A new mathematical model to evaluate simazine removal in three different immobilized-biomass reactors.

A new mathematical model based on the cinetical Langmuir equation is developed to interpret and predict the effectiveness of simazine (SZ) removal in immobilized-biomass reactor (IBR), to consider herbicide-support affinity (Cx), and herbicide-cell affinity (Cy). Three solid supports: sepiolite monolith, granular sepiolite, and alginate were used in pilot-scale reactors that were inoculated with Klebsiella planticola DSZ. The abiotic process was analysed by measuring the SZ sorption capacity of the reactor supports. Sepiolite monolith showed the maximum value for herbicide-support affinity (28.02+/-0.9%). The effectiveness of the biotic process was estimated considering the formation of biomass and SZ biodegradation. Granular sepiolite showed either higher affinity with SZ and viability rate (0.90) throughout the process, and SZ removal rate was 3.39+/-0.06 mg/h. The mathematical model presented in this paper provides useful insights into the interpretation of experimental data as well as prediction for the implementation of biological reactors.

Improving dioxygenase stability by gene chromosome insertion: implementation in immobilized-cell systems.

The immobilization of recombinant cells by using the unstable 3,4-dihydroxyphenylacetate 2,3-dioxygenase was studied as a model. Dioxygenase activity and cell viability were compared in immobilized-cell systems and cells in suspension. Immobilization increased enzyme stability and the efficient degradation of 3,4-dihydroxyphenylacetate. The stability of the cloned enzyme and the viability of the immobilized recombinant cells were well maintained for at least 15 days. We used the strain Escherichia coli CC118-D in which the hpaB gene from Klebsiella pneumoniae, coding for the subunit of 3,4-dihydroxyphenylacetate 2,3-dioxygenase, was inserted into the chromosome. This study has demonstrated that the implementation of E. coli CC118-D in a pilot-scale bioreactor resulted in a 100% stabilization of dioxygenase activity, and could be a useful tool for bioremediation processes.

4-Hydroxybenzoate uptake in Klebsiella planticola strain DSZ1 is driven by DeltapH.

Klebsiella planticola strain DSZ1 has the ability to degrade different aromatic compounds such as benzoate and organochlorinated as propachlor and alachlor. DSZ1 strain cells mineralised 4-hydroxybenzoate (4HBA) through a meta-cleavage pathway, yielding protocatechuate as dihydroxylated intermediate, with a specific rate of CO2 formation 0.12 x 10-6 (cpm/OD) h-1, and a rate of 4-HBA utilisation of 0.75 mmol h-1. Aerobically the 4HBA transport system is driven by gradient of protons (DeltapH), but is not ATP-driven. Under anaerobic conditions, the system can use the nitrate reduction as a final electron acceptor in respiration. A kinetic analysis of the 4HBA transport system revealed a Kt value of 16 microM with a Vmax value of 25 nmol/min.mg at pH 7.

Immobilized native bacteria as a tool for bioremediation of soils and waters: implementation and modeling.

Based on 3,4-dihydroxyphenylacetate (3,4-DHPA) dioxygenase amino acid sequence and DNA sequence data for homologous genes, two different oligonucleotides were designed. These were assayed to detect 3,4-DHPA related aromatic compound-degrading bacteria in soil samples by using the FISH method. Also, amplification by PCR using a set of ERIC primers was assayed for the detection of Pseudomonas GCH1 strain, which used in the soil bioremediation process. A model was developed to understand and predict the behavior of bacteria and pollutants in a bioremediation system, taking into account fluid dynamics, molecular/cellular scale processes, and biofilm formation.

4-Hydroxybenzoate uptake in an isolated soil Acinetobacter sp.

The isolated soil bacteria Acinetobacter strain BEM2 is able to utilize some xenobiotic aromatic compounds as a carbon source. In this study the metabolism of 4-hydroxybenzoate (4-HBA) by strain BEM2 was characterized. Degradation involved a meta-cleavage pathway yielding 3,4-dihydroxybenzoate (3,4-DHBA) as an intermediate and CO(2) as the principal product from the C atoms in the aromatic ring. 4-HBA uptake was studied, and the kinetic parameters were determined. The uptake was shown to be directly coupled to ATP hydrolysis and its synthesis, according to the Mitchell chemiosmotic hypothesis.

Characterization of two novel propachlor degradation pathways in two species of soil bacteria.

