Optimal Conditions For Biodegradation Research Articles

Identification and isolation of efficient phenol-degrading and heavy metal-resistant bacteria from seasonal catchments of the Lut Desert

ABSTRACT The present study was conducted to isolate and identify a phenol-degrading bacterial strain resistant to cadmium obtained from seasonal catchments of the Lut Desert, Iran. Additionally, optimal conditions affecting biological phenol degradation, including pH, temperature, salinity, and carbon-to-nitrogen ratio, were determined using the Taguchi method, and the ability of the purified strain to degrade phenol in different concentrations was investigated. Isolated bacterium strain Bacillus cereus LD-1, capable of phenol degradation and cadmium tolerance, could tolerate and degrade phenol up to a concentration of 1,500 mg/L. All optimized factors except carbon-to-nitrogen ratio had a significant effect on the rate of phenol biodegradation. Among the selected factors, based on the effect size, pH had the highest impact (10.02), followed by salinity (6.16), temperature (5.61), and C:N ratio (2.55) on phenol biodegradation. The optimal conditions for phenol biodegradation were determined as pH of 8, temperature of 30 °C, salinity of 0 g/L, and C:N ratio of 100:30. Under optimal conditions, 80.57% of phenol was decomposed by the LD-1 strain. Considering the high ability of the isolated strain for phenol degradation in the presence of 100 mg/L cadmium, LD-1 can be applied in the biological treatment of phenolic effluents contaminated with heavy metals.

Assessment of the Plasmid Mediated Biodegradation of Crude Oil under Optimal Growth Conditions

The present study was undertaken to assess the role of plasmid-mediated biodegradation of crude oil under optimal growth conditions. Enrichment techniques, turbidometric test, antimicrobial susceptibility testing, plasmid curing test and optimal biodegradation conditions were carried out using standard procedures. The results indicated that 22 of the isolates were observed to have high pollutant degrading potentials (A600nm > 0.3) due to their crude oil utilization ability. Isolates designated as C1, D1, L2 and J3 showed various degrees of growth after curing of their plasmids whereas isolates G2, H4, K4 and I6 were unable to grow after plasmid removal. It was observed that 4 plasmid-borne cells resisted the antibiotics tested after pre-cured examination but these isolates were 95% sensitive to the same antibiotics after post cured test. The results further indicated that isolates which were able to degrade crude oil belonged to genera Bacillus, Pseudomonas sp., Ochrobacterium sp. and Enterobacter sp. Moreso, neutral pH, 35 °C temperature and 3 % crude oil concentration were found to be optimal conditions for crude oil bioaugmentation study. Thus, the study indicated that the crude oil-utilizing bacteria which are part of the soil ecosystem could be exploited for natural and terrestrial remediation of crude oil-polluted environments.

Biodegradation of dibutyl phthalate and diethyl phthalate by indigenous isolate Bacillus sp. MY156: Characterization, stoichiometry, enzyme activity, and physiological response to cell surface

An indigenous bacterial strain, Bacillus sp. MY156, was isolated from a local wastewater treatment plant and utilized for degradation of dibutyl phthalate (DBP) and diethyl phthalate (DEP). The isolate showed a substrate preference of DBP to DEP. The optimal biodegradation conditions were pH 7, 30 °C, 0.2 (in terms of OD600) inoculum size, and 2 % (v v−1) bacterial load. The biodegradation of DBP and DEP as sole carbon source was comprehensively investigated via degradation kinetics and mass balance analysis. The isolate achieved complete degradation and over 80 % removal of 300 mg L−1 DBP within 60 h and 200 mg L−1 DEP in 5 days. The biodegradation of DBP and DEP fitted the inhibitory kinetic model, and the maximum degradation rates for DBP and DEP were 183.34 and 66.90 mg L−1 day−1, respectively. The cell surface responses to biodegradation were investigated by analyses of morphology, Fourier transform-infrared, and extracellular polymeric substance. The potential intermediates were mono-n-butyl phthalate, mono-ethyl phthalate, phthalic acid, and protocatechuic acid by β-oxidation, hydrolysis, and decarboxylation. The esterase and dehydrogenase activities reached the highest at the initial and middle phases during biodegradation. The docking studies also elucidated the relevant enzyme preferred DBP to DEP via binding energy and bond distance.

