Batch growth kinetics of an indigenous mixed microbial culture utilizing m-cresol as the sole carbon source

Acclimation of Isochrysis galbana Parke (Isochrysidaceae) for enhancing its tolerance and biodegradation to high-level phenol in seawater

Marine microalgae with high removal efficiency of phenol are needed for the remediation of polluted seawater in cases involving phenol spills. To achieve this purpose, adaptive laboratory evolution (ALE) was performed by a microalga Isochrysis galbana Parke MACC/H59, which is capable of degrading phenol at concentrations of less than 100 mg L^-1 in 4 d. Two acclimation conditions were used: (i) 90 d at 100 mg L^-1 phenol, and (ii) 90 d at 100 mg L^-1 phenol followed by another 90 d at 200 mg L^-1 phenol. By doing so, two strains (PAS-1 and PAS-2) could be obtained respectively. They grew rapidly at phenol concentrations up to 200 mg L^-1 and 300 mg L^-1, respectively, with a specific growth rate 2.52-3.40 times and 1.93-3.23 times that of the control (without phenol). Also, both strains had a higher removal capacity of phenol than the unacclimated alga. Phenol at an initial concentration of 200 mg L^-1 was completely removed in 5 d thereby. For 300 mg L^-1 phenol, a removal efficiency of 92% was achieved in 10 days by using PAS-2, with a removal rate constant of 30.01 d^-1 (about twice that of PAS-1) and a half-life of 4.90 d (about half that of PAS-1), showing that a better strain may be obtained by extending the acclimation time. The enhancement of phenol biodegradation can be explained by the elevated activity of phenol hydroxylase (PH) in both strains. These results indicated that ALE could be an efficient tool used to enhance the tolerance and biodegradation of marine microalgae to phenol in seawater.

Biodegradation of metformin and guanylurea by aerobic cultures enriched from sludge

Sewage sludge from a municipal wastewater treatment facility employing activated sludge process was pre-incubated with varying substrates and mixtures of substrates including metformin (MET), guanylurea (GUA) and glucose. The biomass from enriched cultures separately utilising MET and glucose/GUA was then used to investigate the kinetics of aerobic biodegradation of MET and GUA, respectively, as individual substrates in batch reactors. The results showed that GUA can be completely degraded as a nitrogen source when glucose is provided as a carbon and energy source. On the contrary, MET can be biodegraded as a sole carbon and energy source. However, formation of by-product GUA in solution, which acts as a nitrogen source, rapidly increased the degradation rate of MET resembling autocatalytic behaviour. At low starting concentration of 5 mg/L, the specific substrate utilisation rates of MET and GUA were 0.0033 day^-1 and 0.0013 day^-1, respectively, which is reported first time in this study. Out of the five biodegradation kinetic models used to describe substrate utilisation, the Quiroga-Sales-Romero (QSR) model was found to predict the measured MET and GUA degradation profile well supported by the goodness of fit parameters. Furthermore, the QSR model was able to describe the autocatalytic degradation of MET and the incomplete biodegradation of GUA in solution.

Co-metabolism kinetics and electrogenesis change during cyanide degradation in a microbial fuel cell

The co-metabolic degradation kinetics, microbial growth kinetics and electricity generation capacity were researched of strain MC-1 in a MFC (microbial fuel cell). The results show that Haldane and Aiba models suit the growth kinetics of a single substrate (sodium acetate) MFC with 0.995 correlation coefficient. Moreover, the Haldane model was appropriate to describe the growth kinetics of a single substrate (sodium cyanide) MFC with 0.986 correlation coefficient. The growth kinetics of a mixed substrate MFC can be explained well by the SKIP model with correlation coefficient 0.995. Second order and three-half order models were found to suitably describe the cyanide degradation process. The maximum output voltage of MFC and the cyanide degradation efficiency were significantly enhanced by using sodium acetate and cyanide as mixed substrates. Also, the trend of electricity production is related to the growth cycle of microorganisms in a MFC.

The co-metabolic degradation kinetics, microbial growth kinetics and electricity generation capacity were researched for strain MC-1 in a MFC.

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 700 ppm KCN after 72 h 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 (S_m) 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.

Kinetic analysis and degradation pathway for m-dichlorobenzene removal by Brevibacillus agri DH-1 and its performance in a biotrickling filter

A strain, Brevibacillus agri DH-1, isolated from dry lands was used to remove m-dichlorobenzene. After 48h culturing, the concentrations of m-dichlorobenzene decreased from 26-130 to 7.87-28.87mg/L and dry cell weight for bacterial growth reached 52.43-75.05mg/L. The growth and degradation kinetics were analyzed by the fitting of Haldane-Andrews model and pseudo first-order model. A degradation pathway was proposed according to major intermediates (phenol), chloride ion variation, ring-opening enzyme activity, and high mineralization (0.47g_Cl-/g_{m-dichlorobenzene}, 0.65 g_co2/g_{m-dichlorobenzene}, 0.15 g_DCW/g_{m-dichlorobenzene}). In addition, the performance in a biotrickling filter (BTF) was evaluated through removal efficiency and pressure drop values with increasing inlet loading rate from 4.10 to 122.57g/m³/h at three empty bed residence time points (30s, 60s, and 90s). The results demonstrated that strain DH-1 possessed high removal efficiency and stable operation in a BTF.

