Biochemical and biotechnological studies on a novel purified bacillus cholesterol oxidase tolerant to solvent and thermal stress

Potential fungicidal and antiaflatoxigenic effects of cinnamon essential oils on Aspergillus flavus inhabiting the stored wheat grains

Wheat is one of the essential crops for the human and animal nutrition, however, contamination with aflatoxigenic fungi, due to the improper storage conditions and high humidity, was the main global threats. So, preventing the growth of aflatoxigenic fungi in stored wheat grains, by using different essential oils was the main objective of this work. Aspergillus flavus EFBL-MU12 PP087400, EFBL-MU23 PP087401 and EFBL-MU36 PP087403 isolates were the most potent aflatoxins producers inhabiting wheat grains. The effect of storage conditions of wheat grains "humidity, temperature, incubation period, and pH" on growth of A. flavus, was assessed by the response surface methodology using Plackett-Burman design and FCCD. The highest yield of aflatoxins EFBL-MU12 B1 and B2 by A. flavus grown on wheat grains were 145.3 and 7.6 μg/kg, respectively, at incubation temperature 35°C, 16% moisture contents, initial pH 5.0, and incubated for 14 days. The tested oils had a powerful antifungal activity for the growth and aflatoxins production by A. flavus in a concentration-dependent manner. Among these oils, cinnamon oil had the highest fungicidal activity for A. flavus at 0.125%, with about 85-90 % reduction to the aflatoxins B1 and B2, conidial pigmentation and chitin contents on wheat grains. From the SEM analysis, cinnamon oils had the most deleterious effect on A. flavus with morphological aberrations to the conidial heads, vegetative mycelia, alteration in conidiophores identity, hyphae shrank, and winding. To emphasize the effect of the essential oils on the aflatoxins producing potency of A. flavus, the molecular expression of the aflatoxins biosynthetic genes was estimated by RT-qPCR. The molecular expression of nor-1, afLR, pKsA and afLJ genes was suppressed by 94-96%, due to cinnamon oil at 0.062% compared to the control. Conclusively, from the results, cinnamon oils followed by the peppermint oils displayed the most fungicidal activity for the growth and aflatoxins production by A. flavus grown on wheat grains.

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.

Physiological and metabolic traits of Taxol biosynthesis of endophytic fungi inhabiting plants: Plant-microbial crosstalk, and epigenetic regulators

Attenuating the Taxol productivity of fungi with the subculturing and storage under axenic conditions is the challenge that halts the feasibility of fungi to be an industrial platform for Taxol production. This successive weakening of Taxol productivity by fungi could be attributed to the epigenetic down-regulation and molecular silencing of most of the gene clusters encoding Taxol biosynthetic enzymes. Thus, exploring the epigenetic regulating mechanisms controlling the molecular machinery of Taxol biosynthesis could be an alternative prospective technology to conquer the lower accessibility of Taxol by the potent fungi. The current review focuses on discussing the different molecular approaches, epigenetic regulators, transcriptional factors, metabolic manipulators, microbial communications and microbial cross-talking approaches on restoring and enhancing the Taxol biosynthetic potency of fungi to be industrial platform for Taxol production.

Aspergillus terreus camptothecin-sodium alginate/titanium dioxide nanoparticles as a novel nanocomposite with enhanced compatibility and anticancer efficiency in vivo

BACKGROUND

Camptothecin derivatives are one of the most prescribed anticancer drugs for cancer patients, however, the availability, efficiency, and water solubility are the major challenges that halt the applicability of this drug.

METHODS

Biosynthetic potency of camptothecin by Aspergillus terreus, open a new avenue for commercial camptothecin production, due to their short-life span, feasibility of controlled growth conditions, and affordability for higher growth, that fulfill the availability of the scaffold of this drug.

RESULTS

Camptothecin (CPT) was purified from the filtrates of A. terreus, and their purity was checked by HPLC, and its chemical structure was verified by LC/MS, regarding to the authentic one. To improve the anticancer efficiency of A. terreus CPT, the drug was conjugated with sodium alginate (SA)/Titanium dioxide nanoparticles (TiO₂NPs) composites, and their physicochemical properties were assessed. From the FT-IR profile, a numerous hydrogen bond interactions between TiO₂ and SA chains in the SA/TiO₂ nanocomposites, in addition to the spectral changes in the characteristic bands of both SA/TiO₂ and CPT that confirmed their interactions. Transmission electron microscopy analysis reveals the spherical morphology of the developed SA/TiO₂NPs nanocomposite, with the average particle size ~ 13.3 ± 0.35 nm. From the results of zeta potential, successful loading and binding of CPT with SA/TiO₂ nanocomposites were observed.

