Ortho-cleavage Pathway Research Articles

Degradation of chlorotoluenes and chlorobenzenes by the dual-species biofilm of Comamonas testosteroni strain KT5 and Bacillus subtilis strain DKT

The cooperation of Bacillus subtilis strain DKT and Comamonas testosteroni KT5 was investigated for biofilm development and toluenes and chlorobenzenes degradation. Bacillus subtilis strain DKT and C. testosteroni KT5 were co-cultured in liquid media with toluenes and chlorobenzenes to determine the degradation of these substrates and formation of dual-species biofilm used for the degradation process. Bacillus subtilis strain DKT utilized benzene, mono- and dichlorinated benzenes as carbon and energy sources. The catabolism of chlorobenzenes was via hydroxylation, in which chlorine atoms were replaced by hydroxyl groups to form catechol, followed by ring fission via the ortho-cleavage pathway. The investigation of the dual-species biofilm composed of B. subtilis DKT and C. testosteroni KT5 (a toluene and chlorotoluene-degrading isolate with low biofilm formation) showed that B. subtilis DKT synergistically promoted C. testosteroni KT5 to develop biofilm. The bacterial growth in dual-species biofilm overcame the inhibitory effects caused by monochlorobenzene and 2-chlorotoluene. Moreover, the dual-species biofilm showed effective degradability toward the mixture of these substrates. This study provides knowledge about the commensal relationships in a dual-culture biofilm for designing multispecies biofilms applied for the biodegradation of toxic organic substrates that cannot be metabolized by single-organism biofilms.

Optimal bioprocess design through a gene regulatory network – Growth kinetic hybrid model: Towards replacing Monod kinetics

Currently, design and optimisation of biotechnological bioprocesses is performed either through exhaustive experimentation and/or with the use of empirical, unstructured growth kinetics models. Whereas, elaborate systems biology approaches have been recently explored, mixed-substrate utilisation is predominantly ignored despite its significance in enhancing bioprocess performance. Herein, bioprocess optimisation for an industrially-relevant bioremediation process involving a mixture of highly toxic substrates, m-xylene and toluene, was achieved through application of a novel experimental-modelling gene regulatory network – growth kinetic (GRN-GK) hybrid framework. The GRN model described the TOL and ortho-cleavage pathways in Pseudomonas putida mt-2 and captured the transcriptional kinetics expression patterns of the promoters. The GRN model informed the formulation of the growth kinetics model replacing the empirical and unstructured Monod kinetics. The GRN-GK framework's predictive capability and potential as a systematic optimal bioprocess design tool, was demonstrated by effectively predicting bioprocess performance, which was in agreement with experimental values, when compared to four commonly used models that deviated significantly from the experimental values. Significantly, a fed-batch biodegradation process was designed and optimised through the model-based control of TOL Pr promoter expression resulting in 61% and 60% enhanced pollutant removal and biomass formation, respectively, compared to the batch process. This provides strong evidence of model-based bioprocess optimisation at the gene level, rendering the GRN-GK framework as a novel and applicable approach to optimal bioprocess design. Finally, model analysis using global sensitivity analysis (GSA) suggests an alternative, systematic approach for model-driven strain modification for synthetic biology and metabolic engineering applications.

Metabolic and Evolutionary Insights in the Transformation of Diphenylamine by a Pseudomonas putida Strain Unravelled by Genomic, Proteomic, and Transcription Analysis.

