Maximum Substrate Concentration Research Articles

TNFα Reduces the Maximum Respiratory Capacity of Mitochondria in Human Airway Smooth Muscle Cells

Previously, we reported that airway inflammation mediated by pro‐inflammatory cytokines such as TNFα induces hypercontractility and increased ATP consumption in human airway smooth muscle (hASM). We also found that TNFα induces an increase in maximum O2 consumption rate as well as mitochondrial biogenesis and an increase in mitochondrial volume density. However, when normalized to mitochondrial volume, maximum O2 consumption rate per mitochondrion is reduced in hASM after TNFα exposure. Unfortunately, standard respirometry (e.g., Seahorse) measures only the averaged maximum O2 consumption rate of a large number of cells. In the present study, we used a quantitative histochemical technique to determine the maximum velocity of the succinate dehydrogenase reaction (SDHmax) together with mitochondrial volume density in individual hASM cells. SDH is a key enzyme in the tricarboxylic acid (TCA) cycle as well as complex II in the electron transport chain (ETC), and SDHmax reflects the maximum respiratory capacity of individual mitochondrion. We hypothesized that TNFα decreases SDHmax per mitochondrion in hASM cells. hASM cells were dissociated from bronchial biopsies obtained during thoracic surgeries in patients with no history of asthma or chronic obstructive pulmonary disease. The hASM cells were treated with TNFα (20 ng/ml) or vehicle (DMSO) for 24 h, and SDHmax was measured using a solution containing 80 mM succinate (maximum substrate concentration) and 1.5 mM nitro blue tetrazolium (NBT) as the reaction indicator. As the SDH reaction proceeded, the hASM cells were imaged in 3D (Z optical slice of 0.5 μm) using an oil‐immersion ×60/1.4 NA objective on a Nikon Eclipse A1 laser scanning confocal system. The change in optical density (OD), reflecting the accumulation of NBT diformazan reaction product in the hASM cell, was measured every 15 s over a 10 min period. Based on the Beer‐Lambert equation, the slope of the change in OD was used to determine SDHmax expressed as mM fumarate/L tissue/min. To determine mitochondrial volume density, the same hASM cells were also loaded with MitoTracker Green (500 nM) and imaged in 3D. We found that mitochondria were more fragmented after TNFα exposure although mitochondrial volume density increased. When SDHmax was normalized to mitochondrial volume, we found that SDHmax per mitochondrion decreased in hASM cells, consistent with the reduction in maximum O2 consumption per mitochondrion that we previously observed. Thus, the increased energetic demand induced by inflammation (TNFα) are met by mitochondrial fragmentation leading to biogenesis and an increase in mitochondrial volume density rather than an increase in mitochondrial respiratory capacity.

Microbial enzymatic assays in environmental water samples: Impact of inner filter effect and substrate concentrations

AbstractAs microbial enzymatic activities initiate the mineralization of organic matter through the microbial loop, it is important to correctly measure those activities and be able to perform inter‐study comparisons. Enzymatic activity assays are typically carried out using fluorogenic substrate analogs, such as 4‐methylumbelliferone and 7‐amino‐4‐methylcoumarin linked to sugar monomers, phosphate group, or amino acids. However, methodological divergences can be found in aquatic science literature, potentially leading to misestimated activities. To highlight some of those methodological key points, we first addressed the potential occurrence of an inner filter effect (IFE), a fluorometric artifact that affects the relationship between fluorophore concentration and fluorescence intensity, due to absorption of exciting or emitted light. It has never been considered in the context of environmental water studies before, despite significantly affecting measured activities. IFE occurred with two out of three tested spectrofluorometers when assaying proteases, although no IFE was detected for phosphatase assays. We also evaluated how substrate concentration ranges might affect kinetic parameters estimation, revealing that a many existing studies might use insufficient maximum substrate concentration. Finally, for single substrate concentration assays, we argued for the use of saturating substrate concentration, as naturally occurring substrates might compete with the fluorogenic analog at trace level. The amendment of a molecule mimicking natural substrates generated a significant inhibition of natural seawater phosphatases and proteases assayed with trace concentrations of fluorogenic substrate, while almost no inhibition occurred at higher concentrations. Those key points need to be addressed in order to assess enzymatic rates and allow inter‐study comparison.

