Mutation breeding of high avermectin B1a-producing strain by the combination of high energy carbon heavy ion irradiation and sodium nitrite mutagenesis based on high throughput screening

Mechanistic insight for improving butenyl-spinosyn production through combined ARTP/UV mutagenesis and ribosome engineering in Saccharopolyspora pogona

Butenyl-spinosyn is a highly effective, wide-spectrum and environmentally-friendly biological insecticide produced by Saccharopolyspora pogona. However, its scale-up is impeded due to its lower titer in wild-type strains. In this work, ARTP/UV mutagenesis and ribosome engineering were employed to enhance the butenyl-spinosyn production, and a stable mutant Saccharopolyspora pogona aG6 with high butenyl-spinosyn yield was successfully obtained. For the first time, the fermentation results in the 5 L bioreactor demonstrated that the butenyl-spinosyn produced by mutant Saccharopolyspora pogona aG6 reached the maximum value of 130 mg/L, almost 4-fold increase over the wild-type strain WT. Furthermore, comparative genomic, transcriptome and target metabolomic analysis revealed that the accumulation of butenyl-spinosyn was promoted by alterations in ribosomal proteins, branched-chain amino acid degradation and oxidative phosphorylation. Conclusively, the proposed model of ribosome engineering combined with ARTP/UV showed the improved biosynthesis regulation of butenyl-spinosyn in S. pogona.

Sensitivity of genotypically diverse rice varieties to radiation and the related changes to antioxidant enzyme activities

PURPOSE

Radiation mutagenesis, which typically involves gamma rays, is important for generating new rice germplasm resources. Determining the appropriate radiation dose range is critical for the success of radiation mutagenesis. Clarifying the sensitivity and tolerance of genotypically diverse rice varieties to gamma irradiation as well as the radiation-induced changes to reactive oxygen species (ROS) generation and antioxidant enzyme activities is crucial for increasing the utility of radiation mutagenesis in rice breeding programs.

MATERIALS AND METHODS

The seeds of the following four rice varieties with different genotypes were used as test materials: indica Zhe 1613, glutinous indica Zhe 1708, japonica Zhejing 100, and glutinous japonica Zhenuo 65. Additionally,60Co was used as the source of gamma rays. The rice seeds were irradiated with 14 doses (0, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, and 750 Gy). Non-irradiated seeds were used as the control. The seedling survival rate for each variety was recorded at 3, 7, 14, and 28 days after sowing. Moreover, the median lethal dose (LD50) and critical dose (LD40) were calculated according to the seedling survival rates at 28 days after sowing. The seedling superoxide anion (O2•-), hydrogen peroxide (H2O2), and malondialdehyde (MDA) contents and the superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) activities were analyzed at 7 days after sowing.

RESULTS

As the radiation dose increased, the seedling survival rate decreased. The seedling survival rate also decreased significantly as the number of days after sowing increased. Among the rice genotypes, the rank-order of the radiation tolerance was as follows: indica Zhe 1613 > glutinous indica Zhe 1708 > japonica Zhejing 100 > glutinous japonica Zhenuo 65. The LD50 values were 426.7 Gy for Zhe 1613, 329.2 Gy for Zhe 1708, 318.3 Gy for Zhejing 100, and 316.6 Gy for Zhenuo 65. Increases in the radiation dose resulted in significant increases in the seedling O2•- and H2O2 contents, but only up to a certain point. Further increases in the radiation dose caused the seedling O2•- and H2O2 contents to decrease. The H2O2 content for each variety peaked when the radiation dose was very close to the LD50. We propose that the radiation dose associated with the highest H2O2 content (±50 Gy) should be used as the recommended dose for the gamma irradiation of rice. The radiation dose that resulted in peak seedling O2•- contents in the analyzed rice varieties was very close to the LD40. In all rice varieties, the MDA content increased as the radiation dose increased. The SOD, CAT, POD, and APX activities increased as the radiation dose increased within a certain range (less than 600 Gy for Zhe 1613 and 400 Gy for the other varieties), but there were slight differences among the rice varieties.

CONCLUSIONS

Genotypically diverse rice varieties vary regarding their sensitivity to gamma irradiation. Our findings suggest that ROS generation and antioxidant enzyme activities are important factors associated with the radiation mutagenesis of rice. The close relationship between the activities of key antioxidant enzymes, such as SOD, POD, APX, and CAT, and the LD50 and LD40 may be exploited to enhance radiation mutagenesis through the use of plant growth regulators.

Nitrogen removal by Rhodococcus sp. SY24 under linear alkylbenzene sulphonate stress: Carbon source metabolism activity, kinetics, and optimum culture conditions

Artificial intervention combined with stress acclimation was used to screen a heterotrophic nitrifying-aerobic denitrifying (HN-AD) bacterial, strain Rhodococcus SY24, resistant to linear alkylbenzenesulfonic acid (LAS) stress. When LAS was<15 mg/L, strain SY24 performed better cell growth and carbon source metabolism activity. The maximum nitrification and denitrification rates of SY24 under LAS stress could reach 1.18 mg/L/h and 1.05 mg/L/h, respectively, which were 13.80 % and 8.81 % higher than those of the original strain CPZ24. Higher LAS tolerance was seen in the functional genes (amoA, nxrA, napA, narG, nirK, nirS, norB, and nosZ). Response surface modeling revealed that 2 mg/L LAS, sodium succinate as a carbon source, 190 rams, and carbon/nitrogen 11 were the ideal culture conditions for SY24 to nitrogen removal under the LAS environment. This study offered a new screening strategy for the functional species, and strain SY24 showed significant LAS tolerance and HN-AD potential.

