Biosorption of hexavalent chromium from aqueous solution by a tropical basidiomycete BDT-14 (DSM 15396)

Summary A tropical white-rot basidiomycete, BDT-14 (DSM 15396) was investigated for its chromium (VI) biosorption potential from an aqueous solution. Pre-treatment of fungal biomass with acid resulted in 100% metal adsorption compared to only 26.64% adsorption without any pre-treatment. Chromium adsorption was a rapid process at early exposure resulting in 60% chromium removal within the first 2 h of exposure. An increase in biomass showed an increase in the total metal ions adsorption but a decrease in specific uptake of metal ions. The concentrations of chromium had a pronounced effect on the rate of adsorption. The adsorption efficiency was 100% when the initial Cr (VI) concentration was 100 mg l⁻¹ with 1,000 mg biomass. Only 47.5% adsorption was observed with 500 mg l⁻¹ Cr (VI) concentration. The adsorption data fit well with the Langmuir and Freundlich isotherm models. Comprehensive characterization of parameters indicates BDT−14 biomass as a promising material for Cr (VI) adsorption.     

Edible macroalga <Emphasis Type="Italic">Ulva prolifera</Emphasis> as microelemental feed supplement for livestock: the fundamental assumptions of the production method

In the present paper, the possibility of the application of marine macroalga Ulva (Enteromorpha) prolifera, as microelemental feed supplement for livestock, was evaluated. The concept was based on two facts: the natural macroalga contains high concentrations of microelements and there is a possibility to greatly increase this content via biosorption. In order to characterize the biosorption process of metal ions by U. prolifera, preliminary experiments were conducted with Cr(III) ions. The effect of temperature, pH and the biomass concentration on the equilibrium of biosorption was investigated. For further experiments (biosorption of Mn(II), Zn(II), Cu(II), Co(II)), the following experimental conditions were chosen: pH 5, 25°C, the biomass concentration 1.0 g l⁻¹. Equilibrium of the biosorption process could be described by the Langmuir equation. The theoretical maximum biosorption capacity was also determined by potentiometric titration of the biomass. The investigation of the external structure of the macroalga and atomic concentration of elements on the surface of the biomass was analyzed using scanning electron microscopy. The content of microelements in the biomass after biosorption increased 110,555; 44,228; 21,177; 2,281 and 1,458 times for Co(II), Cr(III),Cu(II), Zn(II), Mn(II), respectively. Therefore, biomass of U. prolifera enriched with individual microelements, mixed in the proper proportion could be used as feed supplement in animal feeding to cover the nutrient requirements for microelements.     

Nickel(II) biosorption by <Emphasis Type="Italic">Rhodotorula glutinis</Emphasis>

The present study reports the feasibility of using Rhodotorula glutinis biomass as an alternative low-cost biosorbent to remove Ni(II) ions from aqueous solutions. Acetone-pretreated R. glutinis cells showed higher Ni(II) biosorption capacity than untreated cells at pH values ranging from 3 to 7.5, with an optimum pH of 7.5. The effects of other relevant environmental parameters, such as initial Ni(II) concentration, shaking contact time and temperature, on Ni(II) biosorption onto acetone-pretreated R. glutinis were evaluated. Significant enhancement of Ni(II) biosorption capacity was observed by increasing initial metal concentration and temperature. Kinetic studies showed that the kinetic data were best described by a pseudo-second-order kinetic model. Among the two-, three-, and four-parameter isotherm models tested, the Fritz-Schluender model exhibited the best fit to experimental data. Thermodynamic parameters (activation energy, and changes in activation enthalpy, activation entropy, and free energy of activation) revealed that the biosorption of Ni(II) ions onto acetone-pretreated R. glutinis biomass is an endothermic and non-spontaneous process, involving chemical sorption with weak interactions between the biosorbent and Ni(II) ions. The high sorption capacity (44.45 mg g⁻¹ at 25°C, and 63.53 mg g⁻¹ at 70°C) exhibited by acetone-pretreated R. glutinis biomass places this biosorbent among the best adsorbents currently available for removal of Ni(II) ions from aqueous effluents.     

