Candidatus Nitrospira Defluvii Research Articles

Successful operation of nitrifying granules at low pH in a continuous-flow reactor: Nitrification performance, granule stability, and microbial community

Acidic nitrification, as a novel process for treating wastewater without sufficient alkalinity, has received increasing attention over the years. In this study, a continuous-flow reactor with aerobic granular sludge was successful operated at low pH (<6.5) performing high-rate acidic nitrification. Volumetric ammonium oxidation rate of 0.4–1.2 kg/(m3·d) were achieved with the specific biomass activities of 5.8–13.9 mg N/(gVSS·h). Stable partial nitritation with nitrite accumulation efficiency over 85% could be maintained at pH above 6 with the aid of residual ammonium, whereas the nitrite accumulation disappeared when pH was below 6. Interestingly, the granule morphology significantly improved during the acidic operation. The increased secretion of extracellular polymeric substances (especially polysaccharides) suggested a self-protective behavior of microbes in the aerobic granules against acidic stress. 16S rRNA gene sequencing analyses indicated that Candidatus Nitrospira defluvii was always the dominant nitrite-oxidizing bacteria, while the dominant ammonia-oxidizing bacteria shifted from Nitrosomonas europaea to Nitrosomonas mobilis. This study, for the first time, demonstrated the improved stability of aerobic granules under acidic conditions, and also highlighted aerobic granules as a useful solution to achieve high-rate acidic nitrification.

Moving bed biofilm reactor for Pimelodus maculatus reared in RAS: Start-up maturation, bioreactor microbiome and nitrogen removal

Moving bed biofilm reactors (MBBR) are equipment used to remove organic compounds and are frequently tested for aquaculture operations aimed at treating and reusing water. However, a limitation of MBBR is the long maturation period necessary for nitrification to occur efficiently. We evaluated biofilm maturation in MBBR with biomass adhered to support material using enriched medium-NH4Cl and a treatment without enrichment. Two independent recirculating aquaculture systems were established based on a freshwater fish farm that produced a daily total ammonia nitrogen concentration of 1.0 ​mg/L. Each treatment was composed of a reservoir and two experimental bioreactors that received support materials for the colonization of the adhered biomass. The results indicated that the enriched bioreactors performed slower, taking 29 days to reach maturity, while the control treatment matured at 27 days. The species Candidatus Nitrospira defluvii, responsible for acting in the nitrification process became more abundant in the control treatment where it represented 23% of the biofilm composition, while the enriched treatment presented only 3%. The results suggest that the nitrification process in the control treatment performed better than in the enriched bioreactors. However, the use of synthetic media such as NH4Cl and sodium acetate as sources of C:N associated with the Pimelodus maculatus effluent during the start-up process had an important benefit to the maturation time of both bioreactors.

The elevation of salinity above 1% deteriorated nitrification performance and reshaped nitrifier community of an MBR: An often overlooked factor in the treatment of high-strength ammonium wastewater

The effects of synchronous variations of influent salinity with the elevation of NH4+-N concentration on nitrification performance and microbial community structure of bioreactor are often ignored. In this study, we investigated the dynamic response of nitrifying activated sludge to synchronously increased salinity and ammonia loading rate (ALR) in a nitrification membrane bioreactor (MBR). We found that the increase in influent salinity above 1% (from 0.91 to 1.32%) led to the deterioration of the nitrification performance of the MBR. The combined inhibition effect of salinity (1.32%), free ammonia (FA, an average of 1.37 mg/L), and free nitrous acid (FNA, an average of 0.155 mg/L) on nitrite-oxidizing bacteria (NOB) resulted in long-term (35 days) nitrite accumulation. The further increase of salinity and ALR exhibited little influence on the nitrification performance of MBR after the activated sludge had adapted to high salinity (>1%), effective nitrification performance was achieved at high ALR up to 1.71 kg NH4+-N/m3·d and high salinity (2.13%). The microbial analysis showed that the elevated salinity and accumulation of FNA reshaped the microbial community structure of ammonia-oxidizing bacteria (AOB) and NOB. The dominant species of AOB and NOB shifted from the salinity-resistant species Nitrosomonas aestuarii to the species Nitrosomonas mobilis with dual resistant to salinity and FNA, and from non-salinity-resistant species Candidatus Nitrospira defluvii to salinity-resistant species Nitrobacter winogradskyi and Nitrospira marina, respectively. Therefore, the salinity of 1% may be a critical level for the nitrification performance and the shift in the nitrifier community of activated sludge without salinity acclimation.

