Substrate Inhibition Model Research Articles

A comprehensive characterization biotransformation of chlorinated paraffin by human and carp liver microsomes via liquid chromatography-high-resolution mass spectrometry and screening algorithm.

The chlorinated paraffin (CP) monomer 1,2,5,6,9,10-Hexachlorodecane (CP-4) was subjected to in vitro biotransformation using human and carp liver microsomes. Five types of CP-4 metabolites (OH-, keto-, enol-, aldehyde- and carboxy-CP-4) were identified in human liver microsomer while only mono-OH-CP-4 was found in the carp liver microsomes. Kinetic studies revealed that the formation of mono-, di-, tri-hydroxylated CP-4, keto-, enol-, and aldehyde-CP-4 in human liver microsomes was best described by substrate inhibition models, whereas the formation of carboxylated CP-4 metabolites best fit the Michaelis-Menten model. Notably, keto-CP-4, enol-CP-4 and aldehyde-CP-4 were the predominant metabolites. The estimated Vmax values for these metabolites were significantly higher in the human liver microsomes than in the carp liver microsomes. The intrinsic hepatic clearance (CLint) of CP-4 was higher in humans than in carp, indicating species-specific differences in its metabolism. This study also highlighted potential toxicity concerns, with computational predictions showing varying degrees of acute oral toxicity for CP-4 and its metabolites. These findings indicate significant species-specific differences in the biotransformation of CP-4, emphasizing the potential health and environmental risks associated with chlorinated paraffins and their metabolites, and underscore the need for further research to address these concerns.

Biohydrogen production from lignocellulosic hydrolysate: Unveiling the synergistic impact of substrate concentration and furfural inhibition.

Lignocellulosic biomass offers substantial potential as an ideal feedstock for dark fermentative hydrogen production due to its sustainability and cost-effectiveness. The current study examined the influence of furfural on fermentative hydrogen production using lignocellulosic hydrolysate in the presence of furfural. Synthetic lignocellulosic hydrolysate, consisting primarily of 76% xylose, 10% glucose, 9% arabinose, and a mixture of other sugars such as galactose and mannose (85% pentose sugars and 15% hexose sugars), was employed as the substrate. Various substrate concentrations ranging from 2 to 32g/L were tested, along with furfural concentrations of 0, 1, and 2g/L. The investigation aimed to assess the effects of initial substrate concentration, initial furfural concentration, furfural-to-biomass ratio (F/B), and furfural-to-substrate ratio (F/S) on biohydrogen production yields. The maximum specific substrate utilization rates at different substrate concentrations were effectively characterized using Haldane's substrate inhibition model. Among the tested concentrations, the 16g/L emerged as the optimal substrate concentration. The initial furfural concentration was identified as the most significant parameter impacting biohydrogen production, with complete inhibition observed at a furfural concentration of 2g/L. Higher F/S ratios at substrate concentrations ranging from 2 to 16g/L resulted in reduced maximum specific hydrogen production rates (MSHPR) and hydrogen yields. Substrate inhibition was observed at 24g/L and 32g/L. Lactate was the predominant metabolite in all batches containing 2-g/L furfural, as well as in batches with 1-g/L furfural and substrate concentrations of 24 and 32g/L. Furfural at a concentration of 1g/L was not inhibitory in any of the batches. Overall, the mixed cultures in this study could efficiently produce hydrogen from lignocellulosic hydrolysates and degrade furfural, providing new insights into fermentative hydrogen-producing bacteria with furfural tolerance.

Modeling, simulations, and Simulink developments in the analysis of optimal control of temperature and pH in a batch ethanol fermentation process