Immobilization of blue green microalgae on loofa sponge to biosorb cadmium in repeated shake flask batch and continuous flow fixed bed column reactor system

Summary An indigenous strain of blue green microalga, Synechococcus sp., isolated from wastewater, was immobilized onto loofa sponge discs and investigated as a potential biosorbent for the removal of cadmium from aqueous solutions. Immobilization has enhanced the sorption of cadmium and an increase of biosorption (21%) at equilibrium was noted as compared to free biomass. The kinetics of cadmium biosorption was extremely rapid, with (96%) of adsorption within the first 5 min and equilibrium reached at 15 min. Increasing initial pH or initial cadmium concentration resulted in an increase in cadmium uptake. The maximum biosorption capacity of free and loofa immobilized biomass of Synechococcus sp. was found to be 47.73 and 57.76 mg g⁻¹ biomass respectively. The biosorption equilibrium was well described by Langmuir adsorption isotherm model. The biosorbed cadmium was desorbed by washing the immobilized biomass with dilute HCl (0.1 M) and desorbed biomass was reused in five biosorption–desorption cycles without an apparent decrease in its metal biosorption capacity. The metal removing capacity of loofa immobilized biomass was also tested in a continuous flow fixed-bed column bioreactor and was found to be highly effective in removing cadmium from aqueous solution. The results suggested that the loofa sponge-immobilized biomass of Synechococcus sp. could be used as a biosorbent for an efficient removal of heavy metal ions from aqueous solution.     

Decolorization of structurally different textile dyes by Aspergillus niger SA1

The fungal strain, Aspergillus niger SA1, isolated from textile wastewater sludge was screened for its decolorization ability for four different textile dyes. It was initially adapted to higher concentration of dyes (10–1,000 mg l⁻¹) on solid culture medium after repeated sub-culturing. Maximum resistant level (mg l⁻¹) sustained by fungal strain against four dyes was in order of; Acid red 151 (850) > Orange II (650) > Drimarene blue K₂RL (550) > Sulfur black (500). The apparent dye removal for dyes was seen largely due to biosorption/bioadsorption into/onto the fungal biomass. Decolorization of Acid red 151, Orange II, Sulfur black and Drimarine blue K₂RL was 68.64 and 66.72, 43.23 and 44.52, 21.74 and 28.18, 39.45 and 9.33% in two different liquid media under static condition, whereas, it was 67.26, 78.08, 45.83 and 13.74% with 1.40, 1.73, 5.16 and 1.87 mg l⁻¹ of biomass production under shaking conditions respectively in 8 days. The residual amount (mg l⁻¹) of the three products (α-naphthol, sulfanilic acid and aniline) kept quite low i.e., ≤2 in case AR 151 and Or II under shaking conditions. Results clearly elucidated the role of Aspergillus niger SA1 in decolorizing/degrading structurally different dyes into basic constituents.     

Chromate reduction by PVA-alginate immobilized <Emphasis Type="Italic">Streptomyces griseus</Emphasis> in a bioreactor

Microbial reduction of toxic Cr⁶⁺ to the less toxic Cr³⁺ is potentially a useful bioremediation process. Among the matrices tested for whole cell immobilization of an efficient chromate-reducing Streptomyces griseus strain, PVA-alginate was the most effective and was used for reduction of Cr(VI) in a bioreactor. Cr⁶⁺ reduction efficiency decreased as Cr⁶⁺ was increased from 2 to 12 mg l⁻¹ but increased with an increase in biomass concentration. However, increasing the flow rate from 2 to 8 ml h⁻¹ did not significantly affect Cr⁶⁺ reduction. The reduction was faster in simulated effluent than in synthetic medium and complete removal of 8 mg Cr⁶⁺ l⁻¹ from effluent and synthetic medium occurred in 2 and 12 h, respectively. Our results indicate that immobilized S. griseus cells could be applied for the large-scale bioremediation of chromate-containing effluents and wastewaters.     

