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

Texture, flavor and digestibility improvement of high-moisture-extruded meat analogues by incorporating golden biomass of Auxenochlorella pyrenoidosa mutant through auto-controlled fermentation

To improve the quality and sensory characteristics of meat analogues from soya protein isolate (SPI), the golden algal powder (AP) containing 43.8 % protein through auto-controlled fermentation of Auxenochlorella pyrenoidosa mutant (A4-1 strain) was incorporated with SPI at various mass ratios in high-moisture-extrusion (HME) process. The optimal texture, flavor and digestibility were achieved by mixing 5 % of cell-disrupted AP (DAP) with 95 % SPI, showing 210.6 % and 141.7 % increase of the springiness and chewiness with 19.36 % decrease of the hardness. The incorporation of 5 % DAP results in the maximal fiber-rich 3D structure of the extrudates with significantly increased proportion of α-helices in the secondary structure and bound water content. The simulated digestibility in vitro was significantly increased by 37.6 %, with a reduced bitterness and astringency in the extrudate. These findings provided new insights into the utilization of this golden algal powder to enhance the quality and sensory characteristics of SPI-based meat analogues.

Development of fast-growing chlorophyll-deficient Chlorella pyrenoidosa mutant using atmospheric and room temperature plasma mutagenesis

This study successfully obtained a chlorophyll-deficient mutant of Chlorella pyrenoidosa, named A19, using atmospheric and room temperature plasma mutagenesis technology. Compared to the wild-type strain, the A19 mutant exhibited a faster growth rate and appeared yellow under dark conditions. The content of chlorophyll A and chlorophyll B decreased by 80% and 60%, respectively, while lutein content increased by 16%. A19 also demonstrated improved amino acid quality. Transcriptome analysis revealed upregulation of gene expression levels in glycolysis and tricarboxylic acid cycle pathways, promoting central carbon flow towards enhanced production capacity and accelerating growth. Meanwhile, downregulation of genes regulating enzymes in the chlorophyll synthesis pathway explained the observed color change in the mutant strain. These results confirmed that A19 not only shifts its color to yellow but also exhibits faster growth, higher lutein content, and improved metabolic efficiency, making it a promising additive for feed and food applications while reducing cultivation time.

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.

Enhanced lutein and protein production with improved organoleptic properties in a novel yellow strain of Auxenochlorella pyrenoidosa mutant through atmospheric and room temperature plasma mutagenesis and norflurazon-based screening

To achieve the triple purpose of enhancing lutein and protein contents as well as improving organoleptic properties in biomass of Auxenochlorella pyrenoidosa mutant as raw material of future food, a novel yellow mutant, CX41 strain, was successfully selected through atmospheric and room temperature plasma (ARTP) mutagenesis and norflurazon-based screening. CX41 strain exhibited a significantly increased lutein (0.86 mg/g) and protein (49.00 % DW) contents simultaneously, while higher levels of total (33.47 % DW) and essential amino acids (14.78 % DW) were achieved with higher amino acid score (86.49) than that of the original A4-1 strain, a yellow and high protein mutant bred previously. Sensory evaluation showed that CX41 biomass has more comparable to A4-1, while in comparison to the wild type (WT), it has a more inclination towards roasted, with a fainter grassy, woody, rancid and fishy odor, and a significant improvement in taste is reflected by a decrease of 8.40 % in sweetness, a reduction of 14.86 % in bitterness, and an increase of 5.93 % in umami intensity. Metabolome analysis revealed that the superior sensory profile was due to the significantly reduced relative odor activity of β-ionone (herbaceous odor) and substances such as 1-octene, hexanal, 1-octen-3-ol, and heptanal (fishy and rancid odors). The extensive enhancements demonstrated CX41 biomass as a highly promising raw material with high nutrients of lutein and protein as well as excellent taste and flavor for future food application.

Enhancement of non-oleaginous green microalgae Ulothrix for bio-fixing CO2 and producing biofuels by ARTP mutagenesis

Oleaginous green microalgae are often mentioned in algae-based biodiesel industry, but most of them belong to specific genus (Chlorella, Scenedesmus, Botryococcus and Desmodesmus). Thus, the microalgal germplasm resources for biodiesel production are limited. Mutagenesis is regarded as an important technology for expanding germplasm resources. The main purpose of this study is to screen microalgae strains with high carbon dioxide tolerance and high lipid content from mutants derived from indigenous non-oleaginous green microalgae species-Ulothrix SDJZ-17. Two mutants with high CO2 tolerance and high lipid content genetic stability were obtained from the mutants by high-throughput screening, named Ulothrix SDJZ-17-A20 and Ulothrix SDJZ-17-A23. In order to evaluate the potential of CO2 fixation and biofuel production, A20 and A23 were cultured under air and 15% CO2 (v/v) conditions, and their wild-type strains (WT) were used as controls. Under the condition of high CO2 concentration, the growth performance and lipid production capacity of mutant strains A20 and A23 were not only significantly better than those of wild strains, but also better than those of their own cultured under air conditions. Among them, A23 obtained the highest LCE (light conversion efficiency) (14.79%), Fv/Fm (maximal photochemical efficiency of photosystem II) (71.04%) and biomass productivity (81.26 mg L-1 d-1), while A20 obtained the highest lipid content (22.45%). Both mutants can be used as candidate strains for CO2 fixation and biofuel production. By ARTP (atmospheric and room temperature plasma) mutagenesis with high-throughput screening, the mutants with higher CO2 tolerance, photosynthetic efficiency and lipid productivity can be obtained, even if they are derived from non-oleaginous microalgae, which is of great significance for enriching the energy microalgae germplasm bank, alleviating the global warming and energy crisis.