Determination of Optimal Fermentation Condition for N-acetylglucosamine Production Using Mucor circinelloides Extracellular Chitinase

This research aimed to determine the best fermentation condition, consists of pH, temperature, fermentation time and substrate concentration, in N-acetylglucosamine production from shrimp shells using crude extracellular chitinase obtained from Mucor circinelloides mould. The method used was experimental method with fermentation treatment of different pH (5, 6, 7, 8 and 9) and temperature (30, 40, 50, 60, 70 and 80°C). The optimal pH and temperature of fermentation obtained was used to determine the maximum substrate concentration (0.5, 1, 1.5 and 2%) and fermentation time (2, 4, 6 and 24 hours) to produce the highest concentration of N-acetylglucosamine. The optimal pH for fermentation was 8, with chitinase activity of 4.38±0.06 U/ml, while the optimal temperature was 50°C with enzyme activity of 5.42±0.06 U/ml. Substrate concentration and fermentation time affected the N-acetylglucosamine production. The optimal fermentation condition was obtained with substrate concentration of 1.5% and fermentation time of 2 hours resulted to N-acetyl Glucosamine concentration of 2195.83±15.14 ppm.

Growth Inhibition Kinetics of a Pseudomonas Diesel-degrading Strain from Antarctica

Antarctica is one of the largest southernmost continent and most pristine wilderness areas left on earth. Over decades, human activities in this area have resulted in the accumulated pollution of hydrocarbon in the Antarctica mainly due to transportation and logistics activities. The sinking of the supply ships Nella Dan and Bahia Paraiso have resulted in diesel spillage that warrant the utilization and research on diesel-degrading microorganisms in the form of bioremediation to prepare for future disasters. A previously isolated diesel-degrading Pseudomonas sp. strain DRYJ3 has shown effectiveness as a bioremediation tool. Its growth is however strongly inhibited as the diesel concentrations was increased. In this study the inhibitory effect of diesel on the growth rate of this bacterium is modelled according to the Luong, Aiba, Haldane, Hans-Levenspiel, Yano, Teissier and Monod models. Statistical evaluations indicated that the most suitable kinetic model to fit the growth rate on diesel was Luong’s model. The Luong’s constants; maximal growth rate, half saturation constant for maximal growth, maximum substrate concentration that growth ceases, and curve parameter that defines the steepness of the growth rate decline from the maximum rate symbolized by max, Ks, Sm, and n were 0.406 hr-1 (95% CI, 0.269 to 0.881), 0.194 (%v/v) (95% CI, 0.2877 to 0.390), 4.025 (%v/v) (95% CI, 3.820 to 4.229) and 0.378 (95% CI, 0.122 to 0.877) 0.099, respectively. The Luong model predicted Sm value was close to the value of which no growth was observed experimentally suggesting the appropriateness of the model in adhering to observed values.

PENGARUH EKSTRAK METANOL DAUN PEPAYA (Carica papaya L.) TERHADAP AKTIVITAS ENZIM LIPASE

Has conducted research on the effects of methanol extract of leaves papaya (Carica papaya L.) Against Lipase Enzyme Activity. This study aimed to obtain information in a methanol extract inhibits lipase activity. The method used is Complete Random Design (RAL), with goal attainment is done by determining the incubation time lipase enzyme, pH optimum lipase enzyme, and maximum substrate concentration lipase enzyme. And determining the effect of the methanol extract to inhibit the lipase enzyme activity. The results showed that the best incubation time of lipase obtained by time of 120 minutes, the optimum pH 7 and the maximum substrate concentration of 4%. With the highest activity were obtained 16.94 mol /ml.menit, 13.33 mol / ml.menit, and 12.89 mol / ml.menit. The methanol extract of papaya leaves can inhibit the lipase enzyme activity the best concentration of 2% with the acquisition activity of 3.67 mol/ml.menit.Keyword: papaya, lipase, incubation time, optimum pH, substrate concentration.

Batch growth kinetic studies of locally isolated cyanide-degrading Serratia marcescens strain AQ07.

