Thiosphaera Pantotropha Research Articles

Sequential treatment of simulated textile wastewater using zero-valent aluminum under alkaline conditions and biodegradation

The azo dye reactive yellow 145 (RY145) is inherently recalcitrant due to the presence of azo, ethyl sulfone and monochlorotriazine groups. This study explored removal of RY145 using zero valent aluminum (ZVAl) treatment under alkaline conditions followed by aerobic degradation using the bacterial strains Pseudomonas aeruginosa (RS1) and Thiosphaera pantotropha. During pretreatment using 1 g L−1 ZVAl at pH 11, 59% decolorization was observed after 30 min for 50 mg L−1 dye. However, even after carbon source supplementation, the supernatant could not support microbial activity due to the high aluminum concentration in solution at pH 11. After pH adjustment to neutral and Al(OH)3 precipitation, complete decolorization occurred and subsequently microbial degradation of the intermediates could be achieved. ZVAl pretreatment followed by biological treatment could cause an overall TOC reduction of 65% within 96 h. Sorption of dye on the precipitate only contributed to 13% dye removal. The bacterial cultures could utilize nitrogen from the dye intermediates formed after alkaline ZVAl treatment. The sequential treatment also reduced the concentration of total amines and phytotoxicity to Vigna radiata seeds. When a simulated textile wastewater containing 200 mg L−1 of RY145 was subjected to this sequential treatment, complete dye decolorization and 99.2% overall TOC reduction was observed in 30.5 h. The other compounds present in the synthetic wastewater facilitated decolorization as well as mineralization of the dye.

Extracellular synthesis of silver nanoparticles by Thiosphaera pantotropha and evaluation of their antibacterial and cytotoxic effects.

Extracellular biosynthesis of silver nanoparticles (AgNPs) was explored using Thiosphaera pantotropha since this strain exhibits both nitrate- and nitrite-reductase enzyme activity (NaR and NiR, respectively). Optimal AgNP synthesis was achieved using 2mM AgNO3, culture supernatant of nutrient broth grown T. pantotropha, and incubation at 37°C and 180rpm. Under these conditions, the localized surface plasmon resonance peak of silver at 404nm matched well with the average size of the spherical AgNPs based on FEG-TEM micrographs, i.e., 14.6nm (range: 5-51nm). The zeta potential of -33.6mV indicated good stability of the biosynthesized nanoparticles. The XRD spectra demonstrated the simultaneous presence of face-centered cubic crystal structure of AgNPs and AgCl NPs. Ag+ ions were possibly reduced by the NaR and NiR enzymes released into the culture media. The FTIR spectra confirmed the stabilization of the AgNPs by biomolecules present in the culture supernatant of T. pantotropha. The synthesizedAg/AgCl NPs exhibited good antibacterial efficacy against both Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus). The minimum inhibitory concentration (MIC) was 2.5µg/ml for all the bacteria except B. subtilis (MIC of 10µg/ml). The minimum bactericidal concentration (MBC) was 2.5, 10, 20, and 5µg/ml for E. coli, P. aeruginosa, B. subtilis, and S. aureus, respectively. At MBC and higher AgNP concentration, both plating and CLSM imaging confirmed the absence of viable bacteria in treated water. The biogenic AgNPs depicted IC50 of 34.8µg/ml for MCF-7 cells.

Eco-friendly decolorization and degradation of reactive yellow 145 textile dye by Pseudomonas aeruginosa and Thiosphaera pantotropha