Experimental studies and kinetic modeling of the growth of phenol-degrading bacteria in turbulent fluids

Understanding the interaction between microorganisms and fluid dynamics is important for aquatic ecosystems, though only sporadic attention has been focused on this topic in the past. In this study, particular attention was paid to the phenol-degrading bacterial strains Microbacterium oxydans LY1 and Alcaligenes faecalis LY2 subjected to controlled fluid flow under laboratory conditions. These two strains were found to be able to degrade phenols over a concentration range from 50 to 500 mg/L under different turbulence conditions ranging from 0 to 250 rpm. The time it took to reach total phenol degradation decreased when the turbulence was increased in both strains, with increasing energy dissipation rates ranging from 0.110 to 6.241 W/kg, corresponding to changes in the bacterial diffusive sublayer thickness (δ) and enhanced oxygen uptake. Moreover, the maximum specific growth rates of the two strains also increased with the enhancement of turbulence. A model integrating growth inhibition and fluid motion was proposed based on the self-inhibition Haldane model by introducing a turbulence parameter, α. The resulting modified Haldane model was designed to include fluid motion as a variable in the quantification of the physiological responses of microorganisms. This modified Haldane model could be considered a useful laboratory reference when modeling procedures for water environment bioremediation. Graphical abstract Cell nutrition uptake cartoon schematic diagram for M. oxydans LY1 under different turbulent condition (50 and 200 rpm).

Microbial production of succinic acid using crude and purified glycerol from a Crotalaria juncea based biorefinery

Microbial conversion of crude and purified glycerol obtained in the process of biorefining Crotalaria juncea is carried out to produce succinic acid using Escherichia coli. Batch tests are performed for nine different substrate concentrations of commercial, purified and crude glycerol, in order to observe cell growth and substrate utilization rate. Inhibitory (Halden-Andrew, Aiba-Edward, Tessier type and Andrews) as well as non-inhibitory (Monod, Moser and Tessier) models are fitted to the relationship between specific growth rate and substrate concentration obtained from the growth curves. Considering the inhibition effect, Aiba-Edward model ranked 1 out of 7 in case of two samples and Haldane-Andrew model ranked 1 in case of one sample. Aiba-Edward model gave the best fitment for a large range of concentrations of all the three types of glycerol, crude, purified and laboratory grade. Maximum production of succinic acid is obtained from commercial glycerol at pH 7 and 37.5 °C.

Kinetics and Mechanism of Fenpropathrin Biodegradation by a Newly Isolated Pseudomonas aeruginosa sp. Strain JQ-41

A soil bacterium designated strain JQ-41, capable of growth on fenpropathrin as the sole carbon source and energy source, was isolated from a long-term pyrethroid insecticide-treated orchard. Based on the morphology, physio-biochemical characteristics, and 16S rDNA gene analysis, as well as the G+C content of the genomic DNA, the strain JQ-41 was identified as Pseudomonas aeruginosa. Up to 92.3% of 50 mg l(-1) fenpropathrin was degraded by P. aeruginosa strain at 30°C and pH 7 within 7 days. The kinetic parameters q max, K s, and K i were established to be 1.14 day(-1), 38.41 mg l(-1), and 137.67 mg l(-1), respectively, and the critical inhibitor concentration was determined to be 72.72 mg l(-1). Cell surface hydrophobicity of P. aeruginosa strain was enhanced during growth on fenpropathrin. Three metabolites from fenpropathrin degradation were identified by gas chromatography mass spectrometry, and then a possible degradation pathway was proposed. In addition, this isolate was also able to degrade a wide range of synthetic pyrethroid insecticides including cypermethrin, deltamethrin, bifenthrin, and cyhalothrin with the degradation process following the first-order kinetic model. Taken together, our results provide insights into the kinetics and mechanism of fenpropathrin degradation by P. aeruginosa strain and also highlight its promising potential in bioremediation of pyrethroid-contaminated environment.