Quorum sensing responses of r-/K-strategists Nitrospira in continuous flow and sequencing batch nitrifying biofilm reactors.

A better understanding of r-/K-strategists nitrifiers will help to balance the design and operation of bioprocesses for efficient pollution removal from wastewater. The objectives of study were to investigate the nitrite oxidation biokinetics, biofilm property, microbial community and quorum sensing (QS) of nitrifying biofilm in a continuously flow reactor (CFR) and a sequencing batch reactor (SBR). Results showed that nitrite-oxidizing bacteria were estimated to have a nitrite half saturation constant of 76.23 and 224.73 μM in CFR and SBR, respectively. High-throughput and metagenomic sequencing results showed that Nitrospira and Candidatus Nitrospira defluvii were the dominated nitrite-oxidizing taxa performing nitrite oxidation in both reactors. Nitrifying biofilm developed in CFR and SBR showed obviously different properties. Biofilm in SBR had an obviously higher ratio of polysaccharide and protein in extracellular polymeric substances, and higher thickness than in CFR. Metagenomics and chemical analysis revealed various types of acyl-homoserine lactone (AHL) circuit genes (e.g., luxI, lasI, hdtS) and four types of AHL signaling substances (e.g., C6-HSL, C8-HSL, C10-HSL and 3-oxo-C10-HSL) in nitrifying biofilm. The concentrations of these AHLs in biomass and water phases were obviously higher in SBR than that in CFR. Together, AHLs-based QS might affect the formation of nitrifying biofilm and thus contribute to the different biokinetics of Nitrospira in CFR and SBR. Our insights may reveal the molecular mechanism of Nitrospira for different biokinetics, and indicate the AHL association with Nitrospira adaptation to various conditions.

Existence and distribution of novel phylotypes of Nitrospira in water columnsof the South China Sea

SummaryIn the biological nitrogen cycle, nitrite oxidation is performed by nitrite oxidation bacteria, of which Nitrospira is widespread and diverse. Communities of Nitrospira were collected at 25–1500 m depths in the South China Sea. Phylogenetic diversity, community composition, and environmental factors were investigated using high-throughput sequencing targeting the nxrB gene and statistical analyses. The community composition of Nitrospira varied spatially and by depth. Among the 24 OTUs with relatively high abundance, 70% were unclassified and not affiliated with the known Nitrospira genus, suggesting a previously unrecognized high diversity of marine Nitrospira. Five known Nitrospira genera were detected, of which the common marine Nitrospira marina was not the dominant species, whereas Candidatus Nitrospira lenta and Candidatus Nitrospira defluvii dominated in shallow habitats. Comammox Candidatus Nitrospira nitrosa was discovered in the marine ecosystem. The niche differentiation of versatile Nitrospira species was mainly shaped by nitrate, temperature, and DO.

Distribution, Diversity, and Abundance of Nitrite Oxidizing Bacteria in the Subterranean Estuary of the Daya Bay

