Improving of lipid productivity of the oleaginous microalgae Chlorella pyrenoidosa via atmospheric and room temperature plasma (ARTP)

Research Progress of ARTP Mutagenesis Technology Based on Citespace Visualization Analysis

Atmospheric and room temperature plasma (ARTP) mutagenesis technology has been developed rapidly in recent years because of its simple operation, safety, environmental friendliness, high mutation rate, and large mutation library capacity. It has been widely used in traditional fields such as food, agriculture, and medicine, and has been gradually applied in emerging fields such as environmental remediation, bioenergy, and microalgae utilization. In this paper, the Web of Science Core Collection (WOSCC) was used as the data source, and the keywords and core literature of ARTP mutagenesis technology were plotted by citespace software, and the research progress and research hotspots of ARTP mutagenesis technology were analyzed. Through citespace visualization analysis, it is concluded that the country with the largest number of studies is China, the institution with the largest number of studies is Jiangnan University, and the author of the most published papers is Jiangnan University. Through keyword analysis, it is concluded that the most widely used ARTP mutagenesis technology is fermentation-related majors, mainly for biosynthesis and microbial research at the molecular level. Among them, the most widely used microorganisms are Escherichia coli and Saccharomyces cerevisiae.

Engineering Yarrowia lipolytica for Enhanced Gastrodin Production via High-Throughput Screening and Transcriptomics-Guided Optimization

Gastrodin, the principal bioactive component of the renowned herb Gastrodia elata, is extensively utilized in medicinal drugs and nutraceuticals. This study seeks to enhance microbial production of gastrodin through high-throughput screening (HTS) and transcriptomics-guided optimization. Initially, atmospheric pressure and room temperature plasma (ARTP)-mediated mutagenesis were employed to develop a library of mutant strains. Furthermore, a transcription factor-based biosensor and a high-throughput solid-phase extraction mass spectrometry (HP-SPE-MS) were evaluated to establish an HTS method for gastrodin. Consequently, mutant strain MT8 was isolated, producing 9.8 g/L of gastrodin in YPD medium, which represents a 55.6% increase compared to the control strain. Next, key genes identified via transcriptomics were overexpressed in strain MT8, with the overexpression of gene YALI2E01737g, a gene involved in the synthesis of aromatic amino acids, significantly enhancing gastrodin production to reach 10.1 g/L. In addition, fermentation process optimization further improved gastrodin titer up to 13.1 g/L in shaking flasks. This study demonstrated the utility of HTS techniques to enhance gastrodin production and paved the way for its future industrial application.

Mutagenesis and Characterization of Hyaluronidase Production by a New Isolate of Citrobacter portucalensis

Hyaluronidase, a glycosidase, has the capacity to degrade hyaluronic acid. It is employed within both the medical and cosmetic domains and represents an efficacious methodology for the preparation of hyaluronic acid oligosaccharides. The increase in the activity of hyaluronidase has been demonstrated to be an effective method of promoting the production of low molecular weight hyaluronic acid. In the present study, we identified the active hyaluronan-degrading strain Citrobacter portucalensis HA23 from a sodium hyaluronate solution kept at natural room temperature, with independent intellectual property rights. To enhance the strain's enzyme-producing capacity, we employed atmospheric and room temperature plasma (ARTP) technology to select and breed the mutant HA2301 with augmented enzyme-producing capabilities. The enzyme activity of the mutant strain HA2301 was observed to have increased by 58.82% in comparison to that of HA23. It was established that pH 5.5, 37 °C, and 250 rpm represented the optimal culture conditions, with the enzyme activity of the strain reaching 25808 U mL-1 in a medium comprising a carbon source of yeast flour and a nitrogen source of peanut cake flour. The reaction solution of the enzyme with sodium hyaluronate was characterized, with the main products identified as HA2 and HA4. The present text provides a reference for its industrial application.

Rational High-Throughput System for Screening Emodin High-Yielding Mutant from Marine Strains of Aspergillus flavipes HN4-13

Emodin is an anthraquinone compound known for its diverse biological activities, including anti-tumor and anti-inflammatory effects, making it highly applicable in the fields of biology and medicine. The production of emodin using microorganisms represents a sustainable and environmentally friendly approach. A marine-derived Aspergillus flavipes HN4-13 was found to produce emodin, but the yield was too low for industrial production. To develop a high-yielding emodin-producing strain, we established the high-through detection and screening methods of alkaline coloration and deep-well plant culture, enabling the effective selection of high-yielding strains. Following ARTP mutagenesis of the wild strain A. flavipes HN4-13, the resulting mutant strain, M1440, exhibited an increased emodin yield of 124.6 ± 4.95 mg/L. Furthermore, the production of the emodin was enhanced by the exogenous addition of metal ions Mn2+ to the medium. Specifically, the addition of 3 mM Mn2+ resulted in a 133.2% increase in emodin production, with the highest yield reaching 178.6 ± 7.80 mg/L.

Applications of low-temperature plasma technology in microalgae cultivation and mutant breeding: A comprehensive review

Low-temperature plasma (LTP) has gained significant attention recently due to its unique properties and potentially wide applications in agriculture, medicine, and food industry. Microalgae have become important to human life since they provide raw materials and bioactive products to industries. This review especially examines how LTP technology can be utilized to enhance microalgae growth and production of various metabolites and bioactive compounds such as astaxanthin, biofuel, lipid, proteins, and polysaccharides through mutagenesis and/or stimulation. Also, this review suggests that LTP may be combined with multi-omics tools such as proteomics, transcriptome, metabolomics and advanced methods such as single-cell analysis techniques to provide a promising strategy for acquiring desirable strains in algal mutant breeding and for enhancing the production of bioactive compounds in the microalgae. By shedding light on the benefits and applications of LTP, we hope to inspire new solutions to the challenges of commercial-scale microalgae development.