CONCLUSION

The in vivo study authenticates the significant improvement of the antitumor activity of CPT upon loading in SA/TiO₂ nanocomposites, with affordable stability of the green synthesized TiO₂NPs with Aloe vera leaves extract.

Solvent tolerant enzymes in extremophiles: Adaptations and applications

Non-aqueous enzymology has always drawn attention due to the wide range of unique possibilities in biocatalysis. In general, the enzymes do not or insignificantly catalyze substrate in the presence of solvents. This is due to the interfering interactions of the solvents between enzyme and water molecules at the interface. Therefore, information about solvent-stable enzymes is scarce. Yet, solvent-stable enzymes prove quite valuable in the present day biotechnology. The enzymatic hydrolysis of the substrates in solvents synthesizes commercially valuable products, such as peptides, esters, and other transesterification products. Extremophiles, the most valuable yet not extensively explored candidates, can be an excellent source to investigate this avenue. Due to inherent structural attributes, many extremozymes can catalyze and maintain stability in organic solvents. In the present review, we aim to consolidate information about the solvent-stable enzymes from various extremophilic microorganisms. Further, it would be interesting to learn about the mechanism adapted by these microorganisms to sustain solvent stress. Various approaches to protein engineering are used to enhance catalytic flexibility and stability and broaden biocatalysis's prospects under non-aqueous conditions. It also describes strategies to achieve optimal immobilization with minimum inhibition of the catalysis. The proposed review would significantly aid our understanding of non-aqueous enzymology.

Microbial cytosine deaminase is a programmable anticancer prodrug mediating enzyme: antibody, and gene directed enzyme prodrug therapy

Cytosine deaminase (CDA) is a non-mammalian enzyme with powerful activity in mediating the prodrug 5-fluorcytosine (5-FC) into toxic drug 5-fluorouracil (5-FU), as an alternative directed approach for the traditional chemotherapies and radiotherapies of cancer. This enzyme has been frequently reported and characterized from various microorganisms. The therapeutic strategy of 5-FC-CDA involves the administration of CDA followed by the prodrug 5-FC injection to generate cytotoxic 5-FU. The antiproliferative activity of CDA-5-FC elaborates from the higher activity of uracil pathway in tumor cells than normal ones. The main challenge of the therapeutic drug 5-FU are the short half-life, lack of selectivity and emergence of the drug resistance, consistently to the other chemotherapies. So, mediating the 5-FU to the tumor cells by CDA is one of the most feasible approaches to direct the drug to the tumor cells, reducing its toxic effects and improving their pharmacokinetic properties. Nevertheless, the catalytic efficiency, stability, antigenicity and targetability of CDA-5-FC, are the major challenges that limit the clinical application of this approach. Thus, exploring the biochemical properties of CDA from various microorganisms, as well as the approaches for localizing the system of CDA-5-FC to the tumor cells via the antibody directed enzyme prodrug therapy (ADEPT) and gene directed prodrug therapy (GDEPT) were the objectives of this review. Finally, the perspectives for increasing the therapeutic efficacy, and targetability of the CDA-5-FC system were described.

Bioprocess optimization of glutathione production by Saccharomyces boulardii: biochemical characterization of glutathione peroxidase