The evaluation of degradation and growth kinetics of Serratia marcescens strain AQ07 was carried out using three half-order models at all the initial concentrations of cyanide with the values of regression exceeding 0.97. The presence of varying cyanide concentrations reveals that the growth and degradation of bacteria were affected by the increase in cyanide concentration with a total halt at 700ppm KCN after 72h incubation. In this study, specific growth and degradation rates were found to trail the substrate inhibition kinetics. These two rates fitted well to the kinetic models of Teissier, Luong, Aiba and Heldane, while the performance of Monod model was found to be unsatisfactory. These models were used to clarify the substrate inhibition on the bacteria growth. The analyses of these models have shown that Luong model has fitted the experimental data with the highest coefficient of determination (R2) value of 0.9794 and 0.9582 with the lowest root mean square error (RMSE) value of 0.000204 and 0.001, respectively, for the specific rate of degradation and growth. It is the only model that illustrates the maximum substrate concentration (Sm) of 713.4 and empirical constant (n) of 1.516. Tessier and Aiba fitted the experimental data with a R2 value of 0.8002 and 0.7661 with low RMSE of 0.0006, respectively, for specific biodegradation rate, while having a R2 value of 0.9 and RMSE of 0.001, respectively, for specific growth rate. Haldane has the lowest R2 value of 0.67 and 0.78 for specific biodegradation and growth rate with RMSE of 0.0006 and 0.002, respectively. This indicates the level of the bacteria stability in varying concentrations of cyanide and the maximum cyanide concentration it can tolerate within a specific time period. The biokinetic constant predicted from this model demonstrates a good ability of the locally isolated bacteria in cyanide remediation in industrial effluents.

ОЦЕНКА ЭФФЕКТИВНОСТИ ФЕРМЕНТАТИВНОГО ГИДРОЛИЗА ПЛОДОВЫХ ОБОЛОЧЕК ОВСА С ПОДПИТКОЙ ПРИ ВЫСОКИХ НАЧАЛЬНЫХ КОНЦЕНТРАЦИЯХ СУБСТРАТА

The aim of the work was to investigate the enzymatic hydrolysis of a chemical treatment product of oat bran at different substrate concentrations, as well as to evaluate the possibility of increasing the efficiency of hydrolysis at high initial substrate concentrations across different feeding variants. The process of enzymatic hydrolysis of a chemically treatment for oat bran products was carried out at various initial substrate concentrations, as well as with various ways of feeding: first - enzymes, second - substrate. The dependences of the current concentration and the yield of reducing substances (RS) from the initial substrate concentration in the range of 45-200 g / l are determined. The possibility of increasing the yield of reducing substances in both cases of feeding is indicated. It was found that an increase in the initial substrate concentration from 45 g / l to 200 g / l leads to an increase in the final concentration of RS by 81 g / l, while the RS yield is reduced by 33%; the enrichment of enzyme preparations or substrates in enzymatic hydrolysis with a maximum substrate concentration of 200 g / l makes it possible to increase the substrate conversion rate by 10-12%.

Enzymatic synthesis of 3-hydroxypropionic acid at high productivity by using free or immobilized cells of recombinant Escherichia coli

3-Hydroxypropionic acid (3-HP) is an important platform chemical for organic synthesis and high performance polymers. Despite a wealth of reports related to 3-HP biosynthesis in microorganisms, its industrial application still requires further research because of low titer and productivity. Herein an effective enzymatic method for the synthesis of 3-HP was achieved by using free or immobilized recombinant Escherichia coli BL21(DE3) cells harboring a nitrilase gene from environmental sample (NIT190). Under the optimal conditions (100mmol/L Tris-HCl buffer, pH 8.0, 30°C), the maximum substrate concentration which could be completely hydrolyzed by using free cells within 24h was 4.5mol/L (319.5g/L). Furthermore, immobilization of the whole cells enhanced their substrate tolerance (up to 7.0mol/L), stability, and reusability. The immobilized cells could be reused for up to 30 batches, and 70% of enzyme activity was retained after 74 batches in distilled water. The titer (184.7g/L) and productivity (36.9g/(Lh)) were obtained by isolation and purification of 3-HP from the first 30 batches. These results demonstrate that the immobilized cells have potential industrial application for the synthesis of 3-HP.

Waste lubricating oil removal in a batch reactor by mixed bacterial consortium: a kinetic study.