Transcriptomics and metabonomics reveal molecular mechanisms promoting lipid production in Haematococcus pluvialis co-mutated by atmospheric and room temperature plasma with ethanol

Atmospheric and room temperature plasma mutation and co-mutation with ethanol were employed to generate Haematococcus pluvialis mutants AV3 and AV8. These mutants were screened using multiple indices of chlorophyll fluorescence, quantum yield, lethality, growth rate, dry cell weight, and lipid content. Compared to the wild strain, the mutants demonstrated genetic stability (*p > 0.05) over three cultivation periods, with biomass, lipid content, and growth rate increasing by over 16 %, 55 %, and 45 %, respectively. Lipid accumulation was correlated with higher activities of key lipid biosynthesis enzymes, acetyl-CoA carboxylase, and diacylglycerol acyltransferases. Transcriptomic and metabolomic analyses revealed differentially expressed genes and differential metabolites, with significant changes in glutathione, arginine and Pyruvate metabolism pathways. This study provides new insights into the molecular mechanisms behind enhanced lipid synthesis and highlights the potential of plasma mutation for improving lipid production in microalgae, offering a promising avenue for biofuel production.

Engineering industrial yeast for improved tolerance and robustness

As an important cell factory, industrial yeast has been widely used for the production of compounds ranging from bulk chemicals to complex natural products. However, various adverse conditions including toxic products, extreme pH, and hyperosmosis etc., severely restrict microbial growth and metabolic performance, limiting the fermentation efficiency and diminishing its competitiveness. Therefore, enhancing the tolerance and robustness of yeasts is critical to ensure reliable and sustainable production of metabolites in complex industrial production processes. In this review, we provide a comprehensive review of various strategies for improving the tolerance of yeast cells, including random mutagenesis, system metabolic engineering, and material-mediated immobilization cell technology. It is expected that this review will provide a new perspective to realize the response and intelligent regulation of yeast cells to environmental stresses.

Enhancement of Digestive Enzyme Activity in Enterococcus faecalis Using ARTP Mutagenesis

Enterococcus faecalis is used as a probiotic in animal and human food supplements. Atmospheric and room temperature plasma (ARTP) systems have frequently been used to screen for effective mutant probiotics. In this study, E. faecalis was treated with ARTP, and high-yielding digestive enzyme mutant strains were obtained by measuring the activities of α-amylase, lipase, and neutral protease. A total of 833 mutant strains were obtained after 40-60 s of ARTP treatment, and after screening for digestive enzyme activity, EF-448, EF-798, and EF-804 were obtained. The three strains demonstrated an 180% increase in α-amylase activity, a 30% increase in lipase activity, and a more than 40% increase in neutral protease activity. Furthermore, the enzyme activities remained stable after nine generations. In addition, the strains exhibited high auto-aggregation capacity (over 91%) and high cell hydrophobicity (over 93%). After exposure to simulated intestinal fluid for 6 h, the survival rates of EF-448 and EF-798 were 85.71% and 82.32%, respectively. Moreover, the three mutant strains retained antioxidant capacity and DPPH free radical scavenging ability, and there was no hemolysis. A safety experiment has shown that there is no mortality of Macrobrachium rosenbergii within 14 days after receiving injections of mutant strains at different concentrations. In conclusion, this study obtained three mutant strains with high production of digestive enzymes and stable inheritance through ARTP mutagenesis of E. faecalis, providing an efficient microbial resource.

Selection and Genetic Analysis of High Polysaccharide-Producing Mutants in Inonotus obliquus

Inonotus obliquus, a medicinal fungus, has garnered significant attention in scientific research and medical applications. In this study, protoplasts of the I. obliquus HS819 strain were prepared using an enzymatic method and achieved a regeneration rate of 5.83%. To enhance polysaccharide production of I. obliquus HS819, atmospheric and room temperature plasma (ARTP) technology was employed for mutagenesis of the protoplasts. Through liquid fermentation, 32 mutant strains exhibiting diverse characteristics in morphology, color of the fermentation broth, mycelial pellet size, and biomass were screened. Secondary screening identified mutant strain A27, which showed a significant increase in polysaccharide production up to 1.67 g/L and a mycelial dry weight of 17.6 g/L, representing 137.67% and 15% increases compared to the HS819 strain, respectively. Furthermore, the fermentation period was reduced by 2 days, and subsequent subculture cultivation demonstrated stable polysaccharide production and mycelial dry weight. The genome resequencing analysis of the HS819 strain and mutant strain A27 revealed 3790 InDel sites and mutations affecting 612 functional genes associated with polysaccharide synthesis. We predict that our findings will be helpful for high polysaccharide production through genetic engineering of I. obliquus.

Optimizing mycelial protein yield in Pleurotus djamor via ARTP mutagenesis and hybridization strategies

With the world's population rapidly increasing, the demand for high-quality protein is on the rise. Edible fungi breeding technology stands as a crucial avenue to obtain strains with high yield, high-quality protein, and robust stress resistance. To address the protein supply gap, Atmospheric and Room Temperature Plasma (ARTP) mutagenesis, and spore hybridization techniques were employed to enhance Pleurotus djamor mycelium protein production. Beginning with the original strain Pleurotus djamor JD-1, ARTP was utilized to mutate spore suspension. The optimal treatment time for Pleurotus djamor spores, determined to achieve optimal mortality, was 240 s. Through primary and secondary screenings, 6 mutant strains out of 39 were selected, exhibiting improved protein yield and growth rates compared to the original strain. Among these mutagenic strains, 240S-4 showcased the highest performance, with a mycelial growth rate of 9.5±0.71 mm/d, a biomass of 21.45±0.54 g/L, a protein content of 28.75±0.92%, and a remarkable protein promotion rate of 128.03±7.29%. Additionally, employing spore hybridization and breeding, 7 single-nuclei strains were selected for pin-two hybridization, resulting in 21 hybrid strains. The biomass and protein content of 9 hybrid strains surpassed those of the original strains. One hybrid strain, H-5, exhibited remarkable mycelial protein production, boasting a mycelial growth rate of 26.5±0.7 mm/d, a biomass of 21.70±0.46 g/L, a protein content of 28.44±0.22%, and a protein promotion rate of 128.02±1.73%. Notably, both strains demonstrated about a 28% higher mycelial protein yield than the original strains, indicating comparable effectiveness between hybrid breeding and mutagenesis breeding. Finally, we analyzed the original and selected strains by molecular biological identification, which further proved the effectiveness of the breeding method. These findings present novel insights and serve as a reference for enhancing edible fungi breeding, offering promising avenues to meet the escalating protein demand.