The well-known probiotic GRAS Saccharomyces boulardii (CNCM I-745) was used for the first time to produce glutathione (GSH). The culture conditions affecting GSH biosynthesis were screened using a Plackett-Burman design (PBD). Analyzing the regression coefficients for 12 tested variables, yeast extract, glucose, peptone, cysteine, temperature and agitation rate had a positive significant effect on GSH production with a maximum yeild 192 mg/L. The impact of kinetics of adding cysteine was investigated in 19 experiments during the growth time course (0-36 h), and the maximum yield of glutathione (235 mg/L) was obtained by addition of cysteine after 8 h post-inoculation. The most significant variables were further explored at five levels using central composite rotatable design (CCRD), giving a maximum production of GSH (552 mg/L). Using baffled flasks, the yield of GSH was increased to 730 mg/L, i.e., 1.32-fold increment. The two rate-limiting genes of GSH biosynthesis "γ-glutamyl cysteine synthetase (GSH1) and GSH-synthetase (GSH2)" were amplified and sequenced to validate the GSH biosynthetic potency of S. boulardii. The sequences of genes showed 99% similarity with GSH1 and GSH2 genes of S. cerevisiae. Glutathione peroxidase was purified and characterized from S. boulardii with molecular mass and subunit structure of 80 kDa and 35 kDa as revealed from native and SDS-PAGE, ensuring its homodimeric identity. The activity of GPx was reduced by 2.5-fold upon demetallization confirming its metalloproteinic identity. The GPx was strongly inhibited by hydroxylamine and DTNB, ensuring the implication of surface lysine and cysteine residues on the enzyme active site domains.

Biosynthesis and Anti-Mycotoxigenic Activity of Zingiber officinale Roscoe-Derived Metal Nanoparticles

Mycotoxigenic fungi have attracted special attention due to their threat to food security and toxicity to human health. Aqueous extract of Zingiber officinale Roscoe was used as reducing and capping agent for the synthesis of silver (AgNPs), copper (CuNPs), and zinc oxide (ZnONPs) nanoparticles. UV-Visible spectra of the AgNPs, CuNPs, and ZnONPs showed absorption peaks at λmax 416 nm, 472 nm, and 372 nm, respectively. Zeta potential of AgNPs, CuNPs, and ZnONPs were -30.9, -30.4 and -18.4 mV, respectively. ZnONPs showed the highest activity against Aspergillus awamori ZUJQ 965830.1 (ZOI 20.9 mm and MIC 24.7 µg/mL). TEM micrographs of ZnONPs-treated A. awamori showed cracks and pits in the cell wall, liquefaction of the cytoplasmic content, making it less electron-dense. The sporulation and ochratoxin A production of A. awamori was inhibited by ZnONPs in a concentration-dependent pattern. The inhibition percentage of OTA were 45.6, 84.78 and 95.65% for 10, 15, 20 of ZnONPs/mL, respectively.

Identification of cholesterol-assimilating actinomycetes strain and application of statistical modeling approaches for improvement of cholesterol oxidase production by Streptomyces anulatus strain NEAE-94

Background

Cholesterol oxidase biosensors have been used to determine the level of cholesterol in different serum and food samples. Due to a wide range of industrial and clinical applications of microbial cholesterol oxidase, isolation and identification of a new microbial source (s) of cholesterol oxidase are very important.

Results

The local isolate Streptomyces sp. strain NEAE-94 is a promising source of cholesterol oxidase. It was identified based on cultural, morphological and physiological characteristics; in addition to the 16S rRNA sequence. The sequencing product had been deposited in the GenBank database under the accession number KC354803. Cholesterol oxidase production by Streptomyces anulatus strain NEAE-94 in shake flasks was optimized using surface response methodology. The different process parameters were first screened using a Plackett-Burman design and the parameters with significant effects on the production of cholesterol oxidase were identified. Out of the 15 factors screened, agitation speed, cholesterol and yeast extract concentrations had the most significant positive effects on the production of cholesterol oxidase. The optimal levels of these variables and the effects of their mutual interactions on cholesterol oxidase production were determined using Box-Behnken design. Cholesterol oxidase production by Streptomyces anulatus strain NEAE-94 was 11.03, 27.31 U/mL after Plackett-Burman Design and Box-Behnken design; respectively, with a fold of increase of 6.06 times compared to the production before applying the Plackett-Burman design (4.51 U/mL).

Conclusions

Maximum cholesterol oxidase activity was obtained at the following fermentation conditions: g/L (cholesterol 4, yeast extract 5, NaCl 0.5, K₂HPO₄ 1, FeSO₄.7H₂O 0.01, MgSO₄.7H₂O 0.5), pH 7, inoculum size 4% (v/v), temperature 37°C, agitation speed of 150 rpm, medium volume 50 mL and incubation time 5 days.

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.