The oxidation of nitrite to nitrate as the second step of nitrification is vital for the global nitrogen cycle, and the genus Nitrospira is the most widespread nitrite-oxidizing bacteria (NOB) in diverse natural ecosystems. However, our understanding of Nitrospira distribution and their response to dynamic environmental parameters is still limited in the subterranean estuary (STE), a special environment of the mixed zone between land and sea. In this study, Nitrospira communities were collected within 5–10 cm depth intervals of sediments with the physiochemical gradients along the transections of the Daya Bay (DYB) from the landward member to the seaward member. The abundance, community structure of Nitrospira, and their potentially influencing environmental factors were investigated using Q-PCR, the high throughput sequencing targeting Nitrospira nxrB gene, and biostatistics analyses. The abundance of Nitrospira showed uniform distribution along the transections, but significantly decreasing variations were observed from the surface (&amp;lt;20 cm) to the bottom (&amp;gt;20 cm) of sediments. The community diversity and structure of Nitrospira also displayed a remarkable vertical distribution in the DYB (STE), although no significant differences were observed along the transections of STE. Nitrospira marina (N. marina) predominated in the sediments, Candidatus Nitrospira bockiana (Ca. N. bockiana), and Candidatus Nitrospira defluvii (Ca. N. defluvii) were the main Nitrospira species, and Candidatus Nitrospira lenta (Ca. N. lenta) and Nitrospira japonica (N. japonica) also existed with relatively low abundance in the DYB (STE). These findings revealed that Nitrospira species (Ca. N. defluvii, Ca. N. lenta, and N. japonica) derived from activated sludge was also widespread in natural habitats and deduced that the STE may be affected by the pollution derived from terrigenous human activities. The statistical analysis combined with the STE dynamic variation indicated that dissolved organic carbon (DOC), salinity, and ammonium along the sediment depths attributed to the vertical community distribution of the Nitrospira species. In summary, the vertical distribution of Nitrospira and their response to the dynamic physicochemical parameters imply their important role in the nitrite oxidation of the STE and provide insights into the niche differentiation and diversely physiologic metabolism of NOB.

Biochar enhance functional stability of ammonia-oxidizing bioprocess against toxic chemical loading

This study investigated the inhibitory consequences of cetylpyridinium chloride (CPC) on nitrification and the role of the addition of biochar (BC) in enhancing nitrification functional stability. A concentration of 10–40 mg/L CPC led to the pulsed disturbance of ammonium oxidation (AO) (an immediate disruption of 11–41%, followed by recovery) and the press disturbance of nitrite oxidation (NO) (a prolonged disruption of 14–39%). A BC-dosed bioreactor demonstrated significantly higher AO stability against CPC in terms of buffering and resilience to chemical disruption. The addition of BC limited the fraction of freely dissolved CPC in an aqueous (i.e., decreasing the bioavailable CPC) via preferential adsorption, thus mitigating CPC toxicity. While CPC reduced 90% of Nitrosomonas (particularly N. oligotropha) and 93% of Nitrospira (particularly Candidatus Nitrospira defluvii) in the suspended microbiome, which are responsible for AO and NO, respectively, the Nitrosomonas inhibited by CPC was largely recovered in the biofilm microbiome formed on the surface of the BC, enhancing the stability of AO in the presence of CPC. Our study provides a mechanistic explanation for nitrification disruption by toxic chemicals and suggests BC as an effective biowaste-derived additive for the mitigation of the chemical disruption.

Nitrification mainly driven by ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in an anammox-inoculated wastewater treatment system

Anaerobic ammonium oxidation (anammox) process has been acknowledged as an environmentally friendly and time-saving technique capable of achieving efficient nitrogen removal. However, the community of nitrification process in anammox-inoculated wastewater treatment plants (WWTPs) has not been elucidated. In this study, ammonia oxidation (AO) and nitrite oxidation (NO) rates were analyzed with the incubation of activated sludge from Xinfeng WWTPs (Taiwan, China), and the community composition of nitrification communities were investigated by high-throughput sequencing. Results showed that both AO and NO had strong activity in the activated sludge. The average rates of AO and NO in sample A were 6.51 µmol L−1 h−1 and 6.52 µmol L−1 h−1, respectively, while the rates in sample B were 14.48 µmol L−1 h−1 and 14.59 µmol L−1 h−1, respectively. The abundance of the nitrite-oxidizing bacteria (NOB) Nitrospira was 0.89–4.95 × 1011 copies/g in both samples A and B, the abundance of ammonia-oxidizing bacteria (AOB) was 1.01–9.74 × 109 copies/g. In contrast, the abundance of ammonia-oxidizing archaea (AOA) was much lower than AOB, only with 1.28–1.53 × 105 copies/g in samples A and B. The AOA community was dominated by Nitrosotenuis, Nitrosocosmicus, and Nitrososphaera, while the AOB community mainly consisted of Nitrosomonas and Nitrosococcus. The dominant species of Nitrospira were Candidatus Nitrospira defluvii, Candidatus Nitrospira Ecomare2 and Nitrospira inopinata. In summary, the strong nitrification activity was mainly catalyzed by AOB and Nitrospira, maintaining high efficiency in nitrogen removal in the anammox-inoculated WWTPs by providing the substrates required for denitrification and anammox processes.