Enhancing citric acid tolerance of Acetobacter tropicalis using chemical and physical mutagenesis and adaptive evolution to improve the quality of lemon fruit vinegar

The high concentration of citric acid in lemons limits the production of lemon fruit vinegar because it inhibits the metabolism of acetic acid bacteria and reduces the utilization of raw materials. This study aimed to enhance the citric acid tolerance of Acetobacter tropicalis by using complex mutagenesis and adaptive laboratory evolution (ALE) and improving the quality of lemon fruit vinegar. After mutagenesis and ALE, A. tropicalis JY-135 grew well under 40 g/L citric acid, and it showed high physiological activity and excellent fermentation performance under high concentrations of citric acid. The survival rate and ATP content of JY-135 were 15.27 and 9.30 times higher than that of the original strain J-2736. In the fermentation of lemon fruit vinegar, the acid production and the number of aroma-active compounds were 1.61-fold and 2.17-fold than J-2736. In addition, we found that citric acid tolerance of JY-135 is related to the respiratory electron-transport chain and the tricarboxylic acid (TCA) cycle. This work is of great significance for the production of high-quality lemon fruit vinegar and the enrichment of seed resources of acetic acid bacteria.

Mutation breeding of high-stress resistant strains for succinic acid production from corn straw

The production of succinic acid from corn stover is a promising and sustainable route; however, during the pretreatment stage, byproducts such as organic acids, furan-based compounds, and phenolic compounds generated from corn stover inhibit the microbial fermentation process. Selecting strains that are resistant to stress and utilizing nondetoxified corn stover hydrolysate as a feedstock for succinic acid production could be effective. In this study, A. succinogenes CICC11014 was selected as the original strain, and the stress-resistant strain A. succinogenes M4 was obtained by atmospheric and room temperature plasma (ARTP) mutagenesis and further screening. Compared to the original strain, A. succinogenes M4 exhibited a twofold increase in stress resistance and a 113% increase in succinic acid production when hydrolysate was used as the substrate. By conducting whole-genome resequencing of A. succinogenes M4 and comparing it with the original strain, four nonsynonymous gene mutations and two upstream regions with base losses were identified. KEY POINTS: • A high-stress-resistant strain A. succinogenes M4 was obtained by ARTP mutation •  The production of succinic acid increased by 113% • The mutated genes of A. succinogenes M4 were detected and analyzed.

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.

Enhancing (2S)-naringenin production in Saccharomyces cerevisiae by high-throughput screening method based on ARTP mutagenesis

(2S)-Naringenin, a dihydro-flavonoid, serves as a crucial precursor for flavonoid synthesis due to its extensive medicinal values and physiological functions. A pathway for the synthesis of (2S)-naringenin from glucose has previously been constructed in Saccharomyces cerevisiae through metabolic engineering. However, this synthetic pathway of (2S)-naringenin is lengthy, and the genes involved in the competitive pathway remain unknown, posing challenges in significantly enhancing (2S)-naringenin production through metabolic modification. To address this issue, a novel high-throughput screening (HTS) method based on color reaction combined with a random mutagenesis method called atmospheric room temperature plasma (ARTP), was established in this study. Through this approach, a mutant (B7-D9) with a higher titer of (2S)-naringenin was obtained from 9600 mutants. Notably, the titer was enhanced by 52.3% and 19.8% in shake flask and 5 L bioreactor respectively. This study demonstrates the successful establishment of an efficient HTS method that can be applied to screen for high-titer producers of (2S)-naringenin, thereby greatly improving screening efficiency and providing new insights and solutions for similar product screenings.

Enhancing docosahexaenoic acid production in Aurantiochytrium species using atmospheric and room temperature plasma mutagenesis and comprehensive multi-omics analysis

Aurantiochytrium sp. belongs to marine heterotrophic single-cell protist, which is an important decomposer in marine ecosystem. Aurantiochytrium sp. has gained notoriety because of its ability to accumulate high-value docosahexaenoic acid (DHA), but the key factors of DHA synthesis were unclear at present. In this study, Atmospheric and Room Temperature Plasma technology was applied to the mutagenic breeding of Aurantiochytrium sp., and transcriptomics and proteomics were adopted to analyze the DHA-biosynthesis mechanism. According to the growth and DHA accumulation profiles, the mutant strain Aurantiochytrium sp. R2A35 was selected. The DHA content in total lipids was greatly improved from 49.39 % of the wild strain R2 to 63.69 % of the mutant strain. Moreover, the DHA content in the biomass of Aurantiochytrium sp. R2A35 as 39.72 % was the highest DHA productivity reported so far. The differentially expressed genes distinguished from transcriptome and the TMT-identified differential proteins distinguished from proteome confirmed that the expression of acetyl-CoA carboxylase and ketoacyl reductase was up-regulated by 4.78-fold and 6.95-fold, respectively and the fatty acid synthase was concurrently down-regulated by 2.79-fold, so that more precursor was transported to the polyketide synthase pathway, thereby increasing the DHA yield in Aurantiochytrium sp. R2A35. This research would provide reference for the DHA metabolism process and contribute to the understanding of the decomposer - Aurantiochytrium sp. in marine ecosystems.

Synchronous enhancement of astaxanthin and lipid accumulation in Haematococcus lacustris through co-mutation of ethanol and atmospheric and room temperature plasma: Exploration of characteristics and underlying mechanisms

Haematococcus lacustris is a precious algal species renowned for its ability to simultaneous production of astaxanthin and lipid. However, its slow growth rate necessitates the development of appropriate mutagenesis methodologies to effectively enhance its synchronous production of both astaxanthin and lipid. This study introduced the co-mutation of Atmospheric and Room Temperature Plasma (ARTP) and ethanol. The performance and preliminary mechanisms underlying the combined accumulation of astaxanthin and lipid in H. lacustris under both mutations by ARTP and ethanol were comparatively analyzed. Combined astaxanthin and lipid contents relative to total cell mass in the 110-2 strain reached 54.4%, surpassing that of strain 0-3 and the control by 17.0% and 47.6% respectively. Transcriptome level analysis revealed how both ethanol and ARTP induction promote the expressions of carotenoid and lipid synthesis genes and related enzymatic activities. Upregulation of genes associated with cell activity contributed to lipid and astaxanthin metabolism in multi pathways.