Degradation pathway and kinetic analysis for p-xylene removal by a novel Pandoraea sp. strain WL1 and its application in a biotrickling filter

In this study, a novel Pandoraea sp. strain WL1 capable of mineralizing p-xylene as sole carbon and energy source was isolated from the activated sludge of a pharmaceutical wastewater treatment plant. A nearly complete degradation of 16.6∼99.4 mg L(-1)p-xylene in the liquid-phase was achieved within 6∼18 h accompanied by 15.9∼56.3 mg dry cell weight (DCW)L(-1) for bacterial growth. A complete pathway for p-xylene degradation by strain WL1 was presented through identification of a major intermediate (p-toluic acid) and final products (2.193 gCO2 gp-xylene(-1) of CO₂ production and 0.215 g DCW gp-xylene(-1) of bacterial yield). Kinetics of bacterial growth and p-xylene degradation were evaluated using Haldane-Andrews model and pseudo first-order model, respectively. Furthermore, a biotrickling filter (BTF) was employed to evaluate the application of strain WL1 on the removal of gas-phase p-xylene under gas flow rates of 0.41∼1.98 m(3)h(-1) for inlet loading rates of 5∼248 gm(-3)h(-1). The BTF inoculated with strain WL1 proved to be robust against fluctuations of gas flow rates and inlet p-xylene concentrations. All the results obtained highlight the potential of strain WL1 for the treatment of p-xylene.

A novel antifungal is active against Candida albicans biofilms and inhibits mutagenic acetaldehyde production in vitro

The ability of C. albicans to form biofilms is a major virulence factor and a challenge for management. This is evident in biofilm-associated chronic oral-oesophageal candidosis, which has been shown to be potentially carcinogenic in vivo. We have previously shown that most Candida spp. can produce significant levels of mutagenic acetaldehyde (ACH). ACH is also an important mediator of candidal biofilm formation. We have also reported that D,L-2-hydroxyisocaproic acid (HICA) significantly inhibits planktonic growth of C. albicans. The aim of the present study was to investigate the effect of HICA on C. albicans biofilm formation and ACH production in vitro. Inhibition of biofilm formation by HICA, analogous control compounds or caspofungin was measured using XTT to measure biofilm metabolic activity and PicoGreen as a marker of biomass. Biofilms were visualised by scanning electron microscopy (SEM). ACH levels were measured by gas chromatography. Transcriptional changes in the genes involved in ACH metabolism were measured using RT-qPCR. The mean metabolic activity and biomass of all pre-grown (4, 24, 48 h) biofilms were significantly reduced after exposure to HICA (p<0.05) with the largest reductions seen at acidic pH. Caspofungin was mainly active against biofilms pre-grown for 4 h at neutral pH. Mutagenic levels (>40 µM) of ACH were detected in 24 and 48 h biofilms at both pHs. Interestingly, no ACH production was detected from D-glucose in the presence of HICA at acidic pH (p<0.05). Expression of genes responsible for ACH catabolism was up-regulated by HICA but down-regulated by caspofungin. SEM showed aberrant hyphae and collapsed hyphal structures during incubation with HICA at acidic pH. We conclude that HICA has potential as an antifungal agent with ability to inhibit C. albicans cell growth and biofilm formation. HICA also significantly reduces the mutagenic potential of C. albicans biofilms, which may be important when treating bacterial-fungal biofilm infections.

Influence of phenolic substrates utilised by yeast Trichosporon cutaneum on the degradation kinetics

The degradation kinetics of different phenolic substrates utilised by Trichosporon cutaneum R57 was studied. The following compounds were used as substrates: phenol, resorcinol, hydroquinone, 3-nitrophenol, 2,6-dinitrophenol, 3-chloro phenol and p-cresol. The specific degradation rates (Q_s) were described by a Haldane kinetic model. The unknown model parameters were estimated using the mathematical optimisation procedure for direct search. The results obtained demonstrated that Q_s varied greatly in the experiments carried out. The level of biodegradability depended on the different structure and toxicity of compounds used as carbon substrates. The highest Q_s values were observed for less toxic hydroxylated phenols (0.77–0.85 h⁻¹), while the most toxic chlorinated phenols were characterised with the lowest Q_s values (0.224 h⁻¹). The results obtained with different concentrations of resorcinol (from 0.2 to 0.8 g L⁻¹) and 2,6-dinitrophenol (from 0.2 to 0.7 g L⁻¹) demonstrated a growing inhibitory effect directly correlating with the extended time necessary for complete degradation of both compounds.