Shifts in the Abundance and Community Composition of Particle-Associated and Free-Living Nitrospira Across Physicochemical Gradients in the Pearl River Estuary

Nitrospira, a genus of nitrite-oxidizing bacteria, plays an important role in the global nitrogen cycle. However, the distribution patterns of Nitrospira communities and their responses to environmental variables in the estuary are relatively unknown. In this study, Nitrospira communities were collected at two size fractions, 0.2–2.0 μm (free-living) and >2.0 μm (particle-associated), across a physicochemical gradient in the Pearl River Estuary (PRE). The abundance and community composition of Nitrospira bacteria within these two fractions were analysed using qPCR and high-throughput sequencing targeting the nxrB gene. The abundance of particle-associated bacteria decreased dramatically from upstream to downstream, but no significant changes were observed in free-living bacteria, leading to a drastic decrease in the ratio of particle-associated to free-living bacteria (from 36.56 to 0.81). Nitrospira community composition in the PRE also exhibited remarkable spatial variation but no distinct differences in the community composition between particle-associated and free-living fractions. Seven Nitrospira species were detected in water samples from the PRE, of which Nitrospira lenta (N. lenta) and Candidatus Nitrospira defluvii (Ca. N. defluvii) were found to be dominant, and Ca. N. defluvii was observed for the first time in the estuarine environment. A marine Nitrospira, Nitrospira marina (N. marina), was more abundant in winter than in summer, possibly due to strong seawater intrusion in winter. Multivariate statistics revealed that ammonia rather than nitrite was the key factor controlling the community structure of Nitrospira, though different species responded differently to environmental variables. Community network analysis revealed tighter interactions in particle-associated Nitrospira communities than in free-living communities, suggesting that particle association favored interactions. Our analyses indicate that particles play a dominant role in shaping the structure of Nitrospira bacterial communities and imply their major function of the nitrite oxidation in the waters of the PRE.

An efficient oxic-anoxic process for treating low COD/N tropical wastewater: Startup, optimization and nitrifying community structure

In this study, we assessed and optimized a low-dissolved-oxygen oxic-anoxic (low-DO OA) process to achieve a low-cost and sustainable solution for wastewater treatment systems in the developing tropical countries treating low chemical oxygen demand-to-nitrogen ratio (COD/N) wastewater. The low-DO OA process attained complete ammonia removal and the effluent nitrate nitrogen (NO3–N) was below 0.3 mg/L. The recommended hydraulic retention time and sludge retention time (SRT) were 16 h and 20 days, respectively. The 16S rRNA sequencing data revealed that long SRT (20 days) encouraged the growth of nitrite-oxidizing bacteria (NOB) affiliated with “Candidatus Nitrospira defluvii”. Comammox made up 10–20% of the Nitrospira community. NOB and comammox related to Nitrospira were enriched at long SRT (20 days) to achieve good low-DO nitrification performance. The low-DO OA process was efficient and has simpler design than conventional processes, which are keys for sustainable wastewater treatment systems in the developing countries treating low COD/N wastewater.

Inhibitory mechanisms and fate of the analgesic drug acetaminophen in nitrifying activated sludge

This work investigated the inhibitory effects and fate of acetaminophen (N-acetyl-p-aminophenol, APAP) on activated sludge (AS) under nitrifying and aerobic conditions. APAP disrupted the two-step biological nitrification process in a dose-dependent manner. 100 mg/L APAP inhibited ammonia oxidation (the first step of nitrification) accompanied by a significant reduction (> 80 %) of Nitrosomonas oligotropha in relative abundance. 50 mg/L of APAP had no significant effects on ammonia oxidation but interrupted nitrite oxidation (the second step of nitrification) with more than 90 % reduction of Candidatus Nitrospira defluvii. APAP was removed in nitrifying activated sludge via largely the biotransformation route. Both nitrifiers and heterotrophic microorganisms contributed to overall APAP removal. An AS bioreactor was acclimated to 100 mg/L APAP as the sole source of carbon, nitrogen, and energy to enrich the microbial community with APAP-metabolizing heterotrophs. During acclimation, dynamic changes in community phenotypes occurred with significant reduction in species richness and diversity. Community acclimation significantly increased APAP biotransformation rates. 16S rRNA gene-based community profiling showed selective enrichment for Pseudomonas and Sphingomonas, both with demonstrated APAP metabolic capacity.