Propachlor (2-chloro-N-isopropylacetanilide) is an acetamide herbicide used in preemergence. In this study, we isolated and characterized a soil bacterium, Acinetobacter strain BEM2, that was able to utilize this herbicide as the sole and limiting carbon source. Identification of the intermediates of propachlor degradation by this strain and characterization of new metabolites in the degradation of propachlor by a previously reported strain of Pseudomonas (PEM1) support two different propachlor degradation pathways. Washed-cell suspensions of strain PEM1 with propachlor accumulated N-isopropylacetanilide, acetanilide, acetamide, and catechol. Pseudomonas strain PEM1 grew on propachlor with a generation time of 3.4 h and a Ks of 0.17 +/- 0.04 mM. Acinetobacter strain BEM2 grew on propachlor with a generation time of 3.1 h and a Ks of 0.3 +/- 0.07 mM. Incubations with strain BEM2 resulted in accumulation of N-isopropylacetanilide, N-isopropylaniline, isopropylamine, and catechol. Both degradative pathways were inducible, and the principal product of the carbon atoms in the propachlor ring was carbon dioxide. These results and biodegradation experiments with the identified metabolites indicate that metabolism of propachlor by Pseudomonas sp. strain PEM1 proceeds through a different pathway from metabolism by Acinetobacter sp. strain BEM2.

Molecular cloning and analysis of the genes encoding the 4-hydroxyphenylacetate hydroxylase from Klebsiella pneumoniae.

The Klebsiella pneumoniae genes encoding the hydroxylase involved in the meta-cleavage pathway of 4-hydroxyphenylacetic acid (4-HPA) were cloned, and the DNA fragment from the region essential for hydroxylase activity was sequenced. K. pneumoniae 4-HPA hydroxylase was composed of two proteins (HpaA and HpaH) with different molecular masses. HpaA seems to be a flavin-containing hydroxylase with a molecular mass of 58,781 Da. HpaH, with a molecular mass of 18,680 Da, seems to be a "helper" protein required for productive hydroxylation of the substrate. The hpa genes were expressed and the hydroxylase was active in Escherichia coli. Comparison of the enzyme with other monooxygenases indicates that K. pneumoniae 4-HPA hydroxylase is a member of a new family of hydroxylases.

4-Hydroxybenzoate uptake in Klebsiella pneumoniae is driven by electrical potential.

The uptake of 4-hydroxybenzoic acid (4-HBA) in intact cells of a mutant of Klebsiella pneumoniae was investigated. Uptake of 4-HBA was shown to be an inducible system. This uptake system, at pH 7.0, has a high affinity for its substrate (apparent Kt = 13 microM) and a maximal velocity of 27.6 nmol min-1 mg protein-1. Competition studies with various structural analogs indicated a very narrow specificity of the 4-HBA uptake system. The transport system has been inhibited by inhibitors of energy metabolism and its activity has not been detected in the crude shock extracts. The effect of two ionophores, nigericin and valinomycin, on 4-HBA uptake with respect to the external pH has been studied. All observations indicate that 4-HBA uptake is active and energized by the membrane potential.

Transport of 4-hydroxyphenylacetic acid in Klebsiella pneumoniae.

Klebsiella pneumoniae M5a1 has been shown to possess an inducible transport system for 4-hydroxyphenylacetate (4-HPA). This transport system has a Kt of 16.3 microM and a maximal velocity of 31.2 nmol/min (milligrams dry weight). The transport system has been inhibited by inhibitors of energy metabolism with a concomitant decrease in cellular ATP concentrations, and the 4-HPA binding activity has been detected in the crude shock extracts. All these observations indicate that 4-HPA uptake is an active transport which involves a periplasmic binding protein and it seems to be energized by phosphate bond energy.

El sulcus lunatus en el hombre. (Estudio morfologico). / Sulcus lunatus in human brain (Morphologic study)

Los autores presentan una investigacion casuistica sobre la incidencia y predominancia del sulcus lunatus en el cerebro del hombre. Tomando como punto de partida las incongruencias bibliograficas encontradas, se enfoca el trabajo desde un punto de vista estrictamente morfologico y macroscopico. La metodologia empleada consistio en observaciones directas del lobulo occipital, secciones en diferentes planos, mediciones de longitud y diagramacion de los casos examinados. A traves de los resultados obtenidos se arriba a conclusiones de alta significacion con respecto a incidencia, predominancia y bilateralidad. Se senala, ademas, que la diversidad del sulcus lunatus en cuanto a su conformacion anatomica ha obligado a dividir los casos positivos en un grupo con caracteres tipicos y otro con diferentes grados de atipia