Dyes are toxic and inherently resistant to microbial degradation. In this study, decolorization and degradation of textile dye reactive yellow 145 (RY145) were evaluated using pure bacterial strains Pseudomonas aeruginosa (RS1) and Thiosphaera pantotropha ATCC 35512. In nutrient broth under static condition, complete decolorization of 50 mg L−1 RY145 could be achieved within 96 h and 72 h, for Pseudomonas aeruginosa (RS1) and Thiosphaera pantotropha, respectively. In contrast, under shaking condition both the cultures could achieve only 50% decolorization in 96 h. Treatment under sequential static and shaking condition resulted in complete decolorization and 65% mineralization after 96 h. Higher dye concentration in excess of 100 mg L−1 and 50 mg L−1 decreased the extent of dye mineralization in Pseudomonas aeruginosa and Thiosphaera pantotropha, respectively. Even with the repetitive addition of the dye, both the strains were capable of decolorizing the dye. Acclimatized cultures showed 54% decolorization of RY145 in mineral media (MM) even in the absence of a readily degradable external carbon source. Amongst various individual carbon and nitrogen sources, maximum decolorization was observed in MM supplemented with peptone as carbon and nitrogen source at pH 7 under static condition.

Start-up of sequencing batch reactor with Thiosphaera pantotropha for treatment of high-strength nitrogenous wastewater and sludge characterization.

Biological treatment of high-strength nitrogenous wastewater is challenging due to low growth rate of autotrophic nitrifiers. This study reports bioaugmentation of Thiosphaera pantotropha capable of simultaneously performing heterotrophic nitrification and aerobic denitrification (SND) in sequencing batch reactors (SBRs). SBRs fed with 1:1 organic-nitrogen (N) and NH4+-N were started up with activated sludge and T. pantotropha by gradual increase in N concentration. Sludge bulking problems initially observed could be overcome through improved aeration and mixing and change in carbon source. N removal decreased with increase in initial nitrogen concentration, and only 50-60% removal could be achieved at the highest N concentration of 1000mgL-1 at 12-h cycle time. SND accounted for 28% nitrogen loss. Reducing the settling time to 5-10min and addition of divalent metal ions gradually improved the settling characteristics of sludge. Sludge aggregates of 0.05-0.2mm diameter, much smaller than typical aerobic granules, were formed and progressive increase in settling velocity, specific gravity, Ca2+, Mg2+, protein, and polysaccharides was observed over time. Granulation facilitated total nitrogen (TN) removal at a constant rate over the entire 12-h cycle and thus increased TN removal up to 70%. Concentrations of NO2--N and NO3--N were consistently low indicating effective denitrification. Nitrogen removal was possibly limited by urea hydrolysis/nitrification. Presence of T. pantotropha in the SBRs was confirmed through biochemical tests and 16S rDNA analysis.

Parameter identification in the biodesulphurization of an exhaust catalyst

Natural gas contains a small percentage of hydrogen sulphide which should be recovered, before the fuel distribution, since it is a toxic and corrosive component. Sulphur recovery is usually done from a catalysis process where an adsorbent material removes the sulphide from the natural gas. Since this process works continuously with large input flow rates, the catalyst reaches a saturation state and it should be substituted and/or reactivated. Chemical are the most used method for the reactivation of such catalysts; nevertheless alternative methods have been explored from some years ago. In this work a biological method is studied in order to remove the sulphur from an exhaust catalyst used in the Pemex (the Company which manage oil and natural gas in Mexico) sulphur recovery plants. A kinetic analysis is done and a mathematical model, including parameter identification, for Thiosphaera pantotropha is presented. Experimental data from a laboratory set-up are employed to do this study. A removing of around 80% of the sulphide from the exhaust catalyst is obtained from preliminary laboratory experiments. These results are comparable with the reported in the literature and can be used for a future scaling procedure.

Nitrophenol removal by simultaneous nitrification denitrification (SND) using T. pantotropha in sequencing batch reactors (SBR)

Nitrophenol removal was assessed using four identical lab scale sequencing batch reactors R (background control), R1 (4-nitrophenol i.e. 4-NP), R2 (2,4-dinitrophenol i.e. 2,4-DNP), and R3 (2,4,6-trinitrophenol i.e. 2,4,6-TNP). In the present study, the SND based SBR system was used to carry out total nitrogen removal at reduced aeration (DO=2mg/L) using a specifically designed single sludge biomass containing Thiosphaera pantotropha. The concentration of each of the nitrophenols was gradually increased from 2.5 to 200mg/L during acclimation. The nitrophenols were used as the sole source of nitrogen during study. A synthetic feed was designed to direct SND in the bioreactors. It was observed that overall removal for 4-NP was 98% and for 2,4-DNP and 2,4,6 TNP, removals varied between 83% and 84%. The COD removal for 4-NP was 99% and for 2,4-DNP and 2,4,6-TNP was 97–98% during acclimation. Total nitrogen and nitrophenol removals were achieved via SND.

