Evaluation and elimination of inhibitory effects of salts and heavy metal ions on biodegradation of Congo red by Pseudomonas sp. mutant

Effects of heavy metals and metalloids on the biodegradation of organic contaminants

Heavy metals and metalloids (HMMs) inhibit the biodegradation of organic pollutants. The degree of inhibition depends not only on the concentration and bioavailability of HMMs but also on additional factors, such as environmental variables (e.g., inorganic components, organic matter, pH, and redox potential), the nature of the metals, and microbial species. Based on the degradation pattern and metal concentrations causing half biodegradation rate reductions (RC50s), the inhibition of biodegradation was: Hg2+, As2O3 > Cu2+, Cd2+, Pb2+, Cr3+ > Ni2+, Co2+ > Mn2+, Zn2+ > Fe3+. Four patterns were observed: inhibition increases with increasing metal concentration; low concentrations stimulate, while high concentrations inhibit; high concentrations inhibit less; and mild inhibition remains constant. In addition, metal ion mixtures have more complex inhibitory effects on the degradation of organic pollutants, which may be greater than, similar to, or less than that of individual HMMs. Finally, the inhibitory mechanism of HMMs on biodegradation is reviewed. HMMs generally have little impact on the biodegradation pathway of organic pollutants for bacterial strains. However, when pollutants are biodegraded by the community, HMMs may activate microbial populations harbouring different transformation pathways. HMMs can affect the biodegradation efficiency of organic pollutants by changing the surface properties of microbes, interfering with degradative enzymes, and interacting with general metabolism.

Chitosan production by Penicillium citrinum using paper mill wastewater and rice straw hydrolysate as low-cost substrates in a continuous stirred tank reactor

In this study, paper mill wastewater and hemicellulose hydrolysate were evaluated as low-cost substrates for fungal chitosan production using Penicillium citrinum. Submerged fermentation was first studied using a bioreactor operated under batch, fed-batch and continuous modes with paper mill wastewater as the substrate. Very high removal (91%) of organics as chemical oxygen demand (COD) in the wastewater with 160 mg L^-1 chitosan production by P. citrinum was obtained using the bioreactor operated under fed-batch mode for 72 h. Moreover, 86% reduction of phenolics in the wastewater with 89% decolourization efficiency was achieved in the fed-batch experiments with the bioreactor. Under the continuous mode of operation with the bioreactor, maximum chitosan production of 170 mg L^-1 was observed. The effect of acetic acid addition to the wastewater for enhancing chitosan production by the fungus was further studied in a batch system. Chitosan productivity of 2.33 mg L^-1 h^-1 was obtained with 50 mg/L acetic acid. Various models, viz. Monod, Haldane, Andrews, Webb and Yano, were fitted to the experimental data for understanding the kinetics involved in the process. Haldane model accurately fitted the experimental data on biomass specific growth rate, acetic acid consumption rate and chitosan production rate by P. citrinum with acetic acid addition to the wastewater. Fungal fermentation of another low-cost substrate, rice straw hydrolysate, was further studied using the batch-operated bioreactor; and a maximum chitosan titre of 911 mg L^-1 was achieved using the detoxified rice straw hydrolysate.Highlights Low-cost substrates for chitosan production by Penicillium citrinum are reportedAcetic acid addition to paper mill wastewater enhances chitosan productionBiomass growth and chitosan production follow substrate inhibition kineticsFed-batch -operated bioreactor resulted in 91% wastewater treatment efficiencyMaximum chitosan titre of 911 mg L^-1 was achieved with rice straw hydrolysate.

Bacillus subtilis: As an Efficient Bacterial Strain for the Reclamation of Water Loaded with Textile Azo Dye, Orange II

