Optimization of Acid Protease Production by Aspergillus niger I1 on Shrimp Peptone Using Statistical Experimental Design

Medium composition and culture conditions for the acid protease production by Aspergillus niger I1 were optimized by response surface methodology (RSM). A significant influence of temperature, KH2PO4, and initial pH on the protease production was evaluated by Plackett-Burman design (PBD). These factors were further optimized using Box-Behnken design and RSM. Under the proposed optimized conditions, the experimental protease production (183.13 U mL−1) closely matched the yield predicted by the statistical model (172.57 U mL−1) with R2 = 0.914. Compared with the initial M1 medium on which protease production was 43.13 U mL−1, a successful and significant improvement by 4.25 folds was achieved in the optimized medium containing (g/L): hulled grain of wheat (HGW) 5.0; KH2PO4 1.0; NaCl 0.3; MgSO4(7H2O) 0.5; CaCl2 (7H2O) 0.4; ZnSO4 0.1; Na2HPO4 1.6; shrimp peptone (SP) 1.0. The pH was adjusted at 5 and the temperature at 30°C. More interestingly, the optimization was accomplished using two cheap and local fermentation substrates, HGW and SP, which may result in a significant reduction in the cost of medium constituents

Isolation of the Bacillus thuringiensis plasmid carrying Bacthuricin F4 coding genes and evidence of its conjugative transfer

INTRODUCTION: Conjugation is an excellent natural mode of DNA transfer in vivo between bacteria, particularly when these conjugative elements carry technological traits such as bacteriocin encoding genes. In the present work, the bacteriocinogenic plasmid pIBF4 from Bacillus thuringiensis responsible of Bacthuricin F4 synthesis was isolated and characterized. METHODOLOGY: To isolate pIBF4, the total plasmid DNA from a non-bacteriocin transposant carrying the mini-Tn10 spectinomycin selective marker was extracted and used to transform Escherichia coli strain Top10. PIBF4 was extracted from the obtained transformant and then subjected to restriction enzyme analysis. Plasmid curing experiments were conducted to test the stability of pIBF4 at a stringent temperature of 42°C. Conjugative behavior of pIBF4 was assessed by mating experiments using the non-bacteriocin transposant mutant as a donor strain and several Bacillus thuringiensis strains as recipients. RESULTS: The pIBF4 plasmid was isolated and had a molecular weight of 19.1 kb. Ninety-five percent of cells retained the pIBF4 plasmid after 200 generations, demonstrating its high stability. PIBF4 was successfully transferred to Bacillus thuringiensis HD1CryB strain with a transfer frequency of 1x10(-8) transconjugants per donor cell. The study of the recipient host range revealed that pIBF4 is specifically transferable to Bacillus thuringiensis strains with variable transfer frequencies depending on the recipient host strain. CONCLUSION: Our results show that pIBF4 is a 19.1 kb highly stable plasmid transferable by conjugation to Bacillus thuringiensis strains with deferent transfer frequencies.Tunisian Ministry of Higher Education, Scientific Research, and Technolog

Ceramic filters for oil emulsion treatments

This work focused on obtaining low-cost macroporous ceramic tubes to be used as filters or as supports for the preparation of multilayer ceramic membranes. A Tunisian natural clay was used as raw material and cellulose as porogen agent. Cellulose fibers obtained from paper were used. The tubular supports were shape formed by extrusion in order to obtain a low-cost material with high porosity low shrinkage. The characterization of the process has been carried out studying the phase evolution, microstructure, pore structure, mechanical strength, and water permeability at various sintering temperatures. The porosity was improved adding 10 wt.% of cellulose to the clay and sintering temperatures were between 800 and 900°C. The sintered macroporous support with 10 wt.% cellulose, sintered at 850°C exhibited good performance such as porosity 40%, mechanical strength 6.5 MPa, and water permeability 8.5 L/h m. Finally, an emulsion of oil was significantly cleaned. A rejection rate of 50% for 10 min of treatment time was obtained. This work shows the possibility to develop cost-effective ceramic support with controllable pore size, porosity, and high strength for high performance membranes.This work has been partially supported by the Ministry of Economy and Competitiveness of Spain under project MAT2013-48426-C2-1R and the project Medyna “Maghreb-EU research staff exchange on geodynamics, geohazards, and applied geology in Northwest Africa”