Effect of shock and mixed loading on the performance of SND based sequencing batch reactors (SBR) degrading nitrophenols

The effect of nitrophenolic shock loads on the performance of three lab scale SBRs was studied using a synthetic feed. Nitrophenols were biotransformed by Simultaneous heterotrophic Nitrification and aerobic Denitrification (SND) using a specially designed single sludge biomass containing Thiosphaera pantotropha. Reactors R1, R2 and R3 were fed with 200mg/L concentration of 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP), and 2,4,6-trinitrophenol (2,4,6-TNP) whereas reactor R was used as a background control. Three nitrophenolic shock loadings of 400, 600 and 800mg/Ld were administrated by increasing the influent nitrophenolic concentration while keeping the hydraulic retention time as 48h. The shocks were given continuously for a period of 4 days before switching back to normal nitrophenolic loading (200mg/Ld). The reactors were allowed to recover to normal performance level before administrating the next nitrophenolic shock load. The study showed that a nitrophenolic shock load, as high as 600mg/Ld was completely degraded by the 4-NP & 2,4-DNP bioreactors while almost half degraded by the 2,4,6-TNP bioreactor without affecting the reactor’s performance irreversibly. After resuming the normal nitrophenolic loading, it took almost 8–10 days for the reactors to recover from the shock effect. The study was further extended to evaluate the maximum possible mixed nitrophenolic loading (4-NP:2,4-DNP:2,4,6-TNP 1:1:1) to which a reactor (R3) containing 2,4,6-TNP acclimated single sludge biomass can be exposed without hampering the reactor performance irreversibly. The reactor was able to achieve pseudo-steady-state at a mixed nitrophenolic loading of 300mg/Ld with more than 90% removal of all the three nitrophenols, but could remove half of the mixed nitrophenolic loading of 600mg/Ld.

Isolation, identification and removal of filamentous organism from SND based SBR degrading nitrophenols

Four identical lab scale sequencing batch reactors R, R1, R2, and R3, were used to assess nitrophenol biodegradation using a single sludge biomass containing Thiosphaera pantotropha. Nitrophenols [4-Nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP) and 2,4,6-trinitrophenol (2,4,6-TNP)] were biotransformed by heterotrophic nitrification and aerobic denitrification (SND). Reactor R was used as background control, whereas R1, R2, and R3 were fed with 4-NP, 2,4-DNP, and 2,4,6-TNP, respectively. The concentration of each nitrophenol was gradually increased from 2.5 to 200mg/l along with increase in COD, during acclimation studies. The final COD maintained was 4,500mg/l with each nitrophenolic loading of 200mg/l. During late phase of acclimation and HRT study, a filamentous organism started appearing in 2,4-DNP and 2,4,6-TNP bioreactors. Filaments were never found in 4-NP and background control reactor. Biochemistry and physiology behind filamentous organism development, was studied to obtain permanent solution for its removal. The effect of different input parameters such as COD loading, DO levels, SVI etc. were analyzed. The morphology and development of filamentous organism were examined extensively using microscopic techniques involving ESEM, oil immersion, phase contrast, and dark field microscopy. The organism was grown and isolated on selective agar plates and was identified as member of Streptomyses species.