The azo dye orange II is used extensively in the textile sector for coloring fabrics. High concentrations of it are released into aqueous environments through textile effluents. Therefore, its removal from textile wastewater and effluents is necessary. Herein, initially, we tested 11 bacterial strains for their capabilities in the degradation of orange II dye. It was revealed in the preliminary data that B. subtilis can more potently degrade the selected dye, which was thus used in the subsequent experiments. To achieve maximum decolorization, the experimental conditions were optimized whereby maximum degradation was achieved at: a 25 ppm dye concentration, pH 7, a temperature of 35 °C, a 1000 mg/L concentration of glucose, a 1000 mg/L urea concentration, a 666.66 mg/L NaCl concentration, an incubation period of 3 days, and with hydroquinone as a redox mediator at a concentration of 66.66 mg/L. The effects of the interaction of the operational factors were further confirmed using response surface methodology, which revealed that at optimum conditions of pH 6.45, a dye concentration of 17.07 mg/L, and an incubation time of 9.96 h at 45.38 °C, the maximum degradation of orange II can be obtained at a desirability coefficient of 1, estimated using the central composite design (CCD). To understand the underlying principles of degradation of the metabolites in the aliquot mixture at the optimized condition, the study steps were extracted and analyzed using GC-MS(Gas Chromatography Mass Spectrometry), FTIR(Fourier Transform Infrared Spectroscopy), ¹H and carbon 13 NMR(Nuclear Magnetic Resonance Spectroscopy). The GC-MS pattern revealed that the original dye was degraded into o-xylene and naphthalene. Naphthalene was even obtained in a pure state through silica gel column isolation and confirmed using ¹H and ¹³C NMR spectroscopic analysis. Phytotoxicity tests on Vigna radiata were also conducted and the results confirmed that the dye metabolites were less toxic than the parent dye. These results emphasize that B. subtilis should be used as a potential strain for the bioremediation of textile effluents containing orange II and other toxic azo dyes.

Enzymatic biodegradation, kinetic study, and detoxification of Reactive Red-195 by Halomonas meridiana isolated from Marine Sediments of Andaman Sea, India

Azo dyes are a significant class of hazardous chemicals that are extensively utilised in diverse industries. Industries that manufacture and consume reactive azo dyes generate hyper-saline wastewater. The ability of halotolerant bacteria to thrive under extreme environmental conditions thus makes them a potential candidate for reactive azo dye degradation. An efficient halotolerant bacterium (isolate SAIBP-6) with the capability to degrade 87.15% of azo dye Reactive Red 195 (RR-195) was isolated from sea sediment and identified as Halomonas meridiana SAIBP-6. Strain SAIBP-6 maintained potential decolourisation under a wide range of environmental conditions viz. 35-45°C temperature, 50-450 mg/L RR-195, pH 7-9, and 50-150 g/L NaCl. However, maximum decolourisation occurred at 40°C, 200 mg/L RR-195 dye, pH 9, and 50 g/L NaCl, under static conditions. Tyrosinase and azoreductase were responsible for dye degradation. The reaction catalysed by these enzymes followed zero-order kinetics. The maximum velocity (Vmax) of the enzymatic reaction was 4.221 mg/(L.h) and the Michaelis constant (Km) was 517.982 mg/L. Strain SAIBP-6 also efficiently decolourised Reactive Black-5 and Reactive Yellow-160 dye. The biodegradation process was further studied with the help of UV-Vis spectral scan, ultra-high performance liquid chromatography (UPLC), fourier-transform infra-red spectroscopy (FT-IR), and proton nuclear magnetic resonance (¹H NMR) analysis. Finally, cytogenotoxicity assay conducted with the meristematic root tip cells of Allium cepa and phytotoxicity assay conducted with the seeds of Vigna mungo led to the inference that strain SAIBP-6 significantly reduced the toxicity of RR-195 after biodegradation.

Combination of biodegradation and fenton process for efficient removal of PDM/ZnO

In the present study, an investigation was conducted on the removal of polydiallyldimethylammonium chloride-acrylic-acrylamide-hydroxyethyl acrylate/ZnO nanocomposites (PDM/ZnO) through biodegradation and Fenton process coupled treatments. As revealed from the results of the chemical oxygen demand, the total organic carbon, the biochemical oxygen demand and the CO₂ production analysis, PDM/ZnO could be partially biodegraded. The optimal initial pH, the mixed liquid suspended solids concentration and additional carbon source (glucose) dosage in the biodegradation were 7.0, 4.0 g/L and 1.0 g/L, respectively. On the whole, NaCl, the coexisted metal cations (Cu²⁺, Zn²⁺ and Cr³⁺) and additional NH₄Cl inhibited the biodegradation of PDM/ZnO. PDM/ZnO was suggested to adversely affect on microbial community structure and activity. Optimum conditions for Fenton treatment were 50 mg/L Fe²⁺, 20 mL/L H₂O₂ and pH 2.0. Biodegradation showed that 64% of PDM/ZnO was removed. Besides, the combination of Fenton post-treatment could achieve an over 97% removal of PDM/ZnO. Thus, Fenton process combined biodegradation pre-treatment can act as an effective method to remove PDM/ZnO.