Transfer of laboratory-scale experiments to production-scale ethanol fermentation is time-consuming and involves expensive prototype systems from complex experimental designs that determine optimal operating conditions for minimal substrate and product inhibitions. The study developed and validated a Simulink-based model for optimal pH and temperature control using fuzzy logic and PID controllers respectively and taking advantage of 2D and 1D substrate and product inhibition models from which suitable ethanol fermentation reaction rates models were selected. Temperature and pH levels and substrate, product, and biomass concentrations were measured. Selected inhibition models were linear-product, linear substrate-sudden stop product, and linear substrate for cassava, maize, and sorghum, respectively. Fuzzy logic controller ascertained optimal flow rate of acid and base as 0.000196 ml/s and 0.000204 ml/s, respectively, and pH error and rate of pH error as 0.00334 and 0.00368, respectively. F-test two-sample for variances showed no significant difference between model and experimental curves (cassava: F critical = 0.9704, F calculated = 0.1905; maize: F critical 0.9704, F calculated = 0.2149; sorghum: F critical = 0.9704, F calculated = 0.2488). PID logic controller showed model curves and experimental curves with good fit. F-test two-sample for variances showed no significant difference between model and experimental curves (cassava: F critical = 0.9704, F calculated = 0.1288; maize: F critical = 0.9704, F calculated = 0.2083; sorghum: F critical = 0.9704, F calculated = 0.2016). The study provided an improved approach as solution for optimal pH and temperature conditions in order to mitigate substrate and product inhibitions during ethanol fermentation. It illustrated that the application of artificial intelligence-based controllers provides satisfactory outcomes that are desirable for implementation in the industrial space.Graphical

Bioremediation of phenolic compounds in coal‐contaminated environments: Bio‐kinetic studies using a mixed bacterial culture

AbstractTwo distinct bacterial strains were combined in a mixed culture to investigate the degradation of phenol. The mixed cultures consisting of species like Rhodococcus and Bacillus, were isolated from the waste effluent collected from Dankuni coal complex (DCC) in West Bengal. The experimental phenol biodegradation were performed batch wise at an optimized temperature and pH conditions of 37°C and 7.0 for a wide range of phenol concentrations initially, with saline solutions which is not supplemented with nutrients initially. Experimental results concluded a highest possible specific growth rate at 150 mg/L for phenol biodegradation of 2400 mg/L within a span of 72 h. Several significant physicochemical parameters were investigated in order to determine the ideal conditions for phenol breakdown. It was also observed that a spectroscopic study of the intermediate at 260 nm of the phenol biodegradation commenced through the formation of a cis, cis intermediate, indicating ortho‐cleavage pathway. A simulated substrate utilization and growth profiles was obtained by using substrate inhibition model equation using MATLAB R2017a were used to compare for the validation of the obtained experimental growth and substrate characterization data.

Rapid Degradation of Hazardous Amides by Immobilized Engineered Pseudomonas putida KT2440 Based on a Novel Gene Expression Vector.

The amides 4-trifluoromethylnicotinamide, acrylamide, and benzamide are widely used in agriculture and industry, posing hazards to the environment and animals. Immobilized bacteria are preferred in wastewater treatment, but degradation of these amides by immobilized engineered bacteria has not been explored. Here, engineered Pseudomonas putida KT2440 pLSJ15-amiA was constructed by introducing a new amidase gene expression vector into environmentally safe P. putida KT2440. P. putida KT2440 pLSJ15-amiA had high amidase activity, even at 80 °C. P. putida KT2440 pLSJ15-amiA immobilized with calcium alginate exhibited a greater environmental tolerance than free cells. The amides were rapidly degraded by the immobilized cells, but the activity was inhibited by high concentrations of substrates. The substrate inhibition model revealed that the optimum initial concentrations of 4-trifluoromethylnicotinamide, acrylamide, and benzamide for degradation by immobilized cells were 197.65, 350.76, and 249.40 μmol/L, respectively. This study develops a novel and excellent immobilized biocatalyst for remediation of wastewater containing hazardous amides.

Hepatic glucuronidation of tetrabromobisphenol A and tetrachlorobisphenol A: interspecies differences in humans and laboratory animals and responsible UDP-glucuronosyltransferase isoforms in humans.

Tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA), bisphenol A (BPA) analogs, are endocrine-disrupting chemicals predominantly metabolized into glucuronides by UDP-glucuronosyltransferase (UGT) enzymes in humans and rats. In the present study, TBBPA and TCBPA glucuronidation by the liver microsomes of humans and laboratory animals (monkeys, dogs, minipigs, rats, mice, and hamsters) and recombinant human hepatic UGTs (10 isoforms) were examined. TBBPA glucuronidation by the liver microsomes followed the Michaelis-Menten model kinetics in humans, rats, and hamsters and the biphasic model in monkeys, dogs, minipigs, and mice. The CLint values based on the Eadie-Hofstee plots were mice (147) > monkeys (122) > minipigs (108) > humans (100) and rats (98) > dogs (81) > hamsters (47). TCBPA glucuronidation kinetics by the liver microsomes followed the biphasic model in all species except for minipigs, which followed the Michaelis-Menten model. The CLint values were monkeys (172) > rats (151) > mice (134) > minipigs (104), dogs (102), and humans (100) > hamsters (88). Among recombinant human UGTs examined, UGT1A1 and UGT1A9 showed higher TBBPA and TCBPA glucuronidation abilities. The kinetics of TBBPA and TCBPA glucuronidation followed the substrate inhibition model in UGT1A1 and the Michaelis-Menten model in UGT1A9. The CLint values were UGT1A1 (100) > UGT1A9 (42) for TBBPA glucuronidation and UGT1A1 (100) > UGT1A9 (53) for TCBPA glucuronidation, and the activities at high substrate concentration ranges were higher in UGT1A9 than in UGT1A1 for both TBBPA and TCBPA. These results suggest that the glucuronidation abilities toward TBBPA and TCBPA in the liver differ extensively across species, and that UGT1A1 and UGT1A9 expressed in the liver mainly contribute to the metabolism and detoxification of TBBPA and TCBPA in humans.

Biological H2(g) Production and Modelling with Computational Fluid Dynamics (CFD)

In this study, bio-hydrogen gas [bio-H2(g)] production and modeling with a three-phase computational fluid dynamics (CFD) model, heat and mass transfer of bio-hydrogen production, reaction kinetics, and fluid dynamics; It was investigated by dark fermentation process in an anaerobic continuous plug flow reactor (ACPFR). The three-phase CFD model was used to determine the bio-H2(g) production in an ACPFR. The effect of different operating parameters, increasing hydrolic retention times (HRTs) (1, 2, 4, 8, and 12 days), different pH values (4.0, 5.0, 6.0, 7.0, and 8.0), and increasing feed rate as organic loading rates (OLRs) (0.5, 1.0, 2.0, 4.0, 8.0 and 10.0 g COD/l.d) on the bio-H2(g) production rates were operated in municipal sludge wastes (MSW) with Thermoanaerobacterium thermosaccharolyticum SP-H2 methane bacteria during dark fermentation for bio-H2(g) production. The effect of HRT, pH, and feed rate on the bioH2(g) efficiencies and H2(g) production rates were examined in the simulation stage. Production of volatile fatty acids (VFAs) namely, acetic acids, butyric acids, and propionic acids were important points influencing the bio-H2(g) production yields. The artificial neural network (ANN) model substrate inhibition on bio-H2(g) production to the methane (CH4) bacteria was also investigated. The reaction kinetics model used Thermotoga neapolitana microorganisms with the Andrews model of substrate inhibition. Furthermore, the ANN model was well-fitted to the experimental data to simulate the bio-H2(g) production from chemical oxygen demand (COD).

Biodegradation of the nitrile-containing insecticides sulfoxaflor, flonicamid, thiacloprid, and acetamiprid by immobilized Escherichia coli harboring genes of nitrile hydratase and a cobalt transporter

The nitrile-containing insecticides sulfoxaflor, flonicamid, thiacloprid, and acetamiprid are used widely in agriculture, polluting the environment and harming animals. The Co2+-dependent enzyme nitrile hydratase (NHase) is a powerful tool for the degradation of nitrile-containing insecticides. Here, the NHase activities of Escherichia coli pET28a-PsNHase, harboring Pseudomonas stutzeri CGMCC 22915 (Ps) NHase gene, and E. coli pET28a-PsNHase-PsCbiM, harboring genes of PsNHase and a cobalt transporter PsCbiM, were compared. The presence of PsCbiM promoted PsNHase activity. E. coli pET28a-PsNHase-PsCbiM was immobilized using calcium alginate, which increased the tolerance of its NHase to acidic, alkaline, and high-temperature environments. Immobilized E. coli pET28a-PsNHase-PsCbiM was applied to degrade sulfoxaflor, flonicamid, thiacloprid, and acetamiprid. These insecticides were both substrates and inhibitors of immobilized E. coli pET28a-PsNHase-PsCbiM. Substrate inhibition model assays showed that the optimum initial concentrations of sulfoxaflor, flonicamid, thiacloprid, and acetamiprid for degradation by immobilized cells were 455.01, 195.50, 139.20, and 410.26 μmol/L, respectively. Degradation of nitrile-containing insecticides by immobilized engineered E. coli cells was reported here for the first time. This study provides a novel and excellent bioremediation agent for treatment of wastewater contaminated with nitrile-containing insecticides.