Treatment of Acetone Waste Gases Using Slurry-Phase Airlift Embedded with Polyacrylamide-Entrapped Cell Beads

Acetone is the most common chemical used in the Hsinchu Science Park in Taiwan. The three-phase airlift biore-actor was designed to absorb acetone into the 39 L of medium solution and then degraded by 2-L polyacryl-amide (PAA)-entrapped Thiosphaera pantotropha cell beads. The airlift medium was successfully regenerated and circulated for more than 5 months. The elimination capacity of 350-part per million (ppm) acetone at 10 L ∙ min−1 was 258.4 g · m−3hr−1 (160.4 g-C · m−3hr−1) with 100% removal efficiency in Stage II, higher than previously reported biofiltration results. The maximum chemical oxygen demand:nitrogen ratio of 100:2.9 is achieved, and a balanced nutrient state was indicated by the change in redox potential. The pH of the system was maintained at neutral because of the strong buffer agent added to the medium (final buffer intensity, β=1.18 ×10-2 M). The PAA-entrapped cell beads could also provide a good barrier for high salinity gradient environment and the inoculum source to maintain steady operation of the system.

Simultaneous carbon and nitrogen removal from high strength domestic wastewater in an aerobic RBC biofilm

High strength domestic wastewater discharges after no/partial treatment through sewage treatment plants or septic tank seepage field systems have resulted in a large build-up of groundwater nitrates in Rajasthan, India. The groundwater table is very deep and nitrate concentrations of 500–750 mg/l (113–169 as NO 3 −-N) are commonly found. A novel biofilm in a 3-stage lab-scale rotating biological contactor (RBC) was developed by the incorporation of a sulphur oxidising bacterium Thiosphaera pantotropha which exhibited high simultaneous removal of carbon and nitrogen in fully aerobic conditions. T. pantotropha has been shown to be capable of simultaneous heterotrophic nitrification and aerobic denitrification thereby helping the steps of carbon oxidation, nitrification and denitrification to be carried out concurrently. The first stage having T. pantotropha dominated biofilm showed high carbon and NH 4 +-N removal rates of 8.7–25.9 g COD/m 2 d and 0.81–1.85 g N/m 2 d for the corresponding loadings of 10.0–32.0 g COD/m 2 d and 1.0–3.35 g N/m 2 d. The ratio of carbon removed to nitrogen removed was close to 12.0. The nitrification rate increased from 0.81 to 1.8 g N/m 2 d with the increasing nitrogen loading rates despite a high simultaneous organic loading rate. However, it fell to 1.53 g N/m 2 d at a high load of 3.35 g N/m 2 d and 32 g COD/m 2 d showing a possible inhibition of the process. A simultaneous 44–63% removal of nitrogen was also achieved without any significant NO 2 −-N or NO 3 −-N build-up. The second and third stages, almost devoid of any organic carbon, acted only as autotrophic nitrification units, converting the NH 4 +-N from stage 1 to nitrite and nitrate. Such a system would not need a separate carbon oxidation step to increase nitrification rates and no external carbon source for denitrification. The alkalinity compensation during denitrification for that destroyed in nitrification may also result in a high economy.

Biodegradation of trichloroethylene in a rotating biological contactor

A laboratory scale study was carried out to treat synthetic wastewater containing 30 mg/l of trichloroethylene in a rotating biological contactor (RBC). A mixed culture of bacteria consisting of nitrifiers, heterotrophs and Thiosphaera pantotropha could be developed and acclimated to achieve 99.89% removal of trichloroethylene (TCE) from synthetic wastewater at TCE loading of 0.0039 m 3/m 2 d and HRT of 3.5 days. A substrate: CO substrate ratio of 1:100 and above was found to be optimum to avoid enzyme competition. C:N ratio of 100:20 was optimum for the biodegradation of TCE. The system could withstand TCE shock loadings up to 0.309 m 3/m 2 d. The volatilization losses of TCE were 4.8% from the RBC unit.