Effect of Nickel as Stress Factor on Phenol Biodegradation by Stenotrophomonas maltophilia KB2

This study focuses on the phenol biodegradation kinetics by Stenotrophomonas maltophilia KB2 in a nickel-contaminated medium. Initial tests proved that a nickel concentration of 33.3 mg·L⁻¹ caused a cessation of bacterial growth. The experiments were conducted in a batch bioreactor in several series: without nickel, at constant nickel concentration and at varying metal concentrations (1.67–13.33 g·m⁻³). For a constant Ni²⁺ concentration (1.67 or 3.33 g·m⁻³), a comparable bacterial growth rate was obtained regardless of the initial phenol concentration (50–300 g·m⁻³). The dependence µ = f (S₀) at constant Ni²⁺ concentration was very well described by the Monod equations. The created varying nickel concentrations experimental database was used to estimate the parameters of selected mathematical models, and the analysis included different methods of determining metal inhibition constant K_IM. Each model showed a very good fit with the experimental data (R² values were higher than 0.9). The best agreement (R² = 0.995) was achieved using a modified Andrews equation, which considers the metal influence and substrate inhibition. Therefore, kinetic equation parameters were estimated: µ_max = 1.584 h⁻¹, K_S = 185.367 g·m⁻³, K_IS = 106.137 g·m⁻³, K_IM = 1.249 g·m⁻³ and n = 1.0706.

Recent advances in the biodegradation of azo dyes

As dye demand continues to rapidly increase in the food, pharmaceutical, cosmetic, paper, textile, and leather industries, an industrialization increase is occurring. Meanwhile, the degradation and removal of azo dyes have raised broad concern regarding the hazards posed by these dyes to the ecological environment and human health. Physicochemical treatments have been applied but are hindered by high energy and economic costs, high sludge production, and chemicals handling. Comparatively, the bioremediation technique is an eco-friendly, removal-efficient, and cost-competitive method to resolve the problem. This paper provides scientific and technical information about recent advances in the biodegradation of azo dyes. It expands the biodegradation efficiency, characteristics, and mechanisms of various microorganisms containing bacteria, fungi, microalgae, and microbial consortia, which have been reported to biodegrade azo dyes. In addition, information about physicochemical factors affecting dye biodegradation has been compiled. Furthermore, this paper also sketches the recent development and characteristics of advanced bioreactors.

Enhancing the degradation of mixed polycyclic aromatic hydrocarbon and medium-chain-length polyhydroxyalkanoate production by mixed bacterial cultures using modified repeated batch fermentation

AIMS

To increase the biodegradation of phenanthrene (PHE), pyrene (PYR) and fluoranthene (FLU) through mixed cultures of polycyclic aromatic hydrocarbon (PAH)-degrading bacteria, using modified repeated batch fermentation.

METHODS AND RESULTS

Novel bacterial strains of Pseudomonas putida, Pseudomonas sp. and Ralstonia eutropha were cultivated and the biodegradation and conversion of mixed PAH to medium-chain-length polyhydroxyalkanoates (MCL-PHA) was determined. The highest degradation of PAH (100%) and PHA production (50·0%) was obtained in medium containing 30 mmol l^-1 of mixed PAH after three cycles of repeated batch fermentation. The concentration of PAH in the reactor was increased from 30 to 90 mmol l^-1 with repeated additions of PAH, and bacteria were able to produce PHA at 40% of cell dry mass. The MCL-PHA were identified by gas chromatography/mass spectroscopy, with the 3-hydroxydecanoate (3-HD) monomer higher than 75 mol.%.

CONCLUSIONS

This study demonstrated that the biodegradation of PHE, PYR and FLU was enhanced by modified repeated batch fermentation using a mixed culture of bacteria. In addition, this fermentation strategy also increased the production of PHA, with an increase in monomer composition.

SIGNIFICANCE AND IMPACT OF THE STUDY

This was the first study to describe the enhancement of the degradation of mixed solutions of PHE, PYR and FLU, and PHA production, using novel mixed bacterial cultures and modified repeated batch fermentation. The MCL-PHA formed had uniquely high 3-HD content.