Characterisation of acidic sites of Pseudomonas biomass capable of binding protons and cadmium and removal of cadmium via biosorption

Summary The ability of Pseudomonas aeruginosa to accumulate Cd(II) ions from wastewater industries was experimentally investigated and mathematically modelled. From the potentiometric titration and non-ideal competitive analysis (NICA) model, it was found that the biomass contains three acidic sites. The values of proton binding (pK _i =1.66±3.26×10⁻³, 1.92±1.63×10⁻⁴ and 2.16±3.79×10⁻⁴) and binding constant of cadmium metal ions (pK _M1=1.99±2.45×10⁻³ and pK _M2=1.67±4.08×10⁻³) on the whole surface of biomass showed that protonated functional groups and biosorption of Cd(II) ions could be attributed to a monodentate binding to one acidic site, mainly the carboxylic group. From the isothermal sorption experimental data and Langmuir model, it was also found that the value of Langmuir equilibrium (pK _f) constant is 2.04±2.1×10⁻⁵ suggesting that the carboxyl group is the main active binding site. In addition, results showed that the maximum cadmium capacity (q _max) and affinity of biomass towards cadmium metal ions (b) at pH 5.1 and 20 min were 96.5±0.06 mg/g and 3.40×10⁻³± 2.10×10⁻³, respectively. Finally, interfering metal ions such as Pb(II), Cu(II), Cr(III), Zn(II), Fe(II), Mn(II), Ca(II) and Mg(II) inhibited Cd(II) uptake. Comparing the biosorption of Cd(II) by various Pseudomonas isolates from contaminated environment samples (soil and sewage treatment plant) showed that maximum capacities and equilibrium times were different, indicating that there was a discrepancy in the chemical composition between biomasses of different strains.     

Lead uptake and potentiometric titration studies with live and dried cells of Rhodotorula glutinis

The ability of live cells (LC), freeze dried cells (FDC) and oven dried cells (ODC) of the yeast Rhodotorula glutinis to remove lead from aqueous solution has been studied. Discernible differences were found between the biosorption properties of LC and the other two types of cell preparation. The LC preparation exhibited an uptake level of about 12 mg g⁻¹ in a batch contactor with a biomass dosage of 2 g l⁻¹ and an initial lead concentration of 100 mg l⁻¹. This compared with, respectively, about 26 and 30 mg g⁻¹ for the FDC and ODC biosorbents under the same experimental conditions. It is seen that the level of lead uptake by the two latter biosorbents was increased to, respectively, 2.2- and 2.5-fold of the level observed for the LC preparation. The superior performance of the FDC and ODC biosorbents in the lead binding process was attributed to the presence of additional binding sites on their cell wall surfaces as indicated by potentiometric titration data. These binding sites were ascribed to carboxylic and phosphoric groups, which are the primary sites of divalent metal complexation. Modeling of the titration data revealed that subjecting R. glutinis biomass to freeze drying or oven drying increased its proton binding site concentration by a factor of 3. It appears that the two simple physical treatments were able to compromise the R. glutinis cell wall structure in such a way as to make sites normally inaccessible to become active in proton and lead binding.     

