A plasma jet, driven by an active helium atom supplied with an atmospheric and room temperature plasma (ARTP) biological breeding system, was used as a novel method to breed L-arginine high-yielding strains. A mutant with resistance to L-homoarginine and 8-azaguaine, ARG 3-15 (L-HA(r), 8-AG(r), L-His(-)), was screened after several rounds of screening. The L-arginine production of these mutants was more than that of the original strain, increased by 43.79% for ARG 3-15. Moreover, N-acetyl-L-glutamate synthase activity of these mutants was also increased. After a series of passages, the hereditary properties of these mutants were found to be stable. Interestingly, beet molasses was utilized in a co-feeding fermentation and benefited to increase the productivity by 5.88%. Moreover, the fermentation with 1.0 g/L betaine could produce 9.33% more L-arginine than without betaine. In fed-batch fermentation, C. glutamicum ARG 3-15 began to produce L-arginine at the initial of logarithmic phase, and continuously increased over 24 hr to a final titer of 45.36 ± 0.42 g/L. The L-arginine productivity was 0.571 g/L/hr and the conversion of glucose (α) was 32.4% after 96 hr. These results indicated that C. glutamicum ARG 3-15 is a promising industrial producer.
This article focuses on the effects of glycine betaine on preventing caramelization, and increasing DCW and L-lysine production. The additional glycine betaine not only decreased the browning intensity (decreased 4 times), and the concentrations of 5-hydroxymethylfurfural (decreased 7.8 times) and furfural (decreased 12 times), but also increased the availability of glucose (increased 17.5%) for L-lysine production. The DCW and L-lysine production were increased by adding no more than 20 mM glycine betaine, whereas the DCW and L-lysine production were decreased with the reduction of pH values, although pH had a better response to prevent caramelization than did glycine betaine. For L-lysine production, the highest increase (40%) was observed on the media with 20 mM glycine betaine. The crucial enzymes in glycolysis and L-lysine biosynthesis pathway were investigated. The results indicated that additional glycine betaine increases the activity of enzymes in glycolysis, in contrast to the effect of pH. All the results indicated that glycine betaine can be used to prevent caramelization and increase the L-lysine production. By applying this strategy, glucose would not be have to be separated from the culture media during autoclaving so that factories can save production costs and shorten the fermentation period.
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