Fermentative production of self-toxic fungal secondary metabolites

Isolation, anticancer potency, and camptothecin-producing ability of endophytic fungi isolated from Ixora chinensis

Camptothecin (CPT) is an important alkaloid used for anticancer treatment. It is mainly produced by two endangered and overharvested Camptotheca acuminata and Nothapodytes nimmoniana plants. Endophytic fungi are promising alternative sources for CPT production. In the present study, fungi residing within explants of Ixora chinensis were isolated and their CPT-producing capability of their endophytes was verified via thin-layer chromatography, high-performance liquid chromatography, liquid chromatography/high resolution mass spectrometry, and nuclear magnetic resonance analyses and compared with standards. In addition, MTT and sulforhodamine B assays were selected to test the anticancer effect. The endophytic fungi collection of 62 isolates were assigned to 11 genera, with four common genera (Diaporthe, Phyllosticta, Colletotrichum, and Phomopsis) and seven less common genera (Penicillium, Botryosphaeria, Fusarium, Pestalotiopsis, Aspergillus, and Didymella). Moreover, the anticancer activity of extracts was assessed against human lung carcinoma (A549). Among eight potential extracts, only Penicillium sp. I3R2 was found to be a source of CPT, while the remaining seven extracts have not been discovered potential secondary compounds. Thus, other prominent endophytic fungi might be potential candidates of phytochemicals with anticancer properties.

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

Sodium starch octenyl succinate facilitated the production of water-soluble yellow pigments in Monascus ruber fermentation

Natural water-soluble Monascus pigments (WSMPs) have been in increasing demand but have not been able to achieve industrial production due to the low production rate. This study aimed to improve the biosynthesis and secretion of extracellular yellow pigments (EYPs) through submerged fermentation with Monascus ruber CGMCC 10,910 supplemented with sodium starch octenyl succinate (OSA-SNa). The results demonstrated that the yield was 69.68% and 48.89% higher than that without OSA-SNa in conventional fermentation (CF) and extractive fermentation (EF), respectively. The mainly increased EYP components were Y3 and Y4 in CF, but they were mainly Y1 and Y2 as well as secreted intracellular pigments, including Y5, Y6, O1, and O2, in EF. Scanning electron microscopy analysis revealed that the mycelium presented an uneven surface profile with obvious wrinkles and small fragments with OSA-SNa. It was found that a higher unsaturated/saturated fatty acids ratio in the cell membrane resulted in increased permeability and facilitated the export of intracellular yellow pigments into the broth with OSA-SNa treatment. In addition, a higher NAD⁺/NADH ratio and glucose-6-phosphate dehydrogenase activity provided a reducing condition for yellow pigment biosynthesis. Gene expression analysis showed that the expression levels of the key genes for yellow pigment biosynthesis were significantly upregulated by OSA-SNa. This study provides an effective strategy to promote the production of WSMPs by microparticle-enhanced cultivation using OSA-SNa. KEY POINTS: • OSA-SNa addition facilitated the production of Monascus yellow pigments. • Mycelial morphology and membrane permeability were affected by OSA-SNa. • The key gene expression of yellow pigments was upregulated.

Current advances of endophytes as a platform for production of anti-cancer drug camptothecin

Camptothecin (CPT), a well-known monoterpenoid indole alkaloid with broad-spectrum anti-cancer activity, is produced from plants and endophytes. In view of the limitations of plants as sources of camptothecin in productivity and efficiency, endophytes serve as the fast growth, high cost-effectiveness, good reproducibility, and feasible genetic manipulation, so they have the potential to meet the huge market demand of the pharmaceutical industry. In this review, we summarized the isolation, identification and fermentation of CPT-producing endophytes, as well as the biosynthesis, extraction and detection of camptothecin from endophytes. Among them, we put emphasis on increasing the production of camptothecin in endophytes through different strategies such as changing the proportion of carbon, nitrogen and phosphate source, adding the precursors, elicitors or adsorbent resin, utilizing co-culture fermentation or fermenter culture. However, cell subculture and metabolic reprogramming affect the expression of camptothecin biosynthetic genes in CPT-producing endophytes, which poses a challenge to the industrial production of camptothecin. Therefore, it will be useful to gain insights through the review of these researches and provide alternative approaches to develop economical, eco-friendly and reliable natural products.

In-Situ Recovery of Persipeptides from Streptomyces zagrosensis Fermentation Broth by Enhanced Adsorption

Background:

Drug discovery process is growing considerably due to the noteworthy resource of natural products. Persipeptides A and B are cyclopeptide antibiotics, which are produced by Streptomyces zagrosensis UTMC 1154. Although extraction of culture broth with the help of solvent has been optimized previously, no effort for In-Situ extraction of persipeptides has been done yet.

Objective:

To produce a high quantity of persipeptides for further drug evaluation, it is crucial to design approaches aimed at improvement of the extraction yield.

Materials and Methods:

Amberlite XAD-16N was employed into the fermentation culture medium of S. zagrosensis in order to enhance the In-Situ extraction of persipeptides. Effects of resin content (%), resin addition time (h), and fermentation time (day) were investigated by a two-level full factorial experimental design.