Diphenylamine (DPA) is a common soil and water contaminant. A Pseudomonas putida strain, recently isolated from a wastewater disposal site, was efficient in degrading DPA. Thorough knowledge of the metabolic capacity, genetic stability and physiology of bacteria during biodegradation of pollutants is essential for their future industrial exploitation. We employed genomic, proteomic, transcription analyses and plasmid curing to (i) identify the genetic network of P. putida driving the microbial transformation of DPA and explore its evolution and origin and (ii) investigate the physiological response of bacterial cells during degradation of DPA. Genomic analysis identified (i) two operons encoding a biphenyl (bph) and an aniline (tdn) dioxygenase, both flanked by transposases and (ii) two operons and several scattered genes encoding the ortho-cleavage of catechol. Proteomics identified 11 putative catabolic proteins, all but BphA1 up-regulated in DPA- and aniline-growing cells, and showed that the bacterium mobilized cellular mechanisms to cope with oxidative stress, probably induced by DPA and its derivatives. Transcription analysis verified the role of the selected genes/operons in the metabolic pathway: DPA was initially transformed to aniline and catechol by a biphenyl dioxygenase (DPA-dioxygenase); aniline was then transformed to catechol which was further metabolized via the ortho-cleavage pathway. Plasmid curing of P. putida resulted in loss of the DPA and aniline dioxygenase genes and the corresponding degradation capacities. Overall our findings provide novel insights into the evolution of the DPA degradation pathway and suggests that the degradation capacity of P. putida was acquired through recruitment of the bph and tdn operons via horizontal gene transfer.

Substrate Shift Reveals Roles for Members of Bacterial Consortia in Degradation of Plant Cell Wall Polymers.

Deconstructing the intricate matrix of cellulose, hemicellulose, and lignin poses a major challenge in biofuel production. In diverse environments in nature, some microbial communities, are able to overcome plant biomass recalcitrance. Identifying key degraders of each component of plant cell wall can help improve biological degradation of plant feedstock. Here, we sequenced the metagenome of lignocellulose-adapted microbial consortia sub-cultured on xylan and alkali lignin media. We observed a drastic shift on community composition after sub-culturing, independently of the original consortia. Proteobacteria relative abundance increased after growth in alkali lignin medium, while Bacteroidetes abundance increased after growth in xylan medium. At the genus level, Pseudomonas was more abundant in the communities growing on alkali lignin, Sphingobacterium in the communities growing on xylan and Cellulomonas abundance was the highest in the original microbial consortia. We also observed functional convergence of microbial communities after incubation in alkali lignin, due to an enrichment of genes involved in benzoate degradation and catechol ortho-cleavage pathways. Our results represent an important step toward the elucidation of key members of microbial communities on lignocellulose degradation and may aide the design of novel lignocellulolytic microbial consortia that are able to efficiently degrade plant cell wall polymers.

Bacteria Induced Degradation of Anthracene Mediated by Catabolic Enzymes

This investigation evaluated the ability of three bacterial strains, Pseudomonas aeruginosa PSA5, Rhodococcus sp. NJ2, and Cronobacter sp. PSM10, isolated from the petroleum hydrocarbon contaminated soil, for the degradation of anthracene at very high concentration (1000 ppm) in minimal salt media (MSM). A maximum degradation of 94% was attained by PSA5, followed by PSM10 (84%) and a minimum was recorded for NJ2 (78%) after 10 days of incubation periods. Specific activities of catabolic enzymes like C120, C230, 3,4‐PCD, and 4,5‐PCD were recorded that indicates anthracene gets mineralized by these strain through O‐phthalate pathway. However aromatic rings of anthracene dominantly cleavage through ortho cleavage pathway by Pseudomonas aeruginosa PSA5 and Cronobacter sp. PSM10 while through meta cleavage by Rhodococcus sp. NJ2. Biosurfactant production by these strains during degradation of anthracene was also confirmed through the reduction of surface tension of media and formation of emulsification for 24 h with benzene.

