Purification and characterization of extracellular cholesterol oxidase from Enterobacter sp

Improved production of Bacillus subtilis cholesterol oxidase by optimization of process parameters using response surface methodology

BACKGROUND

Cholesterol oxidase has numerous biomedical and industrial applications. In the current study, a new bacterial strain was isolated from sewage and was selected for its high potency for cholesterol degradation (%) and production of high cholesterol oxidase activity (U/OD600).

RESULTS

Based on the sequence of 16S rRNA gene, the bacterium was identified as Bacillus subtilis. The fermentation conditions affecting cholesterol degradation (%) and the activity of cholesterol oxidase (U/OD600) of B. subtilis were optimized through fractional factorial design (FFD) and response surface methodology (RSM). According to this sequential optimization approach, 80.152% cholesterol degradation was achieved by setting the concentrations of cholesterol, inoculum size, and magnesium sulphate at 0.05 g/l, 6%, and 0.05 g/l, respectively. Moreover, 85.461 U of cholesterol oxidase/OD600 were attained by adjusting the fermentation conditions at initial pH, 6; volume of the fermentation medium, 15 ml/flask; and concentration of cholesterol, 0.05 g/l. The optimization process improved cholesterol degradation (%) and the activity of cholesterol oxidase (U/OD600) by 139% and 154%, respectively. No cholesterol was detected in the spectroscopic analysis of the optimized fermented medium via gas chromatography-mass spectroscopy (GC-MS).

CONCLUSION

The current study provides principal information for the development of efficient production of cholesterol oxidase by B. subtilis that could be used in various applications.

Cholesterol Assay Based on Recombinant Cholesterol Oxidase, ABTS, and Horseradish Peroxidase

Cholesterol determination by cholesterol oxidase reaction is a fast, convenient, and highly specific approach with widespread use in clinical diagnostics. Routinely, endpoint measurements with 4-aminophenazone or 4-aminoantipyrine as chromogens and sodium cholate, surfactants, or alcohols as solubilizing agents are used. Here we describe a novel kinetic method to determine cholesterol in 0.05-0.75 mM range in neutral or acidic buffers by use of recombinant cholesterol oxidase from Nocardioides simplex in a coupled reaction with horseradish peroxidase, ABTS as a chromogen, and methyl-β-cyclodextrin as a solubilizing agent.

Purification, characterization, and biological cytotoxic activity of the extracellular cholesterol oxidase produced by Castellaniella sp. COX

A new bacterial strain producing extracellular cholesterol oxidase (ChOx) was isolated and identified as Castellaniella sp. COX. The ChOx was purified by salting-out and ion-exchange chromatography up to 10.4-fold, with a specific activity of 15 U/mg with a molecular mass of 59 kDa. The purified ChOx exhibited pH 8.0 and temperature 40°C for its optimum activity. The enzyme showed stability over a wide pH range and was most stable at pH value 7.0, and at pH 8.0, it retained almost 86% of its initial activity after 3 h of incubation at 37°C. The enzyme possessed a half-life of 8 h at 37°C, 7 h at 40°C, and 3 h at 50°C. A Lineweaver-Burk plot was calibrated to determine its K_m (0.16 mM) and V_max (18.7 μmol·mg^-1 ·min^-1 ). The ChOx activity was enhanced with Ca²⁺ , Mg²⁺ , and Mn²⁺ while it was inhibited by Hg²⁺ , Ba²⁺ , Fe²⁺ , Cu²⁺ , and Zn²⁺ ions. Organic solvents like acetone, n-butanol, toluene, dimethyl sulfoxide, chloroform, benzene, and methanol were well tolerated by the enzyme while iso-propanol and ethanol were found to enhance the activity of purified ChOx. ChOx induced cytotoxicity with an IC₅₀ value of 1.78 and 1.88 U/ml against human RD and U87MG established cell lines, respectively, while broadly sparing the normal human cells.

Production, Purification, and Identification of Cholest-4-en-3-one Produced by Cholesterol Oxidase from Rhodococcus sp. in Aqueous/Organic Biphasic System

Cholest-4-en-3-one has positive uses against obesity, liver disease, and keratinization. It can be applied in the synthesis of steroid drugs as well. Most related studies are focused on preparation of cholest-4-en-3-one by using whole cells as catalysts, but production of high-quality cholest-4-en-3-one directly from cholesterol oxidase (COD) using an aqueous/organic two-phase system has been rarely explored. This study set up an enzymatic reaction system to produce cholest-4-en-3-one. We developed and optimized the enzymatic reaction system using COD from COX5-6 (a strain of Rhodococcus) instead of whole-cell biocatalyst. This not only simplifies and accelerates the production but also benefits the subsequent separation and purification process. Through extraction, washing, evaporation, column chromatography, and recrystallization, we got cholest-4-en-3-one with purity of 99.78%, which was identified by nuclear magnetic resonance, mass spectroscopy, and infrared spectroscopy. In addition, this optimized process of cholest-4-en-3-one production and purification can be easily scaled up for industrial production, which can largely decrease the cost and guarantee the purity of the product.

Production, purification and characterization of cholesterol oxidase from a newly isolated Streptomyces sp

Cholesterol oxidase production (COD) by a new isolate characterized as Streptomyces sp. was studied in different production media and fermentation conditions. Individual supplementation of 1 % maltose, lactose, sucrose, peptone, soybean meal and yeast extract enhanced COD production by 80-110 % in comparison to the basal production medium (2.4 U/ml). Supplementation of 0.05 % cholesterol (inducer) enhanced COD production by 150 %. COD was purified 14.3-fold and its molecular weight was found to be 62 kDa. Vmax (21.93 μM/min mg) and substrate affinity Km (101.3 μM) suggested high affinity of the COD for cholesterol. In presence of Ba(2+) and Hg(2+) the enzyme activity was inhibited while Cu(2+) enhanced the activity nearly threefold. Relative activity of the enzyme was found maximum in triton X-100 whereas sodium dodecyl sulfate inactivated the enzyme. The enzyme activity was also inhibited by the thiol-reducing reagents like Dithiothreitol and β-mercaptoethanol. The COD showed moderate stability towards all organic solvents except acetone, benzene and chloroform. The activity increased in presence of isopropanol and ethanol. The enzyme was most active at pH 7 and 37 °C temperature. This organism is not reported to produce COD.

Gordonia neofelifaecis sp. nov., a cholesterol side-chain-cleaving actinomycete isolated from the faeces of Neofelis nebulosa

A cholesterol side-chain-cleaving bacterial strain, AD-6T, was isolated from fresh faeces of a clouded leopard (Neofelis nebulosa) and was studied using a polyphasic taxonomic approach. 16S rRNA gene sequence analysis showed that the novel strain formed a distinct subline within the genus Gordonia, its closest neighbours being the type strains of Gordonia cholesterolivorans, Gordonia sihwensis and Gordonia hydrophobica, with sequence similarity values of 98.2, 97.8 and 97.6 %, respectively. The gyrB gene sequence of strain AD-6T exhibited similarities of 77–91 % with those of the type strains of recognized species of the genus Gordonia, being most similar to the type strains of G. sihwensis, G. hydrophobica and Gordonia hirsuta (91, 87 and 84 % similarity, respectively). The results of whole-cell fatty acid analyses and DNA–DNA relatedness data readily distinguished the new isolate from its nearest neighbours. Strain AD-6T is therefore considered to represent a novel species of the genus Gordonia, for which the name Gordonia neofelifaecis sp. nov. is proposed. The type strain is AD-6T (=NRRL B-59395T=CCTCC AB-209144T).