Breeding a novel chlorophyll-deficient mutant of Auxenochlorella pyrenoidosa for high-quality protein production by atmospheric room temperature plasma mutagenesis

In the present work, a novel chlorophyll-deficient mutant of Auxenochlorella pyrenoidosa named A4-1 was generated by atmospheric room temperature plasma (ARTP) mutagenesis. Compared to the green wild type (WT) strain, the A4-1 mutant cultured in the dark displayed yellow colour with a 118-fold decrease of chlorophyll a and no detected chlorophyll b. Higher contents of protein (44.22 % DW), total amino acids (AAs, 34.84 % DW) and essential AAs (17.50 % DW) were also achieved, showing 31 %, 22 % and 30 % increases compared to the WT, respectively (p < 0.05). Metabolite profile analysis revealed that the chlorophyll biosynthesis pathway in the A4-1 mutant was probably inhibited in the dark, while more carbon skeletons might be utilized for de novo AAs synthesis. These results demonstrated that the A4-1 mutant not only has extremely low chlorophyll content, but also has higher protein content, making it a very promising candidate to produce microalgal protein for future foods.

Construction of a Compact Array of Microplasma Jet Devices and Its Application for Random Mutagenesis of Rhodosporidium toruloides

A small and efficient DNA mutation-inducing machine was constructed with an array of microplasma jet devices (7 × 1) that can be operated at atmospheric pressure for microbial mutagenesis. Using this machine, we report disruption of a plasmid DNA and generation of mutants of an oleaginous yeast Rhodosporidium toruloides. Specifically, a compact-sized microplasma channel (25 × 20 × 2 mm3) capable of generating an electron density of greater than 1013 cm-3 was constructed to produce reactive species (N2*, N2+, O, OH, and Hα) under helium atmospheric conditions to induce DNA mutagenesis. The length of microplasma channels in the device played a critical role in augmenting both the volume of plasma and the concentration of reactive species. First, we confirmed that microplasma treatment can linearize a plasmid by creating nicks in vitro. Second, we treated R. toruloides cells with a jet device containing 7 microchannels for 5 min; 94.8% of the treated cells were killed, and 0.44% of surviving cells showed different colony colors as compared to their parental colony. Microplasma-based DNA mutation is energy-efficient and can be a safe alternative for inducing mutations compared to conventional methods using toxic mutagens. This compact and scalable device is amenable for industrial strain improvement involving large-scale mutagenesis.

Isolation and identification of high-yielding alkaline phosphatase strain: a novel mutagenesis technique and optimization of fermentation conditions

Isolating and screening enzyme-producing strains from microorganisms and the commercial production of ALPs from microorganisms are of increasing interest. In this work, isolation and identification of high-yielding alkaline phosphatase strain were carried out using atmospheric and room temperature plasma mutagenesis (ARTP) for optimization of fermentation conditions. A strain of alkaline phosphatase-producing bacteria was screened from soil and identified by 16S rRNA gene sequencing as Bacillus amyloliquefaciens and named S-1. This strain had an alkaline phosphatase activity of 2594.73 U/L. Later, mutagenesis breeding of the alkaline phosphatase-producing S-1 strain was conducted using (ARTP), from which a higher alkaline phosphatase-producing positive mutant strain S-52 was screened. A central combination of five factors, including corn starch, yeast extract, metal ions, fermentation temperature and inoculum ratio, was then used to influence the activity of alkaline phosphatase. Results from the response surface methodology showed that the maximum enzyme activity of alkaline phosphatase was 12,110.6 U/L at corn starch, yeast extract and magnesium ions concentrations of 17.48 g/L, 18.052 g/L and 0.744 g/L, respectively; fermentation temperature of 37.192 °C; and inoculation ratio of 5.59%. This study is important for further exploring ARTP mutagenesis in B. amyloliquefaciens and the commercialization of ALPs.

Bioleaching of heavy metals from metal tailings utilizing bacteria and fungi: Mechanisms, strengthen measures, and development prospect

Recovering key metals from secondary sources is an indispensable strategy for preventing metal shortages and reducing the risk of toxic releases into the environment. Metal mineral resources continue to be depleted and the global supply chain will face metal scarcity. The use of microorganisms for metal transformation plays an important role in the bioremediation of secondary resources. It shows great potential for development due to its compatibility with the environment and possible cost effectiveness. The results of the study show that the influence of bioleaching processes and effects are mainly analyzed from microorganisms, mineral properties and leaching environmental conditions. In this review article, we elucidate light on the role and mechanisms of fungi and bacteria involved in extracting different metals from tailings, including acidolysis, complexolysis, redoxolysis, and bioaccumulation. Key process parameters that affect the efficiency based bioleaching are discussed, providing referenceable pathways to improve leaching efficiency. The investigation concludes that exploitation of the functional genetic role of microorganisms and their optimal growth conditions can achieve efficient leaching of metals. It was found that the improvement of microbial performance was achieved at the level of mutagenesis breeding, mixed culture microorganisms, and genetics. Moreover, control of leaching system parameters and removal of passivation films can be achieved by adding biochar and surfactants in the leaching system as an effective means to improve tailings leaching. Knowledge about cells with minerals and their detailed interactions at the molecular level is still relatively scarce and the field could be deepened and this area needs to be further explored in the future. The challenges and the key issues associated with the bioleaching technology development are elaborated as a green and effective bioremediation strategy for the environment and prospects for imminent are also highlighted.

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.

Enhancing Protease and Amylase Activities in Bacillus licheniformis XS-4 for Traditional Soy Sauce Fermentation Using ARTP Mutagenesis

This study was conducted to increase the enzymatic activity of Bacillus licheniformis XS-4, which was isolated from the traditional fermented mash of Xianshi soy sauce. The mutation was induced by atmospheric and room-temperature plasma (ARTP), and a mutant strain, mut80, was obtained. mut80 exhibited significant increases in protease and amylase activity by 90.54% and 143.10%, respectively, and the enhanced enzymatic activities were stably maintained after 20 consecutive incubations. Re-sequencing analysis of mut80 revealed that the mutation sites were located in 1518447(AT-T) and 4253106(G-A) in its genome, which was involved in the metabolic pathways of amino acids. The expression of the protease synthetic gene (aprX) increased 1.54 times, while that of the amylase gene (amyA) increased 11.26 times, as confirmed via RT-qPCR. Using ARTP mutagenesis, the present study proposes a highly efficient microbial resource with enhanced protease and amylase activity provided by B. licheniformis, which can potentially be used to improve the efficiency of traditional soy sauce fermentation.