Bioremoval of hexavalent chromium from water by a salt tolerant bacterium, Exiguobacterium sp. GS1

Pollution of terrestrial surfaces and aquatic systems by hexavalent chromium, Cr(VI), is a worldwide public health problem. A chromium resistant bacterial isolate identified as Exiguobacterium sp. GS1 by 16S rRNA gene sequencing displayed high rate of removal of Cr(VI) from water. Exiguobacterium sp. GS1 is 99% identical to Exiguobacterium acetylicum. The isolate significantly removed Cr(VI) at both high and low concentrations (1–200 μg mL⁻¹) within 12 h. The Michaelis–Menten K _m and V _max for Cr(VI) bioremoval were calculated to be 141.92 μg mL⁻¹ and 13.22 μg mL⁻¹ h⁻¹, respectively. Growth of Exiguobacterium sp. GS1 was indifferent at 1–75 μg mL⁻¹ Cr(VI) in 12 h. At initial concentration of 8,000 μg L⁻¹, Exiguobacterium sp. GS1 displayed rapid bioremoval of Cr(VI) with over 50% bioremoval in 3 h and 91% bioremoval in 8 h. Kinetic analysis of Cr(VI) bioremoval rate revealed zero-order in 8 h. Exiguobacterium sp. GS1 grew and significantly reduced Cr(VI) in cultures containing 1–9% salt indicating high salt tolerance. Similarly the isolate substantially reduced Cr(VI) over a wide range of temperature (18–45  °C) and initial pH (6.0–9.0). The T _opt and initial pH_opt were 35–40  °C and 7–8, respectively. Exiguobacterium sp. GS1 displayed a great potential for bioremediation of Cr(VI) in diverse complex environments.     

Biosorption of Pb<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> by Non-Living Biomass of <Emphasis Type="Italic">Spirulina</Emphasis> sp.

Removal of heavy metals (Pb²⁺, Zn²⁺) from aqueous solution by dried biomass of Spirulina sp. was investigated. Spirulina rapidly adsorbed appreciable amount of lead and zinc from the aqueous solutions within 15 min of initial contact with the metal solution and exhibited high sequestration of lead and zinc at low equilibrium concentrations. The specific adsorption of both Pb²⁺ and Zn²⁺ increased at low concentration and decreased when biomass concentration exceeded 0.1 g l⁻¹. The binding of lead followed Freundlich model of kinetics where as zinc supported Langmuir isotherm for adsorption with their r ² values of 0.9659 and 0.8723 respectively. The adsorption was strongly pH dependent as the maximum lead biosorption occurred at pH 4 and 10 whereas Zn²⁺ adsorption was at pH 8 and 10.     

Biosorption of Cd(II) and Pb(II) onto brown seaweed, Lobophora variegata (Lamouroux): kinetic and equilibrium studies

The present work deals with the biosorption performance of raw and chemically modified biomass of the brown seaweed Lobophora variegata for removal of Cd(II) and Pb(II) from aqueous solution. The biosorption capacity was significantly altered by pH of the solution delineating that the higher the pH, the higher the Cd(II) and Pb(II) removal. Kinetic and isotherm experiments were carried out at the optimal pH 5.0. The metal removal rates were conspicuously rapid wherein 90% of the total sorption occurred within 90 min. Biomass treated with CaCl₂ demonstrated the highest potential for the sorption of the metal ions with the maximum uptake capacities i.e. 1.71 and 1.79 mmol g⁻¹ for Cd(II) and Pb(II), respectively. Kinetic data were satisfactorily manifested by a pseudo-second order chemical sorption process. The process mechanism consisting of both surface adsorption and pore diffusion was found to be complex. The sorption data have been analyzed and fitted to sorption isotherm of the Freundlich, Langmuir, and Redlich–Peterson models. The regression coefficient for both Langmuir and Redlich–Peterson isotherms were higher than those secured for Freundlich isotherm implying that the biosorption system is possibly monolayer coverage of the L. variegata surface by the cadmium and lead ions. FT-IR studies revealed that Cd(II) and Pb(II) binding to L. variegata occurred primarily through biomass carboxyl groups accompanied by momentous interactions of the biomass amino and amide groups. In this study, we have observed that L. variegata had maximum biosorption capacity for Cd(II) and Pb(II) reported so far for any marine algae. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Using biosorption to enrich the biomass of <Emphasis Type="Italic">Chlorella vulgaris </Emphasis>with microelements to be used as mineral feed supplement

