Screening and genetic identification of acidic and neutral protease-producing yeasts strains by 26S rRNA gene sequencing

Statistical versus neural network-embedded swarm intelligence optimization of a metallo-neutral-protease production: activity kinetics and food industry applications

An integrated approach involving response surface methodology (RSM) and artificial neural network-ant-colony hybrid optimization (ANN-ACO) was adopted to develop a bioprocess medium to increase the yield of Bacillus cereus neutral protease under submerged fermentation conditions. The ANN-ACO model was comparatively superior (predicted r2 = 98.5%, mean squared error [MSE] = 0.0353) to RSM model (predicted r2 = 86.4%, MSE = 23.85) in predictive capability arising from its low performance error. The hybrid model recommended a medium containing (gL-1) molasses 45.00, urea 9.81, casein 25.45, Ca2+ 1.23, Zn2+ 0.021, Mn2+ 0.020, and 4.45% (vv-1) inoculum, for a 6.75-fold increase in protease activity from a baseline of 76.63 UmL-1. Yield was further increased in a 5-L bioreactor to a final volumetric productivity of 3.472 mg(Lh)-1. The 10.0-fold purified 46.6-kDa-enzyme had maximum activity at pH 6.5, 45-55 °C, with Km of 6.92 mM, Vmax of 769.23 µmolmL-1 min-1, kcat of 28.49 s-1, and kcat/Km of 4.117 × 103 M-1 s-1, at 45 °C, pH 6.5. The enzyme was stabilized by Ca2+, activated by Zn2+ but inhibited by EDTA suggesting that it was a metallo-protease. The biomolecule significantly clarified orange and pineapple juices indicating its food industry application.

Isolation, Identification, and Characterization of the Native Yeast Strains from Homemade Cheese to Assess their Eliminating Impact on the Aflatoxin B1 and M1 of the Simulated Gastrointestinal Fluid

Background

The occurrence of aflatoxins in food products is a silent threat to human health worldwide. A range of strategies has been introduced to address the bioavailability of aflatoxins, which are considered microbial tools to provide a low-cost and promising approach.

Objectives

The present study focused on the separation of yeast strains from the homemade cheese rind layer to investigate the ability of native yeasts to eliminate AB1 and AM1 from simulated gastrointestinal fluids.

Material and Methods

Homemade cheese samples were prepared from different locations in Tehran provinces and yeast strains were isolated and identified through the biochemical methods and molecular analysis of internal transcribed spacer and D1/D2 domain of 26S rDNA regions. Isolated strains were screened using simulated gastrointestinal fluids, and the ability of yeast strains to absorb aflatoxin was evaluated.

Results

Out of 13 strains, 7 yeast strains were not affected by 5 ppm AFM1 while 11 strains did not show any significant response to 5 mg.L^-1 (ppm) of AFB1. On the other hand, 5 strains were able to successfully tolerate 20 ppm AFB1. Candidate yeasts showed different abilities to remove aflatoxins B1 and M1. In addition, C. lusitaniae, G. geotrichum, G. candidum, and C. sanyaensis exhibited a significant ability to detoxify aflatoxins from the gastrointestinal fluid, respectively.

Conclusion

Our data suggest that yeast communities with essential effects on the quality of homemade cheese appear to be precise candidates for the potential elimination of aflatoxins from the gastrointestinal fluid.

Production of Cocktail Enzymes by Three Cladosporium Isolates and Bioconversion of Orange Peel Wastes into Valuable Enzymes

The current research demonstrates the biotechnological economization of accumulated and inefficiently used agro-industrial orange peel wastes to generate amylase, endoglucanase, exoglucanase, pectinase, and xylanase, industrially essential enzymes with growing demands in enzyme markets, from three Cladosporium isolates. In submerged fermentation (SmF) at 10°C, the isolate AUMC 10865 produced the highest level of amylase (4164 IU/gram dry substrate). Endoglucanase, exoglucanase and xylanase had development peaks (923 IU/gds, 2280 IU/gds, and 1646 IU/gds, respectively in case of Cladosporium sp. AUMC 11366. Pectinase produced the most (7840 IU/gds) in the strain AUMC 11340. At 30°C, the strain AUMC 11340 secretes the most amylase (4120 IU/gds), endoglucanase (2700 IU/gds) and xylanase (3220 IU/gds). Exoglucanase development reached the peak (8750 IU/gds) in the isolate AUMC 10865. The overall production (5570 IU/gds) was instead enhanced by pectinase in the AUMC 11366 isolate. In solid-state fermentation (SSF) at 10°C, the isolate AUMC 10865 outperformed the other two isolates producing 640.0 IU/gds amylase, 763.3 IU/gds endoglucanase, 771.0 IU/gds exoglucanase, 1273.23 IU/gds pectinase and 1062.0 IU/gds xylanase, while the isolate AUMC 11366 produced the least amount of 399.7 IU/gds, 410.0 IU/gds, 413.3 IU/gds, 558.7 IU/gds, and 548.0 IU/gds, respectively. At 30°C, the isolate AUMC 11340 was superiorly producing higher levels of amylase (973.3 IU/gds), endoglucanase (746.0 IU/gds), exoglucanase (1052.0 IU/gds), pectinase (1685.3 IU/gds) and xylanase (1340.0 IU/gds), whereas isolate AUMC 10865 generated the least amounts of amylase (556.7 IU/gds) and exoglucanase (452.7 IU/gfs), and the isolate AUMC 11366 produced the least endoglucanase (256.3 IU/gds), pectinase (857.7 IU/gfs) and xylanase (436.3 IU/gds) amounts.