Breeding of New Strains of Gracilariopsis lemaneiformis with High Agar Content by ARTP Mutagenesis and High Osmotic Pressure Screening

ARTP (atmospheric and room temperature plasma mutagenesis) mutagenesis was tried on G. lemaneiformis, and mutagenesis conditions were confirmed. An osmotic pressure screening program was established. Mutants were identified and characterized of relevant physiological traits. The aim of the study is to try to use ARTP mutagenesis and osmotic pressure screening for the breeding of high-agar G. lemaneiformis. Treatment time of 46 s was found to be an optimal mutagenesis time. The mutagenized spores were initially screened with 58‰ salinity artificial seawater, and then, the surviving spores were screened twice with 60‰ salinity artificial seawater in their vertical growth phase and branch growth phase, respectively. Four fast-growing and hypertonic resistance gametophytes were selected. The actual photosynthetic efficiency [Y(PSII)], photochemical quenching (qL), and non-photochemical quenching (NPQ) of four mutants were measured. The values of Y(PSII) and qL of HAGL-X3 and HAGL-X5 were higher than those of the control in the early stage of salt stress. NPQs of HAGL-X3 and HAGL-X5 were higher than control in most of the times. The growth rates of the four mutants were higher than that of the control. HAGL-X4 was the highest. The agar content was measured; HAGL-X5 displayed the highest agar content among the tested strains. HAGL-X5 was more in line with expectations, because of its high agar content and good hypertonic resistance. In this study, the mutant of G. lemaneiformis with high agar content was obtained by the procedure, which provided a certain reference for the selection of G. lemaneiformis strains with high agar content.

Screening of microalgae species and evaluation of algal-lipid stimulation strategies for biodiesel production

Microalgae is considered an alternative source for biodiesel production producing renewable, sustainable and carbon-neutral energy. Microalgae property changes among species, which determines the efficiency of biodiesel production. Besides the lipid content evaluation, multi-principles (including high lipid productivity, high biomass yield, pollution resistance and desired fatty acid, etc.) for superior oil-producing species screening was proposed in this review and three microalgae species (Chlorella vulgaris, Scenedesmus obliquus and Mychonastes afer) with high bio-lipid producing prospect were screened out based on big data digging and analysis. The multilateral strategies for algal-lipid stimulating were also compared, among which, nutrient restriction, temperature control, heterotrophy and chemicals addition showed high potential in enhancing lipid accumulation; while electromagnetic field showed little effect. Interestingly, it was found that the lipid accumulation was more sensitive to nitrogen (N)-limitation other than phosphorus (P). Nutrient restriction, salinity stress etc. enhanced lipid accumulation by creating a stressed environment. Hence, optimum conditions (e.g. N:15-35 mg/L and P:4-16 mg/L) should be set to balance the lipid accumulation and biomass growth, and further guarantee the algal-lipid productivity. Otherwise, two-step cultivation could be applied during all the stressed stimulation. Different from lab study, effectiveness, operability and economy should be all considered for stimulation strategy selection. Nutrient restriction, temperature control and heterotrophy were highly feasible after the multidimensional evaluation.

ARTP mutagenesis of phospholipase D-producing strain Streptomyces hiroshimensis SK43.001, and its enzymatic properties

Phospholipase D (PLD) is a group of enzymes that act on phospholipid molecules, which is widely used in the fields of food and medicine. PLD is extracted from animals and plants with low transesterification activity and high price. Therefore, it is benefit to screen an efficient PLD producing strain from microorganisms. A highly productive strain of PLD with transphosphatidylation activity, named Streptomyces hiroshimensis SK43.001, was screened from soil in our laboratory and mutated using atmospheric room temperature plasma (ARTP). A mutant strain SK43.001-11 with the highest enzyme activity and superior genetic stability was obtained, and its fermentation enzyme activity was 5.3 U/mL, which was 82% increased comparing to wild strain. The purification of PLD showed that the specific enzyme activity increased to 49.48 U/mg, which was 54.37-fold higher than that of the crude enzyme, with a recovery of 32.31%. In addition, enzymatic properties of PLD have revealed that the optimal pH and temperature were 7.0 and 60 °C, respectively. Metal ion Mg²⁺ and surfactant Triton X-100 made the enzymatic activity increased by 16% and 100%, respectively. The reaction kinetic parameters showed that the mutant PLD had higher affinity for the substrate of egg PC and better catalytic efficiency with K _m, V _max and K _cat of 30.20 mmol/L, 99.70 μmol/min and 76.33 s^-1, respectively. This study may provide important inspiration for obtaining high enzyme activity strains with PLD.

Enhancing biomass and lipid productivity of a green microalga Parachlorella kessleri for biodiesel production using rapid mutation of atmospheric and room temperature plasma

BACKGROUND

Microalgae, with their high adaptability to various stress conditions and rapid growth, are considered excellent biomass resources for lipid production and biodiesel feedstocks. However, lipid yield and productivity of the natural strains are common bottlenecks in their large-scale use for lipid production, which can be overcome by evolving new strains using conventional and advanced mutagenic techniques. It is challenging to generate microalgae strains capable of high lipid synthesis through natural selection. As a result, random mutagenesis is currently considered a viable option in many scenarios. The objective of this study was to explore atmospheric and room temperature plasma (ARTP) as a random mutagenesis technique to obtain high lipid-accumulating mutants of a green microalga for improved biodiesel production.

RESULTS

A green microalgal species was isolated from the Chinese Yellow Sea and identified as Parachlorella kessleri (OM758328). The isolated microalga was subsequently mutated by ARTP to obtain high lipid-accumulating mutants. Based on the growth rate and lipid content, 5 mutants (named M1, M2, M4, M5, and M8) were selected from 15 pre-selected mutants. These five mutants varied in their growth rate from 0.33 to 0.68 day-1, with the lipid content varying between 0.25 g/L in M2 to 0.30 g/L in M8 at 10th day of cultivation. Among the mutants, M8 showed the maximum biomass productivity (0.046 g/L/day) and lipid productivity (20.19 mg/L/day), which were 75% and 44% higher than the wild strain, respectively. The triglyceride (TAG) content of M8 was found to be 0.56 g/L at 16th day of cultivation, which was 1.77-fold higher than that of the wild strain. Furthermore, M8 had the highest saturated fatty acids (C16-18) with the lowermost polyunsaturated fatty acid content, which are favorable properties of a biodiesel feedstock according to international standards.