Assessment of Caffeine-degrading Ability on Bacterial Strains Klebsiella sp. Isolated from Feces of Asian Palm Civet (Luwak)

Asian palm civet (APC) known as Luwak, has an important role in producing the most expensive coffee in the world, Kopi Luwak, which is excreted from its feces. The bacterial diversity in the feces of APC was rarely explored, especially for decaffeination. In the present study, aerobic caffeine-degrading bacteria were successfully isolated from the feces of bred Luwak or Asian palm civet (Paradoxurus hermaphrodite) in Wonosobo (LW) and Lumajang (LL), Java Island-Indonesia and identified using 16s rRNA gene. After identification, they were known as Klebsiella (coded LW1 & LL1). Further, the ability of caffeine degradation was assessed using a Caffeine Agar Medium and Caffeine Liquid Medium (CLM), which were M9 mineral salt with the particular concentration of caffeine. As the additional carbon source, 5 g l 1 of sucrose was added into CLM. Residual caffeine concentration in the CLM was measured periodically using RV/UV-HPLC. LW1 and LL1 were detected to degrade 0.5 g L-1 of caffeine entirely in the CLM for 3 days. If 1 g L-1 of caffeine was introduced, only 63 and 66% of caffeine were degraded respectively for LW1 and LL1. Theobromine did not appear in the CLM, indicated that C8-oxidation is their catabolic pathway. Kinetic parameters of cell growth also have been determined using the different substrate inhibition models to find experimental kinetic data. This is the first report of caffeine-degrading bacteria isolated from the feces of Asian palm civet.

Bio-Hydrogen Production in Packed Bed Continuous Plug Flow Reactor—CFD-Multiphase Modelling

This research study investigates the modelling and simulation of biomass anaerobic dark fermentation in bio-hydrogen production in a continuous plug flow reactor. A CFD multiphase full transient model in long-term horizons was adopted to model dark fermentation biohydrogen production in continuous mode. Both the continuous discharge of biomass, which prevents the accumulation of solid parts, and the recirculation of the liquid phase ensure constant access to the nutrient solution. The effect of the hydraulic retention time (HRT), pH and the feed rate on the bio-hydrogen yield and production rates were examined in the simulation stage. Metabolite proportions (VFA: acetic, propionic, butyric) constitute important parameters influencing the bio-hydrogen production efficiency. The model of substrate inhibition on bio-hydrogen production from glucose by attached cells of the microorganism T. neapolitana applied to the modelling of the kinetics of bio-hydrogen production was used. The modelling and simulation of a continuous plug flow (bio)reactor in biohydrogen production is an important part of the process design, modelling and optimization of the biological H2 production pathway.

Last piece in the puzzle of bisphenols BPA, BPS and BPF metabolism: Kinetics of the in vitro sulfation reaction.

Bisphenols are endocrine-disrupting chemicals ubiquitously present in the environment, with the consequent exposure to humans. In humans, bisphenols are metabolized to glucuronide and sulfate conjugates. Recent studies indicate that sulfation represents an important bisphenol metabolic pathway for the most vulnerable humans, such as the growing fetus. Our aim was to evaluate sulfation kinetics of commonly detected bisphenols in biological samples: bisphenol A (BPA), bisphenol S (BPS), and bisphenol F (BPF). Furthermore, we evaluated estrogenic agonist potencies and long-term stability of these bisphenol sulfates. BPS and BPF sulfates were prepared by chemical synthesis. Sulfation kinetics of the selected bisphenols were tested in pooled human liver cytosol, as a source for soluble phase II enzymes, including liver sulfotransferases, with quantification by LC-MS/MS. A validated transactivation assay using the hERα-Hela 9903cell line was used to determine estrogenic agonist potencies. Moreover, BPA, BPS, and BPF sulfate stabilities were examined under various conditions and during storage. In vitro sulfation of BPA and BPS followed Michaelis-Menten kinetics; BPF sulfation followed a substrate inhibition model. Sulfation rates were comparable for these bisphenols, although their KM values indicated some large differences in affinities. BPA and BPS sulfates are not hERα agonists. The bisphenol sulfates can be considered stable for at least 2 days under these tested media conditions. These data indicate that bisphenol sulfation is an important route in their biotransformation. Compared to glucuronidation, these bisphenols show slower sulfation rates but similar KM values. BPA and BPS metabolic biotransformation by sulfation provides their detoxification as they are without estrogenic activities.

