Mechanistic investigations in biobutanol synthesis via ultrasound-assisted ABE fermentation using mixed feedstock of invasive weeds

Influence of Low-Intensity Ultrasound on ε-Polylysine Production: Intracellular ATP and Key Biosynthesis Enzymes during Streptomyces albulus Fermentation

The effect of low-intensity sonication treatment on cell growth, ε-polylysine (ε-PL) yield and its biological mechanism were investigated, using a 3-L-jar fermenter coupled with an in situ ultrasonic slot with a Streptomyces albulus strain SAR 14-116. Under ultrasonic conditions (28 kHz, 0.37 W cm−2, 60 min), a high biomass of SAR 14-116 and concentration of ε-PL were realized (i.e., they increased by 14.92% and 28.45%, respectively) when compared with a control. Besides this, ultrasonication increased the mycelia viability and intracellular ATP as well as activities of key enzymes involved in the ε-PL biosynthesis pathway, resulting in an improvement in the production of ε-PL. Data on qRT-PCR revealed that ultrasonication also affected the gene expression of key enzymes in the ε-PL biosynthesis pathway, including ε-PL synthetase (PLS). These outcomes provided the basis for understanding the effects of ultrasound-assisted fermentation on the stimulation of metabolite production and fermentation procedure in a fermenter.

Strategic thermosonication-mediated modulation of lactic acid bacteria acidification kinetics for enhanced (post)-fermentation performance

This study explored the feasibility of thermosonication (TS)-prestressed inoculum with different fermentation patterns for regulating microbial (post)-fermentation acidification kinetics. Through a Box-Behnken design, stimulative (20 min, 400 W, 33 kHz, 25 °C) and inhibitive (10 min, 600 W, 33 kHz, 20 °C) effects on the acidification capability of Lactobacillus plantarum A3 were achieved without observing greatly activated/inactivated strains growth, further confirmed by lactose fermentation performed by Streptococcus thermophilus and Lactobacillus bulgaricus. Lactic acid was the major contributing factor responsible for TS-induced acidification modifications corresponding to the potential fluctuations of CoA biosynthesis, fatty acid degradation and chain elongation pathways to TS prestress. Microscopy observations and quantitative extracellular substance assays showed palpable stress disturbance on microbes, but causing insignificant effects on product characteristics. This investigation demonstrated the potential of controlled sonication prestress strategies to achieve dual engineering effects on microbial metabolic behavior, for alleviating post-acidification problem or enhancing process efficiencies.

Effect of low-level ultrasound treatment on the production of L-leucine by Corynebacterium glutamicum in fed-batch culture

Various process intensification methods were proposed to improve the yield, quality, and safety of fermented products. Here, we report the enhancement of L-leucine production by Corynebacterium glutamicum CP using ultrasound-assisted fed-batch fermentation. Response surface methodology was employed to optimize the sonication conditions. At an ultrasonic power density of 94 W/L, frequency of 25 kHz, interval of 31 min, and duration of 37 s, C. glutamicum CP produced 52.89 g/L of L-leucine in 44 h, representing a 21.6% increase compared with the control. The production performance of L-leucine was also improved under ultrasonic treatment. Moreover, the effects of ultrasound treatment on the fermentation performance of L-leucine were studied in terms of cell morphology, cell membrane permeability, and enzyme activity. The results indicate that ultrasonication is an efficient method for the intensification of L-leucine production by C. glutamicum CP.

Ultrasound enhanced biosynthesis of L-theanine from L-glutamine and ethylamine by recombinant γ-glutamyltranspeptidase

A mutant library of the key amino acid residue site E387 in γ-glutamyltranspeptidase was constructed to screen the mutant enzymes with significantly improved thermal stability (E387Q). The reaction temperature of the mutant enzyme (E387Q) was 10℃ higher than that of the parent enzyme. Ultrasound-assisted synthesis of L-theanine by γ-glutamyltranspeptidase was investigated. The effects of ultrasonic power, reaction pH and substrate concentration on the enzymatic synthesis of L-theanine were studied by the response surface method. The results showed that the optimal process conditions are ultrasonic power of 100 W, reaction pH of 9, substrate L-glutamine concentration of 120 mmol/L, reaction temperature of 45℃, and L-theanine yield of 89.1%. The yield of L-theanine is 2.61 times higher than that obtained without ultrasound. Ultrasound can significantly promote the synthesis of L-theanine by γ-glutamyltranspeptidase.

Ultrasound enhanced production of mycelia and exopolysaccharide by Agaricus bitorquis (Quél.) Sacc. Chaidam

Agaricus bitorquis (Quél.) Sacc. Chaidam (ABSC), is a kind of rare edible macrofungi with a variety of biological ingredients, especially its polysaccharides. However, the low yield limits the popularity and promotion of rare edible macrofungi as well as its macrofungi polysaccharides. Hence, developing a positive and effective cultivation method is of great importance. Herein, an efficient ultrasonic (US) stimulation strategy was developed to improve mycelial growth and exopolysaccharides (EPS) biosynthesis from ABSC in submerged cultivation without light. A time design was employed to illustrate the effect of various process parameters including duration, starting point and times of US irradiation on ABSC productivity. 5 min US treatment for once upon ABSC after fermentation for 48 h could significantly improve EPS production and mycelia growth by above 26% and 15.03%, respectively. Furthermore, six times of 5 min US treatment could make the amount of EPS reach 218.78 ± 17.09 mg/g, which was 2.52-fold higher than that of the control. Moreover, the enhanced effect induced by US was further expounded by fermentation kinetics. Besides, the US treatment could increase mycelia permeability, change structure and reduce mycelial diameter to promote mass transfer, resulting in the improvement of EPS production and mycelia accumulation. The results demonstrated that the present proposed US intensification approach could be useful to boost up the fermentation of ABSC, which possibly applied to yield increase and fermentation product acquisition of macrofungi.