophic bacteria in the LUASB reactor. The UASB granule can decompose a variety of organic substances; therefore, the LUASB method could also be effective for producing phototrophic bacterial biomass and polyhydroxyalkanoates (PHAs) from various wastewaters.     

Anammox bacterial abundance, activity, and contribution in riparian sediments of the pearl river estuary

The hypothesis of an anammox hotspot in river riparian zones was put forward based on our investigation on freshwater ecotones for over 25 years and previous anammox research. Here we used a complementary array of methods including isotope-pairing technique, quantitative PCR assays, and 16S rRNA and hydrazine synthase gene (hzsB) clone libraries to document the spatiotemporal evidence for a high abundance zone of anammox bacteria in river riparian sediment with observed abundance of 1.3-12 × 10(6) (summer) and 1.4-20 × 10(8) (winter) hydrazine synthase gene copies g(-1), which is the highest abundance in natural environments recorded so far. Meanwhile high anammox bacterial biodiversity were detected with 'Brocadia' and 'Kuenenia' dominating. However, the high anammox bacterial abundances were not related with high activities and contributions for nitrogen gas generation. The anammox activities ranged from 0.07 to 0.15 nmol N cm(-3) h(-1) (summer) to 1.0-2.6 nmol N cm(-3) h(-1) (winter) with high temporal heterogeneity. The retrieval of archaeal and bacterial amoA sequences indicated that nitrifying microbes might be the major source of nitrite for anammox bacteria in winter, while in summer the anaerobic nitrate reduction is more likely the main source. On the basis of (15)N tracing technology, it was estimated that a total loss of 0.67-9.62 g N m(-2) yr(-1) is linked to anammox in the riparian zone while denitrification contributed 96.2-170.3 g N m(-2) yr(-1) in Pearl River riparian sediments.     

EFFECT OF THE USE OF DIFFERENT LACTIC STARTERS ON THE MICROBIOLOGICAL AND PHYSICOCHEMICAL CHARACTERISTICS OF NATURALLY BLACK TABLE OLIVES OF GEMLIK CULTIVAR

The effect of different lactic acid bacteria cultures on the physicochemical and microbiological characteristics of brined black olives of Gemlik cultivar at low fermentation temperature was studied. Fermentation was carried out according to the traditional Gemlik method with modifications like low salt concentration and lactic starter addition. The brines with 7% salt concentration were inoculated with lactic acid bacteria ( Lactobacillus brevis, Leuconostoc cremoris and L. paramesenteroides ), which were previously isolated from olive fruits at low temperatures and a commercial strain of Lb. plantarum. Fermentation procedures were carried out at controlled temperatures (between 10–12C). Lactic acid bacteria survival was accompanied by yeast development, no Pseudomonas and Enterobacter species were detected in all treatments during fermentation. The highest total titratable acidity, lowest pH and least yeast growth were determined at the brines and fermentation products, which were inoculated with L. cremoris.

PRACTICAL APPLICATIONS

The use of suitable starter cultures is necessary to improve the microbiological control of the naturally black table olive process, help to standardize the fermentation, increase the lactic acid yield and accordingly provide the production of olives with high quality. The requirements mentioned for starter cultures include a rapid and predominant growth, homofermentative metabolism, tolerance to salt, acid and polyphenols, and few growth factor requirements. Especially at the regions where olives were picked later when environmental temperatures are lower, the use of a starter culture that has the ability to grow at low temperatures may be necessary. Use of such starter cultures may help to increase acidification, to control some types of spoilage and to shorten the fermentation process.     

Applying ratio control in a continuous granular reactor to achieve full nitritation under stable operating conditions

A ratio control strategy was implemented in a continuous granular airlift reactor to achieve and maintain 100% partial nitrification to nitrite (i.e., full nitritation). The control strategy was designed to maintain a constant ratio between the dissolved oxygen (DO) and the total ammonia nitrogen (TAN) concentrations (DO/TAN concentration ratio) in the reactor bulk liquid. The experimental results demonstrated the feasibility of full nitritation of a high-strength ammonium wastewater with a granular reactor operating in continuous mode, when implementing a suitable control strategy. The effect of the DO/TAN concentration ratio on partial nitrification was fast and reversible, upon switching from complete to partial nitrification, despite the presence of nitrite-oxidizing bacteria (NOB) in the granule. Even at a DO concentration as high as 7 mg of O(2) L(-1), full nitritation was obtained, decoupling the achievement of partial nitrification in continuous granular reactors from low DO concentrations. Inhibition of NOB by free ammonia was found to contribute poorly to the achievement of partial nitrification. An extremely high volumetric nitrogen loading rate was achieved (6.1 g of N L(-1) day(-1) at 30 °C), demonstrating that very compact reactors are applicable to nitrogen removal via nitrite.     

