Production of a novel FK520 analog in <Emphasis Type="Italic">Streptomyces hygroscopicus</Emphasis>: Improving titer while minimizing impurities

FK520, also called ascomycin, is an immunosuppressive agent produced by Streptomyces hygroscopicus. Engineering the polyketide synthase genes of the parent strain generated novel FK520 analogs with the potential for improved in vivo stability. By replacing the acyl transferase (AT) domain in the polyketide synthase module 8 with an AT specific for methylmalonyl CoA (the rapamycin AT 3), the strain produced 13-desmethoxy-13-methyl-FK520 (13dmmFK520). Process development and scale-up studies of this recombinant S. hygroscopicus strain producing 13dmmFK520 are described here. Production kinetics and compound stability in fermentation broth were significantly different compared to the native FK520. Fermentation of the new strain resulted in the synthesis of a contaminating substance that co-purified with the 13dmmFK520. To optimize 13dmmFK520 production and to facilitate purification, growth parameters and media development were examined. Although a medium was identified that increased product titers by ca. 300%, the ratio of impurity to product was doubled. Lower dissolved oxygen (20% compared to 50% and 80%) increased titers by 20% with no appreciable effect on the concentration of impurity. Increasing the fermentation pH from 6.0 to 6.5 did not change the 13dmmFK520 titer, but reduced the impurity-to-product ratio by approximately 450%. Journal of Industrial Microbiology & Biotechnology (2002) 28, 12–16 DOI: 10.1038/sj/jim/7000208 Received 30 January 2001/ Accepted in revised form 26 August 2001     

Femtosecond laser-based mutagenesis strategy for micronomicin production enhancement of Micromonospora sagamiensis ATCC 21826

In this work, a mutant MX3004 with improved micronomicin (MCR) production was derived from Micromonospora sagamiensis ATCC21826, which was treated with femtosecond laser under the optimized irradiation conditions of 75 mW and 180 s, with a maximum of positive mutation rate of 17.8 % and the mortality rate of 69.2 %. A novel high-throughput method was established using microplate reader by quantifying the concentration of MCR for efficient screening of positive mutant from large numbers of mutants. Consequently, MX3004 displayed the highest MCR production capacity of 126 U/ml and a stable heredity (ten generations). Moreover, under the optimal fermentation conditions in a 7.5 l fermenter, the MCR production of MX3004 reached the maximum of 263 U/ml, which was increased by 484 % compared with the parent strain. The results suggest that femtosecond laser is a suitable method for the MCR production improvement and the screening method has a great potential application for aminoglycoside antibiotic production.     

Genetic relationships among actinomycetes that produce the immunosuppressant macrolides FK506, FK520/FK523 and rapamycin

Summary A polyphasic taxonomic study was undertaken to establish the genetic and phenotypic relationships among six actinomycetes that produce the immunosuppressant macrolides FK506, FK520/FK523 and rapamycin. Chemotaxonomic studies reveal that all have Type I cell walls. Gas chromatography (GC) of fatty acid methyl esters revealed patterns consistent for strains ofStreptomyces with 160 and 150anteiso predominating. Principal component analysis of GC data revealed distinct profiles for each culture. Reciprocal DNA homology studies atT _m -25 showed the rapamycin-producing strain and one FK506-producing strain to have 38–50% homology with the type strain ofStreptomyces hygroscopicus (ATCC 27438). The remaining strains exhibited 6–17% homology. To further explore the relationships among these strains all were probed for the presence of anO-methyltransferase gene specific to this biosynthetic pathway. Among the strains of interest, onlyStreptomyces hygroscopicus subsp.yakushimaensis, the patent strain for FK520/FK523, failed to hybridize with the probes.     

Enhancement of ascomycin production in Streptomyces hygroscopicus var. ascomyceticus by combining resin HP20 addition and metabolic profiling analysis

Combinatorial approach of adsorbent resin HP20 addition and metabolic profiling analysis were carried out to enhance ascomycin production. Under the optimal condition of 5 % m/v HP20 added at 24 h, ascomycin production was increased to 380 from 300 mg/L. To further rationally guide the improvement of ascomycin production, metabolic profiling analysis was employed to investigate the intracellular metabolite changes of Streptomyces hygroscopicus var. ascomyceticus FS35 in response to HP20 addition. A correlation between the metabolic profiles and ascomycin accumulation was revealed by partial least-squares to latent structures discriminant analysis, and 11 key metabolites that most contributed to metabolism differences and ascomycin biosynthesis were identified. Based on the analysis of metabolite changes together with their pathways, the potential key factors associated with ascomycin overproduction were determined. Finally, rationally designed fermentation strategies based on HP20 addition were performed as follows: 2 % v/v n-hexadecane was added at 24 h; 1.0 g/L valine was supplemented at 48 h; 1.0 g/L lysine was added at 72 h. The ascomycin production was ultimately improved to 460 mg/L, a 53.3 % enhancement compared with that obtained in initial condition. These results demonstrated that the combination of HP20 addition and metabolic profiling analysis could be successfully applied to the rational guidance of production improvement of ascomycin, as well as other clinically important compounds.     