Production and Optimization of Xylanase and α-Amylase from Non-Saccharomyces Yeasts (Pichia membranifaciens)

The xylanolytic and amylolytic yeasts were qualitatively determined by Cong red xylan agar and soluble starch agar plates, respectively. The most xylanase and α-amylase inducible strain (AUN-02) was selected and identified using PCR amplification of 26S rRNA gene and sequence analysis. The comparison of the alignment results and phylogenetic analysis of the sequences of the isolated yeast to published rRNA gene sequences in GenBank, confirmed the identification of the isolate as Pichia membranifaciens. Xylanase and α-amylase production by isolated P. membranifaciens were investigated at different pH values (4-8), temperature degrees (20-45°C), incubation time (1-7 days) and various substrates.A higher production of xylanase (38.8 U/mL) and a-amylase (28.7 U/mL) was obtained after 4 days of fermentation of P. membranifaciens. Higher activity of xylanase (36.83 U/mL) and a-amylase (27.7 U/mL) was obtained in the fermentation of P. membranifaciens in a culture medium adjusted to pH 7.0. The optimum temperature showed maximum xylanase and a-amylase activity (42.6 and 32.5 units/mL, respectively) was estimated at 35 °C. The xylanase and a-amylase activities of P. membranifaciens were estimated and compared for the different substrates tested. The strain revealed 100% relative activity of xylanase and a-amylase on beechwood and potato starch, respectively. The affinity of enzymes towards substrate was estimated using Km values. The Km values of xylanase and α-amylase increased in the order of pH’s 7.0, 6.0 and 4.5 (0.85, 1.6 and 3.4 mg xylan/mL and 0.22, 0.43 and 2.8 mg starch/mL, respectively). the yeast P. membranifaciensis is suitable for produce neutral xylanase and α-amylase enzymes. So, it could be used as a promising strain for production of these enzymes in industrial field.

Yeast a potential bio-agent: future for plant growth and postharvest disease management for sustainable agriculture

The native microbial flora and fauna are replaced by commercial chemical fertilizers and pesticides, in the current agricultural system. Imbalance of beneficial microbial diversity and natural competitors increases the severity of plant diseases. Hence, sustainable agricultural practices like bio-inoculant, stress tolerant consortium, crop rotation and mix cropping sequences is only the solution of recharging the microbial population in soils to make healthier for crop productivity and suppression of soil borne phytopathogen. Microorganisms use several direct mechanism activities, e.g. production of plant hormones (indole-3-acetic acid), ammonium, siderophore and nutrient solubilization, and indirect mechanism activities, e.g. hydrogen cyanide, chitinase, protease and antibiotic for plant growth promotion. The plant growth-promoting effect of bacteria, fungi, mycorrhizal fungi and algae is widely explored. Yeast is a single-celled microbe classified as members of the kingdom fungi. Yeast and their product use in the food industry, medical science and biotechnological research purpose but very few literatures reported that yeasts have the ability to produce a group of plant growth-promoting activities and biocontrolling activity. Therefore, the main aim of this mini review is to highlight the application of yeasts as biological agents in different sectors of sustainable farming practices.

Use of PCR-denaturing gradient gel electrophoresis for the discrimination of Candida species isolated from natural habitats

Candida species are opportunistic microbes that cause chronic infections for a human being. Therefore, the exact identification of Candida species is extremely important for improved therapeutic strategy against these species. Identification based on conventional methods cannot differentiate between some of yeasts species, hence PCR based molecular techniques and sequencing could be an alternative tool for the yeasts identification. A quick molecular method based on the polymerase chain reaction (PCR) and Denaturing Gradient Gel Electrophoresis (DGGE) was applied for distinguishing strains belonging to the Candida species. Six different species designated as AH-20, AH-21, AH-22, AH-23, AH-24 and AH-25 were isolated from soil samples, and their exact identification was detected based on the D1/D2 domain of the 26S rRNA gene amplification and sequence determination. Alignment results and the comparison of 26S rRNA gene sequences of the isolates to 26S rRNA gene sequences available in the GenBank database, as well as the phylogenetic analysis, confirmed the accurate position of the isolates as Candida intermedia strain AH-20, Candida boidinii strain AH-21, Candida tropicalis strain AH-22, Candida mengyuniae strain AH-23, Candida maltosa strain AH-24 and Candida maltosa strain AH-25. Fragments of the D1/D2 domain of 26S rRNA gene were amplified using NL1-GC/LS2 primers and separated by the DGGE. Results showed that all Candida species reported in this study were well discriminated by a distinct band in the DGGE profile. Our results demonstrated that DGGE technique using NL1-GC/LS2 primers could use for the rapid discrimination of yeast strains belonging to the same genera.