Microbial Degradation Kinetics Research Articles

Kinetics of Arab Light Crude Oil Degradation by Pseudomonas and Bacillus Strains

The biodegradation of crude oil is a consequence of the presence of a specific enzymatic system in the microorganisms selected: the alkane hydroxylase (AlkH). The enzymatic biodegradation has been described since 1994, when the enzyme was first isolated from P. putida (formerly P. oleovorans), but the kinetics of microbial degradation has been weakly considered. We studied and described in this work the kinetics of Arab Light biodegradation, a light crude oil used for gasoline production (46.4% C7–C12 n-alkanes), using two oleophilic strains (Bacillus licheniformis and Pseudomonas putida). Alkanes were extracted from aqueous solutions in the bioreactors by dichloromethane, with a high ratio aqueous:organic volumes (1:0.2 mL) for the amplification of the GC n-alkane signals, and GC spectra were monitored in time over 40 days. Petroleum emulsions were visualized using optical microscopy as a result of biosurfactant segregation, which is necessary for the enzymatic biodegradation of oil by microorganisms. Kinetic analysis in biodegradation of Arab Light (total petroleum hydrocarbons, TPH) exhibits first-order kinetics with 0.098 d−1 and 0.082 d−1 as kinetic coefficients for 8.6 g/L initial crude oil concentration (30 °C), which results in degradation rates of 843 mg/Ld and 705 mg/Ld in B. licheniformis and P. putida, respectively. These results can be applied for oil spill bioremediation, using these microorganisms with the objective of removing contamination by petroleum alkanes.

Sinking krill carcasses as hotspots of microbial carbon and nitrogen cycling in the Arctic

Krill represent a major link between primary producers and higher trophic levels in polar marine food webs. Potential links to lower trophic levels, such as heterotrophic microorganisms, are less well documented. Here, we studied the kinetics of microbial degradation of sinking carcasses of two dominant krill species Thysanoessa raschii and Meganyctiphanes norvegica from Southwest Greenland. Degradation experiments under oxic conditions showed that 6.0-9.1% of carbon and 6.4-7.1% of nitrogen were lost from the carcasses after one week. Aerobic microbial respiration and the release of dissolved organic carbon were the main pathways of carbon loss from the carcasses. Ammonium release generally contributed the most to carcass nitrogen loss. Oxygen micro profiling revealed anoxic conditions inside krill carcasses/specimens, allowing anaerobic nitrogen cycling through denitrification and dissimilatory nitrate reduction to ammonium (DNRA). Denitrification rates were up to 5.3 and 127.7 nmol N carcass-1 d-1 for T. raschii and M. norvegica, respectively, making krill carcasses hotspots of nitrogen loss in the oxygenated water column of the fjord. Carcass-associated DNRA rates were up to 4-fold higher than denitrification rates, but the combined activity of these two anaerobic respiration processes did not contribute significantly to carbon loss from the carcasses. Living krill specimens did not harbor any significant denitrification and DNRA activity despite having an anoxic gut as revealed by micro profiling. The investigated krill carcasses sink fast (1500-3000 m d-1) and our data show that only a small fraction of the associated carbon is lost during descent. Based on data on krill distribution, our findings are used to discuss the potential importance of sinking krill carcasses for sustaining benthic food webs in the Arctic.

An in vitro model for microbial fructoselysine degradation shows substantial interindividual differences in metabolic capacities of human fecal slurries

Fructoselysine is formed upon heating during processing of food products, and being a key intermediate in advanced glycation end product formation considered to be potentially hazardous to human health. Human gut microbes can degrade fructoselysine to yield the short chain fatty acid butyrate. However, quantitative information on these biochemical reactions is lacking, and interindividual differences therein are not well established. Anaerobic incubations with pooled and individual human fecal slurries were optimized and applied to derive quantitative kinetic information for these biochemical reactions. Of 16 individuals tested, 11 were fructoselysine metabolizers, with Vmax, Km and kcat-values varying up to 14.6-fold, 9.5-fold, and 4.4-fold, respectively. Following fructoselysine exposure, 10 of these 11 metabolizers produced significantly increased butyrate concentrations, varying up to 8.6-fold. Bacterial taxonomic profiling of the fecal samples revealed differential abundant taxa for these reactions (e.g. families Ruminococcaceae, Christenellaceae), and Ruminococcus_1 showed the strongest correlation with fructoselysine degradation and butyrate production (ρ ≥ 0.8).This study highlights substantial interindividual differences in gut microbial degradation of fructoselysine. The presented method allows for quantification of gut microbial degradation kinetics for foodborne xenobiotics, and interindividual differences therein, which can be used to refine prediction of internal exposure.