Effects of Temperature on the Characteristics of Nitrogen Removal and Microbial Community in Post Solid-Phase Denitrification Biofilter Process.

In order to solve the problems of high energy consumption, complex process and low nitrogen removal efficiency in the currently available low carbon source wastewater treatment processes, a novel coagulation sedimentation/post-solid-phase denitrification biofilter process (CS-BAF-SPDB) was proposed. The effect of temperature on the nitrogen removal performance of BAF-SPDB was intensively studied, and the mechanism of the effect of temperature on nitrogen removal performance was analyzed from the perspective of microbial community structure by using the polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that, to realize favorable nitrifying and denitrifying performance simultaneously in the BAF-SPDB unit, the operation temperature should be set above 18 °C. In addition, the influence of the macro operation parameters on the performance of the BAF and SPDB has a direct relationship with the dynamic changes of the micro microbial community. The influence of temperature on nitrification performance in BAF was mainly embodied in the change of composition, amount and activity of ammonia oxidizing bacteria Candidatus Nitrospira defluvii and nitrite oxidizing bacteria Nitrosomonas sp. Nm47, while that on denitrification performance in SPDB is mainly embodied in the change of composition and amount of solid carbon substrate degrading denitrifying bacteria Pseudomonas sp., Myxobacterium AT3-03 and heterotrophic denitrifying bacteria Dechloromonas agitate, Thauera aminoaromatica, Comamonas granuli and Rubrivivax gelatinosus.

Microbiological Characteristics of a Post Solid-Phase Denitrification Biofilter Process

To solve the problems of high energy consumption, complex process, and low nitrogen removal efficiency of the currently available low carbon source wastewater treatment processes, a novel coagulation sedimentation/post solid-phase denitrification biofilter process was proposed. Domestic wastewater with low carbon to nitrogen ratio was treated. The changes in the microbial community structure along the biofilters were studied and the functional bacteria were identified using the polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that the microbial diversity and richness of the microorganisms increased from the bottom to the top along the nitrification filter, while in the denitrification filter, there parameters increased firstly and then decreased from the bottom to the top along the cylinder. A bigger population of nitrifying and denitrifying bacteria was observed at the top and the middle of the nitrification and denitrification biofilter, respectively. Moreover, Nitrosomonas sp. Nm47 and Candidatus Nitrospira defluvii were the predominant nitrifying bacteria in the nitrification biofilter, and Myxobacteria and Rubrivivas gelatinosus were the predominant denitrifying bacteria in the solid-phase denitrification biofilter.

Characterizing Isozymes of Chlorite Dismutase for Water Treatment.

This work investigated the potential for biocatalytic degradation of micropollutants, focusing on chlorine oxyanions as model contaminants, by mining biology to identify promising biocatalysts. Existing isozymes of chlorite dismutase (Cld) were characterized with respect to parameters relevant to this high volume, low-value product application: kinetic parameters, resistance to catalytic inactivation, and stability. Maximum reaction velocities (Vmax) were typically on the order of 104 μmol min-1 (μmol heme)-1. Substrate affinity (Km) values were on the order of 100 μM, except for the Cld from Candidatus Nitrospira defluvii (NdCld), which showed a significantly lower affinity for chlorite. NdCld also had the highest susceptibility to catalytic inactivation. In contrast, the Cld from Ideonella dechloratans was least susceptible to catalytic inactivation, with a maximum turnover number of approximately 150,000, more than sevenfold higher than other tested isozymes. Under non-reactive conditions, Cld was quite stable, retaining over 50% of activity after 30 days, and most samples retained activity even after 90–100 days. Overall, Cld from I. dechloratans was the most promising candidate for environmental applications, having high affinity and activity, a relatively low propensity for catalytic inactivation, and excellent stability.