Novel chemobiosynthetic approach for exclusive production of FK506

FK506, a widely used immunosuppressant, is produced by industrial fermentation processes using various Streptomyces species. Independently of the strain, structurally related compound FK520 is co-produced, resulting in complex and costly isolation procedures. In this paper, we report a chemobiosynthetic approach for exclusive biosynthesis of FK506. This approach is based on the Streptomyces tsukubaensis strain with inactivated allR gene, a homologue of crotonyl-CoA carboxylase/reductase, encoded in the FK506 biosynthetic cluster. This strain produces neither FK506 nor FK520; however, if allylmalonyl-S-N-acetylcysteamine precursor is added to cultivation broth, the production of FK506 is reestablished without FK506-related by-products. Using a combination of metabolic engineering and chemobiosynthetic approach, we achieved exclusive production of FK506, representing a significant step towards development of an advanced industrial bioprocess.     

Liquid chromatography-mass spectrometry characterization of FK506 biosynthetic intermediates in Streptomyces clavuligerus KCTC 10561BP

The development of an efficient analytical method for the reliable detection and identification of the biosynthetic intermediates found in microbial cultures, which usually produce complex intermediates of the metabolites of interest, is essential for further biosynthetic investigations. This study developed a simple and highly selective method for detecting the biosynthetic intermediates involved in the FK506 pathway of Streptomyces clavuligerus KCTC 10561BP involving a cleanup procedure using a solid-phase extraction technique to provide reliable extraction of FK506-related compounds from a cell culture broth and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) to separate and detect the FK506-related intermediates at concentrations as low as 0.2 μg/L in the broth. This method enabled the analytical profiling of the intermediates formed during the biosynthesis of FK506 in this S. clavuligerus strain, which produced FK506 as a main product. Eight FK506 intermediates—FK520, 37,38-dihydroFK506, prolylFK506, 9-decarbonyl-9-hydroxylFK506, 9-deoxoFK506, desmethylFK520, prolylFK520, and 9-deoxoFK520—were identified. This is the first report of the LC-ESI-MS/MS characterization of a wide range of FK506 analogs from a bacterial fermentation broth. The protocol employed in this study may be useful for estimating the structure of the metabolites without the need for a time-consuming isolation process and nuclear magnetic resonance (NMR) spectroscopy.     

Enhancement of FK506 production by engineering secondary pathways of Streptomyces tsukubaensis and exogenous feeding strategies

FK506 is a clinically important macrocyclic polyketide with immunosuppressive activity produced by Streptomyces tsukubaensis. However, the low titer at which it is produced is a bottleneck to its application and use in industrial processes. We have overexpressed five potential targets associated with FK506 production (fkbO, fkbL, fkbP, fkbM, fkbD) which were identified in our previous study, with the aim to improve FK506 production. The results of the analysis showed that the constructed strains with an additional copy of each gene increased FK506 production by approximately 10–40 % compared with the wild-type strain D852. The results of the gene expression analysis indicated that each gene was upregulated. Combinatorial overexpression of the five genes resulted in a 146 % increase in the FK506 titer to 353.2 mg/L, in comparison with the titer produced by D852. To further improve the production of FK506 by the engineered strain HT-FKBOPLMD, we supplemented the medium with various nutrients, including soybean oil, lactate, succinate, shikimate, chorismate, lysine, pipecolate, isoleucine and valine. Optimization of feeding concentrations and times resulted in HT-FKBOPLMD being able to produce approximately 70 % more FK506, thereby reaching the maximal titer of 457.5 mg/L, with lower amounts of by-products (FK520 and 37,38-dihydro-FK506). These results demonstrate that the combination of the metabolically engineered secondary pathways and the exogenous feeding strategies developed here was able to be successfully applied to improve the production of industrially and clinically important compounds.     