Synergistic degradation of pyrene by five culturable bacteria in a mangrove sediment-derived bacterial consortium

A pyrene-degrading microbial consortium was obtained after enrichment with mangrove sediment collected from Thailand. Five cultivable bacteria (Mycobacterium spp. PO1 and PO2, Novosphingobium pentaromativorans PY1, Ochrobactrum sp. PW1, and Bacillus sp. FW1) were successfully isolated from the consortium. Draft genomes of them showed that two different morphotypes of Mycobacterium (PO1 and PO2), possessed a complete gene set for pyrene degradation. PY1 contained genes for phthalate assimilation via protocatechuate, a central intermediate, by meta-cleavage pathway, and PW1 possessed genes for protocatechuate degradation via ortho-cleavage pathway. The occurrence of biosurfactant-producing genes in FW1 suggests the involvement in enhancing the pyrene bioavailability. Biotransformation experiments revealed that Mycobacterium completely degraded 100mgL−1 pyrene within six days, whereas no significant degradation was observed with the others. Notably, PY1 and PW1 exhibited higher activity for protocatechuate degradation than the others. The artificially reconstructed consortia containing Mycobacterium with the other three strains (PY1, PW1 and FW1) showed three-fold higher degradation rate for pyrene than the individual Mycobacterium. The enhanced pyrene biodegradation achieved in the consortium was due to the cooperative interaction of bacterial mixture. Our findings showing that synergistic degradation of pyrene in the consortium will facilitate the application of the defined bacterial consortium in bioremediation.

Degradation of chlorotoluenes by Comamonas testosterone KT5

The isolated Comamonas testosterone KT5 utilized a broad range of toluene and chlorotoluenes, including 2-chlorotoluene, 3-chlorotoluene (3CT), 4-chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,6-dichlorotoluene and 3,4-dichlorotoluene (34DCT) as sources of carbon and energy. The strain was characterized its dissipation capability toward these compounds in both liquid culture and contaminated soil. In liquid cultures, KT5 utilized more than 90% of toluene, 3CT and 34DCT within 60 h at the initial concentration of 2 mM. Moreover, the strain showed a mineralization capacity of mixtures of toluene and chlorinated toluenes. Inoculation with the toluenes-degrading bacterial strain significantly enhanced degradation rates in soil. The dissipation rates of toluene, 3CT and 34DCT in non-sterile soil inoculated with bacteria were 97.8, 93.5 and 68.9% after 30 days, respectively. The biodegradation of toluene and chlorosubstituted toluenes in KT5 was occurred through the upper pathway to form benzoates and then ring fission via ortho-cleavage pathway. In addition, C. testosterone KT5 showed the mineralization capacities of benzoate and chlorinated benzoates with the rates comparably higher than the rates of toluenes. The multiple and efficient toluene degradation properties make this isolate a good candidate for bioremediation of environments contaminated with chlorosubstituted toluenes and benzoates.

Biodegradation of phenol by a native mixed bacterial culture isolated from crude oil contaminated site

An efficient phenol degrading mixed bacterial culture was isolated from sludge sample collected from one of the refinery located in Assam, India. The mixed culture was found to consist of three bacterial strains. These were identified as Stenotrophomonas acidaminiphila, Brevibacterium sp. and Brucella sp. Batch phenol biodegradation experiments were carried out for a wide range of initial phenol concentrations after pH and temperature optimization. It was found that the mixed culture was able to degrade a maximum phenol concentration up to 1000 mg L−1 within 96 h while the maximum specific growth rate (μmax) was observed at 100 mg L−1. The pH and temperature required for optimal phenol degradation was 6.5 and 37 °C respectively. The mixed culture degrades phenol via ortho-cleavage pathway by formation of an intermediate (cis, cis-muconate) which was detected spectrophotometrically at 260 nm. The experimental data were validated by fitting the growth and substrate utilization curves with their corresponding simulated dynamic profiles obtained by solving Haldane's equation via MATLAB R2015a with μmax = 0.155 h−1 and KI = 400 mg L−1.

