Optimization of medium components and physicochemical parameters to simultaneously enhance microbial growth and production of lypolitic enzymes byStenotrophomonassp

Optimization of L-asparaginase production from endophytic Fusarium proliferatum using OFAT and RSM and its cytotoxic evaluation

L-asparaginase from endophytic Fusarium proliferatum (isolate CCH, GenBank accession no. MK685139) isolated from the medicinal plant Cymbopogon citratus (Lemon grass), was optimized for its L-asparaginase production and its subsequent cytotoxicity towards Jurkat E6 cell line. The following factors were optimized; carbon source and concentration, nitrogen source and concentration, incubation period, temperature, pH and agitation rate. Optimization of L-asparaginase production was performed using One-Factor-At-A-Time (OFAT) and Response surface methodology (RSM) model. The cytotoxicity of the crude enzyme from isolate CCH was tested on leukemic Jurkat E6 cell line. The optimization exercise revealed that glucose concentration, nitrogen source, L-asparagine concentration and temperature influenced the L-asparaginase production of CCH. The optimum condition suggested using OFAT and RSM results were consistent. As such, the recommended conditions were 0.20% of glucose, 0.99% of L-asparagine and 5.34 days incubation at 30.50 °C. The L-asparaginase production of CCH increased from 16.75 ± 0.76 IU/mL to 22.42 ± 0.20 IU/mL after optimization. The cytotoxicity of the crude enzyme on leukemic Jurkat cell line recorded IC₅₀ value at 33.89 ± 2.63% v/v. To conclude, the enzyme extract produced from Fusarium proliferatum under optimized conditions is a potential alternative resource for L-asparaginase.

Response and recovery of aerobic granular sludge to pH shock for simultaneous removal of aniline and nitrogen

Considering the pH fluctuation in industrial wastewater, the response and resilience to pH shock should be investigated during aerobic granular sludge (AGS) system operation. In this work, three AGS reactors, namely R1, R2, and R3 for simultaneous removal of aniline and nitrogen were exposed to neutral, acidic, and alkaline conditions, respectively. The removal efficiency of aniline and chemical oxygen demand with pH variation was over 99.9% and 91.0%, respectively after stable in the three reactors. The aniline removal rate modestly decreased in R2 and R3 after pH varied and denitrification was slightly improved in acidic environment with average removal efficiency of 61.2%. The mature AGS could maintain settleability in R1 and R2 with 30 min sludge volume index below 35 mL g^-1 but was unstable under alkaline condition. Correspondingly, the secretion of extracellular polymeric substances especially protein decreased notably in R3. The bacterial groups varied with pH shock, but some could recover after adjustment to original pH value. Proteobacteria was the predominant phylum in the three reactors and Bacteroidetes was enriched in alkaline conditions. In addition, the main functional genera such as Achromobacter, Defluviimonas, Enterobacter, Pseudomonas, and Pseudoxanthomonas, were detected in the system and were found to be responsible for reduction of aniline and nitrogen.

Large-scale production of tauroursodeoxycholic acid products through fermentation optimization of engineered Escherichia coli cell factory

Background

Bear bile powder is a valuable medicinal material characterized by high content of tauroursodeoxycholic acid (TUDCA) at a certain ratio to taurochenodeoxycholic acid (TCDCA). We had created an engineered E. coli harboring two-step bidirectional oxidative and reductive enzyme-catalyzing pathway that could rapidly convert TCDCA to TUDCA at a specific percentage in shake flasks.

Results

We reported here the large-scale production of TUDCA containing products by balancing the bidirectional reactions through optimizing fermentation process of the engineered E. coli in fermenters. The fermentation medium was firstly optimized based on M9 medium using response surface methodology, leading to a glycerol and yeast extract modified M9-GY medium benefits for both cell growth and product conversion efficiency. Then isopropylthio-β-galactoside induction and fed-stock stage was successively optimized. Finally, a special deep-tank static process was developed to promote the conversion from TCDCA to TUDCA. Applying the optimal condition, fermentation was performed by separately supplementing 30 g refined chicken bile powder and 35 g crude chicken bile powder as substrates, resulting in 29.35 ± 2.83 g and 30.78 ± 3.04 g powder products containing 35.85 ± 3.85% and 27.14 ± 4.23% of TUDCA at a ratio of 1.49 ± 0.14 and 1.55 ± 0.19 to TCDCA, respectively, after purification and evaporation of the fermentation broth. The recovery yield was 92.84 ± 4.21% and 91.83 ± 2.56%, respectively.

Conclusion

This study provided a practical and environment friendly industrialized process for producing artificial substitute of bear bile powder from cheap and readily available chicken bile powder using engineered E. coli microbial cell factory. It also put forward an interesting deep-tank static process to promote the enzyme-catalyzing reactions toward target compounds in synthetic biology-based fermentation.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1076-2) contains supplementary material, which is available to authorized users.

Optimization of fermentation conditions through response surface methodology for enhanced antibacterial metabolite production by Streptomyces sp. 1-14 from cassava rhizosphere

Streptomyces species 1-14 isolated from cassava rhizosphere soil were evaluated for their antibacterial efficacy against Fusarium oxysporum f.sp. cubense race 4 (FOC4). Of the 63 strains tested, thirteen exhibited potent antibacterial properties and were further screened against eight fungal pathogens. The strain that showed maximum inhibition against all of the test pathogens was identified by 16S rDNA sequencing as Streptomyces sp. 1-14, was selected for further studies. Through the propagation of Streptomyces sp. 1-14 in soil under simulated conditions, we found that FOC4 did not significantly influence the multiplication and survival of Streptomyces sp. 1-14, while indigenous microorganisms in the soil did significantly influence Streptomyces sp. 1-14 populations. To achieve maximum metabolite production, the growth of Streptomyces 1-14 was optimized through response surface methodology employing Plackett-Burman design, path of steepest ascent determinations and Box-Behnken design. The final optimized fermentation conditions (g/L) included: glucose, 38.877; CaCl2•2H2O, 0.161; temperature, 29.97°C; and inoculation amount, 8.93%. This optimization resulted in an antibacterial activity of 56.13% against FOC4, which was 12.33% higher than that before optimization (43.80%). The results obtained using response surface methodology to optimize the fermentation medium had a significant effect on the production of bioactive metabolites by Streptomyces sp. 1-14. Moreover, during fermentation and storage, pH, light, storage temperature, etc., must be closely monitored to reduce the formation of fermentation products with reduced antibacterial activity. This method is useful for further investigations of the production of anti-FOC4 substances, and could be used to develop bio-control agents to suppress or control banana fusarium wilt.

Statistical optimization of medium components and physicochemical parameters to simultaneously enhance bacterial growth and esterase production by Bacillus thuringiensis

Bacillus thuringiensis is a genus extensively studied because of its high potential for biotechnological application, principally in biocontrol techniques. However, the optimization of esterase production by this strain has been scarcely studied. The aim of this work was to select and optimize the physicochemical and nutritional parameters that significantly influence the growth and esterase production of B. thuringiensis. To this purpose, 6 nutritional factors and 2 physicochemical parameters were evaluated using a Plackett-Burman design. Significant variables were optimized using a Box-Behnken design and through the desirability function to select the levels of the variables that simultaneously maximize microbial growth and esterase production. The optimum conditions resulting from simultaneous optimization of the responses under study were found to be 1 g/L glucose, 15 g/L peptone, and 3.25 g/L NaCl. Under these optimal conditions, it was possible to achieve a 2.5 log CFU/mL increase in bacterial growth and a 113-fold increase in esterase productivity, compared with minimal medium without agitation.