Species Differences in Oxidative Metabolism of Regorafenib

1. Despite the prevalence of laboratory animals such as monkeys, rats, and mice in clinical drug trials, we know little regarding the oxidation of regorafenib in these test subjects. This study aimed to elucidate species differences in the kinetics of regorafenib oxidation into two metabolites: regorafenib N-oxide (M-2) and hydroxyregorafenib (M-3). 2. M-2 formation best fitted the Hill equation and showed positive cooperativity in liver and small intestinal microsomes from all species. For all species, M-2 formation had a higher maximum velocity in microsomes from the liver than the small intestines. Maximum velocity was also higher in microsomes from humans and monkeys than those from rats and mice. M-3 formation was well-fitted to the Hill equation and showed positive cooperativity in all microsomes, except those form rat small intestines, where it exhibited biphasic kinetics. At half the maximum velocity, substrate concentration for M-2 and M-3 formation was lower in microsomes from humans than from other species. Moreover, M-2 was the major metabolite in microsomes from humans, monkeys, and mice, whereas M-2 and M-3 were the major metabolites in rat microsomes. 3. M-2 and M-3 formation involving CYP3A4 and CYP3A5 fitted to the Hill equation. However, M-3 formation involving CYP2J2 fitted to the substrate inhibition model. 4. Our study confirmed species differences in regorafenib oxidative metabolism.

Mass balance and kinetics of biodegradation of endocrine disrupting phthalates by Cellulosimicrobium funkei in a continuous stirred tank reactor system

This study investigated the potential ofCellulosimicrobium funkeifor degrading dimethyl phthalate (DMP) and diethyl phthalate (DEP). Effect of different initial concentrations of phthalates on their biodegradation and growth ofC. funkeiwas examined using shake flasks and a continuous stirred tank reactor (CSTR). Complete degradation of both DMP and DEP was achieved in CSTR, even up to 3000 and 2000 mg/L initial concentrations, respectively. Simultaneous degradation of the phthalates in mixture, i.e. more than 80% and 55% biodegradation efficiency were achieved at 1000 and 2000 mg/L initial concentrations of DMP and DEP, respectively, using the CSTR. Mass balance analysis of the degradation results suggested proficient degradation of DMP and DEP with biomass yield values of 0.64 and 0.712, respectively. The high values of inhibition constant Kiestimated using the Tessier and Edward substrate inhibition models indicated very good tolerance ofC. funkeitoward biodegradation of DMP and DEP.

Effect of Culture Condition and Growth Kinetics on Phenol Biodegradation by an Indigenous Rhodococcus pyridinivorans Strain PDB9T NS-1

The US Environmental Protection Agency listed phenolic compounds as priority pollutants, and their occurrence in water systems poses serious health risks to humans and other living species. The culture conditions are extremely crucial for microbial growth, enzymatic and cellular metabolic activities. Thus, the effects of different culture parameters like pH, temperature (°C), and agitation speed (RPM) on the indigenous Rhodococcus pyridinivorans strain PDB9T NS-1 were modeled using response surface methodology (RSM) and central composite design (CCD). The results showed that the main effect of pH and interaction between pH and agitation speed had a significant to a moderately significant effect on phenol degradation by the indigenous R. pyridinivorans strain PDB9T NS-1. Almost complete phenol degradation was obtained at an optimal setting of pH 7.5, 187 rpm, and 34 °C in 18 h. Growth and phenol degradation kinetics of the actinomycetes was examined in a batch shake flask under the optimized conditions. The growth of Rhodococcus species at varying initial levels of the phenol followed a Pamukoglu and Kargi substrate inhibition model with half-saturation constant (Ks ) of 54.21 mg/l, maximum specific growth rate (µ max) of 0.169 (1/h), substrate inhibition constant (Ksi ) of 243.26 mg/l. The results obtained from the optimization of culture conditions and growth kinetics by the indigenous R. Pyridinivorans strain PDB9T NS-1 suggest the potential of the system in the treatment of phenolic wastewater.