CONCLUSION

The mutant strain of P. kessleri developed by the ARTP technique exhibited significant improvements in biomass productivity, lipid content, and biodiesel quality. Therefore, the biomass of this mutant microalga could be a potential feedstock for biodiesel production.

Mutagenesis of high-efficiency heterotrophic nitrifying-aerobic denitrifying bacterium Rhodococcus sp. strain CPZ 24

Breeding high-efficiency heterotrophic nitrifying-aerobic denitrifying (SND) bacteria is important for the removal of biological nitrogen in wastewater treatment. In this study, a high-efficiency SND mutant strain, ΔRhodococcus sp. CPZ 24, was obtained by ultraviolet-diethyl sulfate compound mutagenesis. The maximum nitrification and denitrification rates were 3.77 and 1.37 mg·L^-1·h^-1, respectively 30.30 % and 17.10 % higher than those of wild bacteria. Biolog technology and network model analysis revealed that ΔCPZ 24 significantly improved the utilisation ability and metabolic activity of organic carbon sources. Furthermore, the expression levels of the nitrogen removal function genes nxrA, nosZ, amoA, and norB in strain ΔCPZ 24 increased significantly. In actual sewage, mutant bacteria ΔCPZ 24 have a 95.05 % ammonia-nitrogen degradation rate and a 96.67 % nitrate-nitrogen degradation rate. These results suggested that UV-DES compound mutation was a successful strategy to improve the nitrogen removal performance of SND bacteria in wastewater treatment.

Strategic Development of Aurantiochytrium sp. Mutants With Superior Oxidative Stress Tolerance and Glucose-6-Phosphate Dehydrogenase Activity for Enhanced DHA Production Through Plasma Mutagenesis Coupled With Chemical Screening

Thraustochytrids, such as Aurantiochytrium and Schizochytrium, have been shown as a promising sustainable alternative to fish oil due to its ability to accumulate a high level of docosahexaenoic acid (DHA) from its total fatty acids. However, the low DHA volumetric yield by most of the wild type (WT) strain of thraustochytrids which probably be caused by the low oxidative stress tolerance as well as a limited supply of key precursors for DHA biosynthesis has restricted its application for industrial application. Thus, to enhance the DHA production, we aimed to generate Aurantiochytrium SW1 mutant with high tolerance toward oxidative stress and high glucose-6 phosphate dehydrogenase (G6PDH) activities through strategic plasma mutagenesis coupled with chemical screening. The WT strain (Aurantiochytrium sp. SW1) was initially exposed to plasma radiation and was further challenged with zeocin and polydatin, generating a mutant (YHPM1) with a 30, 65, and 80% higher overall biomass, lipid, and DHA production in comparison with the parental strains, respectively. Further analysis showed that the superior growth, lipid, and DHA biosynthesis of the YHMP1 were attributed not only to the higher G6PDH and enzymes involved in the oxidative defense such as superoxide dismutase (SOD) and catalase (CAT) but also to other key metabolic enzymes involved in lipid biosynthesis. This study provides an effective approach in developing the Aurantiochytrium sp. mutant with superior DHA production capacity that has the potential for industrial applications.

Biocontrol Effect of Bacillus subtilis YPS-32 on Potato Common Scab and Its Complete Genome Sequence Analysis

Potato common scab is caused by Streptomyces, which resides in soil and has become a serious disease in potato planting areas worldwide. In this study, we obtained a Bacillus subtilis YPS-32 strain by natural screening, and atmospheric and room-temperature plasma (ARTP) mutagenesis and field trial results showed that B. subtilis YPS-32 has a control efficacy of 83.70% against potato common scab. The complete genome of B. subtilis YPS-32 was sequenced, and multiple genes related to the synthesis of antibiotics and plant growth promoters were detected. Based on the genomic information for B. subtilis YPS-32, the sfp gene-inactivated (related to the synthesis of secondary metabolites) mutant strain B. subtilis YPS-32Δsfp was constructed. Analysis of crude extract metabolites using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) techniques revealed that strain YPS-32 encodes antagonists, such as surfactin and fengycin, which have antimicrobial effects. This study clarifies the mode of action by which B. subtilis YPS-32 antagonizes Streptomyces scabies and provides a reference for further research on antibacterial genes in the future.

Mutation breeding of Aspergillus niger by atmospheric room temperature plasma to enhance phosphorus solubilization ability

Background

Phosphorus (P) is abundant in soils, including organic and inorganic forms. Nevertheless, most of P compounds cannot be absorbed and used by plants. Aspergillus niger v. Tiegh is a strain that can efficiently degrade P compounds in soils.

Methods

In this study, A. niger xj strain was mutated using Atmospheric Room Temperature Plasma (ARTP) technology and the strains were screened by Mo-Sb Colorimetry with strong P-solubilizing abilities.

Results

Compared with the A. niger xj strain, setting the treatment time of mutagenesis to 120 s, four positive mutant strains marked as xj 90-32, xj120-12, xj120-31, and xj180-22 had higher P-solubilizing rates by 50.3%, 57.5%, 55.9%, and 61.4%, respectively. Among them, the xj120-12 is a highly efficient P solubilizing and growth-promoting strain with good application prospects. The growth characteristics such as plant height, root length, and dry and fresh biomass of peanut (Arachis hypogaea L.) increased by 33.5%, 43.8%, 43.4%, and 33.6%, respectively. Besides available P, the chlorophyll and soluble protein contents also vary degrees of increase in the P-solubilizing mutant strains.

Conclusions

The results showed that the ARTP mutagenesis technology can improve the P solubilization abilities of the A. niger mutant strains and make the biomass of peanut plants was enhanced of mutant strains.

Genetic and non-genetic tailoring of microalgae for the enhanced production of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) - A review

The myriad health benefits associated with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) laid the path for their application in the functional foods and nutraceutical industries. Fish being primarily exploited for extraction of EPA and DHA are unsustainable sources; thus, oleaginous microalgae turn out to be an alternative sustainable source. This review paper aims to provide the recent developments in the context of enhancing EPA and DHA production by utilising non-genetic tailoring and genetic tailoring methods. We have also summarized the legislation, public perception, and possible risks associated with the usage of genetically modified microalgae focusing on EPA and DHA production.

