Oxygen radical based on non-thermal atmospheric pressure plasma alleviates lignin-derived phenolic toxicity in yeast

Enhanced Bioremediation of 4-Chlorophenol by Electrically Neutral Reactive Species Generated from Nonthermal Atmospheric-Pressure Plasma

4-Chlorophenol (4-CP) is a chlorinated aromatic compound with broad industrial applications. It is released into the environment as an industrial byproduct and is highly resistant to biodegradation. Pseudomonas sp. in the environment and activated sludge are used for 4-CP bioremediation; however, the degradation of 4-CP takes a long time. Consequently, the toxicity of 4-CP is a major barrier to its bioremediation. In this study, we investigated the synergistic effect of electrically neutral reactive species on the bacterial bioremediation of 4-CP. Our results showed that the concentration of 4-CP decreased from 2.0 to 0.137 mM and that it was converted to 4-chlorocatechol (4-CC; 0.257 mM), 4-chlororesorcinol (0.157 mM), hydroquinone (0.155 mM), and trihydroxy chlorobenzene and their respective ring-cleaved products following irradiation of neutral reactive species. These compounds were less toxic than 4-CP, except for 4-CC, which reduced the toxicity of 4-CP to Pseudomonas putida. When the neutral reactive species-treated 4-CP fraction was added to P. putida cultured in a synthetic sewage medium for 48 h, the 4-CP concentration was reduced to 0.017 mM, whereas nontreated 4-CP (2.0 mM) was hardly degraded by P. putida. These results suggest that the biodegradation of 4-CP can be efficiently improved by combining irradiation of neutral reactive species with microbial treatment. The irradiation of neutral reactive species of environmental pollutants may additionally lead to further improvements in bioremediation processes.

Modification of bioethanol production in an innovative pneumatic digester with non-thermal cold plasma detoxification

An anaerobic pneu-mechanical digester (PD) was designed to ferment lignocellulosic compounds. So, wheat and rice straws were pretreated using an ultrasound-acid, and then thermal-acid hydrolysis was conducted. Hydrolysis optimization was performed using the response surface method and the optimal points for time, temperature, and acid concentration were 45 min, 148.4 °C, and 2.04 % v/v, respectively. Cold plasma was then used as detoxification to reduce the amount of inhibitory compounds and acids. This method was capable of reducing the amounts of acetic acid, formic acid and furfural by 73, 83 and 68 % in hydrolyzed biomass, respectively. The biomass was fermented in a PD for 20 days and compared with a conventional digester (CD). The obtained results showed that the PD could increase the efficiency of bioethanol by 37 % in the detoxified state and 22 % in the non-detoxified state after 20 days of fermentation compared to the CD. Moreover, H₂S, CO and O₂ were measured during fermentation process. In PD, the amount of H₂S and O₂ was lower than CD, but CO was significantly higher in the PD.

Artificial AmyR::XlnR transcription factor induces α-amylase production in response to non-edible xylan-containing hemicellulosic biomass

Filamentous fungi belonging to the Aspergillus genus are one of the most favored microorganisms for industrial enzyme production because they can secrete large amounts of proteins into the culture medium. α-Amylase, an enzyme produced by Aspergillus species, is important for food and industrial applications. The production of α-amylase is induced by starch, mainly obtained from the edible biomass; however, the increasing demand for foods is limiting the application of the latter. Therefore, it is expected that using the non-edible biomass, such as rice straw, could improve the competition for industrial application starch containing resources. The transcription factor AmyR activates the transcription of amylolytic enzyme genes, while the transcription factor XlnR activates the transcription of xylanolytic enzyme genes in response to xylose. In this study, we aimed to construct an artificial AmyR::XlnR transcription factor (AXTF) by replacing the DNA-binding domain (1-159 amino acids) of XlnR with that (1-68 aa) of AmyR, which is capable of inducing amylolytic enzyme production in response to xylan-containing hemicellulosic biomass. The chimeric transcription factor AXTF was constructed and expressed using the gapA promoter in the amyR-deficient mutant strain SA1. When the AXTF strain was cultured in the minimal medium containing xylose as the carbon source, the amyB, amyF, agdB, and agdE transcription levels were 41.1-, 11.3-, 37.9-, and 23.7-fold higher, respectively, than those of the wild-type strain. The α-amylase and α-glucosidase activities in the culture supernatant of the AXTF strain grown with xylose for 48 h were 696.6 and 536.1 U/mL, respectively, while these activities were not detected in the culture supernatant of the wild-type and SA1 strains. When rice straw hydrolysate was used as a carbon source, the α-amylase and α-glucosidase activities were 590.2 and 362.7 U/mL, respectively. Thus, we successfully generated an Aspergillus nidulans strain showing amylolytic enzyme production in response to non-edible xylan-containing hemicellulosic biomass by transforming it with the chimeric transcription factor AXTF. Furthermore, the use of genes encoding engineered transcription factors is advantageous because introducing such genes into an industrial Aspergillus strain has similar simultaneous effects on multiple amylase genes controlled by AmyR.