The impact of succinate trace on pWW0 and ortho-cleavage pathway transcription in Pseudomonas putida mt-2 during toluene biodegradation

Toluene is a pollutant catabolised through the interconnected pWW0 (TOL) and ortho-cleavage pathways of Pseudomonas putida mt-2, while upon succinate and toluene mixtures introduction in batch cultures grown on M9 medium, succinate was previously reported as non-repressing. The effect of a 40 times lower succinate concentration, as compared to literature values, was explored through systematic real-time qPCR monitoring of transcriptional kinetics of the key TOL Pu, Pm and ortho-cleavage PbenR, PbenA promoters in mixed-substrate experiments. Even succinate trace inhibited transcription leading to bi-modal promoters expression. Potential carbon catabolite repression mechanisms and novel expression patterns of promoters were unfolded. Lag phase was shortened and biomass growth levels increased compared to sole toluene biodegradation suggesting enhanced pollutant removal efficiency. The study stressed the noticeable effect of a preferred compound’s left-over on the main route of a bioprocess, revealing the beneficiary supply of low preferred substrates concentrations to design optimal bioremediation strategies.

Transcriptional kinetics of the cross-talk between the ortho-cleavage and TOL pathways of toluene biodegradation in Pseudomonas putida mt-2

The TOL plasmid promoters are activated by toluene leading to gene expression responsible for the degradation of the environmental signal. Benzoate is formed as an intermediate, activating the BenR protein of the chromosomal ortho-cleavage pathway that up-regulates the chromosomal PbenA promoter and the TOL Pm promoter resulting in cross-talk between the two networks. Herein, the transcriptional kinetics of the PbenR and PbenA promoters in conjunction with TOL promoters was monitored by real-time PCR during toluene biodegradation of different concentrations in batch cultures. The cross-talk between the two pathways was indicated by the simultaneous maximal expression of the Pm and PbenR promoters, as well as the transcriptional activation from PbenA occurring prior to PbenR, which indicates the potential up-regulation of PbenA by the TOL XylS protein. The repressory effect of toluene on Pr was evident for concentrations higher than 0.3mM suggesting a threshold value for restoring the promoter’s activity, while all the other promoters followed a specific expression pattern, regardless of the initial inducer concentration. Induction of the system with higher toluene concentrations revealed an oscillatory behaviour of Pm, the expression of which remained at high levels until the late exponential phase, demonstrating a novel function of this network.

Biodegradation of 3-chlorobenzoate and 3-hydroxybenzoate by polyurethane foam immobilized cells of Bacillus sp. OS13

Due to widespread use, persistence and toxicity, 3-chlorobenzoate (3-CBA) is well-known as an environmental pollutant. Bacillus sp. OS13, isolated as a 2-nitrotoluene tolerant, has the ability to utilize 3-CBA (4mM) as a sole source of carbon and energy. Nevertheless, this organism has also simultaneously utilized the 4-chlorophthalate, 3-hydroxybenzoate, protocatechuate and 2-chlorobenzoate as a growth substrate. In order to achieve our study objective, firstly we followed the response surface methodology (RSM), and assessed the optimal growth conditions of pH (7.20) and temperature (33°C) for Bacillus sp. OS13 to degrade the 3-CBA. We also determined the two major degradation products (i.e., 3-hydoxybenzoate and protocatechuate) of 3-CBA by using HPLC and GC–MS. Additionally, the activities of 3-hydroxybenzoate-4-hydroxylase and protocatechuate 3,4-dioxygenase enzymes in the cell-free extract were also observed. Thus, in Bacillus sp. OS13, 3-CBA was transformed into protocatechuate via 3-hydroxybenzoate with the release of chloride ions and thereby enter into the ortho-cleavage pathway. In addition, there was complete degradation of 3-CBA (4mM) and 3-hydroxybenzoate (4mM) by the polyurethane foam (PUF)-immobilized cells of Bacillus sp. within 60h. Furthermore, when the initial concentrations of both substrates were increased to 10mM, the same PUF-immobilized cells were degraded approximately 98% of both substrates within 60h. Our findings would be very useful towards the environmental management of 3-CBA in the surrounding contaminated environment.