The paper discusses biosorption of Cr(III), Cu(II), Mn(II), Zn(II) and Co(II) to the biomass of Chlorella vulgaris, to produce a biologically bound, concentrated form of microelements. The kinetics of biosorption was described with a pseudo-second order equation and equilibrium with the Langmuir isotherm. The mechanism of biosorption was identified as cation-exchange with alkaline metals. Cation-exchange capacity was evaluated as 4.07 meq g⁻¹. The effect of operation conditions, pH and temperature, on biosorption performance was investigated and the best operation conditions for biosorption were selected (pH 5, temperature 25 °C). The maximum sorption capacity of microelements was determined in single-metal system at pH 5 and 25 °C: Zn(II) 3.30 meq g⁻¹, Cu(II) 1.77 meq g⁻¹, Co(II) 1.75 meq g⁻¹, Cr(III) 1.74 meq g⁻¹, Mn(II) 0.764 meq g⁻¹. Biosorption experiments were also carried out in multi-metal system. The biomass of C. vulgaris enriched with microelements via the process of biosorption in both single- and multi-metal system was discussed in terms of preparation of feed supplement for laying hens and piglets. The experiments showed that 1 kg of conventional feed for laying hens can be supplemented with 0.20 g of the biomass enriched with microelements and for piglets with 0.15 g of the preparation.     

Evaluation of the bioremoval of Cr(VI) and TOC in biofilters under continuous operation using response surface methodology

In the present study, the bioremoval of Cr(VI) and the removal of total organic carbon (TOC) were achieved with a system composed by an anaerobic filter and a submerged biofilter with intermittent aeration using a mixed culture of microorganisms originating from contaminated sludge. In the aforementioned biofilters, the concentrations of chromium, carbon, and nitrogen were optimized according to response surface methodology. The initial concentration of Cr(VI) was 137.35 mg l⁻¹, and a bioremoval of 85.23% was attained. The optimal conditions for the removal of TOC were 4 to 8 g l⁻¹ of sodium acetate, >0.8 g l⁻¹ of ammonium chloride and 60 to 100 mg l⁻¹ of Cr(VI). The results revealed that ammonium chloride had the strongest effect on the TOC removal, and 120 mg l⁻¹ of Cr(VI) could be removed after 156 h of operation. Moreover, 100% of the Cr(VI) and the total chromium content of the aerobic reactor output were removed, and TOC removals of 80 and 87% were attained after operating the anaerobic and aerobic reactors for 130 and 142 h, respectively. The concentrations of cells in both reactors remained nearly constant over time. The residence time distribution was obtained to evaluate the flow through the bioreactors.     

Biosorption of Ni (II) by Schizosaccharomyces pombe: kinetic and thermodynamic studies

The potential of the dried yeast, wild-type Schizosaccharomyces pombe, to remove Ni(II) ion was investigated in batch mode under varying experimental conditions including pH, temperature, initial metal ion concentration and biosorbent dose. Optimum pH for biosorption was determined as 5.0. The highest equilibrium uptake of Ni(II) on S. pombe, q _e, was obtained at 25 °C as 33.8 mg g⁻¹. It decreased with increasing temperature within a range of 25–50 °C denoting an exothermic behaviour. Increasing initial Ni(II) concentration up to 400 mg L⁻¹ also elevated equilibrium uptake. No more adsorption took place beyond 400 mg L⁻¹. Equilibrium data fitted better to Langmuir model rather than Freundlich model. Sips, Redlich–Peterson, and Kahn isotherm equations modelled the investigated system with a performance not better than Langmuir. Kinetic model evaluations showed that Ni(II) biosorption process followed the pseudo-second order rate model while rate constants decreased with increasing temperature. Gibbs free energy changes (ΔG°) of the system at 25, 30, 35 and 50 °C were found as −1.47E + 4, −1.49E + 4, −1.51E + 4, and −1.58E + 4 J mol⁻¹, respectively. Enthalpy change (ΔH°) was determined as −2.57E + 3 J mol⁻¹ which also supports the observed exothermic behaviour of the biosorption process. Entropy change (ΔS°) had a positive value (40.75 J mol⁻¹ K⁻¹) indicating an increase in randomness during biosorption process. Consequently, S. pombe was found to be a potential low-cost agent for Ni(II) in slightly acidic aqueous medium. In parallel, it has been assumed to act as a separating agent for Ni(II) recovery from its aqueous solution.     

