Identification and iterative combinatorial mutagenesis of a new naringinase-producing strain, Aspergillus tubingensis MN589840

Recent progress of atmospheric and room-temperature plasma as a new and promising mutagenesis technology

At present, atmospheric and room-temperature plasma (ARTP) is regarded as a new and powerful mutagenesis technology with the advantages of environment-friendliness, operation under mild conditions, and fast mutagenesis speed. Compared with traditional mutagenesis strategies, ARTP is used mainly to change the structure of microbial DNA, enzymes, and proteins through a series of physical, chemical, and electromagnetic effects with the organisms, leading to nucleotide breakage, conversion or inversion, causing various DNA damages, so as to screen out the microbial mutants with better biological characteristics. As a result, in recent years, ARTP mutagenesis and the combination of ARTP with traditional mutagenesis have been widely used in microbiology, showing great potential for application. In this review, the recent progress of ARTP mutagenesis in different application fields and bottlenecks of this technology are systematically summarized, with a view to providing a theoretical basis and technical support for better application. Finally, the outlook of ARTP mutagenesis is presented, and we identify the challenges in the field of microbial mutagenesis by ARTP.

Optimization of limonin invertase production by scaling up Aspergillus tubingensis UA13 fermentation to a 5-l scale

The enzymatic approach is a highly effective and the major scientific method to eliminating bitter components in citrus-derived products nowadays. Microbial production of limonin invertase stands out due to its pivotal role in the removal of the bitter substance, limonin. The optimization of fermentation parameters and the study of scale-up fermentation are imperative for product commercialization. In this study, we focused on optimizing stirring speed, fermentation temperature, and initial pH to enhance the growth and limonin invertase production by the Aspergillus tabin strain UA13 in a 5-l stirred-tank bioreactor. Our results revealed the following optimal parameters are: a stirring speed of 300 rpm, a fermentation temperature of 35°C and a pH 5.0. Under these optimized conditions, the limonin invertase activity reached its peak at 63.38 U ml-1, representing a 1.67-fold increase compared to the unoptimized conditions (38.10 U ml-1), while also reducing the fermentation duration by 12 h. Furthermore, our research demonstrated that limonin invertase effectively hydrolyze limonin in grapefruit juice, reducing its content from 13.28 to 2.14 μg ml-1, as determined by HPLC, resulting in a 6.21-fold reduction of the bitter substance.

Application of Atmospheric and Room-Temperature Plasma (ARTP) to Microbial Breeding

Atmospheric and room-temperature plasma (ARTP) is an efficient microbial mutagenesis method with broad application prospects. Compared to traditional methods, ARTP technology can more effectively induce DNA damage and generate stable mutant strains. It is characterized by its simplicity, cost-effectiveness, and avoidance of hazardous chemicals, presenting a vast potential for application. The ARTP technology is widely used in bacterial, fungal, and microalgal mutagenesis for increasing productivity and improving characteristics. In conclusion, ARTP technology holds significant promise in the field of microbial breeding. Through ARTP technology, we can create mutant strains with specific genetic traits and improved performance, thereby increasing yield, improving quality, and meeting market demands. The field of microbial breeding will witness further innovation and progress with continuous refinement and optimization of ARTP technology.

Genetic variation reveals the enhanced microbial hyaluronan biosynthesis via atmospheric and room temperature plasma

This study reveals the genetic and biochemical changes underlying the enhanced hyaluronan (HA) biosynthesis in Streptococcus zooepidemicus. After multiple rounds of atmospheric and room temperature plasma (ARTP) mutagenesis combined with novel bovine serum albumin/cetyltrimethylammonium bromide coupled high-throughput screening assay, the HA yield of the mutant was increased by 42.9% and reached 0.813 g L^-1 with a molecular weight of 0.54 × 10⁶ Da within 18 h by shaking flask culture. HA production was increased to 4.56 g L^-1 by batch culture in 5-L fermenter. Transcriptome sequencing exhibits that distinct mutants have similar genetic changes. Regulation in direction of metabolic flow into the HA biosynthesis, by enhancing genes responsible for the biosynthesis of HA including hasB, glmU and glmM, weaking downstream gene (nagA and nagB) of UDP-GlcNAc and significantly down-regulating transcription of wall-synthesizing genes, resulting in the accumulation of precursors (UDP-GlcA and UDP-GlcNAc) increased by 39.74% and 119.22%, respectively. These associated regulatory genes may provide control point for engineering of the efficient HA-producing cell factory.