Comparative genome analysis of Oceanimonas sp. GK1, a halotolerant bacterium with considerable xenobiotics degradation potentials

The growing pollution by xenobiotic compounds generated through both natural and anthropogenic activities has endangered the environment. The advent of the next generation sequencing has provided fast and cost-effective tools to explore genomes to discover novel xenobiotic-degrading genes. A Gram-negative marine halotolerant Oceanimonas sp. GK1 was analyzed for main physiological and genetically important characteristics at the genome scale while being compared with six other phylogenetically-close sequenced genomes. This exploration revealed high potential of Oceanimonas sp. GK1 for biodegradation of xenobiotics compounds such as phenol. More specifically, the isolate utilizes phenol via the ortho-cleavage pathway as a carbon source in the citrate cycle. This was further confirmed by the significant shortage of carbohydrate active enzymes in Oceanimonas sp. GK1 genome, which has forced this bacterium during the course of evolution to change its metabolism and physiology to benefit unusual carbon and energy sources to survive under harsh conditions.

Assessment of phenol-degrading ability of Acinetobacter sp. B9 for its application in bioremediation of phenol-contaminated industrial effluents

Successful bioremediation of a phenol-contaminated environment requires application of those microbial strains that have acquired phenol tolerance and phenol-degrading abilities. A newly isolated strain B9 of Acinetobacter sp. was adapted to a high phenol concentration by growing sequentially from low- to high-strength phenol. The acclimatised strain was able to grow and completely degrade up to 14 mM of phenol in 136 h. The degradation rates were found to increase with an increase in the phenol concentration from 2.0 to 7.5 mM. The strain preferred neutral to alkaline pH range for growth and phenol degradation, with the optimum being pH 8.0. The optimum temperature for phenol degradation was found to be in the range of 30–35°C. Transmission electron micrographs showed a disorganised and convoluted cell membrane in the case of phenol-stressed cells, showing a major effect of phenol on the membrane. Enzymatic and gas chromatography-mass spectrometry studies show the presence of an ortho-cleavage pathway for phenol degradation. Efficient phenol degradation was observed even in the presence of pyridine and heavy metals as co-toxicants showing the potential of strain in bioremediation of industrial wastes. Application of strain B9 to real tannery wastewater showed 100% removal of initial 0.5 mM phenol within 48 h of treatment.

Isolation of an extremely halophilic arhaeon Natrialba sp. C21 able to degrade aromatic compounds and to produce stable biosurfactant at high salinity

Natrialba sp. strain C21 was isolated from oil contaminated saline water in Ain Salah (Algeria) and has exhibited a good potential for degrading phenol (3% v/v), naphthalene (3% v/v), and pyrene (3% v/v) at high salinity with high growth, enzymatic activity and biosurfactant production. Successful metabolism of aromatic hydrocarbon compounds of the strain Natrialba sp. C21 appears to require the ortho-cleavage pathway. Indeed, assays of the key enzymes involved in the ring cleavage of catechol 1, 2-dioxygenase indicated that degradation of the phenol, naphthalene and pyrene by strain Natrialba sp. C21 was via the ortho-cleavage pathway. Cells grown on aromatic hydrocarbons displayed greater ortho-activities mainly towards catechol, while the meta-activity was very low. Besides, biosurfactants derived from the strain C21 were capable of effectively emulsifying both aromatic and aliphatic hydrocarbons and seem to be particularly promising since they have particular adaptations like the increased stability at high temperature and salinity conditions. This study clearly demonstrates for the first time that strain belonging to the genera Natrialba is able to grow at 25% (w/v) NaCl, utilizing phenol, naphthalene, and pyrene as the sole carbon sources. The results suggest that the isolated halophilic archaeon could be a good candidate for the remediation process in extreme environments polluted by aromatic hydrocarbons. Moreover, the produced biosurfactant offers a multitude of interesting potential applications in various fields of biotechnology.