Isolation and Selection of Protein-Rich Mutants of Chlorella vulgaris by Fluorescence-Activated Cell Sorting with Enhanced Biostimulant Activity to Germinate Garden Cress Seeds

Microalgae are a promising feedstock with proven biostimulant activity that is enhanced by their biochemical components (e.g., amino acids and phytohormones), which turns them into an appealing feedstock to reduce the use of fertilisers in agriculture and improve crop productivity and resilience. Thus, this work aimed to isolate protein-rich microalgal mutants with increased biostimulant activity. Random mutagenesis was performed with Chlorella vulgaris, and a selection of protein-rich mutants were sorted through fluorescence-activated cell sorting (FACS), resulting in the isolation of 17 protein-rich mutant strains with protein contents 19-34% higher than that of the wildtype (WT). Furthermore, mutant F4 displayed a 38%, 22% and 62% higher biomass productivity, growth rate and chlorophyll content, respectively. This mutant was then scaled up to a 7 L benchtop reactor to produce biomass and evaluate the biostimulant potential of this novel strain towards garden cress seeds. Compared to water (control), the germination index and the relative total growth increased by 7% and 19%, respectively, after the application of 0.1 g L-1 of this bioproduct, which highlights its biostimulant potential.

ARTP mutagenesis of Aureobasidium pullulans RM1603 for high pullulan production and transcriptome analysis of mutants

Pullulan is a microbial exopolysaccharide produced by Aureobasidium spp. with excellent physical and chemical properties, resulting in great application value. In this study, a novel strain RM1603 of Aureobasidium pullulans with high pullulan production of 51.0 ± 1.0 g·L- 1 isolated from rhizosphere soil was subjected to atmospheric and room temperature plasma (ARTP) mutagenesis, followed by selection of mutants to obtain pullulan high-producing strains. Finally, two mutants Mu0816 and Mu1519 were obtained, with polysaccharide productions of 58.7 ± 0.8 and 60.0 ± 0.8 g∙L- 1 after 72-h fermentation, representing 15.1 and 17.6% increases compared with the original strain, respectively. Transcriptome analysis of the two mutants and the original strain revealed that the high expression of α/β-hydrolase (ABHD), α-amylase (AMY1), and sugar porter family MFS transporters (SPF-MFS) in the mutants may be related to the synthesis and secretion of pullulan. These results demonstrated the effectiveness of ARTP mutagenesis in A. pullulans, providing a basis for the investigation of genes related to pullulan synthesis and secretion.

High capacities of carbon capture and photosynthesis of a novel organic carbon-fixing microalgae in municipal wastewater: From mutagenesis, screening, ability evaluation to mechanism analysis

The development of wastewater treatment processes capable of reducing and fixing carbon is currently a hot topic in the wastewater treatment field. Microalgae possess a natural carbon-fixing advantage, and microalgae that can symbiotically coexist with indigenous bacteria in actual wastewater attract more significant attention. Ultraviolet (UV) mutagenesis and dissolved organic carbon (DOC) acclimation were applied to strengthen the carbon-fixing performance of microalgae in this study. The mechanisms associated with microalgal water purification ability, gene regulation at the molecular level and photosynthetic potential under different trophic modes resulting from carbon fixation and transformation were disclosed. The superior performance of Chlorella sp. MHQ2 was eventually screened out among a large number of mutants generated from 3 wild-type Chlorella strains. Results indicated that the dry cell weight of the optimal species Chlorella sp. HQ mutant MHQ2 was 1.91 times that of the wild strain in the pure algal system, more carbon from municipal wastewater (MW) were transferred to the microalgae and re-entered into the biological cycle through resource utilization. In addition, COD, NH3-N and TP removal efficiencies of MW by Chlorella sp. MHQ2 were found to increase to 95.8% (1.1-times), 96.4% (1.4-times), and 92.9% (1.2-times), respectively, under the extra DOC supply and the assistance of indigenous bacteria in the MW. In the transcriptome analysis of the logarithmic phase, the glycolytic pathway was inhibited, and the pentose phosphate pathway was mainly carried out for microalgal life activities, further promoting efficient energy utilization. Upon analysis of carbon capture capacity and photosynthetic potential in trophic mode, the addition of NaHCO3 increased the photosynthetic rate of Chlorella sp. MHQ2 in mixotrophy whereas it was attenuated in autotrophy. This study could provide a new perspective for the study of resource utilization and microalgae carbon- fixing mechanisms in the actual wastewater treatment process.

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.

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.