Inhibitory effects of metal ions on reductive dechlorination of polychlorinated biphenyls and perchloroethene in distinct organohalide-respiring bacteria

Bioremediation of sites co-contaminated with organohalides and metal pollutants may have unsatisfactory performance, since metal ions can potentially inhibit organohalide respiration. To understand the detailed impact of metals on organohalide respiration, we tested the effects of four metal ions (i.e., Cu²⁺, Cd²⁺, Cr³⁺ and Pb²⁺), as well as their mixtures, on reductive dechlorination of perchloroethene (PCE) and polychlorinated biphenyls (PCBs) in three different cultures, including a pure culture of Dehalococcoides mccartyi CG1, a Dehalococcoides-containing microcosm and a Dehalococcoides-Geobacter coculture. Results showed that the inhibitive impact on organohalide respiration depended on both the type and concentration of metal ions. Interestingly, the metal ions might indirectly inhibit organohalide respiration through affecting non-dechlorinating populations in the Dehalococcoides-containing microcosm. Nonetheless, compared to the CG1 pure culture, the Dehalococcoides-containing microcosm had higher tolerance to the individual metal ions. In addition, no synergistic inhibition was observed for reductive dechlorination of PCE and PCBs in cultures amended with metal ion mixtures. These results provide insights into the impact of metal ions on organohalide respiration, which may be helpful for future in situ bioremediation of organohalide-metal co-contaminated sites.

Investigating the biodegradation of sulfadiazine in soil using Enterobacter cloacae T2 immobilized on bagasse

The application of the antibiotic sulfadiazine (SD) in veterinary medicine has created serious environmental issues due to its high mobility and non-degradability. A novel immobilized cell system has been developed and showed significant SD biodegradation potential in soil.

Decolorization and detoxification of water-insoluble Sudan dye by Shewanella putrefaciens CN32 co-cultured with Bacillus circulans BWL1061

Effluents loaded with various synthetic dyes are considered as a huge burden to the surrounding ecosystems. Sudan dyes are relatively difficult to decolorize due to its water-insolubility. In the present study, the strain Shewanella putrefaciens CN32 was firstly applied to decolorize Sudan dyes under the anaerobic condition, and the physicochemical parameters on the decolorization were optimized. The results demonstrated that the suitable decolorization condition was temperature 26 °C, initial pH 7.0-8.0 and NaCl concentrations 0-20 g/L. Electron competitive acceptors including nitrite, nitrate, dimethyl sulphoxide and oxygen could cause the significant inhibition to the decolorization of Sudan dyes. Biosurfactant rhamnolipid played a positive role in enhancing the decolorization of Sudan I. The co-culture of S. putrefaciens CN32 and Bacillus circulans BWL1061 is reported for the first time to accelerate the decolorization through improving the synergistic effect of enzymatic degradation and biological reductive effect. The highest decolorization of 90.23% to Sudan I was achieved within 108 h, suggesting that co-culture technique has a good potential in the treatment of dyeing wastewater. Furthermore, the microbial toxicity tests indicated that the toxicity of Sudan I to Escherichia coli BL21 and Bacillus subtilis 168 was obviously decreased after the decolorization.

Use of RSM modeling for optimizing decolorization of simulated textile wastewater by Pseudomonas aeruginosa strain ZM130 capable of simultaneous removal of reactive dyes and hexavalent chromium

Remediation of colored wastewater loaded with dyes and metal ions is a matter of interest nowadays. In this study, 220 bacteria isolated from textile wastewater were tested for their potential to decolorize each of the four reactive dyes (reactive red-120, reactive black-5, reactive yellow-2, and reactive orange-16) in the presence of a mixture of four different heavy metals (Cr, Zn, Pb, Cd) commonly found in textile effluents. Among the tested bacteria, the isolate ZM130 was found to be the most efficient in decolorizing reactive dyes in the presence of the mixture of heavy metals and was identified as Pseudomonas aeruginosa strain ZM130 by 16S rRNA gene analysis. The strain ZM130 was highly effective in simultaneously removing hexavalent chromium (25 mg L(-1)) and the azo dyes (100 mg L(-1)) from the simulated wastewater even in the presence of other three heavy metals (Zn, Pb, Cd). Simultaneous removal of chromium and azo dyes ranged as 76.6-98.7 % and 51.9-91.1 %, respectively, after 180 h incubation. On the basis of quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), optimal salt content, pH, carbon co-substrate content, and level of multi-metal mixtures for decolorization of reactive red-120 in a simulated textile wastewater by the strain ZM130 were predicted to be 19.8, 7.8, and 6.33 g L(-1) and a multi-metal mixture (Cr 13.10 mg L(-1), Pb 26.21 mg L(-1), Cd 13.10 mg L(-1), Zn 26.21 mg L(-1)), respectively. Moreover, the strain ZM130 also exhibited laccase and nicotinamide adenine dinucleotide (reduced)-dichlorophenolindophenol reductase (NADH-DCIP reductase) activity during the decolorization of reactive red-120. However, the laccase activity was found to be maximum in the presence of 300 mg L(-1) of the dye as compared to other concentrations. Hence, the isolation of this strain might serve as a potential bio-resource required for developing the strategies aiming at bioremediation of the wastewater contaminated with dyes and heavy metals.