Naringinase Biosynthesis by Aspergillus niger on an Optimized Medium Containing Red Grapefruit Albedo

This study aimed to develop a method of naringinase biosynthesis by Aspergillus niger KMS on an optimized culture medium. The concentration of the six medium components in shake flasks was optimized by the Box and Wilson factor gradient method. Naringinase's substrate, naringin, powdered albedo, flavedo, and red grapefruit segment membranes were used to stimulate naringinase biosynthesis. Rhamnose was chosen as the carbon source, while the nitrogen source was yeast extract and sodium nitrate. Naringinase biosynthesis was most favorable in the culture medium with the following composition (g 100 mL): 3.332-NaNO₃; 3.427-yeast extract; 0.184-KH₂PO₄; 0.855-red grapefruit albedo; 0.168-naringin; 2.789-rhamnose. The obtained Aspergillus niger KMS culture fluid was concentrated, thereby precipitating the protein. As a result, a naringinase preparation with high activity, equal to 816 µmol × min^-1 × g^-1, was obtained.

Improvement of macrolactins production by the genetic adaptation of Bacillus siamensis A72 to saline stress via adaptive laboratory evolution

BACKGROUND

Macrolactins, a type of macrolide antibiotic, are toxic to the producer strains. As such, its level is usually maintained below the lethal concentration during the fermentation process. To improve the production of macrolactins, we applied adaptive laboratory evolution technology to engineer a saline-resistant mutant strain. The hypothesis that strains with saline resistance show improved macrolactins production was investigated.

RESULTS

Using saline stress as a selective pressure, we engineered a mutant strain with saline resistance coupled with enhanced macrolactins production within 60 days using a self-made device. As compared with the parental strain, the evolved strain produced macrolactins with 11.93% improvement in non-saline stress fermentation medium containing 50 g/L glucose, when the glucose concentration increased to 70 g/L, the evolved strain produced macrolactins with 71.04% improvement. RNA sequencing and metabolomics results revealed that amino acid metabolism was involved in the production of macrolactins in the evolved strain. Furthermore, genome sequencing of the evolved strain revealed a candidate mutation, hisD^D41Y, that was causal for the improved MLNs production, it was 3.42 times higher than the control in the overexpression hisD^D41Y strain. Results revealed that saline resistance protected the producer strain from feedback inhibition of end-product (macrolide antibiotic), resulting in enhanced MLNs production.

CONCLUSIONS

In the present work, we successfully engineered a mutant strain with enhanced macrolactins production by adaptive laboratory evolution using saline stress as a selective pressure. Based on physiological, transcriptomic and genetic analysis, amino acid metabolism was found to benefit macrolactins production improvement. Our strategy might be applicable to improve the production of other kinds of macrolide antibiotics and other toxic compounds. The identification of the hisD mutation will allow for the deduction of metabolic engineering strategies in future research.

Optimization of process parameters for naringinase production by Aspergillus tubingensis UA13 and pilot scale-up study

To improve the naringinase production of Aspergillus tubingensis UA13, shorten the fermentation period, and verify its industrial application value, naringinase production conditions were optimized, and 5 L scale-up study in stirred tank bioreactor was carried out. Parameters, including carbon, nitrogen sources and inducer, optimal seed age, inoculum amount, temperature and pH, were adjusted and optimized in shaking flask. Keeping pH at the optimal value 6 in bioreactor, dissolved oxygen was monitored during the fermentation and the optimal stirring rate was investigated. In 5 L scale-up study, the highest naringinase activity was 72.62 U/mL, which was 1.75 times higher than that (41.52 U/mL) in shaking flask and the fermentation period was shortened by 24 h.