The metagenomic approach to characterization of the microbial community shift during the long-term cultivation of anammox-enriched granular sludge

A metagenomic approach was used to investigate how the microbial community composition changes when an anammox-based granular sludge reactor is seeded with nitritation-anammox biomass from a wastewater treatment plant. In the seed sample, the abundance of Candidatus Kuenenia stuttgartiensis was similar to Candidatus Jettenia caeni (12.63 vs. 11.68%). This biomass was typical in terms of microbial nitrogen conversion; both ammonia (Nitrosomonas sp.) and nitrite (Nitrospira sp.) oxidizing bacteria were detected. In the lab-scale reactor, Candidatus Kuenenia stuttgartiensis and Candidatus Jettenia caeni bacteria were also present in equal proportions (18.57 vs. 20.89%). On the contrary, Candidatus Nitrospira defluvii bacteria were highly abundant in this reactor, but no known ammonia-oxidizing bacteria were detected. In light of recent studies showing that Nitrospira sp. are capable of complete nitrification, the results presented here may well indicate that both stages of nitrification in the anammox-based granular sludge reactor were performed by this bacteria.

Principal component analysis for interaction of nitrifiers and wastewater environments at a full-scale activated sludge plant

This study investigated the relationship between wastewater environments and the nitrifiers at a full-scale plant using principal component analysis. Ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were detected by florescent in situ hybridization, polymerase chain reaction, phylogenetic analysis, real-time quantitative polymerase chain reaction. Pyrosequencing was also used in profiling the ammonia monooxygenase locus of ammonia-oxidizing bacteria community. It was found that the dominant ammonia-oxidizing bacteria sequences were related to uncultured ammonia-oxidizing bacterium, uncultured Nitrosomonadaceae bacterium, Nitrosomonas sp., and uncultured bacterium. In addition, Nitrobacter clones were related to uncultured alpha proteobacterium, uncultured bacterium, uncultured Nitrobacter sp., and uncultured Bradyrhizobium sp., whereas Nitrospira clones were similar to uncultured bacterium, Candidatus Nitrospira defluvii, uncultured Nitrospira sp., and uncultured Nitrospirae bacterium. The ammonia-oxidizing bacteria and nitrite-oxidizing bacteria ranged 2.83 × 108–1.33 × 1010 and 1.25 × 1010–1.13 × 1011 copies L−1, respectively, equivalent to nitrite-oxidizing bacteria: ammonia-oxidizing bacteria ratio of 10:1. The first three parts of the principal components analysis accounted for 76.8% of the explained variance. The first principal component (44.4%) designated that ammonia-oxidizing bacteria and Nitrospira were mainly influenced by seasonal variations, followed by chemical oxygen demand concentration and nitrogen species (i.e., ammonia, nitrite, and nitrate). The second principal component (19.1%) showed no information about the nitrifiers’ interaction with environmental factors, whereas Nitrobacter demonstrated a high correlation with ammonia on the third principal component (13.3%). These results revealed that the species of Nitrobacter were less influenced by environmental conditions than ammonia-oxidizing bacteria and Nitrospira spp.

Molecular and Kinetic Characterization of Planktonic Nitrospira spp. Selectively Enriched from Activated Sludge

Nitrospira spp. are chemolithoautotrophic nitrite-oxidizing bacteria (NOB), which are ubiquitous in natural and engineered environments. However, there exist few independent biokinetic studies on Nitrospira spp., likely because their isolation and selective enrichment from environmental consortia such as activated sludge can be challenging. Herein, planktonic Nitrospira spp. cultures closely related to Candidatus Nitrospira defluvii (Nitrospira lineage I) were successfully enriched from activated sludge in a sequencing batch reactor by maintaining sustained limiting extant nitrite and dissolved oxygen concentrations. Morphologically, the enrichment consisted largely of planktonic cells with an average characteristic diameter of 1.3 ± 0.6 μm. On the basis of respirometric assays, estimated maximum specific growth rate (μmax), nitrite half saturation coefficient (KS), oxygen half saturation coefficient (KO), and biomass yield coefficient (Y) of the enriched cultures were 0.69 ± 0.10 d-1, 0.52 ± 0.14 mg-N/L, 0.33 ± 0.14 mg-O2/L, and 0.14 ± 0.02 mg-COD/mg-N, respectively. These parameters collectively reflect not just higher affinities of this enrichment for nitrite and oxygen, respectively, but also a higher biomass yield and energy transfer efficiency relative to Nitrobacter spp. Used in combination, these kinetic and thermodynamic parameters can help toward the development and application of energy-efficient biological nutrient removal processes through effective Nitrospira out-selection.