Aerobic decolorization, degradation and detoxification of azo dyes by a newly isolated salt-tolerant yeast Scheffersomyces spartinae TLHS-SF1

Isolation, identification and characterization of a salt-tolerant yeast capable of degrading and detoxifying azo dyes were investigated in this study. Possible degradation pathway of Acid Scarlet 3R was proposed through analyzing metabolic intermediates using UV-Vis and HPLC-MS methods. Furthermore, the Microtox test was performed to evaluate the acute toxicity of the dye before and after biodegradation. The results showed that a salt-tolerant yeast named TLHS-SF1 was isolated and identified as Scheffersomyces spartinae basing on 26S rDNA analysis. The optimal decolorization and growth parameters were: sucrose 2 g L(-1), (NH4)2SO4 0.6 g L(-1), yeast extract 0.08 g L(-1), NaCl ⩽ 30 g L(-1), 160 rmin(-1), 30 °C and pH 5.0-6.0. More than 90% of 80 mg L(-1) 3R could be decolorized within 16 h under the optimal conditions. 3R was possibly degraded successively through azo-reduction, deamination and desulfonation pathways, and its acute toxicity obviously decreased by strain TLHS-SF1.

Effects of metal ions on the catalytic degradation of dicofol by cellulase

A new technique whereby cellulase immobilized on aminated silica was applied to catalyze the degradation of dicofol, an organochlorine pesticide. In order to evaluate the performance of free and immobilized cellulase, experiments were carried out to measure the degradation efficiency. The Michaelis constant, Km, of the reaction catalyzed by immobilized cellulase was 9.16 mg/L, and the maximum reaction rate, Vmax, was 0.40 mg/L/min, while that of free cellulase was Km=8.18 mg/L, and Vmax=0.79 mg/L/min, respectively. The kinetic constants of catalytic degradation were calculated to estimate substrate affinity. Considering that metal ions may affect enzyme activity, the effects of different metal ions on the catalytic degradation efficiency were explored. The results showed that the substrate affinity decreased after immobilization. Monovalent metal ions had no effect on the reaction, while divalent metal ions had either positive or inhibitory effects, including activation by Mn2+, reversible competition with Cd2+, and irreversible inhibition by Pb2+. Ca2+ promoted the catalytic degradation of dicofol at low concentrations, but inhibited it at high concentrations. Compared with free cellulase, immobilized cellulase was affected less by metal ions. This work provided a basis for further studies on the co-occurrence of endocrine-disrupting chemicals and heavy metal ions in the environment.

Burkholderia vietnamiensis C09V as the functional biomaterial used to remove crystal violet and Cu(II)

Burkholderia vietnamiensis C09V (B.V. C09V) was used to remove both crystal violet (CV) and Cu(II) because dye effluents often contain dyes and metal ions. Inhibiting the strain׳s growth through the biosorption of Cu(II) on B.V. C09V and promoting its growth by using CV as a carbon source led to the degradation of CV (30mg/L). It fell to 36.9 percent and the amount of Cu(II) (50mg/L) removed rose to 34.9 percent in the presence of both CV and Cu(II). This outcome is comparable to the single presence of CV and Cu(II). EDS analysis showed that Cu(II) was adsorbed onto the strain (the atomic percentage of Cu(II) was 1.9 percent), while kinetic studies indicated that firstly, the decolorization of CV fitted well to the pseudo first-order degradation kinetic model and secondly, the biosorption of Cu(II) fitted well to the pseudo second-order kinetic model. The degradation rate constants of CV were stable in the 0.101-0.0068/h range and R(2) was both higher than 0.981 when Cu(II) concentrations were present. Furthermore, the biosorption capacity of Cu(II) ranged from 38.8 to 20.3mg/g at the CV concentration of 30mg/L (both R(2)>0.96). This suggests that the strain has the potential to degrade CV and facilitate the biosorption of Cu(II) in dye effluent.