The growth kinetics and biodegradation of two waste lubricating oil samples including waste engine oil (WEO) and waste transformer oil (WTO) were studied using pure isolates and mixed culture of Ochrobactrum sp. C1 and Bacillus sp. K1. The mixed culture significantly influenced degradation efficiency of the pure isolates through bioaugmentation process. In particular, the mixed culture was capable of growing on various n-alkanes and polycyclic aromatic hydrocarbons and was able to tolerate unusually high concentrations of waste lubricants (WEO-86.0g/L and WTO-81.5g/L). The initial concentration of waste lubricating oils has been varied in the range of 1-10% (v/v). Under this experimental range, the bacterial growth has been observed to follow Haldane-type kinetics characterizing the presence of substrate inhibition. Haldane model was used to fit the exponential growth data and the following kinetic parameters were obtained: μ max=0.078h(-1), K S=23.101g/L, K i=43.844g/L for WEO; and μ max=0.044h(-1), K S=10.662g/L, K i=58.310g/L for WTO. The values of intrinsic kinetic parameters, like specific growth rate μ max, half saturation constant, K S, inhibition constant, K i and the maximum substrate concentration, S max and growth yield coefficient Y x/s , have been determined using each model hydrocarbon and their mixture as limiting substrate. Relative changes in the values of the kinetic parameters have been correlated to the number of carbon atoms present in n-alkanes. The metabolites from degradation of model hydrocarbon compounds have been identified by GC-MS to elucidate the possible pathway of waste lubricating oil degradation process.

CHARACTERIZATION OF CRUDE EXTRACT POLYPHENOLOXIDASE ENZYME FROM BLACK TIGER SHRIMP (Penaeus monodon)

Shrimp is a very important export commodity with high market value world wide. However, it is still facing problem related to the waste and deterioration quality as main issues for the shrimp industry. In this experiment, polyphenoloxidase from the carapace of Penaeus monodon was extracted and characterized. The research was carried out to obtain the optimum extraction condition and to evaluate the properties of enzyme i.e., pH, optimum temperature for activating enzyme, kinetic enzyme, and chelating on metal ion. The best method for PPO enzyme extraction used buffer with 1:3 proportion. The optimum activity of enzyme was at pH 7 and temperature of 35°C. The kinematic enzyme (Km) value and the maximum substrate concentration were 5.42 mM and 7.5 mM, respectively. Na+, Ca2+, Zn2+, and EDTA with concentration 5 and 10 mM inhibited enzyme activity. Cu2+at concentration of 10 mM and Mn2+ at concentration 5 mM also inhibited enzyme activity Keywords: carapace, characterization, polyphenoloxidase, shrimp

CHARACTERIZATION OF CRUDE EXTRACT POLYPHENOLOXIDASE ENZYME FROM BLACK TIGER SHRIMP (Penaeus monodon)

<p>Shrimp is a very important export commodity with high market value world wide. However, it is still facing problem related to the waste and deterioration quality as main issues for the shrimp industry. In this experiment, polyphenoloxidase from the carapace of Penaeus monodon was extracted and characterized. The research was carried out to obtain the optimum extraction condition and to evaluate the properties of enzyme i.e., pH, optimum temperature for activating enzyme, kinetic enzyme, and chelating on metal ion. The best method for PPO enzyme extraction used buffer with 1:3 proportion. The optimum activity of enzyme was at pH 7 and temperature of 35°C. The kinematic enzyme (Km) value and the maximum substrate concentration were 5.42 mM and 7.5 mM, respectively. Na<sup>+</sup>, Ca<sup>2+</sup>, Zn<sup>2+</sup>, and EDTA with concentration 5 and 10 mM inhibited enzyme activity. Cu<sup>2+</sup>at concentration of 10 mM and Mn<sup>2+</sup> at concentration 5 mM also inhibited enzyme activity</p> <p>Keywords: carapace, characterization, polyphenoloxidase, shrimp</p>

Isolation and identification of Paracoccus sp. FD3 and evaluation of its formaldehyde degradation kinetics