Biodegradation of low density polyethylene (LDPE) by Paenibacillus Sp. and Serratia Sp. isolated from marine soil sample

Low Density Polyethylene (LDPE) is recalcitrant and poses serious threats to our environment. The present study explored the LDPE biodegradation potential of aerobic bacteria enriched from offshore of RK beach Visakhapatnam. These isolates were specifically enriched in MSAM medium which contains LDPE as the source of carbon and energy for the growth. Six strains were isolated; among these S-6 & S-2 are the most potent strains which were attributed to the degrading ability. The phenotypic fingerprint such as Gen III biolog was used to identify the LDPE degrading S-6 as Paenibacillus sp. and S-2 as Serratia sp. respectively. Gen III Microlog, a phenotypic microarray; have been used for analysis of relative capabilities for substrate utilization of S-6 and S- 2 strains. The contact time of 72 h, temperature of 37 °C, pH of 7.1, inoculum volume 4% v/v, and weight of LDPE films 0.030 g were found to be optimal conditions for biodegradation of LDPE. Efficiency of these microbes (Paenibacillus sp. and Serratia sp) in degradation of LDPE was studied by percent weight reduction during a time period of 35 days. The Paenibacillus sps. proved to be most efficient with a weight loss of 22.46% compared to Serratia sps. with a weight loss of 9.5%. These bacterial species are capable of utilising LDPE as the sole carbon and energy source.

Two strains of bacteria from oilfield slickwater and their performance in partially hydrolyzed polyacrylamide biodegradation

Partially hydrolyzed polyacrylamide (HPAM) is widely used in oil recovery, but the HPAM residues also induce environmental pollution. In this study, two strains of bacteria, SCE2 and NMYGYB4, have been isolated from oilfield slickwater and identified as Tistrella bauzanensis (SCE2) and Brucella sp. (NMYGYB4). The optimal biodegradation conditions of Tistrella bauzanensis SCE2 were inoculation time 36 h, shaking speed 175 rpm, inoculum amount 3% (v/v), pH 3.0, and incubation temperature 37 °C with urea and glucose as the nitrogen and carbon sources. And the optimal biodegradation conditions of Brucella sp. NMYGYB4 were 12 h, 185 rpm, 2% (v/v), pH 7.0 and 37 °C with yeast powder and sucrose as the nitrogen carbon sources. HPAM removal rate of Tistrella bauzanensis SCE2 and Brucella sp. NMYGYB4 reached 75.3% and 63.59% at optimal conditions. The degraded samples were analyzed with GPC, FTIR, 1H NMR and HPLC. The results showed that HPAM was broken into small fragments, and amide group has been converted into carboxyl group, and no toxic acrylamide monomer was produced. The specific activities of extracellular amidases of Tistrella bauzanensis SCE2 and Brucella sp. NMYGYB4 were 5.31 U/mg and 4.79 U/mg, respectively. This work will provide novel bacteria strains for HPAM-containing wastewater treatment.

Integrated anaerobic-aerobic biodegradation of mixed chlorinated solvents by electrolysis coupled with groundwater circulation in a simulated aquifer.

Chlorinated solvents are widespread subsurface contaminants that are often present as complex mixtures. Complete biodegradation of mixed chlorinated solvents remains challenging because the optimal redox conditions for biodegradation of different chlorinated solvents differ significantly. In this study, anaerobic and aerobic conditions were integrated by electrolysis coupled with groundwater circulation for biodegradation of a mixture of chloroform (CF, 8.25mg/L), 1,2-dichloroethane (DCA, 7.01mg/L), and trichloroethylene (TCE, 4.56mg/L). A two-dimensional tank was filled with field sandy and silty-clayed sediments to simulate aquifer conditions, a pair of electrodes was installed between an injection well and abstraction well, and groundwater circulation transported cathodic H2 and anodic O2 to produce multiple redox conditions. Microbial community analysis demonstrated that the system constructed a habitat suitable for the co-existence of aerobic and anaerobic microbes. After 50days of treatment, 93.1%, 100%, and 87.3% of CF, 1,2-DCA, and TCE were removed without observed intermediates, respectively. Combined with compound specific isotope analysis, the degradation of 1,2-DCA and CF was mainly attributed to aerobic oxidation and reductive dechlorination, respectively, and TCE was removed by both aerobic and anaerobic biodegradation. Our findings provide a new and efficient strategy for in situ bioremediation of groundwater contaminated by mixed chlorinated solvents.