Enhancement of butanol tolerance and butanol yield in Clostridium acetobutylicum mutant NT642 obtained by nitrogen ion beam implantation

As a promising alternative biofuel, biobutanol can be produced through acetone/butanol/ethanol (ABE) fermentation. Currently, ABE fermentation is still a small-scale industry due to its low production and high input cost. Moreover, butanol toxicity to the Clostridium fermentation host limits the accumulation of butanol in the fermentation broth. The wild-type Clostridium acetobutylicum D64 can only produce about 13 g butanol/L and tolerates less than 2% (v/v) butanol. To improve the tolerance of C. acetobutylicum D64 for enhancing the production of butanol, nitrogen ion beam implantation was employed and finally five mutants with enhanced butanol tolerance were obtained. Among these, the most butanol tolerant mutant C. acetobutylicum NT642 can tolerate above 3% (v/v) butanol while the wide-type strain can only withstand 2% (v/v). In batch fermentation, the production of butanol and ABE yield of C. acetobutylicum NT642 was 15.4 g/L and 22.3 g/L, respectively, which were both higher than those of its parental strain and the other mutants using corn or cassava as substrate. Enhancing butanol tolerance is a great precondition for obtaining a hyper-yield producer. Nitrogen ion beam implantation could be a promising biotechnology to improve butanol tolerance and production of the host strain C. acetobutylicum.     

提高展青霉(Penicillium patulum)产灰黄霉素效价的诱变育种研究

为进一步筛选高产灰黄霉素的工业生产菌株,分别对前期采用紫外线-氯化锂（UV-LiCl）、半导体激光（LD laser）及CO2激光（CO2laser）对展青霉FS80-1复合诱变获得三株高产菌株进行液体发酵和固体培养比较。结果表明,通过UV-LiCl复合诱变获得突变菌株GM120-43的液体发酵产灰黄霉素效价11 982μg/mL,比出发菌株提高37.52%,固体培养效价为89 496μg/g（干重）,比出发菌株提高80.04%。;半导体激光诱变获得突变株LD100-1的液体发酵效价9 440μg/mL,固体培养效价119 766μg/g干重,比出发菌株FS80-1提高了140%;两个突变株的生物学特性均发生不同程度的变化,突菌株GM120-43适合于液体发酵生产,突变株LD100-1适合于固体发酵培养。     

Improvement of milbemycin-producing <Emphasis Type="Italic">Streptomyces bingchenggensis</Emphasis> by rational screening of ultraviolet- and chemically induced mutants

Milbemycin antibiotics are produced by Streptomyces hygroscopicus subsp. aureolacrimosus and a newly isolated Streptomyces bingchenggensis, respectively. According to the biosynthetic pathway of milbemycins generated by S. hygroscopicus subsp. aureolacrimosus, a rational screening procedure with UV irradiation and N-methyl-N′-nitroso-N-nitrosoguanidine (NTG) mutation was performed to obtain high milbemycin-producing S. bingchenggensis. Aminoacetic acid (Glycine)-resistant mutants (AA^r), propionate-resistant mutants (PRP^r), streptomycin-resistant mutants (STR^r) and 2-deoxy-d-glucose-resistant mutants (DOG^r) were selected successively. A strain S. bingchenggensis BC-109-6 with AA^r, PRPr, STR^r and DOG^r was obtained and its production of milbemycin A3 and A4 reached 1,450 μg/ml, which was 80% higher than that of the ancestral strain S. bingchenggensis BC-101-4. The subculture experiments indicated that the hereditary characteristic of high productivity of S. bingchenggensis BC-109-6 was stable. The production of milbemycin A3 and A4 by S. bingchenggensis BC-109-6 in a 50-l fermentor could reach 1,380 μg/ml after 360 h batch fermentation.     

Comparative metabolic profiling-based improvement of rapamycin production by Streptomyces hygroscopicus

Rapamycin is a clinically important macrocyclic polyketide with immunosuppressive activity produced by Streptomyces hygroscopicus. To rationally guide the improvement of rapamycin production, comparative metabolic profiling analysis was performed in this work to investigate the intracellular metabolic changes in S. hygroscopicus U1-6E7 fermentation in medium M1 and derived medium M2. A correlation between the metabolic profiles and rapamycin accumulation was revealed by partial least-squares to latent structures analysis, and 16 key metabolites that most contributed to the metabolism differences and rapamycin production were identified. Most of these metabolites were involved in tricarboxylic acid cycle, fatty acids, and shikimic acid and amino acids metabolism. Based on the analysis of key metabolites changes in the above pathways, corresponding exogenous addition strategies were proposed as follows: 1.0 g/L methyl oleate was added at 0 h; 1.0 g/L lysine was added at 12 h; 0.5 g/L shikimic acid was added at 24 h; 0.5 g/L sodium succinate, 0.1 g/L phenylalanine, 0.1 g/L tryptophan, and 0.1 g/L tyrosine were added at 36 h, successively, and a redesigned fermentation medium (M3) was obtained finally on the basis of M2. The production of rapamycin in M3 was increased by 56.6 % compared with it in M2, reaching 307 mg/L at the end of fermentation (120 h). These results demonstrated that metabolic profiling analysis was a successful method applied in the rational guidance of the production improvement of rapamycin, as well as other industrially or clinically important compounds.     