The use of free and immobilized <Emphasis Type="Italic">Cunninghamella elegans</Emphasis> for removing cobalt ions from aqueous waste solutions

This paper discusses the possible application to use free and immobilized Cunninghamella elegans for the removal of cobalt from aqueous waste solutions. Results indicated that the maximum uptake occurred at; pH 4.0–5.5 ± 0.2, temperature range between 15 and 50°C and stirring rate 250 rpm. The uptake increased with the increase of metal ion concentration up to 40 ppm. Also, it was found that the best biomass weights used for biosorption were 0.25 and 0.5 g for both free and immobilized biomass. The reuse of control alginate beads, alive and dead immobilized Cunninghamella elegans beads was investigated for five cycles. Results showed that the percent uptake decreased slightly after the first cycle. While, in the case of alginate beads there was increase in the second cycle then returned to the same level of uptake. The uptake of cobalt in the presence of Cr(VI) and Cd(II) at different mixture concentrations 40, 50 and 60 ppm was investigated. The results showed that the uptake amount of Co(II) in the presence of other metal ions was lower than Co(II) alone except for Ca-alginate beads. SEM studies for control alginate beads, alive and dead immobilized Cunninghamella elegans beads were conducted to investigate the beads before and after the accumulation of cobalt ions.     

Biosorption of uranium(VI) by Aspergillus fumigatus

Aspergillus fumigatus removed uranium(VI) very rapidly and reached equilibrium within 1 h of contact of biomass with the aqueous metal solution. Biosorption data fitted to Langmuir model of isotherm and a maximum loading capacity of 423 mg U g^–1 dry wt was obtained. Distribution coefficient as high as 10,000 (mg U g^–1)/(mg U ml^–1) at a residual metal ion concentration of 19 mg l^–1 indicates its usefulness in removal of uranium(VI) from dilute waste streams. Optimum biosorption was seen at pH 5.0 and was independent of temperature (5–50°C ). Initial metal ion concentration significantly influenced uptake capacity which brought down % (w/w) uranium(VI) removal from 90 at 200 mg U l^–1 to 35 at 1000 mg U l^–1. Presence of 0.84 mmol Fe²⁺, Fe³⁺, Ca²⁺ and Zn²⁺ had no effect on uranium(VI) biosorption unlike Al³⁺ (0.84 mM) which was inhibitory.     

Kinetic and Equilibrium Studies of Cr(VI) Biosorption by Dead <Emphasis Type="Italic">Bacillus licheniformis</Emphasis> Biomass

Many studies have been carried out on the biosorption capacity of different kinds of biomass. However, reports on the kinetic and equilibrium study of the biosorption process are limited. In our experiments, the removal of Cr(VI) from aqueous solution was investigated in a batch system by sorption on the dead cells of Bacillus licheniformis isolated from metal-polluted soils. Equilibrium and kinetic experiments were performed at various initial metal concentrations, pH, contact time, and temperatures. The biomass exhibited the highest Cr(VI) uptake capacity at 50°C, pH 2.5 and with the initial Cr(VI) concentration of 300 mg/g. The Langmuir and Freundlich models were considered to identify the isotherm that could better describe the equilibrium adsorption of Cr(VI) onto biomass. The Langmuir model fitted our experimental data better than the Freundlich model. The suitability of the pseudo first-order and pseudo second-order kinetic models for the sorption of Cr(VI) onto Bacillus licheniformis was also discussed. It is better to apply the pseudo second-kinetic model to describe the sorption system.     