Optimization of Polystyrene Biodegradation by Bacillus cereus and Pseudomonas alcaligenes Using Full Factorial Design.

Microplastics (MP) are a global environmental problem because they persist in the environment for long periods of time and negatively impact aquatic organisms. Possible solutions for removing MP from the environment include biological processes such as bioremediation, which uses microorganisms to remove contaminants. This study investigated the biodegradation of polystyrene (PS) by two bacteria, Bacillus cereus and Pseudomonas alcaligenes, isolated from environmental samples in which MPs particles were present. First, determining significant factors affecting the biodegradation of MP-PS was conducted using the Taguchi design. Then, according to preliminary experiments, the optimal conditions for biodegradation were determined by a full factorial design (main experiments). The RSM methodology was applied, and statistical analysis of the obtained models was performed to analyze the influence of the studied factors. The most important factors for MP-PS biodegradation by Bacillus cereus were agitation speed, concentration, and size of PS, while agitation speed, size of PS, and optical density influenced the process by Pseudomonas alcaligenes. However, the optimal conditions for biodegradation of MP-PS by Bacillus cereus were achieved at γMP = 66.20, MP size = 413.29, and agitation speed = 100.45. The best conditions for MP-PS biodegradation by Pseudomonas alcaligenes were 161.08, 334.73, and 0.35, as agitation speed, MP size, and OD, respectively. In order to get a better insight into the process, the following analyzes were carried out. Changes in CFU, TOC, and TIC concentrations were observed during the biodegradation process. The increase in TOC values was explained by the detection of released additives from PS particles by LC-MS analysis. At the end of the process, the toxicity of the filtrate was determined, and the surface area of the particles was characterized by FTIR-ATR spectroscopy. Ecotoxicity results showed that the filtrate was toxic, indicating the presence of decomposition by-products. In both FTIR spectra, a characteristic weak peak at 1715 cm−1 was detected, indicating the formation of carbonyl groups (−C=O), confirming that a biodegradation process had taken place.

Enhancing fluoroglucocorticoid defluorination using defluorinated functional strain Acinetobacter. pittii C3 via humic acid-mediated biotransformation

Defluorination is a key factor in reducing biologically accumulated carcinogenic and teratogenic toxicity of fluoroglucocorticoids (FGCs). To enhance defluorination efficiency, a highly efficient defluorination-degrading strain Acinetobacter. pittii C3 was isolated, and the promotion mechanism through humic acid (HA)-mediated biotransformation was investigated. Optimal biodegradation conditions for Acinetobacter sp. pittii C3 were pH of 7.0, temperature of 25 ℃, and HA content of 5.5 mg/L, according to response surface methodology analysis. The attenuation rate constant and maximum defluorination percentage of triamcinolone acetonide (TA) in HA-mediated biotransformation system (HA-C3) were 3.99 × 10−2 and 96%, respectively, which were 2.22 and 1.24 times higher than those in the unitary C3 biodegradation system (U-C3), respectively. The major defluorination pathways included elimination, hydrolysis, and hydrogenation, with contributions of 24.5%, 32.4%, and 43.1%, respectively. The bio-reductive hydrodefluorination rate was enhanced by 1.89 times that of HA-mediated, while the other two defluorination pathways exhibited insignificant changes. HA, as the congeries of negatively charged microbes and hydrophobic TA, accelerates the electron transfer rate between Acinetobacter. pittii C3 and TA through the quinone groups. Furthermore, the mutual conversion between the functional groups of hydroxyl oxidation and ketone reduction of HA provided electron donors for TA reductive defluorination and hydrogenation and electron acceptors for TA oxidation. This study provides an effective strategy for FGC-enhanced detoxification using natural HA.