Implicit Analytic Solution of Michaelis-Menten-Monod Kinetics.

An analytic solution to enzyme kinetics expressed by the Michaelis–Menten–Monod mathematical framework is presented. The analytic solution describes the implicit problem with the independent variable, normally time, substituted with the concentration of the reaction product. The analytic solution provides the substrate, enzyme, and microbial biomass concentration instantaneously and over all time domains without the use of numerical integration schemes or iterative solvers required to overcome transcendental functions. Experiments of NO2– nitrification by Candidatus Nitrospira defluvii at temperatures ranging between 10 and 32 °C were used for validation tests with the numerical solution by finite differences and the implicit analytic solution presented here. Results showed that both finite differences and analytic solutions matched the experiments particularly well, with a correlation coefficient greater than 0.99 and residuals smaller than 2.75%.

Investigation of Archaeal and Bacterial community structure of five different small drinking water networks with special regard to the nitrifying microorganisms

Total microbial community structure, and particularly nitrifying communities inhabiting five different small drinking water networks characterized with different water physical and chemical parameters was investigated, using cultivation-based methods and sequence aided Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis. Ammonium ion, originated from well water, was only partially oxidized via nitrite to nitrate in the drinking water distribution systems. Nitrification occurred at low ammonium ion concentration (27–46μM), relatively high pH (7.6–8.2) and over a wide range of dissolved oxygen concentrations (0.4–9.0mgL−1). The nitrifying communities of the distribution systems were characterized by variable most probable numbers (2×102–7.1×104 MPN L−1) and probably originated from the non-treated well water. The sequence aided T-RFLP method revealed that ammonia-oxidizing microorganisms and nitrite-oxidizing Bacteria (Nitrosomonas oligotropha, Nitrosopumilus maritimus, and Nitrospira moscoviensis, ‘Candidatus Nitrospira defluvii’) were present in different ratios in the total microbial communities of the distinct parts of the water network systems. The nitrate generated by nitrification was partly utilized by nitrate-reducing (and denitrifying) Bacteria, present in low MPN and characterized by sequence aided T-RFLP as Comamonas sp. and Pseudomonas spp. Different environmental factors, like pH, chemical oxygen demand, calculated total inorganic nitrogen content (moreover nitrite and nitrate concentration), temperature had important effect on the total bacterial and archaeal community distribution.

From chlorite dismutase towards HemQ - the role of the proximal H-bonding network in haeme binding.

Chlorite dismutase (Cld) and HemQ are structurally and phylogenetically closely related haeme enzymes differing fundamentally in their enzymatic properties. Clds are able to convert chlorite into chloride and dioxygen, whereas HemQ is proposed to be involved in the haeme b synthesis of Gram-positive bacteria. A striking difference between these protein families concerns the proximal haeme cavity architecture. The pronounced H-bonding network in Cld, which includes the proximal ligand histidine and fully conserved glutamate and lysine residues, is missing in HemQ. In order to understand the functional consequences of this clearly evident difference, specific hydrogen bonds in Cld from 'Candidatus Nitrospira defluvii' (NdCld) were disrupted by mutagenesis. The resulting variants (E210A and K141E) were analysed by a broad set of spectroscopic (UV-vis, EPR and resonance Raman), calorimetric and kinetic methods. It is demonstrated that the haeme cavity architecture in these protein families is very susceptible to modification at the proximal site. The observed consequences of such structural variations include a significant decrease in thermal stability and also affinity between haeme b and the protein, a partial collapse of the distal cavity accompanied by an increased percentage of low-spin state for the E210A variant, lowered enzymatic activity concomitant with higher susceptibility to self-inactivation. The high-spin (HS) ligand fluoride is shown to exhibit a stabilizing effect and partially restore wild-type Cld structure and function. The data are discussed with respect to known structure-function relationships of Clds and the proposed function of HemQ as a coprohaeme decarboxylase in the last step of haeme biosynthesis in Firmicutes and Actinobacteria.