Showing papers by "Domingo Cantero published in 2012"

Optimization of culture media for ethanol production from glycerol by Escherichia coli

Abstract: The culture media for glycerol to ethanol biotransformation by Escherichia coli under anaerobic conditions was optimized. A Plackett-Burman screening design was used to determine which factors were significant with a 95% confidence interval. A full factorial 2 2 and response surface model were employed to determine the optimum conditions for the selected response variable. The response variable considered in this work was biomass productivity (Q X ). Profiles for biomass growth, glycerol consumption and ethanol production were obtained at optimum conditions and fermentation parameters were calculated. Glycerol to ethanol yield and ethanol specific productivity were determined to be 845 g kg −1 of glycerol and 212 g kg −1 h −1 of cell mass respectively. Optimized culture media is presented along with the main results and experimental profiles obtained from this work.

Study of the role played by NfsA, NfsB nitroreductase and NemA flavin reductase from Escherichia coli in the conversion of ethyl 2-(2'-nitrophenoxy)acetate to 4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (D-DIBOA), a benzohydroxamic acid with interesting biological properties.

Abstract: Benzohydroxamic acids, such as 4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (D-DIBOA), exhibit interesting herbicidal, fungicidal and bactericidal properties. Recently, the chemical synthesis of D-DIBOA has been simplified to only two steps. In a previous paper, we demonstrated that the second step could be replaced by a biotransformation using Escherichia coli to reduce the nitro group of the precursor, ethyl 2-(2′-nitrophenoxy)acetate and obtain D-DIBOA. The NfsA and NfsB nitroreductases and the NemA xenobiotic reductase of E. coli have the capacity to reduce one or two nitro groups from a wide variety of nitroaromatic compounds, which are similar to the precursor. By this reason, we hypothesised that these three enzymes could be involved in this biotransformation. We have analysed the biotransformation yield (BY) of mutant strains in which one, two or three of these genes were knocked out, showing that only in the double nfsA/nfsB and in the triple nfsA/nfsB/nemA mutants, the BY was 0%. These results suggested that NfsA and NfsB are responsible for the biotransformation in the tested conditions. To confirm this, the nfsA and nfsB open reading frames were cloned into the pBAD expression vector and transformed into the nfsA and nfsB single mutants, respectively. In both cases, the biotransformation capacity of the strains was recovered (6.09 ± 0.06% as in the wild-type strain) and incremented considerably when NfsA and NfsB were overexpressed (40.33% ± 9.42% and 59.68% ± 2.0% respectively).

Strategies for pH control in a biofilter packed with sugarcane bagasse for hydrogen sulfide removal

Abstract: The biological removal of hydrogen sulfide at low concentration (<120 ppmv) was studied in a laboratory-scale biofilter packed with sugarcane bagasse and inoculated with a sulfur-oxidizing bacterial consortium isolated from activated sludge from a wastewater treatment plant (WWTP) Inlet loads from 131 to 202 g Sm(-3) h(-1) were supplied to the biofilter, and empty bed residence times (EBRTs) of 30, 20 and 10 s were tested In all cases, the removal efficiency was greater than 99% Two methods for the pH control were tested: increasing the phosphate buffer capacity of the mineral medium (method I), and a new method, which involves the addition of solid CaCO(3) to the bagasse at the upper inlet of the biofilter (method II) For method I, pH increased gradually along the bed (from the bottom to the top), from a constant value of 30 to 70 For method II, pH was constant (24 ± 08) along the bed, and then a steep increase of pH was observed at the top to 71 We suggest the use of CaCO(3) instead of phosphate buffer because the former is less expensive, it is a simple method and the results obtained with the two methods are similar

Effect of VOCs and methane in the biological oxidation of the ferrous ion by an acidophilic consortium

Abstract: During the elimination of H2S from biogas in an aqueous ferric sulphate solution, volatile organic compounds (VOCs) and methane are absorbed and may have an effect on the subsequent biological regeneration of ferric ion. This study was conducted to investigate the effect of maximum concentrations of methane and some VOCs found in biogas on the ferrous oxidation of an acidophilic microbial consortium (FO consortium). The presence and impact of heterotrophic microorganisms on the activity of the acidophilic consortium was also evaluated. No effect on the ferrous oxidation rate was found with gas concentrations of 1500 mg toluene m−3, 1400 mg 2-butanol m−3 or 1250 mg 1,2-dichloroethane m−3, nor with methane at gas concentrations ranging from 15–25% (v/v). A tenfold increase in VOCs concentrations totally inhibited the microbial activity of the FO consortium and the heterotrophs. The presence of a heterotrophic fungus may promote the autotrophic growth of the FO consortium.