Construction of biotreatment platforms for aromatic hydrocarbons and their future perspectives

Aromatic hydrocarbons (AHCs) are one of the major environmental pollutants introduced from both natural and anthropogenic sources. Many AHCs are well known for their toxic, carcinogenic, and mutagenic impact on human health and ecological systems. Biodegradation is an eco-friendly and cost-effective option as microorganisms (e.g., bacteria, fungi, and algae) can efficiently breakdown or transform such pollutants into less harmful and simple metabolites (e.g., carbon dioxide (aerobic), methane (anaerobic), water, and inorganic salts). This paper is organized to offer a state-of-the-art review on the biodegradation of AHCs (monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs)) and associated mechanisms. The recent progress in biological treatment using suspended and attached growth bioreactors for the biodegradation of AHCs is also discussed. In addition, various substrate growth and inhibition models are introduced along with the key factors governing their biodegradation kinetics. The growth and inhibition models have helped gain a better understanding of substrate inhibition in biodegradation. Techno-economic analysis (TEA) and life cycle assessment (LCA) aspects are also described to assess the technical, economical, and environmental impacts of the biological treatment system.

Stability and Performance Analysis of Bioethanol Production with Delay and Growth Inhibition in a Continuous Bioreactor with Recycle

This paper proposes and analyzes a mathematical model for the production of bioethanol in a continuous bioreactor with recycling. The kinetics correspond to the use of Saccharomyces bayanus for the fermentation of sugars found in wastewater from soft drinks. The proposed model considers product growth latency, which was experimentally found in batch studies of ethanol production. Furthermore, the inhibition effect of ethanol is expressed by a modified version of the classical Andrew’s model for substrate inhibition. The proposed model consists of only three ordinary differential equations containing a minimal number of operating parameters, which include the bioreactor residence time, glucose feed concentration, recycle ratio and the fraction of biomass removed from the reactor by the flow. The positivity and the boundedness of solutions of the model were confirmed under reasonable restrictions of parameters. The stability analysis showed that there is a value of residence time at which an exchange of stability occurs between the trivial washout and non-washout solutions. This critical value depends only on the substrate feed concentration, biomass death rate, recycle ratio and purge fraction. Dynamic simulations of the model were carried out for substrate concentration in the range of 100–250 g/L, commonly used for the production of ethanol. An inverse response due to the inhibition effects of ethanol was observed in the time evolution of substrate and biomass concentrations. Parametric studies showed that ethanol concentration increases with the recycle ratio, with the inverse of residence time and with the inverse of purge fraction. The effect of ethanol latency has, on the other hand, a substantial effect on ethanol concentration. Despite its unstructured nature and the fact that some parameters such as temperature and acidity were not taken into consideration, the proposed model managed to provide useful results on the bioreactor-settler stability and the effect of key parameters on its dynamic behavior, which could pave the way for future optimization studies.

A Computational Approach to Incorporate Metabolite Inhibition in the Growth Kinetics of Indigenous Bacterial Strain Bacillus subtilis MN372379 in the Treatment of Wastewater Containing Congo Red Dye.

A rigorous knowledge of the bacterial growth kinetics is essential for the scaling-up and optimization of biodegradation process conditions in a bioreactor. Although a great deal of literature is available on the modeling of bacterial growth kinetics considering the inhibition at high substrate-loading, the inhibition caused by toxic metabolic byproducts was not accounted in the bacterial growth kinetics. This work primarily aimed at developing a parametric bacterial growth model to account for metabolite inhibition, indicated by a decelerating log-phase growth, which was rarely discussed in the previous studies. An efficient azo-dye degrading bacterium (Bacillus subtilis MN372379) was isolated from the sludge-waste nearby a carpet-dyeing unit. The isolated bacterial strain was used to decolorize the simulated wastewater containing Congo red dye. This study proposed a computational approach to calculate specific bacterial growth rate time-averaged over the entire sigmoidal log phase (including the decelerating phase) for incorporating the effect of metabolite-inhibition, in contrast to the conventional studies where only the initial part (accelerating) of log phase was considered. The nature of metabolite inhibition was also determined and found to be non-competitive. Next, the computed time-averaged specific bacterial growth rate was incorporated into three substrate inhibition models to account for both, the metabolite and substrate inhibitions, and subsequently their kinetic parameters were also determined. Finally, the initial dye concentration and inoculum size were optimized to yield maximum dye utilization rate. This study paves the way for predicting bacterial growth kinetic with improved accuracy to enable a better optimization of bioreactors at the industrial scale.