Kinetic modeling of microbial degradation and antioxidant reduction in lychee juice subjected to UV radiation and shelf life during cold storage

Lychee juice is highly perishable food and typical thermal processing may cause alteration in product quality. This study was conducted to investigate the kinetic model of microbial degradation (total plate count and yeast and mold count) and antioxidant properties reduction (total phenolic compound, total flavonoid content and antioxidant activity by DPPH and FRAP assays) of lychee juice subjected to various ultraviolet UV radiation doses (0–74.88 J/cm2). Physical and chemical properties of lychee juice treated with UV treatment and shelf life during cold storage at 4 °C compared to pasteurized sample (85 °C 15 s) were also determined. Kinetics of microbial degradation and antioxidant properties reduction were best-fitted by first-order kinetic model with coefficient of determination (R2) values and rate constants (k) ranging from 0.9759 to 0.9935 and 0.0008–0.1060, respectively. No significant difference was observed in pH, °Brix, %titratable acidity, total flavonoid content and antioxidant activity by DPPH assay. Based on microbial shelf life, UV radiation could extent the shelf life of lychee juice approximately 7 days compared to control sample during storage at 4 °C. The data of present research contribute to support the application of UV radiation treatment as a promising technique to preserve quality, prevent microbial spoilage and improve shelf life of lychee juice during cold storage.

Microbial degradation kinetics and molecular mechanism of 2,6-dichloro-4-nitrophenol by a Cupriavidus strain

2,6-Dichloro-4-nitrophenol (2,6-DCNP) is an emerging chlorinated nitroaromatic pollutant, and its fate in the environment is an important question. However, microorganisms with the ability to utilize 2,6-DCNP have not been reported. In this study, Cupriavidus sp. CNP-8 having been previously reported to degrade various halogenated nitrophenols, was verified to be also capable of degrading 2,6-DCNP. Biodegradation kinetics assay showed that it degraded 2,6-DCNP with the specific growth rate of 0.124 h−1, half saturation constant of 0.038 mM and inhibition constant of 0.42 mM. Real-time quantitative PCR analyses indicated that the hnp gene cluster was involved in the catabolism of 2,6-DCNP. The hnpA and hnpB gene products were purified to homogeneity by Ni-NTA chromatography. Enzymatic assays showed that HnpAB, a FAD-dependent two-component monooxygenase, converted 2,6-DCNP to 6-chlorohydroxyquinol with a Km of 3.9 ± 1.4 μM and a kcat/Km of 0.12 ± 0.04 μΜ−1 min−1. As the oxygenase component encoding gene, hnpA is necessary for CNP-8 to grow on 2,6-DCNP by gene knockout and complementation. The phylogenetic analysis showed that the hnp cluster originated from the cluster involved in the catabolism of chlorophenols rather than nitrophenols. To our knowledge, CNP-8 is the first bacterium with the ability to utilize 2,6-DCNP, and this study fills a gap in the microbial degradation mechanism of this pollutant at the molecular, biochemical and genetic levels. Moreover, strain CNP-8 could degrade three chlorinated nitrophenols rapidly from the synthetic wastewater, indicating its potential in the bioremediation of chlorinated nitrophenols polluted environments.

MICROBIAL LEACHING OF CHROMIUM FROM SOLIDIFIED WASTE FORMS – A KINETIC STUDY

In this study, Thiobacillus thiooxidans (T. thiooxidans) was used to study the microbial stability / degradation of cement-based waste forms. The waste forms contained a chromium salt (CrCl3·6H2O), cement and other additives viz., lime and gypsum in two different proportions. The experimental samples of all the simulated waste forms showed evidence of microbial growth as indicated by substantial increase in sulfate. Chromium leached from the waste forms was found to be lowest in cement – lime solidified waste forms (0.061 mg·l-1) and highest in cement gypsum waste forms (0.22 mg·l-1) after 30 days of exposure. These values were lower than the toxicity characteristic leaching procedure (TCLP), regulatory limit (5 mg·l-1). Model equations based on two shrinking core models (acid dissolution and bulk diffusion model), were used to analyze the kinetics of microbial degradation of cement based waste forms. The bulk diffusion model was observed to fit the data better than the acid dissolution model, as indicated by good correlation coefficients

Modelling of kinetics of microbial degradation of simulated leachate from tobacco dust waste

AbstractThis paper presents a kinetic analysis of the biodegradation of organic pollutants in a batch bioreactor and investigates the kinetic properties of activated sludge using different mathematical models. The treatment was conducted for different initial concentrations of leachate from 500 mg dm−3 to 5000 mg dm−3 and initial concentrations of activated sludge from 1.84 g dm−3 to 6.62 g dm−3 over 48 h. Four different kinetic models were applied to the data. The kinetic analysis was performed with the traditional Monod model, the modified Monod model with endogenous metabolism, the Haldane model, and the Haldane model extended to include endogenous metabolic consumption and known as the Endo-Haldane model. Kinetic parameters for each model were determined using differential analysis and the Nelder-Mead method of non-linear regression. The lowest deviations and very good matches with the experimental data were achieved using the Endo-Haldane model. This indicated that this model best described the process of biodegradation of leachate from tobacco waste composting. This is due to this model incorporating the effects both of inhibition and endogenous metabolism.