Quantitative estimation of Thiosphaera pantotropha from aerobic mixed culture

This paper reports the successful modification of a plate count media to selectively enumerate Thiosphaera pantotropha from mixed culture and suppress the growth of Pseudomonas. Fourteen samples were prepared in the laboratory and analysed for standard plate count (SPC) on a selective medium which was slightly modified by increasing the concentration of MgSO 4 from 0.1 to 0.3 g/l to prevent growth of other organisms. The samples were actually contaminated by Pseudomonas, but the results show that the formation of Pseudomonas colonies was prevented, while no inhibition of growth of Thiosphaera pantotropha occurred. This shows that the modified medium can be used for quantitative estimation of Ts. pantotropha. This is important as the aerobic denitrification potential of the organism could prove useful in wastewater treatment.

Quantum Mechanical Interpretation of Nitrite Reduction by Cytochrome cd1 Nitrite Reductase from Paracoccus pantotrophus

The reduction of nitrite to nitric oxide in respiratory denitrification is catalyzed by a cytochrome cd(1) nitrite reductase in Paracoccus pantotrophus (formerly known as Thiosphaera pantotropha LMD 92.63). High-resolution structures are available for the fully oxidized [Fülöp, V., Moir, J. W., Ferguson, S. J., and Hajdu, J. (1995) Cell 81, 369-377; Baker, S. C., Saunders, N. F., Willis, A. C., Ferguson, S. J., Hajdu, J., and Fülöp, V. (1997) J. Mol. Biol. 269, 440-455] and fully reduced forms of this enzyme, as well as for various intermediates in its catalytic cycle [Williams, P. A., Fülöp, V., Garman, E. F., Saunders, N. F., Ferguson, S. J., and Hajdu, J. (1997) Nature 389, 406-412]. On the basis of these structures, quantum mechanical techniques (QM), including density functional methods (DFT), were combined with simulated annealing (SA) and molecular mechanics techniques (MM) to calculate the electronic distribution of molecular orbitals in the active site during catalysis. The results show likely trajectories for electrons, protons, substrates, and products in the process of nitrite reduction, and offer an interpretation of the reaction mechanism. The calculations indicate that the redox state of the d(1) heme and charges on two histidines in the active site orchestrate catalysis locally. Binding of nitrite to the reduced iron is followed by proton transfer from His345 and His388 to one of the oxygens of nitrite, creating a water molecule and an [Fe(II)-NO(+)] complex. Valence isomerization within this complex gives [Fe(III)-NO]. The release of NO from the ferric iron is influenced by the protonation state of His345 and His388, and by the orientation of NO on the d(1) heme. Return of Tyr25 to a hydrogen-bonding position between His345 and His388 facilitates product release, but a rebinding of Tyr25 to the oxidized iron may be bypassed in steady-state catalysis.

The greek key protein apo-pseudoazurin folds through an obligate on-pathway intermediate

Folding of the 123 amino acid residue Greek key protein apo-pseudo azurin from Thiosphaera pantotropha has been examined using stopped-flow circular dichroism in 0.5 M Na2SO4at pH 7.0 and 15 °C. The data show that the protein folds from the unfolded state with all eight proline residues in their native isomers (seven trans and one cis) to an intermediate within the dead-time of the stopped-flow mixing (50 ms). The urea dependence of the rates of folding and unfolding of the protein were also determined. The ratio of the folding rate to the unfolding rate (extrapolated into water) is several orders of magnitude too small to account for the equilibrium stability of the protein, consistent with the population of an intermediate. Despite this, the logarithm of the rate of folding versus denaturant concentration is linear. These data can be rationalised by the population of an intermediate under all refolding conditions. Accordingly, kinetic and equilibrium measurements were combined to fit the chevron plot to an on-pathway model (U⇔I⇔N). The fit shows that apo-pseudoazurin rapidly forms a compact species that is stabilised by 25 kJ/mol before folding to the native state at a rate of 2 s−1. Although the data can also be fitted to an off-pathway model (I⇔U⇔N), the resulting kinetic parameters indicate that the protein would have to fold to the native state at a rate of 86,000 s−1(a time constant of only 12 μs). Similarly, models in which this intermediate is bypassed also lead to unreasonably fast refolding rates. Thus, the intermediate populated during the refolding of apo-pseudoazurin appears to be obligate and on the folding pathway. We suggest, based on this study and others, that some intermediates play a critical role in limiting the search to the native state.

