Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.97, #3)
Anaerobic reduction of a sulfonated azo dye, Congo Red, by sulfate-reducing bacteria by Patricia Esteves Diniz; Ana Teresa Lopes; Ana Rosa Lino; Maria Luisa Serralheiro (pp. 147-163).
The capacity for anaerobic decolorization of a sulfonated azo dye, Congo Red, by a strain of a sulfate-reducing bacterium was evaluated. After optimizing the growth rate of the bacteria on a simple carbon source and terminal electron acceptor pair, lactate and sulfate, respectively, the effect of the dye concentration on their growth rate was analyzed. The decolorization rate was affected by the dye concentration in the growth medium. The azo-bond cleavage mechanism of reductive decolorization with the formation of benzidine was consistent with the results, as this metabolite was identified by high-performance liquid chromatography. Several fractions of the culture medium, including lysed cell extracts, were examined for the capacity to reduce the azo dye. This reduction capacity was found in the culture medium in which the cells had previously grown. The results showed that the mechanism of reductive decolorization of this sulfonated azo dye was extracellular and nonenzymatic, consistent with the production of sulfide anion by the microorganisms while growing on lactate and sulfate. The sulfide anions were the cause of the reduction leading to the disappearance of color in the medium. To increase the rate of decolorization, the presence of ferrous ion was also necessary together with the lactate and sulfate substrates.
Keywords: Sulfonated azo dye; Congo red; reduction; sulfate-reducing bacteria; central composite design; experimental planning
Optimization of yield in kinetically controlled synthesis of ampicillin with immobilized penicillin acylase in organic media by Andrés Illanes; Soledad Anjarí; Rosa Arrieta; Carolina Aguirre (pp. 165-179).
Immobilized penicillin acylase is a moderately priced versatile enzyme, that is able to catalyze the synthesis of derived penicillins and cephalosporins from the corresponding β-lactam nuclei and proper side-chain precursors. Kinetically controlled synthesis is a better strategy when product yield is a key issue. Yield should increase at reduced water activity by depressing the competing hydrolytic reactions in favor of synthesis; therefore, organic cosolvents can be a suitable reaction media for synthesis. Using response surface methodology and product yield as objective function, temperature and pH were optimized in the kinetically controlled synthesis of ampicillin using previously screened cosolvents and reaction conditions. Optimum pH was 6.0 for ethylene glycol (EG) and glycerol (GL) and 6.6 for 1–2 propanediol (PD); optimum temperature was 30°C for GL and for EG and PD was in the lower extreme of the range studied, optimum lying below 26°C. Maximum molar yields predicted by the model were 58,51, and 46% for EG, GL, and PD, respectively, which were experimentally validated. Highest yield in aqueous buffer was always <40%. Molar yields about 60% compare favorably with values reported for the kinetically and thermodynamically controlled synthesis of ampicillin and other derived penicillins.
Keywords: Penicillin acylase; ampicillin; β-lactam antibiotics; enzymatic synthesis; organic cosolvents
Application of spontaneous suction phase-dispersing (SSPD) extractors in the extraction of penicillin G by J. Chen; H. Z. Liu; B. Wang; W. Zhang; Z. T. An (pp. 181-192).
The extraction of penicillin G from an aqueous solution with butylacetate (BA) and tributyl phosphate (TBP) as extractants was carried out at pH 4 with spontaneous suction phase-dispersing (SSPD) extractors under various operating conditions. Four kinds of SSPD extractors were tested with results compared to those obtained by using an extractor with mechanical stirrers. Rotation speed and different extraction systems were found to influence the penicillin recovery and the stability of emulsion formed during extraction. The percentage of extraction under optimum conditions was 91% without formation of emulsion. The laser particle size measurement instrument combined with SSPD can be used to measure the emulsion droplet size in situ.
Keywords: Spontaneous suction phase-dispersing (SSPD); reactive extraction; penicillin G; emulsion droplet size, in situ
Production, purification, and characterization of a polygalacturonase from a new strain of kluyveromyces marxianus isolated from coffee wet-processing wastewater by Manuel Serrat; Rose Catalina Bermúdez; Tomás Gonzáles Villa (pp. 193-208).
A new high polygalacturonase (PG)-producing Kluyveromyces marxianus strain was isolated from coffee wet-processing wastewater. PG production in this strain is not repressed in the presence of 100g/L of glucose and, being growth-associated, reached its maximum accumulation in the culture medium at the beginning of the stationary phase. Oxygen and galacturonic acid negatively regulated enzyme synthesis, and glucose as the carbon source afforded better enzyme yields than lactose. The data reported here show that this strain exhibits the highest index of PG production among the wild-type strains reported so far (18.8U/mL). PG was readily purified by ion-exchange chromatography on SP-Sepharose FF. The activity corresponded to a single protein with an M r of 41.7 kDa according to sodium dodecyl sulfate polyacrylamide gel electrophoresis. The enzyme was stable in the pH range of 3.0–5.0 and displayed an optimal temperature of 55°C; it showed a typical endo-splitting way of substrate hydrolysis and exhibited a fair degree of activity on pectin with a high degree of esterification.
Keywords: Polygalacturonase; pectin; production; characterization; Kluyveromyces marxianus
Nutritional profile of food yeast kluyveromyces fragilis biomass grown on whey by Deepen Paul; Rupak Mukhopadhyay; Bishnu P. Chatterjee; Arun K. Guha (pp. 209-218).
Biomass of food yeast Kluyveromyces fragilis (MTCC 188) grown on deproteinized whey supplemented with 0.8% diammonium hydrogen phosphate and 10 ppm indole-3-acetic acid, had a crude protein content of 37%. The true protein content based on nitrogen fractionation procedure was 28.1%. Total nucleic acid content was 4.82%. This amount does not appear to be toxicologically offensive. Crude fiber, ash, and lipid content of K. fragilis dry cells were found to be 4.9%, 16%, and 7.8%, respectively. Essential fatty acids of both ω-3 and ω-6 series were found present in the fat of the yeast and represented 21.5% of the total fatty acids. All the essential amino acids were present in the proteins of K. fragilis; however, sulfur containing amino acids were found in lower amounts. Calculated protein scores indicate moderate biological value. Bvitamins in the biomass were present as expected, but folic acid and pyridoxine were present in high concentration.
Keywords: Kluyveromyces fragilis ; whey; single-cell protein; food grade yeast; biomass; chemical score