Metabolomics-based engineering for biofuel and bio-based chemical production in microalgae and cyanobacteria: A review

Metabolomics, an essential tool in modern synthetic biology based on the design-build-test-learn platform, is useful for obtaining a detailed understanding of cellular metabolic mechanisms through comprehensive analyses of the metabolite pool size and its dynamic changes. Metabolomics is critical to the design of a rational metabolic engineering strategy by determining the rate-limiting reaction and assimilated carbon distribution in a biosynthetic pathway of interest. Microalgae and cyanobacteria are promising photosynthetic producers of biofuels and bio-based chemicals, with high potential for developing a bioeconomic society through bio-based carbon neutral manufacturing. Metabolomics technologies optimized for photosynthetic organisms have been developed and utilized in various microalgal and cyanobacterial species. This review provides a concise overview of recent achievements in photosynthetic metabolomics, emphasizing the importance of microalgal and cyanobacterial cell factories that satisfy industrial requirements.

Improved Neomycin Sulfate Potency in Streptomyces fradiae Using Atmospheric and Room Temperature Plasma (ARTP) Mutagenesis and Fermentation Medium Optimization

To improve the screening efficiency of high-yield neomycin sulfate (NM) Streptomyces fradiae strains after mutagenesis, a high-throughput screening method using streptomycin resistance prescreening (8 μg/mL) and a 24-deep well plates/microplate reader (trypan blue spectrophotometry) rescreening strategy was developed. Using this approach, we identified a high-producing NM mutant strain, Sf6-2, via six rounds of atmospheric and room temperature plasma (ARTP) mutagenesis and screening. The mutant displayed a NM potency of 7780 ± 110 U/mL and remarkably stable genetic properties over six generations. Furthermore, the key components (soluble starch, peptone, and (NH₄)₂SO₄) affecting NM potency in fermentation medium were selected using Plackett-Burman and optimized by Box-Behnken designs. Finally, the NM potency of Sf6-2 was increased to 10,849 ± 141 U/mL at the optimal concentration of each factor (73.98 g/L, 9.23 g/L, and 5.99 g/L, respectively), and it exhibited about a 40% and 100% enhancement when compared with before optimization conditions and the wild-type strain, respectively. In this study, we provide a new S. fradiae NM production strategy and generate valuable insights for the breeding and screening of other microorganisms.

Performance intensification of CO2 absorption and microalgae conversion (CAMC) hybrid system via low temperature plasma (LTP) treatment

CO₂ absorption and microalgae conversion (CAMC) hybrid system is a promising alternative for simultaneous carbon capture and utilization. It can not only overcome the challenge of high energy consumption solvent thermal regeneration in chemical CO₂ absorption, but also enhance the carbon conversion efficiency in biological conversion process. However, the discordance between CO₂ absorption and bio-conversion rate has become the key to limiting the development of CAMC system. Therefore, in this study, low temperature plasma (LTP) mutation breeding technology was used to training Chlorella strains by combining undirected mutagenesis and directional screening. Then, the mutagenic microalgae were cultivated and evaluated in CAMC system. It was found that compared with original Chlorella L166, the OD₆₈₀ of mutant strain L166-M₃ in CAMC system increased 7.8%, and the maximum specific growth rate improved 27.5%. The carbon sequestration rate of wild Chlorella L166 increased from 82.9% to 93.7% after mutation treatment, the activity of RubisCO, and the content of NADPH produced by photoreaction increased 37.2% and 17.2%. In addition, lipid production of L166-M₃ increased to 6.89 mg/L, which was 15.4% higher than original Chlorella L166. It could be observed that LTP mutation breeding could be used as a potential method for training algae species and improve the overall performance of CAMC system.

Metabolic Analysis of Schizochytrium Mutants With High DHA Content Achieved With ARTP Mutagenesis Combined With Iodoacetic Acid and Dehydroepiandrosterone Screening

High DHA production cost caused by low DHA titer and productivity of the current Schizochytrium strains is a bottleneck for its application in competition with traditional fish-oil based approach. In this study, atmospheric and room-temperature plasma with iodoacetic acid and dehydroepiandrosterone screening led to three mutants, 6–8, 6–16 and 6–23 all with increased growth and DHA accumulations. A LC/MS metabolomic analysis revealed the increased metabolism in PPP and EMP as well as the decreased TCA cycle might be relevant to the increased growth and DHA biosynthesis in the mutants. Finally, the mutant 6–23, which achieved the highest growth and DHA accumulation among all mutants, was evaluated in a 5 L fermentor. The results showed that the DHA concentration and productivity in mutant 6–23 were 41.4 g/L and 430.7 mg/L/h in fermentation for 96 h, respectively, which is the highest reported so far in literature. The study provides a novel strain improvement strategy for DHA-producing Schizochytrium.

Enhancing l-glutamine production in Corynebacterium glutamicum by rational metabolic engineering combined with a two-stage pH control strategy

l-glutamine is a semi-essential amino acid widely used in the food and pharmaceutical industries. The microbial synthesis of l-glutamine is limited by lack of effective strains with high titer and safety. First, ARTP mutagenesis combined with high-throughput screening generated an l-glutamine-producing strain of Corynebacterium glutamicum with titer of 25.7 ± 2.7 g/L. Subsequently, a series of rational metabolic approaches were used to further improve l-glutamine production, which included increasing the carbon flow to l-glutamine (proB and NCgl1221 knockout), enhancing the catalytic efficiency of the key enzyme (glnE knockout and glnA screening and overexpression) and reinforcement of ATP regeneration (ppk overexpression and RBS optimization). Finally, we proposed a two-stage pH control strategy to address the inconsistent effect of pH on cell growth and l-glutamine production. These combined strategies led to a 186.0% increase of l-glutamine titer compared to that of the initial strain, reaching 73.5 ± 3.1 g/L with a yield of 0.368 ± 0.034 g/g glucose.

