Advances in biotin biosynthesis and biotechnological production in microorganisms.

Biotin, also known as vitamin H or B7, acts as a crucial cofactor in the central metabolism processes of fatty acids, amino acids, and carbohydrates. Biotin has important applications in food additives, biomedicine, and other fields. While the ability to synthesize biotin de novo is confined to microorganisms and plants, humans and animals require substantial daily intake, primarily through dietary sources and intestinal microflora. Currently, chemical synthesis stands as the primary method for commercial biotin production, although microbial biotin production offers an environmentally sustainable alternative with promising prospects. This review presents a comprehensive overview of the pathways involved in de novo biotin synthesis in various species of microbes and insights into its regulatory and transport systems. Furthermore, diverse strategies are discussed to improve the biotin production here, including mutation breeding, rational metabolic engineering design, artificial genetic modification, and process optimization. The review also presents the potential strategies for addressing current challenges for industrial-scale bioproduction of biotin in the future. This review is very helpful for exploring efficient and sustainable strategies for large-scale biotin production.

Elimination of the mycotoxin citrinin production in the industrial important strain Monascus purpureus SM001.

The application of the high-producing pigments industrial strain Monascus purpureus SM001 has been greatly limited by the synchronous production of mycotoxin citrinin. Here we have tried both traditional mutagenesis and metabolic engineering methods to eliminate the production of citrinin. Traditional chemical and physical mutagens were applied to induce mutagenesis, and a bio-screening method based on the antibacterial activity of citrinin against Bacillus subtilis was designed to select mutants. Among the resulting four citrinin-free mutants, only mutant MU2411 can maintain the similar pigments yield. A binary vector system was constructed and successfully disrupted the polyketide synthase gene pksCT in M. purpureus SM001 through the Agrobacterium tumefaciens-mediated transformation. The resulting citrinin-free DeltapksCT mutants maintained the same level of pigments yield. The established Monascus genetic system was comprehensively evaluated and showed high efficiency and specificity, which provides us a potential approach to manipulate and improve industrial Monascus strains.

Medium optimization for enhanced production of cytosine-substituted mildiomycin analogue (MIL-C) by Streptoverticillium rimofaciens ZJU 5119.

Cytosine-substituted mildiomycin analogue (MIL-C) was produced effectively by supplementing cytosine into the culture of Streptoverticillium rimofaciens. In order to improve the yield of MIL-C, statistically-based experimental designs were applied to optimize the fermentation medium for S. rimofaciens ZJU 5119. Fifteen culture conditions were examined for their significances on MIL-C production using Plackett-Burman design. The Plackett-Burman design and one-variable-at-a-time design indicated that glucose and rice meal as the complex carbon sources, and peanut cake meal and NH4NO3 as the complex nitrogen sources were beneficial for MIL-C production in S. rimofaciens ZJU 5119. The results of further central composition design (CCD) showed that the optimal concentration of glucose, rice meal and peanut cake meal were 18.7 g/L, 64.8 g/L and 65.1 g/L, respectively. By using this optimal fermentation medium, the MIL-C concentration was increased up to 1336.5 mg/L, an approximate 3.8-fold improvement over the previous concentration (350.0 mg/L) with un-optimized medium. This work will be very helpful to the large-scale production of MIL-C in the future.

A high-throughput method for screening of rapamycin-producing strains of Streptomyces hygroscopicus by cultivation in 96-well microtiter plates.

A novel high-throughput cultivation method was developed to rapidly screen large numbers of rapamycin-producing mutants of Streptomyces hygroscopicus by duplicate culturing of isolates on the surfaces of agar-solidified 96 wells in microtiter plates. One copy of the cultures was used for the rapamycin bioassay and the other identical copy, representing potentially high yielding strains, was preserved for further study. By integrating 96-well solid cultivation and the bioassay, we screened more than 7000 isolates and found 10 high-yielding strains. From these, one mutant produced 420 mug rapamycin/ml, which was double the yield of parent strain used in the submerged fermentation process.

