Phenylalanine ammonia lyase production by gamma irradiated and analog-resistant mutants of Rhodotorula glutinis

Mutants resistant to phenylalanine analogs (L-tyrosine, p-fluoro-D, L-phenylalanine (PFP) and trans-cinnamic acid) were isolated from a wild type strain of Rhodotorula glutinis A-97 by mutagenic treatment with gamma radiation and screened for phenylalanine ammonia lyase (PAL) production. One such mutant, gammaT11 (resistant to L-tyrosine), exhibited four times the PAL activity of the parent wild strain A-97. Mutant isolate gammaTFP5.6 which was selected as L-tyrosine and PFP resistant isolate, produced inducible PAL activity at levels 5.94-fold higher than the wild-type A-97 and 2.66-fold higher than its parent mutant isolate gammaT5 which was resistant to L-tyrosine. The mutant isolate gammaTC5d which was resistant to L-tyrosine and trans-cinnamic acid, exhibited 3.48 and 1.56-fold increase in PAL activity compared to the parent wild strain A-97 and its parent mutant isolate gammaT5, respectively. Different media have been examined for the induction of PAL.     

Ethanol production by Kluyveromyces lactis immobilized cells in copolymer carriers produced by radiation polymerization

The conditions for batch and continuous production of ethanol, using immobilized growing yeast cells of Kluyveromyces lactis, have been optimized. Yeast cells have been immobilized in hydrogel copolymer carriers composed of polyvinyl alcohol (PVA) with various hydrophilic monomers, using radiation copolymerization technique. Yeast cells were immobilized through adhesion and multiplication of yeast cells themselves. The ethanol production of immobilized growing yeast cells with these hydrogel carriers was related to the monomer composition of the copolymers and the optimum monomer composition was hydroxyethyl methacrylate (HEMA). In this case by using batch fermentation, the superior ethanol production was 32.9 g L(-1) which was about 4 times higher than that of cells in free system. The relation between the activity of immobilized yeast cells and the water content of the copolymer carriers was also discussed. Immobilized growing yeast cells in PVA: HEMA (7%: 10%, w/w) hydrogel copolymer carrier, were used in a packed-bed column reactor for the continuous production of ethanol from lactose at different levels of concentrations (50, 100 and 150) g L(-1). For all lactose feed concentrations, an increase in dilution rates from 0.1 h(-1) to 0.3 h(-1) lowered ethanol concentration in fermented broth, but the volumetric ethanol productivity and volumetric lactose uptake rate were improved. The fermentation efficiency was lowered with the increase in dilution rate and also at higher lactose concentration in feed medium and a maximum of 70.2% was obtained at the lowest lactose concentration 50 g L(-1).     

Continuous production of L-phenylalanine by Rhodotorula glutinis immobilized cells using a column reactor

Studies have been conducted on L-phenylalanine (L-Phe) production and phenylalanine ammonia lyase (PAL) stabilization in the presence of several optimum effectors and reducing agents under bioconversion of transcinnamic acid (t-CA) conditions during repeated batch operations. L-Phe production was maximized and reuseability of PAL catalyst was extended to eight consecutive cycles (repeated batches) in the presence of optimum effectors (glutamic acid, polyethylene glycol and glycerol), thioglycolic acid and sparging with nitrogen gas. These best optimum bioconversion conditions desensitize the PAL catalyst to substantially elevated higher substrate t-CA concentrations and inhibit inactivation of PAL enzyme over longer reaction periods compared to the control. The fed batch mode operation of bioconversion of total t-CA (300 mM) to L-Phe was superior (65.2%, conversion), comparing with conventional batch and repeated batch (58.4%, conversion) operations after 120 h. Gamma irradiation process was employed to polymerize and crosslink polyvinyl alcohol (PVA) with N,N'-methylene-bisacrylamide (BIS) agent. The use of immobilized PAL biocatalyst containing cells in PVA-BIS copolymer gel carrier produced by radiation polymerization is obviously advantageous with regards to the yield of L-Phe which was increased in average 1.2-fold when compare to those obtained with free cells during optimum bioconversion process. When comparing the magnitudes of gamma irradiation effects on immobilized entrapped yeast cells in PVA-BIS copolymer gel carrier using scanning electron microscopy it was show that yeast cells were protected and capable to overcome these conditions and had normal shape and other features as free (unirradiated) intact yeast cells. Optimum conditions for continuous production of L-Phe by PVA-BIS copolymer carrier entrapped yeast cells in a packed bed column reactor in recycle fed-batch mode were investigated. Under these optimum conditions L-Phe accumulated to concentration 240.1 mM represts a total conversion yield of 80% (w/w) from (300 mM) t-CA after 84 h of reaction process, which was higher than that obtained after 120 h of reaction, 65.2% (w/w) from (300 mM) t-CA with free cells in fed-batch mode. The results also demonstrated that during about 4 weeks of repeated continuous recycle fed batch mode experiments (using immobilized cells in packed bed reactor), the final production of L-Phe concentrations decreased gradually in eight consecutive runs with no sign of breakage or disintegration of the carrier gel beads.     