Biodegradation of Methyl Orange by alginate-immobilized Aeromonas sp. in a packed bed reactor: external mass transfer modeling

Azo dyes are recalcitrant and xenobiotic nature makes these compounds a challenging task for continuous biodegradation up to satisfactorily levels in large-scale. In the present report, the biodegradation efficiency of alginate immobilized indigenous Aeromonas sp. MNK1 on Methyl Orange (MO) in a packed bed reactor was explored. The experimental results were used to determine the external mass transfer model. Complete MO degradation and COD removal were observed at 0.20 cm bead size and 120 ml/h flow rate at 300 mg/l of initial dye concentration. The degradation of MO decreased with increasing bead sizes and flow rates, which may be attributed to the decrease in surface of the beads and higher flux of MO, respectively. The experimental rate constants (k ps) for various beads sizes and flow rates were calculated and compared with theoretically obtained rate constants using external film diffusion models. From the experimental data, the external mass transfer effect was correlated with a model J D = K Re (-(1 - n)). The model was tested with K value (5.7) and the Colburn factor correlation model for 0.20, 0.40 and 0.60 bead sizes were J D = 5.7 Re (-0.15), J D = 5.7 Re (-0.36) and J D = 5.7 Re (-0.48), respectively. Based on the results, the Colburn factor correlation models were found to predict the experimental data accurately. The proposed model was constructive to design and direct industrial applications in packed bed reactors within acceptable limits.

Biodecolorization of Reactive Black-5 by a metal and salt tolerant bacterial strain Pseudomonas sp. RA20 isolated from Paharang drain effluents in Pakistan

Discharge of untreated azo dyes contaminated textile wastewater into soil and water bodies causes severe contamination. The present study was conducted to isolate dye degrading bacterial strains from a textile industry wastewater carrying drain in the neighborhood of Faisalabad, Pakistan. Seventy six bacterial strains were initially isolated and was screened using liquid mineral salts medium spiked with Reactive Black-5 azo dye. The strain RA20 was found to be the most efficient azo dye degrading bacterial isolate and was identified by amplifying and sequencing its 16S rRNA. Analysis indicated that this strain belonged to genus Pseudomonas and was designated as Pseudomonas sp. RA20. It had the highest decolorization activity at pH 8 and 25 °C incubation temperature under static conditions using yeast extract as an additional C source. This strain was also effective in decolorizing structurally related other reactive dyes including Reactive Orange 16, Reactive Yellow 2 and Reactive Red 120 but with varying efficacy. RA20 decolorized Reactive Black-5 significantly in the presence of up to 30 g L⁻¹ NaCl; however, the decolorization rate was significantly (p≤0.05) reduced beyond this salt concentration. Moreover, this bacterial strain also exhibited moderate tolerance to different heavy metals including zinc (Zn), cadmium (Cd), chromium (Cr), lead (Pb) and copper (Cu). RA20 also decolorized Reactive Black-5 in the presence of a mixture of the selected heavy metals depending upon their concentrations. This study highlights the importance of Pseudomonas sp. RA20 as a prospective biological resource for bioremediation of water and soils contaminated with azo dyes.

Enhanced production of thrombinase by Streptomyces venezuelae: kinetic studies on growth and enzyme production of mutant strain

This investigation provides the enhanced production of thrombinase, a fibrinolytic enzyme using mutant Streptomyces venezuelae. Initially the mutagenesis of the marine isolate was done by UV and Ethyl methane sulfonate (EMS) and their mutational efficiencies were compared. The mutants were selected based on their high thrombinase activity and used for further studies. The mutant was found to be more halo and thermo tolerant comparing to wild. The effect of Dissolved oxygen level was also determined and the mutant offered the maximum specific growth rate as 0.2404 (h(-1)). The mutant showed high resistance to higher initial lactose concentration and the inhibition concentration was found to be 155.1mg/mL. The effect of S(0)/X(0) ratio on specific substrate consumption and production rate were also investigated. Both mutant and wild showed increase in specific substrate consumption and production rate at higher S(0)/X(0) ratio but the mutant showed better values than the wild strain.