Modeling the kinetics of microbial degradation of deicing chemicals in porous media under flow conditions

A quantitative knowledge of the fate of deicing chemicals in the subsurface can be provided by joint analysis of lab experiments with numerical simulation models. In the present study, published experimental data of microbial degradation of the deicing chemical propylene glycol (PG) under flow conditions in soil columns were simulated inversely to receive the parameters of degradation. We evaluated different scenarios of an advection-dispersion model including different terms for degradation, such as zero order, first order and inclusion of a growing and decaying biomass for their ability to explain the data. The general break-through behavior of propylene glycol in soil columns can be simulated well using a coupled model of solute transport and degradation with growth and decay of biomass. The susceptibility of the model to non-unique solutions was investigated using systematical forward and inverse simulations. We found that the model tends to equifinal solutions under certain conditions.

Microbially-influenced degradation of solidified/stabilized metal waste

In the present study, a refined microbially-influenced degradation method was used to evaluate the stability of a solidified synthetic waste containing chromium salt, cement and fly ash in two different proportions. The experimental samples showed evidence of microbial growth by leaching of sulfate. Chromium leached by Thiobacillus thiooxidans from the experimental samples ‘C1’ (10.26% CrCl 3 · 6H 2O; 89.74% cement) and ‘FC1’ (10.26% CrCl 3 · 6H 2O; 10% fly ash; 79.74% cement), after 30 days of exposure was 14.53 mg/g and 9.53 mg/g, respectively. The corresponding concentration of chromium in the leachate was 0.189 mg/l and 0.124 mg/l, respectively, which was lower than the toxicity characteristic leaching procedure (TCLP), regulatory limit (5 mg/l). Replacement of cement by 10% fly ash in FC1 restricted the leaching of chromium more effectively. Model equations based on two shrinking core models namely, acid dissolution and bulk diffusion model, were used to analyze the kinetics of microbial degradation. Of the two approaches, the bulk diffusion model fit the data better than the acid dissolution model as indicated by the correlation coefficients of >0.97.

Naphthalene Biodegradation from Non-Aqueous-Phase Liquids in Batch and Column Systems: Comparison of Biokinetic Rate Coefficients

The kinetics of microbial degradation of naphthalene from a two-component non-aqueous-phase liquid (NAPL) coated onto uniformly sized nonporous particles were evaluated in a completely mixed batch reactor (CMBR) system and in flow-through column systems to examine the differences in the biodegradation kinetic coefficients, micro(max), the maximum specific growth rate coefficient, and K(s), the half saturation constant in the two systems. The values of these coefficients were estimated by nonlinear least-squares regression of the naphthalene mineralization profiles obtained from both CMBR and column biodegradation experiments. The results show that the range of values for micro(max) and K(s) obtained from column systems are very similar to the range of values obtained from CMBR systems. This suggests that coefficients estimated from CMBR or column systems are equally applicable for modeling studies. The presence of microorganisms and the development of biofilms at the NAPL-water interface reduced the mass transfer rates of naphthalene from the NAPL by 60% in CMBR and by 70% in column systems. If such changes in mass transfer coefficients are not accounted for, significantly erroneous values of biokinetic coefficients may be obtained.

Kinetic analysis of data obtained from studies on microbial degradation of cement waste forms, using shrinking core models

Model equations based on analytical solutions of two shrinking core models (acid dissolution or shrinking unreacted core (SUC) model, and bulk diffusion model), were used to analyze the kinetics of microbial degradation of cement waste forms. Two current approaches of waste form microbial stability evaluation (Nuclear Regulatory Commission (NRC) method and refined biofilm formation) were used to generate the data. Good linear correlations with R 2>0.95 were obtained for the leaching data from both the NRC and biofilm approaches, using the model equation based on the bulk diffusion concept. Analyses using the model equation based on the acid dissolution model generally gave poor correlations except when data obtained from biofilm formation method was normalized.