A formaldehyde-degrading bacterium strain, FD3, was isolated from contaminated soil and identified as Paracoccus sp. based on partial 16S rRNA gene sequence analysis. In batch culture, the bacterium metabolized 5,000 and 8,000 mg/L formaldehyde completely within 16 and 18 h, respectively, at 30°C (pH 7.0) with agitation at 150 rpm. The degradation kinetics was found to follow a first-order model at all initial formaldehyde concentrations with regression values greater than 0.99. Formaldehyde degradation rates increased from 532.37 to 2283.04 mg/L/h as the initial concentration of formaldehyde was increased from 1,000 to 8,000 mg/L. The growth of strain FD3 on formaldehyde as a sole carbon and energy source was well described by the Luong model with a maximal specific growth rate of 0.1754/h, a half-saturation constant of 309.02 mg/L, and a maximum substrate concentration of 3875.53 mg/L. Due to its high tolerance and degradation capacity to formaldehyde, Paracoccus sp., FD3 is considered an excellent candidate for use in degrading formaldehyde in wastewaters.

Karakterisasi Enzim Amilase Dari Kecambah Biji Jagung Ketan (Zea mays ceratina L.)

The research about characterization of the amylase enzyme from germination glutinous corn seed ( Zea mays ceratina L.) was done. The aims of this research is to know the effect of germination time to the activity of the amylase enzyme and characteristics of the amylase enzyme from germination glutinous corn seed ( Zea mays ceratina L.). The research was conducted through four phases that is germination stage, extraction, isolation, and characterization. The research device used was Completelly Randomized Design (CRD) and to be continued by BNJ test critical level 5%. Result showed that the germination time that produces the highest activity was 36 hours and the activity of enzyme was 0.0557 sec -1 . Isolation of the amylase enzyme purified by salting out method used technical (NH 4 ) 2 SO 4 at concentration 55% with activity of 0.0394 sec -1 . The optimum pH was 9, and the activity of enzyme was 0.0207 sec -1 . Maximum substrate concentration with the activity 0.0476 sec -1 give at 12.5% (w/v), while the optimum temperature for activity 0.0229 sec -1 was 70 o C. From examination manner analysis for all of free variables results very real effect on the amylase enzyme activity, while the BNJ test critical level of 5% showed a real difference with the other treatments of every variable.

Relevance of the Luong model to describe the biodegradation of phenol by mixed culture in a batch reactor

The kinetics of phenol biodegradation by mixed culture in a batch reactor was investigated over a wide range of initial phenol concentrations (40–350 mg L-1). The temperature (30°C), the stirring velocity (200 rpm), mineral salt supplementation, namely NaH2PO4 (3 g L-1), KH2PO4 (3 g L-1), MgSO4 (0.1 g L-1), (NH4)2SO4 (1 g L-1), as well as the initial pH (8) were kept constant. All experiments were carried out at a given initial bacterial concentration of 0.08 g L-1 (based on the optical density determination, 0.079). Irrespective of the culture conditions, total phenol degradation was recorded for a culture time ranging from 15.6 to 49.0 h. In addition, the optimal value of the maximum specific growth rate was observed for 125 mg L-1 of phenol. These results show the relevance of the specific microbial consortium used. The Luong equation accurately matched growth kinetics and enabled the relation between the maximum specific growth rates (μ m ) and the initial phenol concentration (S o ) to be described. It could also be used to deduce the substrate saturation coefficient (K s ) and the maximum substrate concentration (S m ) above which growth ceases. The kinetic constants of the Luong equation for phenol were $$ {\mu_m} = {1}.0{4} {{\text{h}}^{ - {1}}},{K_s} = {153}.{2} {\text{mg}} {{\text{L}}^{ - {1}}},{S_m} = {54}0 {\text{mg}} {{\text{L}}^{ - {1}}}\,{\text{and}}\,n = 0.{9} $$ , respectively.

