RESUMO

The use of multi-enzymatic systems for the industrial production of chemical compounds is currently considered an important green tool in synthetic organic chemistry. Gluconic acid is a multi-functional organic acid widely used in the chemical, pharmaceutical, food, textile, and construction industries. Its industrial production from glucose by fermentation using Aspergillus niger has drawbacks including high costs related to cell growth and maintenance of cell viability. This study presents an innovative one-step multi-enzymatic system for gluconic acid production from starch using Aspergillus niger whole-cells in association with amylolytic enzymes. Using soluble starch as substrate, the following results were achieved for 96 h of reaction: 134.5 ± 4.3 g/L gluconic acid concentration, 98.2 ± 1.3 % gluconic acid yield, and 44.8 ± 1.4 gGA/gwhole-cells biocatalyst yield. Although the process has been developed using starch as raw material, the approach is feasible for any substrate or residue that can be hydrolyzed to glucose.

RESUMO

ABSTRACT Despite its high toxicity, cyanide is used in several industrial processes, and as a result, large volumes of cyanide wastewater need to be treated prior to discharge. Enzymatic degradation of industrial cyanide wastewater by cyanide dihydratase, which is capable of converting cyanide to ammonia and formate, is an attractive alternative to conventional chemical methods of cyanide decontamination. However, the main impediment to the use of this enzyme for the biodegradation of cyanide is its intolerance to the alkaline pH at which cyanide waste is kept and its low thermoresistance. In the present study, the catalytic properties of whole Escherichia coli cells overexpressing a cyanide dihydratase gene from Bacillus pumilus were compared to those of the purified enzyme under conditions similar to those found in industrial cyanide wastewater. In addition, the capacity of whole cells to degrade free cyanide in contaminated wastewater resulting from the gold mining process was also determined. The characteristics of intracellular enzyme, relative to purified enzyme, included increased thermostability (>60% activity at 50°C), as well as greater tolerance to heavy metals, and to a lesser extent pH (20% activity remaining at pH 9.0) On the other hand, enzymatic degradation of 70% of free cyanide (initial concentration 528 mM) in the industrial sample was achieved only after dilution. Nevertheless, the increased thermostability observed for intracellular CynD suggest that whole cells of E. coli overexpressing CynD are suited for process that operate at elevated temperatures (50°C), a limitation observed for the purified enzyme.

RESUMEN A pesar de su alta toxicidad, el cianuro es usado en diversos procesos industriales, y como resultado, grandes volúmenes de aguas residuales de cianuro deben ser tratados antes de su descarga. Una alternativa atractiva a los métodos químicos convencionales de descontaminación es la degradación enzimática por la enzima cianuro dihidratasa, la cual es capaz de convertir cianuro en amonio y ácido fórmico. No obstante, la inactivación de esta enzima a pH superior a 8.5 y su poca termoestabilidad han sido el principal impedimento para la implementación exitosa de esta alternativa de biorremediación. En el presente estudio, las propiedades catalíticas de células completas de Escherichia coli que sobre expresan el gen de cianuro dihidratasa de Bacillus pumilus se estudian bajo condiciones similares a las encontradas en aguas residuales industriales de cianuro y los resultados se discuten en comparación con las de la enzima purificada. Además, se determinó la capacidad de las células completas para degradar el cianuro libre en aguas residuales resultantes del proceso de extracción de oro. Las características de la enzima intracelular, relativa a la enzima purificada, incluyeron un incremento en la termoestabilidad (>60% actividad a 50°C), así como mayor tolerancia a metales pesados y en menor medida al pH (20% actividad residual a pH 9.0). Por otra parte, la degradación enzimática del 70% del cianuro libre en la muestra industrial (concentración inicial 528 mM) se logró solo después de la dilución de la muestra. Sin embargo, el incremento en la termoestabilidad observado para CynD intracelular sugiere que las células completas de E. coli que sobre expresan CynD son adecuadas para procesos que operan a temperaturas elevadas (50°C), una limitación observada para la enzima purificada.

RESUMO

Microbial whole cells are efficient, ecological, and low-cost catalysts that have been successfully applied in the pharmaceutical, environmental, and alimentary industries, among others.Microorganism immobilization is a good way to carry out the bioprocess under preparative conditions. The main advantages of this methodology lie in their high operational stability, easy upstream separation, and bioprocess scale-up feasibility.Cell entrapment is the most widely used technique for whole cell immobilization. This technique-in which the cells are included within a rigid network-is porous enough to allow the diffusion of substrates and products, protects the selected microorganism from the reaction medium, and has high immobilization efficiency (100% in most cases).

Assuntos

RESUMO

Cyanide is toxic to most living organisms. The toxicity of cyanide derives from its ability to inhibit the enzyme cytochrome C oxidase of the electronic transport chain. Despite its high toxicity, several industrial processes rely on the use of cyanide, and considerable amounts of industrial waste must be adequately treated before discharge. Biological treatments for the decontamination of cyanide waste include the use of microorganisms and enzymes. Regarding the use of enzymes, cyanide dihydratase (CynD), which catalyzes the conversion of cyanide into ammonia and formate, is an attractive candidate. Nevertheless, the main impediment to the effective use of this enzyme for the biodegradation of cyanide is the marked intolerance to the alkaline pH at which cyanide waste is kept. In this work, we explore the operational capabilities of whole E. coli cells overexpressing Bacillus pumilus CynD immobilized in three organic polymer matrices: chitosan, polyacrylamide, and agar. Remarkably, the immobilized cells on agar and polyacrylamide retained more than 80% activity even at pH 10 and displayed high reusability. Conversely, the cells immobilized on chitosan were not active. Finally, the suitability of the active complexes for the degradation of free cyanide from a solution derived from the gold processing industry was demonstrated.

Assuntos

RESUMO

Currently, the power and usefulness of biocatalysis in organic synthesis is undeniable, mainly due to the very high enantiomeric excess reached using enzymes, in an attempt to emulate natural processes. However, the use of isolated enzymes has some significant drawbacks, the most important of which is cost. The use of whole cells has emerged as a useful strategy with several advantages over isolated enzymes; for this reason, modern research in this field is increasing, and various reports have been published recently. This review surveys the most recent developments in the enantioselective reduction of carbon-carbon double bonds and prochiral ketones and the oxidation of prochiral sulfides using whole cells as biocatalytic systems.

Assuntos