Environmental factors and kinetics of microbial degradation of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) in an aqueous medium

AbstractEnvironmental factors such as oxygen, temperature, and microbial species may have significant effects on decomposition of biodegradable polymers. A representative biodegradable, thermoplastic polymer, poly(3‐hydroxybutyrate‐co‐hydroxyvalerate) (PHBV), was decomposed in an aqueous medium under controlled laboratory conditions by soil microbes for the intrinsic degradation kinetics and the effects of the environmental factors on polymer biodegradation. The amount of proteins, including the PHBV depolymerases, that attached to the polymer surfaces was quite constant during the period of significant mass loss of the polymer specimens. The microbial polymer degradation followed a zero‐order rate model, so the residual mass fraction of PHBV films declined linearly with time. The mixed aerobic microbial organisms from fertile soil showed a higher activity of polymer degradation than an aerobic PHBV‐producing bacterium and the mixed anaerobes in the same soil. The mixed anaerobic microorganisms from barren soil decomposed the polymer at a slower rate than the anaerobes from fertile soil, and this was attributed to fewer microbial cells in the barren soil instead of the difference in the microbial species. The temperature effect on PHBV degradation can be described with an Arrhenius equation, and the activation energy is around 16 kcal/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 205–213, 2003

Effect of mass-transfer limitations on bioavailability of sorbed naphthalene in synthetic model soil matrices

External and internal mass-transfer resistances influencing the bioavailability of sorbed naphthalene in a synthetic model matrix for soil aggregates were investigated in batch experiments in mixed reactors. Amberlite® adsorption resins (XAD4 and XAD7) were used as the synthetic model for soil aggregates. The effect of hydrodynamic conditions in the slurry phase on the diffusive transport across a stagnant film surrounding the model particles was studied. In addition, a mechanistic model was developed based on mass balances, diffusion equations, a nonlinear sorption isotherm, and microbial degradation kinetics. Experimental results could be explained well with this model. In the absence of external transfer limitations, intraparticle effective diffusion coefficients of (3.55 ± 0.10) × 10−9 m2/s and (5.29 ± 0.86) × 10−10 m2/s were determined for naphthalene in Amberlite XAD4 and XAD7, respectively.

Carbon Tetrachloride Degradation: Effect of Microbial Growth Substrate and Vitamin B12 Content

Microbial degradation kinetics of carbon tetrachloride (CT) under reducing conditions were investigated for different cultures, fed with 1,2-propanediol, dextrose, propionaldehyde, or acetate and nitrate, in the anaerobic step of an anaerobic/aerobic operation sequence. Methanogenesis was inhibited due to the aerobic step. CT biodegradation rates followed first-order kinetics with respect to CT concentration and biomass and were not affected by the presence of growth substrate. CT degradation rates increased linearly with higher intracellular vitamin B12 content. The culture fed 1,2-propanediol had the highest vitamin B12 content, which was 3.8, 4.7, and 16 times that of the propionaldehyde-, dextrose-, and acetate-fed cultures, respectively, and its first-order degradation rate constant was 2.8, 4.5, 6.0 times that for those cultures, respectively. No CT degradation occurred with culture liquid, suggesting that intracellular factors were responsible for CT degradation. The propanediol culture was able to sustain a constant CT degradation rate for a 16-day test period without substrate addition. Compared to a propanediol-fed culture grown only under anaerobic conditions, the propanediol culture grown under the sequential anaerobic/aerobic condition resulted in more biomass growth and a greater CT degradation rate per unit of propanediol fed, although its CT degradation rate per unit of biomass was lower.

Formulating microbial biocontrol agents

Micro-organisms can be used to provide a crop protection effect, but to exploit this it is necessary to deliver viable micro-organisms as a formulated product suitable for agronomic application, which presents a significant challenge to formulation technology. Gram-negative bacterial cells can be formulated in a dry form which is shelf-stable at elevated temperatures for periods exceeding six months. This paper presents the key physical requirements of the dried formulation required to generate this stability, and a predictive mathematical model of the kinetics of microbial degradation as a function of key physical parameters, for example storage temperature and relative humidity. © 1999 Society of Chemical Industry

Formulating microbial biocontrol agents

Micro-organisms can be used to provide a crop protection effect, but to exploit this it is necessary to deliver viable micro-organisms as a formulated product suitable for agronomic application, which presents a significant challenge to formulation technology. Gram-negative bacterial cells can be formulated in a dry form which is shelf-stable at elevated temperatures for periods exceeding six months. This paper presents the key physical requirements of the dried formulation required to generate this stability, and a predictive mathematical model of the kinetics of microbial degradation as a function of key physical parameters, for example storage temperature and relative humidity.