Growth and colour development of some surface ripening bacteria with Debaryomyces hansenii on aseptic cheese curd

The growth of five bacteria isolated from red-smear cheeses, Brevibacterium aurantiacum, Corynebacterium casei, Corynebacterium variabile, Microbacterium gubbeenense and Staphylococcus saprophyticus in mixed cultures with Debaryomyces hansenii on aseptic model cheese curd at 10 and 14 degrees C was investigated. At both temperatures, C. casei and Micro. gubbeenense had a longer lag phase than C. variabile, Brevi. aurantiacum and Staph. saprophyticus. In all cultures, lactose was utilised first and was consumed more rapidly at 14 degrees C than at 10 degrees C, i.e., 6 d at 14 degrees C and 10 d at 10 degrees C. This utilisation coincided with the exponential growth of Deb. hansenii on the cheese surface. Lactate was also used as a carbon source and was totally consumed after 21 d at 14 degrees C and approximately 90% was consumed after 21 d at 10 degrees C regardless of the ripening culture. Small differences (<0.5 pH unit) in the surface-pH during ripening were noticeable between ripening cultures. Differences in the colour development of the mixed cultures with the yeast control were only noticeable after 15 d for Brevi. aurantiacum and after 21 d for the other bacteria. Regardless of the organisms tested, colour development and colour intensity were also greater at 14 degrees C than at 10 degrees C. This study has provided useful information on the growth and contribution to colour development of these bacteria on cheese.     

Removal of pharmaceuticals and personal care products (PPCPs) from urban wastewater in a pilot vertical flow constructed wetland and a sand filter

Removal efficiencies and elimination kinetics of 13 pharmaceuticals and personal care products (PPCPs) and BOD5, TSS, and ammonium were evaluated in a pilot vertical subsurface-flow constructed wetland (VFCW) and compared with those obtained by a sand filter. On the basis of the observed removals, the PPCPs studied were grouped in relation to their removal efficiency into (i) PPCPs very efficiently removed, that is, >95% removal in one of the systems (caffeine, salicylic acid, methyl dihydrojasmonate, CA-ibuprofen, hydrocinnamic acid, oxybenzone, ibuprofen, OH-ibuprofen); (ii) PPCPs moderately removed, with removals between 70 and 90% in the two systems (naproxen, diclofenac, galaxolide, and tonalide); and finally (iii) PPCPs poorly removed, with elimination rates of <30% (carbamazepine). At design hydraulic loading rate (HLR) the planted VFCW and the nonplanted SF exhibited similar PPCP removal efficiencies, but the VFCWwas less sensitive to removal decline in overloading conditions (up to 2 times the design HLR). Moreover, under a clogging simulation, the HLR and the presence of vegetation were some of the key aspects affecting the PPCPs, BOD5, and ammonium removal from domestic wastewater. The VFCW evaluated was more efficient in terms of removal efficiency and loading rate for most of the PPCPs studied in comparison to constructed wetlands of other configurations (i.e., horizontal subsurface flow) and SF (nonplanted). The shorter hydraulic residence time (a few hours) in VFCW compared to that in other CW configurations ranging from days to weeks makes VFCWs a very appropriate wastewater treatment option in space-limited areas.     

Mechanisms and factors affecting sorption of microcystins onto natural sediments

The sorption of microcystins (MCs) to fifteen lake sediments and four clay minerals was studied as a function of sediment/clay properties, temperature, and pH through well-controlled batch sorption experiments. All sorption data for both sediments and clays are well described by a nonlinear Freundlich model (n(f) varies between 0.49 and 1.03). The sorption process for MCs exhibited different adsorptive mechanisms in different lake sediments mainly dependent on the sediment organic matter (OM). For sediments with lower OM (i.e., less than 8%), the sorption of MCs decreases with increasing OM and is dominated by the competition for adsorption sites between MCs and OM. In contrast, MC sorption to organic-rich (i.e., more than 8%) sediments increases with increasing OM and is dominated by the interaction between MCs and adsorbed OM. The sorption thermodynamics of MCs onto sediments showed that MC sorption is a spontaneous physisorption process with two different mechanisms. One mechanism is an exothermic process for sediment with lower OM, and the other is an endothermic process for sediment with higher OM. Furthermore, the sorption of MCs onto sediments is pH dependent (sorption decreased with increasing pH). These results provide valuable informations for a better understanding of the natural abiotic attenuation mechanisms for MCs in aquatic ecosystems.     