Back propagation neural network model for predicting the performance of immobilized cell biofilters handling gas-phase hydrogen sulphide and ammonia

Lab scale studies were conducted to evaluate the performance of two simultaneously operated immobilized cell biofilters (ICBs) for removing hydrogen sulphide (H₂S) and ammonia (NH₃) from gas phase. The removal efficiencies (REs) of the biofilter treating H₂S varied from 50 to 100% at inlet loading rates (ILRs) varying up to 13 g H₂S/m³·h, while the NH₃ biofilter showed REs ranging from 60 to 100% at ILRs varying between 0.5 and 5.5 g NH₃/m³·h. An application of the back propagation neural network (BPNN) to predict the performance parameter, namely, RE (%) using this experimental data is presented in this paper. The input parameters to the network were unit flow (per min) and inlet concentrations (ppmv), respectively. The accuracy of BPNN-based model predictions were evaluated by providing the trained network topology with a test dataset and also by calculating the regression coefficient (R²) values. The results from this predictive modeling work showed that BPNNs were able to predict the RE of both the ICBs efficiently.

Aerobic degradation of phenolics and aromatic hydrocarbons in presence of cyanide

Present study focused on the degradation of a mixture of phenol, cresol, xylenol, quinoline, and indole along with cyanide, commonly found in coke oven wastewater, using aerobic mixed culture. It was found that xylenol and indole were difficult to degrade, when the concentrations were above 250 mg/L. It was observed that free cyanide (2.5mg/L and above) has the potency to holdup the oxidation of organics (250 mg/L) until the cyanide concentration drops to a minimum level. Final TOC in the mixed pollutant system was less than 4 mg/L, indicating the absence of other organic byproducts. Experimental results highlight effect of free cyanide on removal of organics and the combined toxic influence of cyanide and organics on the microbes treating coking wastewater. The proposed mathematical model was able to predict the biodegradation of mixed pollutant system satisfactorily.

Biodegradation of m-cresol by aerobic granules in a sequencing batch reactor

The present study was aimed at the development of aerobic granules in a sequencing batch reactor for the biodegradation of m-cresol. The reactor was started with 100 mg L(-1)of m-cresol. Aerobic granules first appeared within 1 month of the start-up of the reactor. The granules were large and strong and had a compact structure. The diameter of stable granules on day 200 was in the range of 1.5 - 5 mm. The integrity coefficient and density of the granules was found to be 98% and 1046 kg m(-3), respectively. The settling velocity of the granules was found to be in the range of 2-6 x 10(-2) m s(-1). The aerobic granules were able to degrade m-cresol up to 800 mg L(-1) at a removal efficiency of 87%. UV and GC/MS studies confirmed that the biodegradation ofm-cresol occurred via catechol via the ortho-cleavage pathway. The specific m-cresol degradation rate in aerobic granules followed the Haldane model for substrate inhibition. A high specific m-cresol degradation rate of up to 0.718 g m-cresol g(-1)VSS(-1)d(-1) was sustained up to an m-cresol concentration of 400 mgL(-1). The higher removal efficiency and good settling characteristics of aerobic granules make the sequencing batch reactor method suitable for enhancing the microorganism potential for biodegradation of inhibitory compounds.

Biodegradation dynamics and cell maintenance for the treatment of resorcinol and p-cresol by filamentous fungus Gliomastix indicus

Biodegradation of resorcinol and p-cresol using fungus Gliomastix indicus MTCC 3869 was investigated in batch culture experiments at 28°C temperature and pH of 6 in the medium up to the initial concentration of 1300 mg/L and 700 mg/L for resorcinol and p-cresol, respectively. Five specific growth kinetic models and five specific degradation rate models were fitted to the experimental data in order to get best fitted kinetic models. The variation of observed growth yield and maintenance energy requirement with the initial substrate concentration was also studied. The model for maintenance energy coefficient was fitted to the experimental data. The model parameters were: m(1)=0.0135 h(-1), k=0.054, μ(max)=0.132 h(-1) for resorcinol and m(1)=0.0229 h(-1), k=0.011, μ(max)=0.102 h(-1) for p-cresol. Two mathematical models comprising of two sets of ODE were solved simultaneously to get degradation profiles with time. The model with varying growth yield and maintenance energy was found to be most appropriate biodegradation model.

Functional consortia for cresol-degrading activated sludges: toxicity-to-extinction approach

The conventional roll tube and plating techniques are typically time consuming and can culture in vitro only a small fraction of microbes in natural microflora. This study utilizes a novel, simple, and rapid method, the toxicity-to-extinction approach, to obtain the minimal functional consortium that can effectively degrade meta- (m-), para- (p-), and ortho- (o-) cresols. The original sludge had 16 major bands by denaturing gradient gel electrophoresis (DGGE). Microbial diversity decreased as the cresol concentration increased. The functional strains acquired under toxic stress by dosed cresols that individually degraded m-, p-, and o-cresols were identified. Catechol 1,2-dioxygenase (C12D) and catechol 2,3-dioxygenase (C23D) activities in cell-free extracts were determined spectrophotometrically and were correlated with noted changes in microbial communities under cresol stress. The proposed toxicity-to-extinction approach is feasible for isolating a functional consortium from sludge for cresol degradation.