Degradative impact of Alternaria multiformis on novel polymeric biocomposites with the fillers of industrial waste materials under different pH and temperature conditions

The impact of Alternaria multiformis on novel polymeric biocomposites formed from epoxidized linseed oil and various types of fillers: pine needles (PN), pine bark (PB), grain mill waste (GW), rapeseed cake (RC) and specimen without filler (WF) under different pH and temperature conditions has been studied. Identification of fungal strain A. multiformis 0065 isolated from synthetic polymer was based on molecular and morphological analysis. Tested fungal strain showed significant production of polyphenol oxidase and weak production of amylase, endoglucanase, xylanase, and lipase. Polymeric biocomposites PB, GW, RC, and WF exposed to A. multiformis for four weeks showed the greatest weight loss at pH 4 or pH 5 and at a temperature of 26 °C, suggesting the optimal conditions for biodegradation of polymeric biocomposites studied. The attenuated total reflectance infrared spectroscopy (ATR-IR) and scanning electron microscopy (SEM) analysis confirmed biodegradation of polymeric biocomposites after fungal attack. ATR-IR technique revealed changes in the intensities of the signals, demonstrating dependence of degradation on the type of the filler. SEM analysis showed significant alterations of the specimen surfaces, indicating degradative impact of A. multiformis. Identification of the most biodegraded constituents could help in the creation of more environmentally friendly biocomposites.

Optimization of Biodegradation Characteristics of Sphingopyxis sp. YF1 against Crude Microcystin-LR Using Response Surface Methodology.

Sphingopyxis sp. YF1 has proven to be efficient in biodegrading microcystin (MC)-leucine (L) and arginine (R) (MC-LR); however, the optimal environmental factors to biodegrade the toxin have not been investigated. In this study, the biodegrading characteristics of strain YF1 against MC-LR were assessed under diverse environmental factors, including temperature (20, 30 or 40 °C), pH (5, 7 or 9) and MC-LR concentration (1, 3 or 5 µg/mL). Data obtained from the single-factor experiment indicated that MC-LR biodegradation by strain YF1 was temperature-, pH- and MC-LR-concentration-dependent, and the maximal biodegradation rate occurred at 5 µg/mL/h. Proposing Box-Behnken Design in response surface methodology, the influence of the three environmental factors on the biodegradation efficiency of MC-LR using strain YF1 was determined. A 17-run experiment was generated and carried out, including five replications performed at the center point. The ANOVA analysis demonstrated that the model was significant, and the model prediction of MC-LR biodegradation was also validated with the experimental data. The quadratic statistical model was established to predict the interactive effects of the environmental factors on MC-LR biodegradation efficiency and to optimize the controlling parameters. The optimal conditions for MC-LR biodegradation were observed at 30 °C, pH 7 and 3 µg/mL MC-LR, with a biodegradation efficiency of 100% after 60 min. The determination of the optimal environmental factors will help to unveil the detailed biodegradation mechanism of MC-LR by strain YF1 and to apply it into the practice of eliminating MC-LR from the environment.

Novel Polyhydroxybutyrate-Degrading Activity of the Microbulbifer Genus as Confirmed by Microbulbifer sp. SOL03 from the Marine Environment.

Ever since bioplastics were globally introduced to a wide range of industries, the disposal of used products made with bioplastics has become an issue inseparable from their application. Unlike petroleum-based plastics, bioplastics can be completely decomposed into water and carbon dioxide by microorganisms in a relatively short time, which is an advantage. However, there is little information on the specific degraders and accelerating factors for biodegradation. To elucidate a new strain for biodegrading poly-3-hydroxybutyrate (PHB), we screened out one PHB-degrading bacterium, Microbulbifer sp. SOL03, which is the first reported strain from the Microbulbifer genus to show PHB degradation activity, although Microbulbifer species are known to be complex carbohydrate degraders found in high-salt environments. In this study, we evaluated its biodegradability using solid- and liquid-based methods in addition to examining the changes in physical properties throughout the biodegradation process. Furthermore, we established the optimal conditions for biodegradation with respect to temperature, salt concentration, and additional carbon and nitrogen sources; accordingly, a temperature of 37°C with the addition of 3% NaCl without additional carbon sources, was determined to be optimal. In summary, we found that Microbulbifer sp. SOL03 showed a PHB degradation yield of almost 97% after 10 days. To the best of our knowledge, this is the first study to investigate the potent bioplastic degradation activity of Microbulbifer sp., and we believe that it can contribute to the development of bioplastics from application to disposal.