Chlorobenzene Degradation via Ortho-Cleavage Pathway by Newly Isolated Microbacterium sp. Strain TAS1CB from a Petrochemical-Contaminated Site

Chlorobenzene (CB), a dense nonaqeuous phase liquid (DNAPL), is categorized as a priority pollutant by the US EPA. It enters into ecosystems via solid and liquid waste discharge. Bioremediation is a key technique to remediate such contaminated sites. The present study aimed to isolate a chlorobenzene-degrading bacterium, determine the metabolic pathway for chlorobenzene degradation, and characterize biosurfactant production. Microbacterium sp. strain TAS1CB was isolated from contaminated sites and identified by 16S rRNA gene sequencing. Cells possessing positive chemotaxis for CB indicated their ability to degrade CB. Cells degraded CB via production of chlorobenzene dioxygenase, which converted CB to chlorocatechol. Chlorobenzene dioxygenase production was higher at 7 pH and 30°C. Intermediate metabolite analysis by UV scanning, HPLC, and GC-MS analysis revealed production of chlorocatechol and cis-cis muconate. Thus, Microbacterium was able to degrade CB via an ortho-cleavage pathway. In addition to chlorobenzene dioxygenase production, cells also produced biosurfactant which pseudosolubilized CB and increased degradation rate. Chemical characterization showed it to be a glycolipid-type biosurfactant. A phytotoxity study showed 60% of toxicity decreased after 72 hrs of degradation by isolate.

Biochemical and molecular mechanisms involved in simultaneous phenol and Cr(VI) removal by Acinetobacter guillouiae SFC 500-1A.

Bioremediation has emerged as an environmental friendly strategy to deal with environmental pollution. Since the majority of polluted sites contain complex mixtures of inorganic and organic pollutants, it is important to find bacterial strains that can cope with multiple contaminants. In this work, a bacterial strain isolated from tannery sediments was identified as Acinetobacter guillouiae SFC 500-1A. This strain was able to simultaneously remove high phenol and Cr(VI) concentrations, and the mechanisms involved in such process were evaluated. The phenol biodegradation was catalized by a phenol-induced catechol 1,2-dioxygenase through an ortho-cleavage pathway. Also, NADH-dependent chromate reductase activity was measured in the cytosolic fraction. The ability of this strain to reduce Cr(VI) to Cr(III) was corroborated by detection of Cr(III) in cellular biomass after the removal process. While phenol did not affect significantly the chromate reductase activity, Cr(VI) was a major disruptor of catechol dioxygenase activity. Nevertheless, this activity was high even in presence of high Cr(VI) concentrations. Our results suggest the potential application of A. guillouiae SFC 500-1A for wastewaters treatment, and the obtained data provide the insights into the removal mechanisms, dynamics, and possible limitations of the bioremediation.

Phenol Biodegradation and Metal Removal by a Mixed Bacterial Consortium

ABSTRACTThis paper reports the tolerance and biodegradation of phenol by a heavy metal–adapted environmental bacterial consortium, known as consortium culture (CC). At the highest tolerable phenol concentration of 1200 mg/L, CC displayed specific growth rate of 0.04 h−1, phenol degradation rate of 6.11 mg L−1 h−1 and biomass of 8.45 ± 0.35 (log10 colony-forming units [CFU]/ml) at the end of incubation. Phenol was degraded via the ortho-cleavage pathway catalyzed by cathechol-1,2-dioxygenase with specific activity of 0.083 (µmol min−1 mg−1 protein). The different constituent bacterial isolates of CC preferentially grow on benzene, toluene, xylene, ethylbenzene, cresol, and catechol, suggesting a synergistic mechanism involved in the degradation process. Microtox assay showed that phenol degradation was achieved without producing toxic dead-end metabolites. Moreover, lead (Pb) and cadmium (Cd) at the highest tested concentration of 1.0 and 0.1 mg/L, respectively, did not inhibit phenol degradation by CC. Simultaneous metal removal during phenol degradation was achieved using CC. These findings confirmed the dual function of CC to degrade phenol and to remove heavy metals from a mixed-pollutant medium.