ARTP Mutagenesis of Schizochytrium sp. PKU#Mn4 and Clethodim-Based Mutant Screening for Enhanced Docosahexaenoic Acid Accumulation

Schizochytrium species are one of the best oleaginous thraustochytrids for high-yield production of docosahexaenoic acid (DHA, 22:6). However, the DHA yields from most wild-type (WT) strains of Schizochytrium are unsatisfactory for large-scale production. In this study, we applied the atmospheric and room-temperature plasma (ARTP) tool to obtain the mutant library of a previously isolated strain of Schizochytrium (i.e., PKU#Mn4). Two rounds of ARTP mutagenesis coupled with the acetyl-CoA carboxylase (ACCase) inhibitor (clethodim)-based screening yielded the mutant A78 that not only displayed better growth, glucose uptake and ACCase activity, but also increased (54.1%) DHA content than that of the WT strain. Subsequent optimization of medium components and supplementation improved the DHA content by 75.5 and 37.2%, respectively, compared with that of mutant A78 cultivated in the unoptimized medium. Interestingly, the ACCase activity of mutant A78 in a medium supplemented with biotin, citric acid or sodium citrate was significantly greater than that in a medium without supplementation. This study provides an effective bioengineering approach for improving the DHA accumulation in oleaginous microbes.

Responses of Alpha-linolenic acid strain (C-12) from Chlorella sp. L166 to low temperature plasma treatment

LTP treatment was applied to induce a high-content alpha-linolenic acid (ALA) strain (C-12) from Chlorella sp. L166, the ALA content of C-12 was increased by 48.37%. The mechanism of LTP induction were examined. The results showed that LTP could facilitate pH change, induce malondialdehyde (MDA) production, cause protein leakage, and destroyed the microalgae cells. The genes of C-12 encoding pyruvate dehydrogenase (E₂) were up-regulated 2.47-fold, and acetyl-CoA carboxylase (ACCase) down-regulated 0.48-fold compared to the wild type, these changed in the direction of ALA accumulation. Furthermore, the enzymes in DNA replication were significantly up regulated. Take ALA and biomass accumulation into account, LTP technology had a positive effect on ALA accumulation. Global view of metabolic variation also suggested that C-12 had an excellent adaptability to the changes of pH and peroxidation of LTP production. C-12 could be a promising ALA source of alternative materials for it do not compete with land.

Enhancement of heterologous protein production in Corynebacterium glutamicum via atmospheric and room temperature plasma mutagenesis and high-throughput screening

Atmospheric and room temperature plasma (ARTP) is a new and efficient mutation breeding technique. In this study, we discuss a strategy combining ARTP mutagenesis and high-throughput screening to engineer Corynebacterium glutamicum towards high yield production of heterologous proteins. First, three target strains, MC2, MA8, and MA6, were screened from the mutant library with enhanced green fluorescent protein (EGFP) as the reporter protein, and their growth stability and the influence of heterologous protein production were verified. Second, genes encoding three high-value medicinal proteins (glycoprotein D, gD; endoxylanase, XynA; and variable domain of heavy chain of heavy-chain antibody, VHH) were expressed in the mutagenized strain, which confirmed its applicability for an increased biosynthesis of other heterologous proteins. During the large-scale fermentation of C. glutamicum for VHH production, the fermentation characteristics of the best mutant MA6 were verified. Compared to the original strain, the yield of VHH obtained with strain MA6 was increased by nearly 91 % to approximately 862 mg/L. Finally, through systematic genome analysis mutations in five genes were obtained. These genes code for putative proteases or are potentially related to the bacterial restriction repair systems. These findings will help to obtain optimized chassis cells and provide a direction for in-depth research on genetic targets that can increase protein production.

ARTP Mutagenesis to Improve Mycelial Polysaccharide Production of Grifola frondosa Using a Mixture of Wheat Bran and Rice Bran as Substrate

Mycelial polysaccharides from Grifola frondosa have shown potential for the prevention of chronic diseases. Atmospheric and room temperature plasma (ARTP) technology was used to enhance the ability of G. frondosa to efficiently utilize a mixture of rice bran and wheat bran in the production of mycelial polysaccharides. The ARTP-mutant G. frondosa GFA2 had an improved growth rate of 6.0 mm/d and polysaccharide yield of 2.65 g/L and showed stable genetic characteristics. Uniform design experiments showed that polysaccharide yield could be increased to 5.90 g/L using the optimized conditions of 10.0 g/L rice bran and 110.0 g/L wheat bran while omitting KH2PO4 and MgSO4·7H2O. Gas chromatography demonstrated that GFA2 polysaccharides were composed of the monosaccharides rhamnose, arabinose, fucose, xylose, mannose, glucose, and galactose. This study provides an effective strategy for improving polysaccharide production in edible fungi while proposing the added-value utilization of rice and wheat brans.

Metabolic Engineering for Carotenoid Production Using Eukaryotic Microalgae and Prokaryotic Cyanobacteria

Eukaryotic microalgae and prokaryotic cyanobacteria are diverse photosynthetic organisms that produce various useful compounds. Due to their rapid growth and efficient biomass production from carbon dioxide and solar energy, microalgae and cyanobacteria are expected to become cost-effective, sustainable bioresources in the future. These organisms also abundantly produce various carotenoids, but further improvement in carotenoid productivity is needed for a successful commercialization. Metabolic engineering via genetic manipulation and mutational breeding is a powerful tool for generating carotenoid-rich strains. This chapter focuses on carotenoid production in microalgae and cyanobacteria, as well as strategies and potential target genes for metabolic engineering. Recent achievements in metabolic engineering that improved carotenoid production in microalgae and cyanobacteria are also reviewed.

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

Naringinase was mainly obtained by microbial fermentation, and mutagenesis was a major way for obtaining excellent mutants. The aim of this study was to screen out a high naringinase yielding mutant to enhance the potential application value of its industrialization and compare the effects of different mutagenic methods on the enzyme activity of the strain. A novel producing naringinase strain, Aspergillus tubingensis MN589840, was isolated from mildewed pomelo peel, later subjected to mutagenesis including UV, ARTP and UV-ARTP. After five rounds iterative mutagenesis, the mutants U1, A6 and UA13 were screened out with 1448·49, 1848·71, 2475·16 U mg^-1 enzyme activity, the naringinase productivity raised by 79·08, 123·56 and 206%, respectively. In addition, the naringinase activity of three mutants rose after each round of iterative mutagenesis. These results indicated that the mutagenesis efficiency of UV-ARTP was higher than that of single ARTP, and both are better than UV. In summary, the iterative UV-ARTP mutagenesis is an effective strategy for screening high naringinase-producing strains.