Progeny of high muscling sires have reduced muscle response to adrenaline in sheep

This study investigated the impact of variation in Australian sheep breeding values (ASBVs) for yearling eye muscle depth (YEMD) within Merino and Poll Dorset sires on intermediary metabolism of progeny. Specifically, the change in the blood concentrations of lactate, non-esterified fatty acids (NEFA) and glucose in response to administration of an exogenous dose of adrenaline was studied. The experiment used 20 Merino and Merino cross Poll Dorset mixed sex sheep. The sires were selected across a range of YEMD ASBVs. The sheep were fitted with indwelling jugular catheters and administered seven levels of adrenaline over a period of 4 days at 4 months of age (0.1, 0.2, 0.4, 0.6, 0.9, 1.2 and 1.6 μg/kg liveweight (LW)) and 16 months of age (0.1, 0.2, 0.6, 1.2, 1.8, 2.4 and 3.0 μg/kg LW). A total of 16 blood samples were collected between −30 min and 130 min relative to administration of the adrenaline challenge and were later measured for the plasma concentrations of lactate, NEFA and glucose. These data were then used to calculate the time to maximum substrate concentration, the maximum concentration and the area under curve (AUC) between 0 and 10 min, thus reflecting the substrate's response to exogenous adrenaline. Selection for muscling led to decreased muscle response due to adrenaline, as indicated by lower maximum concentrations and AUC for lactate. The muscles’ response to adrenaline was more prominent at 16 months of age than at 4 months of age. Thus, animals selected for increased muscling have lower levels of glycogenolysis in situations where endogenous adrenaline levels are increased like pre-slaughter. This may minimise the risk of poor meat quality in these animals, as they will express higher muscle concentrations of glycogen at slaughter. Adipose tissue was more sensitive to adrenaline in young lambs from high YEMD sires. This shows that high muscled growing lambs utilise their adipose tissue deposits in times of stress to produce energy. This may explain the phenotypic leanness of these animals. Blood glucose levels that are indicative of liver response to adrenaline decreased with selection for muscling. This response may indicate a potential limiting of glucose that is available within animals selected for muscling, leanness and growth for brain function.

Production of polyhydroxyalkanoates in open, mixed cultures from a waste sludge stream containing high levels of soluble organics, nitrogen and phosphorus

In this study, the production of polyhydroxyalkanoates (PHAs) from waste activated sludge (WAS) was evaluated. PHAs were produced from fermented WAS pretreated via high-pressure thermal hydrolysis, a stream characterised by high levels of nutrients (approximately 3.5 g N L −1 and 0.5 g P L −1) and soluble organics. PHA-storing organisms were successfully enriched at high organic loading rates (6 g COD sol L −1 d −1) under aerobic dynamic feeding in sequencing batch reactors at a sludge retention time of 6 d with a short feast length less than 20% of the cycle, and a maximum substrate concentration during feast of 1 g COD VFA L −1. The biomass enrichment, characterised by a decrease in species evenness based on Lorenz curves, provided a biomass that accumulated 25% PHA on a dry-biomass basis with yields on VFA of 0.4 Cmol Cmol −1 in batch tests. The PHA consisted of ∼70 mol% 3-hydroxybutyrate and ∼30 mol% 3-hydroxyvalerate, and presented high thermal stability ( T d = 283–287 °C) and a molecular mass ranging from 0.7 to 1.0 × 10 6 g mol −1. Overall PHA storage was comparable to that achieved with other complex substrates; however, lower PHA storage rates (0.04–0.05 Cmol PHA −1 Cmol X −1 h −1) and productivities (3–4 Cmol PHA L −1 h −1) were probably associated with a biomass-growth and high-respiration response induced by high levels of non-VFA organics (40–50% of COD sol in feed) and nutrients. PHA production is feasible from pretreated WAS, but the enrichment and accumulation process require further optimisation. A milder WAS pretreatment yielding lower levels of non-VFA organics and readily available nutrients may be more amenable for improved performance.

Adsorbent as an essential participant in photocatalytic processes of water and air purification: Computer simulation study

The influence of adsorbent on the kinetics of (photo)catalytic oxidation processes was studied using the simple single and double stage reaction mechanisms with the adsorption stages corresponding to Langmuir model. It was found that in the static reactor in all cases the usage of adsorbent leads to the prolongation of substrate ( A) removal and product ( P) accumulation kinetic curves but the substrate concentration becomes lower during almost all (photo)catalytic process. Fitting of experimental data points of acetone photocatalytic oxidation reaction demonstrated a good correlation with proposed reaction mechanism. Calculated adsorption constants values are close to those reported in literature. The using of adsorbent in flowing conditions leads to the decrease of maximum outlet substrate concentration in the case if the inlet substrate concentration is too high to be oxidized completely for one run. Kinetics simulation in the case of (photo)catalytic reaction with intermediate demonstrates that adsorbent could accumulate additional intermediate quantity thus keeping catalyst surface more active and contributing to faster substrate ( A) removal.