Isolation and Screening of High-Yielding α-Amylase Mutants of Bacillus subtilis by Heavy Ion Mutagenesis

To improve fermentative production of α-amylase, heavy-ion mutagenesis technology was used to irradiate Bacillus subtilis (B. subtilis) to obtain the high yielding mutants in this study. After continuous cultivation for 12 generations, eight mutants exhibited positive mutation rate with greater H/C. The α-amylase production was stable and obviously exceeded that by the parent strain, which shows that the mutants have a good genetic stability. Among the mutants, the α-amylase activity of B. subtilis KC-180-2 was 72.26 U·mL^-1, which was 82.34% higher than that of the original strain. After optimization of fermentation conditions and media, the α-amylase activity of B. subtilis KC-180-2 reached a maximum of 156.83 U·mL^-1 at 36 h in a bioreactor. In addition, the optimized fermentation temperature of B. subtilis KC-180-2 was increased to 49℃, indicating B. subtilis KC-180-2 possesses high-temperature resistance, which has great application prospects for industrial fermentation for α-amylase production.

Screening and mutagenesis of high-efficient degrading bacteria of linear alkylbenzene sulfonates

As a widely used detergent, anionic surfactant linear alkylbenzene sulfonates (LAS) is a common toxic pollutant in wastewater. In this study, Pseudomonas sp. strain H6 was isolated from activated sludge and municipal wastewater, which had good degradation effect on LAS. The results showed that strain H6 could grow with LAS as the sole carbon source. When the concentration of LAS was less than 100 mg/L, strain H6 could degrade more than 80% of the LAS within 24 h. Meanwhile, the growth of strain H6 increased with the increase of LAS concentration, reaching the maximum growth at the presence of 100 mg/L LAS. When the concentration of LAS was over 100 mg/L, strain H6's cell growth and degradation of LAS showed a downward trend due to the strong toxicity of LAS, and the degradation rate of LAS almost tended to zero with 500 mg/L LAS. Further mutagenesis analysis of strain H6 showed that positive mutation occurred under ultraviolet and nitrite mutagenesis with using ampicillin to increase the screening pressure, and the degradation rate of LAS was 44.91% higher than that of original strain.

High-Throughput Screening Technology in Industrial Biotechnology

Based on the development of automatic devices and rapid assay methods, various high-throughput screening (HTS) strategies have been established for improving the performance of industrial microorganisms. We discuss the most significant factors that can improve HTS efficiency, including the construction of screening libraries with high diversity and the use of new detection methods to expand the search range and highlight target compounds. We also summarize applications of HTS for enhancing the performance of industrial microorganisms. Current challenges and potential improvements to HTS in industrial biotechnology are discussed in the context of rapid developments in synthetic biology, nanotechnology, and artificial intelligence. Rational integration will be an important driving force for constructing more efficient industrial microorganisms with wider applications in biotechnology.

Improvement of vincamine production of endophytic fungus through inactivated protoplast fusion

Improvement of the production of vincamine in endophytic fungus VINI-7 was performed by using the inactivated protoplast fusion method. The preparation conditions of protoplasts were optimized by systematic trials with various parameters, and inactivated protoplast fusion was subsequently performed. The mycelium in logarithmic growth phase was treated with 1500 U/mL lywallzyme, 1500 U/mL lysozyme, 2000 U/mL cellulase, and 1000 U/mL snailase solution for 3 h at 30 °C and had the best conditions, in which the concentration of the protoplast was 3.17 × 10⁷ cells/mL. Protoplasts were inactivated by heat, ultraviolet, microwave, sodium nitrite, and diethyl sulfate, respectively. Subsequently, protoplasts inactivated by different methods were subjected to respective protoplast fusion. The results showed that the yield of vincamine in fusants inactivated by mutagens was generally higher than that of fusants inactivated by heat. The highest yield of vincamine in two fusants (U-U1 and N-N1) was 31.6 and 38.7 mg, which increased to 162.24 and 221.16%, respectively, as compared to the parent strain (12.05 mg). LC-MS/MS analysis showed that U-U1 and N-N1 fusants could produce vincamine. Furthermore, the results of genetic stability experiments indicated that U-U1 and N-N1 were genetically stable.

Heavy-ion mutagenesis significantly enhances enduracidin production by Streptomyces fungicidicus

To improve fermentative production of enduracidin, heavy-ion beams generated by the Heavy Ion Research Facility in Lanzhou (HIRFL), China, were employed for the first time to generate mutations in Streptomyces fungicidicus. Initial screening detected 44 positive mutants with larger inhibition zone, which were subsequently tested based on flask fermentation. Finally, 20 mutants showed 20% increase in enduracidin production, when compared with the original strain. Among them, enduracidin production by the three mutants (M13, M30, and M34) was significantly higher than that by the original strain. In particular, mutant M30 exhibited highest enduracidin production, which was 114% higher than that obtained with the original strain. Following culture optimization, the maximal enduracidin yield obtained by M30 reached 918.5 mg/L in 10 days, which was 34% higher than that noted in the control.