Bisphenol A removal by the Chlorophyta Picocystis sp.: optimization and kinetic study

The Chlorophyta Picocystis sp. isolated from a Tunisian household sewage pond appears promising for effective removal of Bisphenol A (BPA). Efficient and cost-effective technology for contaminants remediation relies on a tradeoff between several parameters such as removal efficiency, microorganism growth, and its tolerance to contaminant toxicity. This article demonstrates the optimum conditions achieving the highest removal rates and the minimal growth inhibition in batch cultures of Picocystis using response surface methodology. A central composite face-centered (CCF) design was used to determine the effects on removal and growth inhibition of four operating parameters: temperature, inoculum cell density, light intensity, and initial BPA concentration. Results showed that the maximal BPA removal was 91.36%, reached the optimal culture conditions of 30.7 °C, 25 × 105 cells ml−1 inoculum density, 80.6 µmol photons m−2 s−1 light intensity, and initial BPA concentration of 10 mg l−1. Various substrate inhibition models were used to fit the experimental data, and robustness analysis highlighted the Tessier model as more efficient to account for the interaction between Picocystis and BPA and predict removal efficiency. These results revealed how Picocystis respond to BPA contamination and suggest that optimization of experimental conditions can be effectively used to maximize BPA removal in the treatment process. Highlights Surface response methodology was applied for optimization of BPA removal by the Chlorophyta Picocystis sp. Temperature, light intensity, inoculum cell density and initial BPA concentration were selected as factors that may affect BPA removal and microalgae growth. The optimal conditions for the maximum BPA removal and minimum growth inhibition were 30.7 °C; 80.6 µmol photons m−2 s−1; 25 × 105 cells ml−1 and 10 mg l−1 BPA. Teissier model was selected to fit the kinetic of BPA removal by Picocystis with R 2 = 0.92.

Environmental influences on uptake kinetics and partitioning of strontium in age-0 lake sturgeon (Acipenser fulvescens): effects of temperature and ambient calcium activities

Nonessential elements like Sr2+ are incorporated via Ca2+ transport proteins due to their similar chemical properties and are substituted for Ca2+ in hard structures of fishes. Few studies have investigated the uptake kinetics of nonessential elements or the effect the ambient environment has on uptake rates. We tested the hypothesis that temperature and environmental Ca2+ activity would influence uptake and subsequent deposition rates of Sr2+ in the fin rays of lake sturgeon (Acipenser fulvescens). Michaelis–Menten substrate inhibition models were used to measure the kinetics of Sr2+ uptake on lake sturgeon larvae that were exposed to varying temperature and Ca2+ activities. Sr2+ influx increased at higher temperatures (maximum JmaxSr = 56.5 pmol·g−1·h−1) and decreased when larvae were exposed to increasing activities of Ca2+ (minimum JmaxSr = 6.4 pmol·g−1·h−1), indicating Ca2+ has an inhibitory effect on Sr2+ influx. Furthermore, Sr2+ was preferentially accumulated in fin rays and partitioning was significantly affected by temperature and Ca2+ activity, providing, for the first time, an understanding of the underlying physiological mechanisms involved in elemental uptake and deposition of nonessential metals in sturgeons.

Kinetics of growth, plantaricin and lactic acid production in whey permeate based medium by probiotic Lactobacillus plantarum CRA52

In the present study, the prospect of alternate carbon and nitrogen sources was ascertained for plantaricin (PL) and lactic acid (LA) production from the probiotic lactic acid bacteria Lactobacillus plantarum CRA52. The alternate carbon sources used in the present study were whey permeate (WP) and palmyra palm sugar (PJ), and the alternate nitrogen source was whey protein hydrolysate (WPH). Experimental use of WP as carbon source and WPH as nitrogen source led to enhanced production of LA and PL, with the yield being 17.69 gL-1 and 462.32 AUmL−1 respectively. WP and WPH concentration ratio of 2:1 was found to be optimal for the production of PL and LA. Kinetic modeling revealed that Aiba substrate inhibition model exhibited best fit for the experimental data. On performing a medium based process economic analysis, WP and WPH-based medium were economical for the production of LA. The present investigation validates the potential of WP-WPH based medium for heightened economical production of PL and LA. It is envisaged that this study will lend fundamental insights in order to leverage the innate nutritional potential of raw products such as PJ and WP for economical production of industrially relevant products.