BIODEGRDATION OF POLYAROMATIC HYDROCARBON USING LOCALLY PSEUDOMONAS PUTIDA H18 ISOLATED FROM PETROLEUM CONTAMINATED LOCATIONS

Polycyclic aromatic hydrocarbons (PAHs) are the major sources of pollution that cause dangerous effects on human and other organisms. Biodegradation of PAHs in the contaminated area is an engaging remediation technique and its accommodation depends on the optimal condition for the PAH-degrading isolates. In the current study, four bacterial strains were isolated from polluted area with petrochemical compounds with the ability for biodegradation of phenanthrene and pyrene. Only one strain has high biodegradation ratio of phenanthrene and pyrene. The optimization process for biodegradation of phenanthrene and pyrene was executed and qualified under different conditions of shaking, static, pH, temperature, inoculum sizes, salt concentration, carbon and nitrogen sources. Phylogenetic tree based on 16S rDNA genetic analysis sequence indicates that this bacterial isolate was belonged to genus Pseudomonas and identified as Pseudomonas putida (H 18). The optimal conditions for biodegradation were observed in media containing phenanthrene and pyrene as sole carbon source, yeast extract as nitrogen source, and 4% of inoculum size, at pH 8 and 35oC under static condition for 8 days. The maximum biodegradation efficiency was reached to 92% of phenanthrene and pyrene and was confirmed by using GS-mass spectroscopy.

Biodegradation and Bioaccumulation of Decachlorobiphenyl (DCB) by Native Strain Pseudomonas extremaustralis ADA-5

Decachlorobiphenyl (DCB) is one of the 209 polychlorinated biphenyls congeners characterized by its high toxicity and chemical stability. It is produced by industrial activities. A possible strategy to eliminate DCB is by bacterial degradation. The main objective of this study was to define the optimal conditions for biodegradation and bioaccumulation of DCB by Pseudomonas extremaustralis ADA-5 isolated from a worm intestine. Bacterial growth kinetics were determined in minimal medium with added biphenyl and DCB. By GC coupled to mass spectrometry, we found that the strain had the ability to degrade 9.75% of available DCB, using it as a carbon source and was able to accumulate 19.98% of this pollutant in biomass. Membrane lipids may be altered by DCB. Phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CL) were identified by thin-layer chromatography as the membrane lipids of the cell. At 250 mg L−1 of DCB in the culture medium, membranes showed a 30% decrease in the PE concentration, an 18% increase in the PG, and a 12% increase in CL. ADA-5 was able to catabolize DCB and may be used for bioremediation of highly chlorinated toxic compounds in soil.

Heavy metals and antibiotics resistance of bacteria isolated from Marchica lagoon: biodegradation of anthracene on submerged aerated fixed bed reactor

ABSTRACT Heavy metals resistant and polyaromatic hydrocarbon (PAH)-degrading bacteria isolated from Marchica lagoon. Six isolates, Pseudomonas putida, Orchobactrum antropi, Staphylococus epidermidis, Brevundimonas diminuta, Serratia ficaria and Bacillus anthracis were characterized on the basis of biochemical and 16S rDNA. The strains that showed high resistance to heavy metals were also studied for their antibiotics resistance and growth kinetics. The minimal inhibitory concentrations (MIC) of metals at variant concentrations (10-38 mM) were determined in liquid and solid medium. Strains were showed an extreme resistance against metals with the MIC values of Cu (9 mM), Cd (6.25 mM), Cr (2.5 mM), Ag (0,625), and Hg (0,156). Furthermore, growth rates were decreased in the presence of metals (compared to the control). The anthracene elimination from synthetic wastewater was determined in a submerged aerobic fixed-film reactor. Optimal conditions for bacterium growth and biodegradation of anthracene are determined as: temperature of 37 °C, pH 7, and initial anthracene concentration of 20 mg/l. It emerged that at anthracene concentrations 5-40 mg/l, COD removal efficiency were 84.62%; 90.62%; 91.36% and 71.4% respectively.