Enhancement of Ethanol Fermentation in Saccharomyces cerevisiae Sake Yeast by Disrupting Mitophagy Function

Saccharomyces cerevisiae sake yeast strain Kyokai no. 7 has one of the highest fermentation rates among brewery yeasts used worldwide; therefore, it is assumed that it is not possible to enhance its fermentation rate. However, in this study, we found that fermentation by sake yeast can be enhanced by inhibiting mitophagy. We observed mitophagy in wild-type sake yeast during the brewing of Ginjo sake, but not when the mitophagy gene (ATG32) was disrupted. During sake brewing, the maximum rate of CO₂ production and final ethanol concentration generated by the atg32Δ laboratory yeast mutant were 7.50% and 2.12% higher than those of the parent strain, respectively. This mutant exhibited an improved fermentation profile when cultured under limiting nutrient concentrations such as those used during Ginjo sake brewing as well as in minimal synthetic medium. The mutant produced ethanol at a concentration that was 2.76% higher than the parent strain, which has significant implications for industrial bioethanol production. The ethanol yield of the atg32Δ mutant was increased, and its biomass yield was decreased relative to the parent sake yeast strain, indicating that the atg32Δ mutant has acquired a high fermentation capability at the cost of decreasing biomass. Because natural biomass resources often lack sufficient nutrient levels for optimal fermentation, mitophagy may serve as an important target for improving the fermentative capacity of brewery yeasts.     

Cloning and Expression of Genes Encoding F107-C and K88-1NT Fimbrial Proteins of Enterotoxigenic Escherichia coli from Piglets

We cloned two genes coding F107-C and K88-1NT fimbrial subunits from strains E. coli C and 1NT isolated from Thua Thien Hue province, Vietnam. The mature peptide of faeG gene from strain E. coli 1NT (called faeG-1NT) is 100 % similarity with faeG gene, while the CDS of fedA gene from strain C (called fedA-C) has a similarity of 97 % with the fedA gene. Expression of the faeG-1NT and fedA-C genes in E. coli BL21 Star™ (DE3) produced proteins of ~31 and 22 kDa, respectively. The effect of IPTG concentration on the K88-1NT and F107-C fimbriae production was investigated. The results showed that 0.5 mM IPTG is suitable for higher expression of K88-1NT subunit, while 0.75 mM IPTG strongly stimulated expression of F107-C subunit. The optimal induction time for expression was also examined. Generally, highest expression of K88-1NT subunit occurred after 6 h of induction, while that of F107-C subunit is after 14 h.     

He-Ne laser irradiation of folate-producing Candida utilis and optimization of culture conditions under submerged fermentation

In an attempt to obtain a microbial strain with higher yield of folate for industrial applications, we mutated the wild strain Candida utilis Y1.0 using a novel mutagenic process, i.e., irradiation by a helium–neon (He-Ne) laser with an output power of 20 mW and an exposure time of 20 min. The yield of folate in the mutated cells reached 1,102 ng/mL, which was 20.4-fold that of the wild strain. The mutant strain Y3.636 was relatively stable in terms of folate production through eight successive transfers of cultures and batch fermentation in a 3.7-L stirred-tank fermenter. Optimization further increased the yield of the mutant by 110 %, i.e., to 2,314?±?13 ng/mL. The optimal culture conditions for folate production were: cultivation in fermentation culture medium composed of 62.5 g/L glucose, 15 g/L corn liquor, 3 g/L (NH₄)₂SO₄, 3 g/L MgSO₄, and 1 g/L glutamic acid; inoculum size of 9 %; incubation at 28 °C and 196 rpm for 36 h. A time-course study of cell growth and folate production by mutant strain Y3.636 strongly suggested that folate production in C. utilis is growth-associated.     

Glycerol Production by Fermenting Yeast Cells Is Essential for Optimal Bread Dough Fermentation

Glycerol is the main compatible solute in yeast Saccharomyces cerevisiae. When faced with osmotic stress, for example during semi-solid state bread dough fermentation, yeast cells produce and accumulate glycerol in order to prevent dehydration by balancing the intracellular osmolarity with that of the environment. However, increased glycerol production also results in decreased CO₂ production, which may reduce dough leavening. We investigated the effect of yeast glycerol production level on bread dough fermentation capacity of a commercial bakery strain and a laboratory strain. We find that Δgpd1 mutants that show decreased glycerol production show impaired dough fermentation. In contrast, overexpression of GPD1 in the laboratory strain results in increased fermentation rates in high-sugar dough and improved gas retention in the fermenting bread dough. Together, our results reveal the crucial role of glycerol production level by fermenting yeast cells in dough fermentation efficiency as well as gas retention in dough, thereby opening up new routes for the selection of improved commercial bakery yeasts.