Optimization of process parameters for the continuous ethanol production by Kluyveromyces lactis immobilized cells in hydrogel copolymer carrier

In the present study the optimized parameters for highest ethanol productivity by Kluyveromyces lactis immobilized cells bioreactor were obtained using the method of Lagrange multipliers. Immobilized growing yeast cells in PVA: HEMA (7%: 10%, w/w) hydrogel copolymer carrier produced by radiation polymerization were used in a packed-bed column reactor for the continuous production of ethanol from lactose at different levels of concentrations (50, 100 and 150) gL(-1). The results indicate that volumetric ethanol productivity is influenced by substrate concentration and dilution rate. The highest value 7.17 gL(-1) h(-1) is obtained at higher lactose concentration (150 gL(-1)) in feed medium and 0.3 h(-1) dilution rate. The same results have been obtained through the application of "LINGO" software for mathematical optimization.     

Optimization of reaction conditions and stabilization of phenylalanine ammonia lyase-containing Rhodotorula glutinis cells during bioconversion of trans-cinnamic acid to L-phenylalanine

Studies were performed to elucidate the optimal reaction conditions (pH, temperature, ammonia concentration and biocatalyst loading) for bioconversion of trans-cinnamic acid (t-CA) to L-phenylalanine (L-Phe) by L-phenylalanine ammonia lyase (PAL) containing Rhodotorula glutinis cells. All treatments with permeabilizing agents stimulated L-Phe production and also enhanced instability of the catalyst, except Triton X-100 which gave a superior (56%) increase in conversion as compared to the control and a significant stabilization of PAL enzyme. Inclusion of several activity modifiers and stabilizer additives in reaction mixtures were shown to enhance the yield of L-Phe and maintained PAL stability over several successive incubations during the bioconversion process. Maximum stabilization of PAL and enhancement of L-Phe production was achieved with addition of 20% polyhydric alcohol (glycerol). The production of L-Phe continued to the fifth cycle and the total yield increased 2.3 times compared to the yield produced by the control (without glycerol addition) during the repeated batch process. Reducing agents such as 2-mercaptoethanol and thioglycolic acid were added to the bioconversion mixture in order to reduce the effects of oxygen on PAL catalyst life. Production of L-Phe by addition of 400 mgL(-1) of thioglycolic acid was maximized over the control by 55%. When both 20% glycerol and 400 mgL(-1) thioglycolic acid were simultaneously present in the reaction mixture, reuseability and stability of biocatalyst (PAL) were extended to eight consecutive cycles and conversion rate and overall productivity of L-Phe were higher than that of the control. These results may lead to improvements in the production of the essential amino acid L-Phe.     

Investigating the antimicrobial,antioxidant and cytotoxic activities of the biological synthesized glutathione selenium nano-incorporation

BioMetals - Aqueous glutathione selenium nano-incorporation (GSH-SeN-Inco) was prepared by gamma radiation in presence of microbial glutathione (GSH) and selenium dioxide. The novel prepared...     

A novel approach for adding smart functionalities to cellulosic fabrics

A water soluble nanocomposite, based on Ag-nanoparticles (Ag-NPs) loaded on hyperbranched poly (amide-amine, HBPAA) was prepared, characterized and utilized in functional finishing as well as in combined reactive dyeing/and functional finishing of linen, cotton and viscose fabrics. Incorporation of the nanocomposite alone and in combination with reactive dyes in easy care finishing formulations brought about an outstanding antibacterial functionality of the finished and the dyed/finished fabrics even after 15 laundering cycles along with a slight negative impact on other performance properties. Improvement or decrement in the functional, comfort, and dyeing properties is governed by the type of cellulosic substrate.     

Gentamicin-Assisted Mycogenic Selenium Nanoparticles Synthesized Under Gamma Irradiation for Robust Reluctance of Resistant Urinary Tract Infection-Causing Pathogens

Biological Trace Element Research - The purpose of this research is to compare and enhance the antimicrobial and antibiofilm potentials of the biogenic selenium nanoparticles (Se NPs) produced by...