Influence of the order of reagent addition on NDMA formation during chloramination

The formation of the potent carcinogen, N-nitrosodimethylamine (NDMA), during chlorine disinfection has caused significant concern among drinking water and wastewater recycling utilities practicing intentional or unintentional chloramination. Previous research modeled NDMA formation as arising from a reaction between monochloramine and organic nitrogen precursors, such as dimethylamine, via an unsymmetrical dimethylhydrazine (UDMH) intermediate. Contrary to the importance of monochloramine indicated by previous studies, hypochlorite formed an order of magnitude more NDMA than monochloramine when applied to a secondary municipal wastewater effluent containing excess ammonia. Experiments involving variation of the order that each reagent (i.e., hypochlorite, ammonium chloride, and dimethylamine) was added to solution suggest two factors that may be more important for NDMA formation than the presence of monochloramine: (i) the chlorination state of organic nitrogen precursors and (ii) the partial formation of dichloramine. Although dichloramine formation was most influenced by the pH conditions under which inorganic chloramine formation was performed, mixing effects related to the order of reagent addition may be important at full-scale plants. Chloramination strategies are suggested that may reduce NDMA formation by nearly an order of magnitude.     

Bioaugmentation and adsorption treatment of coking wastewater containing pyridine and quinoline using zeolite-biological aerated filters

Bioaugmented zeolite-biological aerated filters (Z-BAFs), i.e. adding isolated degrading bacteria into the BAFs with zeolite as fillings, were designed to treat coking wastewater containing high concentrations of pyridine and quinoline and to explore the bacterial community of biofilm on the zeolite surface. The investigation was carried out for 91 days of column operation and the treatment of pyridine, quinoline, total organic carbon (TOC), and ammonium was shown to be highly efficient by bioaugmentation and adsorption. Biomass determination and bacterial diversity detection based on 16S rDNA and rRNA techniques supported the treatment data and indicated that bioaugmentation could recover the bacterial richness and diversity from pyridine and quinoline loading shocks. However, bioaugmentation accelerated the shift of the bacterial community structure resulting in a more distinct difference from the starting community. Clone library analysis revealed that pyridine and quinoline were more harmful to Bacterodietes among all ingenious bacteria, and bioaugmentation promoted the growth of Planctomycetes in the biofilm. Moreover, the introduced bacteria did not remain dominant in the bioaugmented biofilm, indicating the indigenous degrading bacteria played the most significant role in the treatment. This bioaugmented Z-BAF method was shown to be an alternative technology for the treatment of wastewater containing pyridine and quinoline or other N-heterocyclic aromatic compounds.     

Tannery wastewater treatment by sequencing batch biofilm reactor

The paper reports the results of an investigation aimed to evaluate the performances of an innovative process for treating tannery wastewater. In such a process biological degradation, carried out in a sequencing batch biofilm reactor (SBBR), is combined with chemical oxidation by ozone. The treatment was carried out at laboratory scale on a real primary effluent coming from a centralized plant treating the wastewater of a large tannery district in Northern Italy. SBBR performances without and with ozonation were compared with very satisfactory results particularly in the latter instance when the recorded COD, TKN, and TSS average removals, (96%), (92%), and (98%), respectively, permitted to achieve the fixed limits enforced by Italian regulation without needing any additional polishing step. With or without ozonation, the process that resulted was characterized by a specific sludge production (0.1 kgVSS/kg CODremoved) significantly lower than the values featuring conventional biological systems (i.e., 0.3-0.5 VSS/kg CODremoved). Moreover, as in the reactor the biomass density results were very high, i.e., 98 gVSS/Lsludge, it was possible to achieve and maintain biomass concentration as high as 20 gVSS/L.     

Radio frequency electric fields processing of orange juice

The non-thermal process of radio frequency electric fields (RFEF) has been shown to inactivate bacteria in apple juice at moderately low temperatures, but has yet to be extended to inactivate bacteria in orange juice. An 80 kW RFEF pasteurizer was used to process pulp-free orange juice at flow rates of 1.0 and 1.4 l/min. Escherichia coli K12 in orange juice was exposed to electric field strengths of 15 and 20 kV/cm at frequencies of 21, 30, and 40 kHz. Ascorbic acid (Vitamin C) content and color of the juice before and after treatment were analyzed. Electrical energy costs were calculated using the measured voltage and current. An energy balance was performed using the inlet and outlet temperatures. Processing at an outlet temperature of 65 °C reduced the population of E. coli by 3.3 log relative to the control. Increasing the treatment time and temperature and decreasing the frequency enhanced the level of inactivation. Varying the electric field strength over the range of conditions used had no effect on the inactivation. No loss in ascorbic acid or enzymatic browning was observed due to RFEF processing. The electrical energy determined using the voltage and current was 180 J/ml. This was in good agreement with the energy calculated using the temperature data. The electrical cost was $0.0026/l of orange juice. The results provided the first evidence that the RFEF process inactivates bacteria in orange juice at moderately low temperatures.