Effective removal of polymer quaternary ammonium salt by biodegradation and a subsequent Fenton oxidation process.

In this paper, a process combining biodegradation and Fenton oxidation was proposed for the removal of polydiallyldimethylammonium chloride-acrylic-acrylamide-hydroxyethyl acrylate (PDM) in aqueous phase. Biodegradation of PDM was investigated in activated sludge systems, and the effects of the solution pH, mixed liquid suspended solids (MLSS), salinity, co-substrate, and initial substrate concentration, were studied. The biodegradation process was well-described with the Monod model and the values of the kinetics parameters vmax, ks were 0.05 h-1 and 333 mg/L. The optimal biodegradation conditions in the experimental range were determined to be: pH = 7.0, 0%-0.01% (w/v) NaCl, 4000 mg/L of MLSS, and 500 mg/L of glucose as co-substrate. FT-IR analysis indicated that PDM molecules biodegradation partly. The microbial community structures and dehydrogenase activity analysis revealed that PDM showed some toxicity to microorganisms in activated sludge. The effects of several parameters, including the pH and chemical doses, were investigated for removing PDM in Fenton oxidation process. The optimal Fenton oxidation process conditions in the experimental range were pH = 2.0, Fe2+ concentration of 40 mg/L, and H2O2 dosage of 23 mL/L. PDM was treated by biodegradation and subsequent Fenton oxidation under the optimal operating conditions. The removal efficiency was 44.5% after the biodegradation process and further increased to 85.5% after Fenton oxidation. The combined process was revealed to be a promising solution for achieving effective and economical removal of PDM.

Biodegradation kinetics of diuron by Pseudomonas aeruginosa FN and optimization of biodegradation using response surface methodology

AbstractDiuron is a selective and the most persistent herbicide. Widespread use of this compound has led to the elevated concentrations of diuron in groundwater and wastewater. The main objectives of this study were to investigate biodegradation of diuron by Pseudomonas aeruginosa FN and evolved degradation product, 3,4‐dichloroanilines (3,4‐DCA). The influence of temperature, initial optical density of Pseudomonas aeruginosa FN and initial diuron concentration were examined to further optimize biodegradation of diuron, and the effect of these factors were investigated by the response surface methodology (RSM) and full factorial design (FFD). The optimal biodegradation conditions were obtained at T = 25°C, γ (diuron) = 0.5 mg/L and initial optical density of 0.2. The biodegradation kinetic of diuron was described by Monod model and the obtained value of F‐test was grater that 0.96 which showed good correlation between Monod model and experimental results.

Microbial degradation of organophosphorus pesticides: novel degraders, kinetics, functional genes, and genotoxicity assessment.

Farmland soil sprayed with organophosphorus pesticides (OPs) annually was investigated for the identification and characterization of OP-degrading microorganisms. Six bacterial strains were identified, including Brevundimonas faecalis MA-B12 and Alcaligenes faecalis subsp. parafaecalis MA-B13 for methamidophos degradation, Citrobacter freundii TF-B21 and Ochrobactrum intermedium TF-B23 for trichlorfon degradation, Ochrobactrum intermedium DV-B31 for dichlorvos degradation, and Bacillus cereus for dimethoate degradation. The optimal biodegradation conditions for OPs were obtained at pH 7.0 and incubation temperature ranging from 28 to 37 °C. In an 8-day batch test, biodegradation of the four OPs all followed first-order kinetics, with biodegradation rates ranging from 58.08 to 96.42%. Functional genes responsible for OPs degradation were obtained, including ophB, ampA, opdE, opd, opdA, and mpd. As these strains were indigenous strains isolated from farmland soils, they can be potentially used as bacterial consortium for the bioremediation of mixed OP-contaminated soils. A time-course genotoxicity assessment of the degradation products was done by a bacterial whole-cell bioreporter, revealing that biodegradation of trichlorfon, dichlorvos, and dimethoate resulted a decreased genotoxicity within 5 days, which, however, significantly increased on day 8. The result demonstrated that more toxic products may be produced during the biodegradation processes of OPs, and more attention should be put not only on the pesticides themselves, but also on the toxic effects of their degradation products. To the best of our knowledge, this is for the first time that the genotoxicity of OP degradation products was evaluated by the bioreporter assay, broadening our understanding on the genotoxic risks of OPs during biodegradation process. Graphical Abstract.