[Expression of the soluble human Fas ligand in Dictyostelium discoideum].

An expression system is described for high-yield production of recombinant soluble human FasL (shFasL) in Dictyostelium discoideum cells. DNA encoding amino acids 141 - 281 of hFasL was PCR amplified from cDNA derived from activated human neutrophils. The resulting product was fused with a DNA fragment encoding hCG-beta signal peptide and cloned in the expression vector pMB12neo. Dictyostelium strain AX3 was transfected with this plasmid, yielding a recombinant strain called AX3-pCESFL95-H3. In order to improve the shFasL expression level, pMB12neo was optimized by replacing its transcriptional terminator/ polyadenylation segment of the 2H3 gene with an actin8 terminator/polyadenylation segment, yielding derived expression vector pMB74. The recombinant Dictyostelium strain called AX3-pLu8 was generated with this new plasmid. When the recombinant cells were cultivated in a complex HL-5C medium, a cell density of (1.5 - 2) x 10(7)/mL was reached, and the shFasL level expressed by strains AX3-pCESFL95-H3 and AX3-pLu8 was 23.5 microg/L and 206 microg/L, respectively. By using a newly developed synthetic medium called SIH as culture medium, higher cell density of (4 - 5) x 10(7)/mL was achieved. Correspondently, 111 microg/L and 420 microg/L shFasL were secreted by recombinant strains AX3-pCESFL95-H3 and AX3-pLu8, respectively.

Effects of medium composition on the production of plasmid DNA vector potentially for human gene therapy.

Plasmid vector is increasingly applied to gene therapy or gene vaccine. The production of plasmid pCMV-AP3 for cancer gene therapy was conducted in a modified MBL medium using a recombinant E. coli BL21 system. The effects of different MMBL components on plasmid yield, cell mass and specific plasmid DNA productivity were evaluated on shake-flask scale. The results showed that glucose was the optimal carbon source. High plasmid yield (58.3 mg/L) was obtained when 5.0 g/L glucose was added to MMBL. Glycerol could be chosen as a complementary carbon source because of the highest specific plasmid productivity (37.9 mg DNA/g DCW). After tests of different levels of nitrogen source and inorganic phosphate, a modified MMBL medium was formulated for optimal plasmid production. Further study showed that the initial acetate addition (less than 4.0 g/L) in MMBL improved plasmid production significantly, although it inhibited cell growth. The results will be useful for large-scale plasmid production using recombinant E. coli system.

[Advances in the research of human defensins].

Human defensin is a family of cationic antimicrobial peptides in human being. During the last two decades a series of endogenous alpha-and beta-human defensins have been discovered. They are important components of the first barrier in human's body against the invasion of various microorganisms, and they are thought to play an important role in linking the innate and adaptive defense system of human being. The recent advances in the research of human defensins were reviewed, including their discovery, molecular and genetic properties, expression regulation, and mechanisms of antimicrobial activity. The possibility to produce human defensins via genetic engineering was also discussed. And the application outlook of human defensins in medicine and curing patients infected with antibiotics-resistant microbials was presented.

Improvement of industry-applied rifamycin B-producing strain, Amycolatopsis mediterranei, by rational screening.

An industrially applied rifamycin B-producing strain, Amycolatopsis mediterranei XC 1-02, was used for further screening. A special mutation and screening procedure was adopted to select a strain, which can alleviate the inhibition caused by both aromatic amino acid and p-hydroxybenzoic acid in the pathway of rifamycin B biosynthesis as well as enhance the production of propionate, one of the precursors of rifamycin B biosynthesis. By the above methods, a strain A. mediterranei XC 9-25 was obtained, and its rifamycin B productivity in shaking flask reaches 10 g/L, which is 2.38 times higher than that of the ancestral strain XC 1-02. The productivity of rifamycin B fed-batch fermentation in 60000 L fermentor with A. mediterranei XC 9-25 reached 19.11 g/L.