Operational Boundaries for Nitrite Accumulation in Nitrification Based on Minimum/Maximum Substrate Concentrations That Include Effects of Oxygen Limitation, pH, and Free Ammonia and Free Nitrous Acid Inhibition

Recent studies on shortcut biological nitrogen removal (SBNR), which use the concept of denitrification from nitrite, have reported the key factors affecting nitrite build-up, such as dissolved oxygen (DO) limitation, pH, and free ammonia (FA) and free nitrous acid (FNA) inhibition. This study extends the concept of the traditional minimum substrate concentration (S(min)) to explain the simultaneous effect of those factors. Thus, we introduce the minimum DO concentration (DO(min)) and the maximum substrate concentration (S(max)) that are needed to support a steady-state biological system. We define all three values as the MSC values. The model provides a method to identify good combinations of pH, DO, and total ammonium nitrogen (TAN) to support shortcut nitritation. We use MSC curves to show that the effect of DO-alone and the effect of DO plus direct pH inhibition cannot give strong enough selection against nitrite oxidizing bacteria to work in a practical setting. However, adding the FA and FNA effects gives a strong selection effect that is accentuated near pH 8. Thus, a generalized conclusion is that having pH approximately 8 is favorable in many situations. We defined a specific operational boundary to achieve shortcut nitritation coupled to anaerobic ammonium oxidation (ANAMMOX), in which the effluent concentrations of total nitrite and total ammonium should be approximately equal. Experimental results for alkaline and acidic nitrite-accumulating systems match the trends from the MSC approach. In particular, acidic systems had to maintain higher total ammonium, total nitrite, and DO concentrations. The MSC values are a practical tool to define the operational boundaries for selecting ammonium-oxidizing bacteria while suppressing nitrite-oxidizing bacteria.

Assessment of the hydrolytic performance of locally sourced crude amylases on root (cassava & potato) and cereal (maize) starches for syrup production

Starches from cassava, potato and maize were hydrolysed by locally sourced crude amylases to assess and compare the performance of the enzymes in converting root and cereal starches to glucose syrup. Standard amylases (Sigma USA) served as the reference enzymes. Selected physical and sensory characteristics of the syrups produced were evaluated simultaneously with the syrups produced by the standard amylases. The crude amylases showed higher (P amylases increased with increase in substrate concentration up to a maximum substrate concentration of 10%. The crude alpha amylase exhibited a dextrinization time of 2.5h, 2.75h and 3.0h for maize, cassava and potato starches and produced 13%, 12% and 11.8% glucose respectively. The crude gluco-amylase had maximum saccharification time of 72h for cassava and potato starches, 84h for maize and produced 24.37%, 21.8% and 21% glucose respectively. The crude amylases produced syrups in the type II category with Dextrose Equivalent (DE) of 47 and 50 from potato and cassava starches respectively, while syrup from maize starch fall within type III category with DE of 61. Potato starch syrup exhibited higher (P < 0.05) apparent viscosity and low (P < 0.05) mean score for colour and taste than cassava and maize syrups.

Rapid and high biodegradation of phenols catalyzed by Candida tropicalis NCIM 3556 cells

Cells of 19 yeast cultures, belonging to genus Candida were screened for biodegradation of phenol. The cultures procured from NCIM culture collection and were selected so as to contain a representative of varied strains of the species. These were grown in MGYP medium and tested for biodegradation of phenol. C. tropicalis (CT) nos. 3118, 3556 and C. lipolytica 3472 effectively degraded >90% 2 g l −1 phenol. The C. tropicalis 3556 strain was selected for further studies as it metabolized >95% phenol in just 16 h as compared to the other two which took 48 h. The maximum substrate concentration that could be completely degraded was 2 g l −1. A study of induction, of different concentration of phenol in the growth medium showed that toxicity to cell growth increased with increasing phenol levels in growth media. Biodegradation of phenol derivatives – o-cresol, m-cresol, 2,6-dimethyl phenol, α-naphthol, o-chlorophenol and p-nitrophenol, by the selected three strains indicated that the specificity of each culture varied for different substrate.