English

In this study, we have isolated four different species from effluent contaminated soil using a mixture of aniline and 4-chloroaniline (4CA) as principal carbon sources. The four species were identified as Pseudomonas stutzeri A, Comamonas testosterone B, Pseudomonas putida C and Stenotrophomonas maltophilia D. Growth studies on aniline and 4CA as single and mixed substrates demonstrated that the bacteria preferred to grow on and utilize aniline rather than 4CA. However, despite 100% disappearance of the parent substrates, the degradation of 4CA was always characterized by incomplete dechlorination and 4-chlorocatechol accumulation. HPLC-UV analysis showed that 4-chlorocatechol was further degraded via an ortho-cleavage pathway by the bacterial consortium. This hypothesis was supported by the results from enzyme assays of the crude cell extract of the consortium revealing catechol 1,2-dioxygenase activity which converted catechol and 4-chlorocatechol to cis,cis-muconic acid and 3-chloro-cis,cis-muconic acid, respectively. However, the enzyme had a much higher conversion rate for catechol than for 4-chlorocatechol, indicating preference for non-chlorinated substrates. Members of the bacterial consortium were also characterized individually. All isolates were able to assimilate aniline. P. putida C was able to grow on 4CA solely, while S. maltophilia D was able to grow on 4-chlorocatechol. These results suggest that the degradation of 4CA in the presence of aniline by the bacterial consortium was a result of interspecies interactions. Key words: Chloroaniline, Pseudomonas, Comamonas, HPLC, catechol.

Degradation kinetics and pathway of phenol by Pseudomonas and Bacillus species

This article elucidates that strain Pseudomonas aeruginosa (IES-Ps-1) is a versatile toxic organic compound degrader. With the degradation of malathion and cypermethrin (studied by other researchers previously), this strain was able to degrade phenol. Two other indigenous soil flora (i.e., Pseudomonas sp. (IES-S) and Bacillus subtilis (IES-B)) were also found to be potential phenol degraders.Phenol was degraded with Monod kinetics during growth in nutrient broth and mineral salts medium. Before entering into the growth inhibition phase, strains IES-Ps-1, IES-S and IES-B could tolerate up to 400, 700 and 500 mg/L phenol, respectively, when contained in nutrient broth. However, according to the Luong–Levenspiel model, the growth of strains IES-Ps-1, IES-S and IES-B would cease at 2000, 2174 and 2190 mg/L phenol, respectively. Strain IES-Ps-1 degraded 700, 900 and 1050 mg/L phenol contained in mineral salts medium with the specific rates of 0.034, 0.075 and 0.021 h−1, respectively. All these strains grew by making clusters when exposed to phenol in order to prevent damages due to high substrate concentration. These strains transformed phenol into catechol, which was then degraded via ortho-cleavage pathway.

Biodegradation of 4-aminobenzenesulfonate by indigenous isolate Shinella yambaruensis SA1 and its validation by genotoxic analysis

Shinella yambaruensis SA1, an indigenous strain, was isolated from sludge of wastewater treatment plant. The isolate SA1 efficiently degraded 0.58 mM of 4-aminobenzenesulfonate (4-ABS) after 6 h incubation and utilized it as a sole source of carbon, nitrogen and energy under aerobic conditions. The isolate SA1 retained its potential to degrade 4-ABS when grown in medium supplemented upto 3% (w/v) NaCl. The LC/MS based analysis of degradation products and assay of ring opening enzymes indicated that 4-ABS was degraded via ortho cleavage pathway. The efficiency of 4-ABS biodegradation was evaluated by scoring chromosomal aberrations in mice which showed 53% reduction in the genotoxicity of biologically treated samples as compared to pure 4-ABS. Thus, SA1 could be a potential isolate for developing sequential anoxic-aerobic system for achieving mineralization of polar aromatic amine intermediates generated after breakdown of textile dyes.