Simultaneous carbon and nitrogen removal in a mixed culture aerobic RBC biofilm

A mixed culture biofilm was developed with a sulfur oxidising, heterotrophic bacterium Thiosphaera pantotropha, autotrophic nitrifiers and other heterotrophs in a three stage rotating biological contactor (RBC). Specific benefits due to peculiar properties of T. pantotropha of simultaneous heterotrophic nitrification and aerobic denitrification were derived in the reactor investigated for a combined carbon and nitrogen removal from a synthetic domestic sewage. The first stage biofilm which contained T. pantotropha showed high COD and NH 4 +-N removal rates of 5.8–14.1 g COD/m 3·d and 0.47–1.1 g N/m 2·d for the corresponding loading rates of 6.9–20.7 g COD/m 3·d and 0.69–2.09 g N/m 2·d, respectively. Contrary to the conventional units designed for a concurrent carbon removal and nitrification, the nitrification rates increased linearly with an increase in organic loading rate before stabilising at about 1 g N/m 2·d corresponding to a COD loading rate of about 15 g/m 2·d and a nitrogen loading rate of 1.5 g N/m 2·d showing a change in the order of reaction from first to zero. A simultaneous nitrogen removal of 20–68% was also obtained. The system's performance indicated that a single stage aerobic biofilm can be developed to meet the increasingly stringent regulations on effluent nitrogen discharges affording several advantages over the conventional systems, e.g. low buffer requirements, no need for external carbon source for denitrification, etc., which may result in substantial reduction in the treatment cost.

Nitrous oxide reductase (nosZ) gene-specific PCR primers for detection of denitrifiers and three nosZ genes from marine sediments.

Two PCR primer sets for the nitrous oxide reductase gene (nosZ) were developed. The initial primers were based on three sequences in GenBank and used to amplify nosZ from continental shelf sediments and from two denitrifiers in culture, Thiosphaera pantotropha and Pseudomonas denitrificans. Three unique marine sediment nosZ genes were identified and sequenced. The marine nosZ genes were most closely related to the nosZ genes of Paracoccus denitrificans or to Rhizobium meliloti. Alignment of all nosZ sequences currently available (n = 10) facilitated redesign of the PCR primers. Three new primer sets which amplify 1100 bp, 900 bp and 250 bp regions of the nosZ gene were designed and tested. The new primers robustly amplified nosZ fragments from samples in which the initial nosZ primers were only marginally successful.

Nitrous oxide reductase ( nosZ) gene-specific PCR primers for detection of denitrifiers and three nosZ genes from marine sediments

Two PCR primer sets for the nitrous oxide reductase gene ( nosZ) were developed. The initial primers were based on three sequences in GenBank and used to amplify nosZ from continental shelf sediments and from two denitrifiers in culture, Thiosphaera pantotropha and Pseudomonas denitrificans. Three unique marine sediment nosZ genes were identified and sequenced. The marine nosZ genes were most closely related to the nosZ genes of Paracoccus denitrificans or to Rhizobium meliloti. Alignment of all nosZ sequences currently available ( n=10) facilitated redesign of the PCR primers. Three new primer sets which amplify 1100 bp, 900 bp and 250 bp regions of the nosZ gene were designed and tested. The new primers robustly amplified nosZ fragments from samples in which the initial nosZ primers were only marginally successful.

Genes coding for respiratory complexes map on all three chromosomes of the Paracoccus denitrificans genome.