Efficacy of bacterial consortium-AIE2 for contemporaneous Cr(VI) and azo dye bioremediation in batch and continuous bioreactor systems, monitoring steady-state bacterial dynamics using qPCR assays

Bacterial consortium-AIE2 with a capability of contemporaneous Cr(VI) reduction and azo dye RV5 decolourization was developed from industrial wastewaters by enrichment culture technique. The 16S rRNA gene based molecular analyses revealed that the consortium bacterial community structure consisted of four bacterial strains namely, Alcaligenes sp. DMA, Bacillus sp. DMB, Stenotrophomonas sp. DMS and Enterococcus sp. DME. Cumulative mechanism of Cr(VI) reduction by the consortium was determined using in vitro Cr(VI) reduction assays. Similarly, the complete degradation of Reactive Violet 5 (RV5) dye was confirmed by FTIR spectroscopic analysis. Consortium-AIE2 exhibited simultaneous bioremediation efficiencies of (97.8 ± 1.4) % and (74.1 ± 1.2) % in treatment of both 50 mg l⁻¹ Cr(VI) and RV5 dye concentrations within 48 h of incubation at pH 7 and 37°C in batch systems. Continuous bioreactor systems achieved simultaneous bioremediation efficiencies of (98.4 ± 1.5) % and (97.5 ± 1.4) % after the onset of steady-state at 50 mg l⁻¹ input Cr(VI) and 25 mg l⁻¹ input RV5 concentrations, respectively, at medium dilution rate (D) of 0.014 h⁻¹. The 16S rRNA gene copy numbers in the continuous bioreactor as determined by real-time PCR assay indicated that Alcaligenes sp. DMA and Bacillus sp. DMB dominated consortium bacterial community during the active continuous bioremediation process.     

Chromium(VI) resistance and removal by <Emphasis Type="Italic">Acinetobacter haemolyticus</Emphasis>

The present work highlighted the studies on Cr(VI) reduction by cells of Acinetobacter haemolyticus (A. haemolyticus). The strain tolerated 90 mg Cr(VI) l⁻¹ in LB broth compared to only 30 mg Cr(VI) l⁻¹ in LB agar. From the FTIR analysis, the Cr(III) species formed was also most likely to form complexes with carboxyl, hydroxyl, and amide groups from the bacteria. A TEM study showed the absence of precipitates on the cell wall region of the bacteria. Instead, microprecipitates were observed in the cytoplasmic region of the cells, suggesting the transportation of Cr(VI) into the cells. Intracellular reduction of Cr(VI) was supported by a reductase test using soluble crude cell-free extracts. The specific reductase activity obtained was 0.52 μg Cr(VI) reduced per mg of protein an hour at pH 7.2 and 37°C. Our results indicated that A. haemolyticus can be used as a promising microorganism for Cr(VI) reduction from industrial wastewaters.     

Improved guggulsterone production from sugars, precursors, and morphactin in cell cultures of Commiphora wightii grown in shake flasks and a bioreactor

Cell cultures of Commiphora wightii (Arnott.) Bhandari were grown in shake flasks and a bioreactor and an increase in guggulsterone accumulation up to 18 μg l⁻¹ was recorded in cells grown in the production medium containing a combination of sucrose:glucose (4% total), precursors (phenylalanine, pyruvic acid, xylose, and sodium acetate), morphactin, and 2iP. A yield of 10 g l⁻¹ biomass and ∼200 μg l⁻¹ guggulsterone was recorded in a 3-l flask and in a 2-l stirred tank bioreactor compared with 6.6 g biomass and 67 μg l⁻¹ guggulsterone in 250-ml flasks. Increased vessel size was correlated with increased biomass and guggulsterone accumulation. 2iP alone was not effective for biomass and guggulsterone accumulation in cell cultures of C. wightii.