Industrial relevance

The RFEF process has been shown to inactivate E. coli in apple juice at moderately low temperatures, but has yet to be extended to inactivate bacteria in orange juice. An RFEF pilot plant pasteurizer was used to process orange juice at rates of up to 1.4 l/min. RFEF processing reduced the population of E. coli by 99.3% at 60 °C and a hold time of 3 s, whereas conventional heating at the same conditions had no effect on the E. coli. This work demonstrated that the non-thermal RFEF process can be extended to inactivate bacteria in orange juice.     

Enrichment and characterization of chlorinated organophosphate ester-degrading mixed bacterial cultures

Chlorinated organophosphate ester (OPE)-degrading enrichment cultures were obtained using tris(2-chloroethyl) phosphate (TCEP) or tris(1,3-dichloro-2-propyl) phosphate (TDCPP) as the sole phosphorus source. In cultures with 46 environmental samples, significant TCEP and TDCPP degradation was observed in 10 and 3 cultures, respectively, and successive subcultivation markedly increased their degradation rates. 67E and 45D stable enrichment cultures obtained with TCEP and TDCPP, respectively, completely degraded 20 muM of the respective compounds within 6 h and also the other, although the degradation rate of TCEP by 45D was relatively slow. We confirmed chloride ion generation on degradation in both cases and the generation of 2-chloroethanol (2-CE) and 1,3-dichloro-2-propanol (1,3-DCP) as metabolites of TCEP and TDCPP, respectively. 67E and 45D also showed dehalogenation ability toward 2-CE and 1,3-DCP, respectively. Addition of inorganic phosphate did not significantly influence their ability to degrade the chlorinated OPEs but markedly increased their dehalogenation ability, which was maximum at 0.2 mM of inorganic phosphate and decreased at a higher concentration. Denaturing gradient gel electrophoresis analysis showed that dominant bacteria in 67E are related to Acidovorax spp. and Sphingomonas spp. and those in 45D are Acidovorax spp., Aquabacterium spp., and Sphingomonas spp. This analysis indicated the relationship of the Sphingomonas- and Acidovorax-related bacteria with the cleavage of the phosphoester bond and dehalogenation, respectively, in both cultures. This is the first report on bacterial enrichment cultures capable of degrading both TCEP and TDCPP.     

Relative susceptibility and transcriptional response of nitrogen cycling bacteria to quantum dots

Little is known about the potential impacts of accidental or incidental releases of manufactured nanomaterials to microbial ecosystem services (e.g., nutrient cycling). Here, quantum dots (QDs) coated with cationic polyethylenimine (PEI) were more toxic to pure cultures of nitrogen-cycling bacteria than QDs coated with anionic polymaleic anhydride-alt-1-octadecene (PMAO). Nitrifying bacteria (i.e., Nitrosomonas europaea) were much more susceptible than nitrogen fixing (i.e., Azotobacter vinelandii, Rhizobium etli, and Azospirillum lipoferum) and denitrifying bacteria (i.e., Pseudomonas stutzeri). Antibacterial activity was mainly exerted by the QDs rather than by their organic coating or their released QD components (e.g., Cd and Zn), which under the near-neutral pH tested (to minimize QD weathering) were released into the bacterial growth media at lower levels than their minimum inhibitory concentrations. Sublethal exposure to QDs stimulated the expression of genes associated with nitrogen cycling. QD-PEI (10 nM) induced three types of nitrogenase genes (nif, anf, and vnf) in A. vinelandii, and one ammonia monooxygenase gene (amoA) in N. europaea was up-regulated upon exposure to 1 nM QD-PEI. We previously reported up-regulation of denitrification genes in P. stutzeri exposed to low concentrations of QD-PEI. (1) Whether this surprising stimulation of nitrogen cycling activities reflects the need to generate more energy to overcome toxicity (in the case of nitrification or denitrification) or to synthesize organic nitrogen to repair or replace damaged proteins (in the case of nitrogen fixation) remains to be determined.