Formulating microbial biocontrol agents

Micro-organisms can be used to provide a crop protection effect, but to exploit this it is necessary to deliver viable micro-organisms as a formulated product suitable for agronomic application, which presents a significant challenge to formulation technology. Gram-negative bacterial cells can be formulated in a dry form which is shelf-stable at elevated temperatures for periods exceeding six months. This paper presents the key physical requirements of the dried formulation required to generate this stability, and a predictive mathematical model of the kinetics of microbial degradation as a function of key physical parameters, for example storage temperature and relative humidity. © 1999 Society of Chemical Industry

Microbial degradation kinetics of solid alkane dissolved in nondegradable oil phase

An Acinetobacter species was isolated and found to be able to grow on crude oil n-alkanes and solid alkanes at room temperature as the sole carbon source. The growth of the isolate on n-heneicosane dissolved in non-biodegradable pristane has been studied. A kinetic model of the growth of microorganism on the hydrophobic substrate dissolved in non-biodegradable oil droplet assuming direct contact of cell with oil droplet was developed and validated with a model system of crude oil biodegradation. The model was focused on the substrate transport to the cell being contact with the surface of droplet. The high value of saturation constant of n-heneicosane, K s = 0.086 kg m −3, and the maximum specific growth rate, μ m = 0.60 h −1, were obtained. The transport limitation was considered and estimated. The high value of attached cell fraction was reasonable to explain the observed growth rate by the direct contact model and varied with time till it reached a plateau at the stationary growth phase. By considering the direct contact of the cells with the surface of pristane and the transport of n-heneicosane to the cell, the degradation of hydrophobic substrate in the oil phase could be elucidated.

Stoichiometry and kinetics of microbial toluene degradation under denitrifying conditions.

Batch experiments were carried out to investigate the stoichiometry and kinetics of microbial degradation of toluene under denitrifying conditions. The inoculum originated from a mixture of sludges from sewage treatment plants with alternating nitrification and denitrification. The culture was able to degrade toluene under anaerobic conditions in the presence of nitrate, nitrite, nitric oxide, or nitrous oxide. No degradation occurred in the absence of Noxides. The culture was also able to use oxygen, but ferric iron could not be used as an electron acceptor. In experiments with 14C-labeled toluene, 34% +/- 8% of the carbon was incorporated into the biomass, while 53% +/- 10% was recovered as 14CO2, and 6% +/- 2% remained in the medium as nonvolatile water soluble products. The average consumption of nitrate in experiments, where all the reduced nitrate was recovered as nitrite, was 1.3 +/- 0.2 mg of nitrate-N per mg of toluene. This nitrate reduction accounted for 70% of the electrons donated during the oxidation of toluene. When nitrate was reduced to nitrogen gas, the consumption was 0.7 +/- 0.2 mg per mg of toluene, accounting for 97% of the donated electrons. Since the ammonia concentration decreased during degradation, dissimilatory reduction of nitrate to ammonia was not the reductive process. The degradation of toluene was modelled by classical Monod kinetics. The maximum specific rate of degradation, k, was estimated to be 0.71 mg toluene per mg of protein per hour, and the Monod saturation constant, Ks, to be 0.2 mg toluene/l. The maximum specific growth rate, mu max, was estimated to be 0.1 per hour, and the yield coefficient, Y, was 0.14 mg protein per mg toluene.

Aerobic Acetate Degradation near the Capillary Fringe of Roadside Soil: Field Simulations from Soil Microcosms

AbstractWe studied the aerobic degradation of acetate in a roadside soil to assess the reduction of O2 demand imposed by an alternative highway deicing agent on groundwater. Aseptic uniform sand samples adjacent to the capillary fringe of a state highway shoulder in southeastern Massachusetts were placed in sterile serum bottles at 5°C, forming a series of aerobic soil microcosms. The samples were dosed with a reagent‐grade glacial acetic acid solution, then sampled at various time intervals and analyzed by ion chromatography in a laboratory determination of the microbial degradation kinetics. The aerobic reaction rates were slower than those observed in loamy sand near the ground surface in an earlier study. A steady state transport model for the alternative highway deicing agent calcium magnesium acetate [CMA; Ca0.3 Mg0.7(C2H3O2)2] was derived, including infiltration and degradation. Simulations were run using the observed microcosm kinetics for a range of assumed snowmelt rates. The resulting profiles suggest that microbial activity within the uniform sand near the capillary fringe has the potential to reduce O2 demand by CMA on groundwater for slow (<5×10−7 m/s) snowmelt rates at 5°C under aerobic conditions. More rapid infiltration passes more CMA to the underlying aquifer.