The genome of Paracoccus denitrificans (strain Pd1222) consists of three distinct DNA molecules when separated by standard pulsed-field gel electrophoresis with apparent molecular sizes of approximately 2, 1.1, and 0.64 Mb. When the separated chromosomes are digested by restriction enzymes and sizes of resulting fragments are summed up, the three chromosomes are composed of 1.83, 1.16, and 0.67 Mb. Since their migration behavior relative to size standards is largely independent of electrophoresis conditions, at least the two smaller chromosomes most likely represent linear molecules. The size analysis presented here allows an unequivocal distinction between groups of different strains of P. denitrificans and of Thiosphaera pantotropha, confirming an earlier cytochrome c analysis. When the genome was analyzed with different probes coding for respiratory enzymes, essential genes were found spread over all three chromosomes without any obvious clustering on any of the three forms.

New roles for CO2 in the microbial metabolism of aliphatic epoxides and ketones.

Short-chain aliphatic epoxides and ketones are two classes of toxic organic compounds formed biogenically and anthropogenically. In spite of their toxicity, these compounds are utilized as primary carbon and energy sources or are generated as intermediate metabolites in the metabolism of other compounds (e.g., alkenes, alkanes, and secondary alcohols) by a number of diverse bacteria. One bacterium capable of using both classes of compounds is the gram-negative aerobe Xanthobacter strain Py2. Studies of epoxide and ketone (acetone) metabolism by Xanthobacter strain Py2 have revealed a central role for CO2 in these processes. Both classes of compounds are metabolized by carboxylation reactions that produce beta-keto acids as products. The epoxide- and ketone-converting enzymes are distinct carboxylases with molecular properties and cofactor requirements unprecedented for other carboxylases. Epoxide carboxylase is a four-component multienzyme complex that requires NADPH and NAD+ as cofactors. In the course of epoxide carboxylation, a transhydrogenation reaction occurs wherein NADPH undergoes oxidation and NAD+ undergoes reduction. Acetone carboxylase is a multimeric (three-subunit) ATP-dependent enzyme that forms AMP and inorganic phosphate as ATP hydrolysis products in the course of acetone carboxylation. Recent studies have demonstrated that acetone metabolism in diverse anaerobic bacteria (sulfate reducers, denitrifiers, phototrophs, and fermenters) also proceeds by carboxylation reactions. ATP-dependent acetone carboxylase activity has been demonstrated in cell-free extracts of the anaerobic acetone-utilizers Rhodobacter capsulatus, Rhodomicrobium vannielii, and Thiosphaera pantotropha. These studies have identified new roles for CO2 as a cosubstrate in the metabolism of two classes of important xenobiotic compounds. In addition, two new classes of carboxylases have been identified, the investigation of which promises to reveal new insights into biological strategies for the fixation of CO2 to organic substrates.

Thiosphaera pantotropha: a sulphur bacterium capable of simultaneous heterotrophic nitrification and aerobic denitrification

Thiosphaera pantotropha, a facultative anaerobe is capable of mixotrophic and heterotrophic growth on a wide range of substrates. It can oxidize reduced sulfur compounds, nitrify ammonia heterotrophically to nitrite, and reduce nitrate or nitrite to nitrogen gas irrespective of the ambient dissolved oxygen concentration.1 The ammonia oxygenase has similarities with that of autotrophic nitrifiers (such as, light sensitivity, Mg2+ requirement, and NAD(P)H utilization), so has hydroxylamine oxidoreductase (cytochrome C oxidation, hydrazine inhibition) but there are some differences too (e.g., hydroxylamine inhibition of ammonia oxidation).2 It is the denitrifying enzyme system expression and operation under aerobic conditions, however, which is shrouded with controversy. The typical enzyme system of the bacterium throws open interesting possibilities of its applications for wastewater treatment. T. pantotropha has been tested in mixed bacterial cultures in suspended as well as fixed film systems to treat simulated industrial and domestic wastewaters. It has also been used in a flocculating algal-bacterial system to treat synthetic fertilizer wastewater. Fixed film systems have yielded better results. High rates of simultaneous removal of organics and nitrogen have been achieved. This indicates a vast improvement over conventional treatment strategies.