Optimization of p-cresol biodegradation using novel bacterial strains isolated from petroleum hydrocarbon fallout

Two potential p-cresol degrading bacterial strains were isolated from petroleum refinery wastewater and identified as Stenotrophomonas sp. (MF004205) strain DBK3 and Bacillus sp. (MF004206) strain DBK4 based on 16S rDNA gene sequencing. While DBK4 was able to utilize p-cresol up to 500 mg L−1 in about 2 days, isolated DBK3 restricted its growth till 600 mg L−1 initial p-Cresol concentration. Further studies were carried out using strain DBK3, which utilized p-cresol as the sole source of carbon. Growth kinetic studies were conducted to determine optimal environmental conditions for growth and biodegradation of p-cresol. Degradation of p-cresol at various preliminary concentrations were also studied at their optimum physiological conditions. 100 mg L−1 p-cresol was found to be the optimal pollutant concentration for growth whereas the ideal temperature and pH for growth and degradation were found to be 37 °C and 7.0 respectively. Microbial growth was monitored spectrophotometrically while residual p-cresol was measured via High Performance Liquid Chromatography (HPLC). Various growth kinetic parameters were estimated by fitting the experimental data to several established substrate inhibition kinetic models by non-linear regression analysis via MATLAB R2017b. The best fit was achieved using Haldane’s kinetic model (maximum growth rate, μmax = 0.1160 h−1 and inhibition constant, KI = 387 mg L−1). The experimental growth kinetic data also fitted reasonably well with Aiba, Yano and Webb model.

Bacterial behaviour in the biodegradation of phenol by indigenous bacteria immobilized in Ca-alginate beads

ABSTRACTThe phenol biodegradation by Ca-alginate immobilized indigenous bacteria was performed in batch system. The effects of some operational parameters were evaluated, including % weight of alginate, calcium and CaCl2, diameter of spheres; jellification time; solution concentration; adaptation concentration and alginate/cells ratio. The optimal biodegradation conditions were found for 2% and 3% of weight for respectively the sodium alginate and calcium chloride. The hardening time was 30 min and beads diameter of 4 cm. The degradation efficiency of the immobilized strains in these conditions exceeds 800 mg·L−1. The results show that the mass transfer flow (nutritional intake) which depends on the concentration gradient (dC/dz), the physical-chemical properties of alginate beads through the diffusivity coefficient (D), govern the bacterial kinetics and the spatial and temporal behaviour of bacteria.

Biodegradation of seven phthalate esters by Bacillus mojavensis B1811

Phthalate esters (PAEs) are one of the most widely used groups of plasticizers and have been considered threats to the environment and human health. This study investigated the efficient biodegradation of seven phthalate esters (PAEs) by Bacillus mojavensis B1811. The results showed that di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), benzyl butyl phthalate (BBP) and dipentyl phthalate (DPP) could be almost completely degraded by strain B1811 within four days in mineral salt medium (MSM) under shaking conditions, while only 5.9% of the dimethyl phthalate (DMP) and 42.9% of the diethyl phthalate (DEP) present, which both have short alkyl chains, were degraded by strain B1811 under the same conditions. An esterase activity assay also indicated that the specific activities of esterases induced by PAEs with longer alkyl chains were much higher than those of esterases induced by PAEs with short alkyl chains. High-performance liquid chromatography-electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS) was applied to identify the major metabolites of the seven PAEs. The PAEs were first degraded to the corresponding phthalate monoesters and then degraded to phthalic acid; phthalic acid was rapidly degraded to produce benzoic acid which was subsequently converted to protocatechuate and ultimately transformed to CO2 and H2O. The optimal conditions for biodegradation were also obtained and an exponential model was the best model to represent the PAEs depletion. It is therefore concluded that B. mojavensis B1811 offers great application potential in the bioremediation of environments polluted with PAEs.