Results:

The main factors of resin content (%) and the interaction of resin content (%) with resin addition time (day) were found to be important using ANOVA. The results showed the amount of 0.33 % (w.v^-1) amberlite XAD-16N added at 27.2 h post-inoculation was the most effective combination to increase the efficiency of In-Situ adsorption capacity of persipeptides.

Conclusions:

The provided method requires 3.3 g resin and 200 mL methanol for the extraction of persipeptides from each liter of fermentation culture of S. zagrosensis in less than 15 min. Apart from cost-efficiently and simplicity, this procedure enhanced the recovery of persipeptides by 7 % and 3 times, compared to ISP2 medium without any resin after 4 and 7 days of fermentation, respectively. Therefore, this method can be regarded as a cost-efficient enhancement approach for the production of these newly-discovered metabolites before implementing the genetic manipulation or intensive media optimization, demanding considerable time and effort.

Bacteria Associated With Shiraia Fruiting Bodies Influence Fungal Production of Hypocrellin A

Hypocrellin A (HA) is a natural red perylenequinone pigment from Shiraia fruiting body, which was used clinically on various skin diseases and developed as a photodynamic therapy agent against cancers. The fruiting bodies may harbor a diverse but poorly understood microbial community. In this study, we characterized the bacterial community of Shiraia fruiting body using a combination of culture-based method and Illumina high-throughput sequencing, and tested the involvement of some companion bacteria in fungal HA production using the fungal-bacterial confrontation assay. Our results revealed that the bacterial community in the fruiting body was dominated by Bacillus and Pseudomonas. Some Pseudomonas isolates such as P. fulva, P. putida, and P. parafulva could stimulate fungal HA accumulation by Shiraia sp. S9. The bacterial treatment of P. fulva SB1 up-regulated the expression of polyketide synthase (PKS) for HA biosynthesis and transporter genes including ATP-binding cassette (ABC) and major facilitator superfamily transporter (MFS) for HA exudation. After the addition of live P. fulva SB1, the mycelium cultures of Shiraia sp. S9 presented a higher HA production (225.34 mg/L), about 3.25-fold over the mono-culture. On the other hand, B. cereus was capable of alleviating fungal self-toxicity from HA via down-regulation of HA biosynthetic genes or possible biodegradation on HA. To our knowledge, this is the first report on the diversified species of bacteria associated with Shiraia fruiting bodies and the regulation roles of the companion bacteria on fungal HA biosynthesis. Furthermore, the bacterial co-culture provided a good strategy for the enhanced HA production by Shiraia.

Nonribosomal peptides in fungal cell factories: from genome mining to optimized heterologous production

Fungi are notoriously prolific producers of secondary metabolites including nonribosomal peptides (NRPs). The structural complexity of NRPs grants them interesting activities such as antibiotic, anti-cancer, and anti-inflammatory properties. The discovery of these compounds with attractive activities can be achieved by using two approaches: either by screening samples originating from various environments for their biological activities, or by identifying the related clusters in genomic sequences thanks to bioinformatics tools. This genome mining approach has grown tremendously due to recent advances in genome sequencing, which have provided an incredible amount of genomic data from hundreds of microbial species. Regarding fungal organisms, the genomic data have revealed the presence of an unexpected number of putative NRP-related gene clusters. This highlights fungi as a goldmine for the discovery of putative novel bioactive compounds. Recent development of NRP dedicated bioinformatics tools have increased the capacity to identify these gene clusters and to deduce NRPs structures, speeding-up the screening process for novel metabolites discovery. Unfortunately, the newly identified compound is frequently not or poorly produced by native producers due to a lack of expression of the related genes cluster. A frequently employed strategy to increase production rates consists in transferring the related biosynthetic pathway in heterologous hosts. This review aims to provide a comprehensive overview about the topic of NRPs discovery, from gene cluster identification by genome mining to the heterologous production in fungal hosts. The main computational tools and methods for genome mining are herein presented with an emphasis on the particularities of the fungal systems. The different steps of the reconstitution of NRP biosynthetic pathway in heterologous fungal cell factories will be discussed, as well as the key factors to consider for maximizing productivity. Several examples will be developed to illustrate the potential of heterologous production to both discover uncharacterized novel compounds predicted in silico by genome mining, and to enhance the productivity of interesting bio-active natural products.

Strategies to enhance the production of pinoresinol and its glucosides by endophytic fungus (Phomopsis sp. XP-8) isolated from Tu-chung bark

To improve the production yield of (+)-pinoresinol (Pin), (+)-pinoresinol monoglucoside (PMG), and (+)-pinoresinol diglucoside (PDG), different methods were conducted, including co-culture with resveratrol-producing Alternaria sp. MG1 spores and addition of Tu-chung in a medium at the start of cultivation, ultrasound treatment (40 kHZ, 10 min) on 5-day culture, and addition of ethanol and sodium butyrate on Day 3, followed by cultivation for an additional period of 2 days. At the end of the cultivation period (5 days), the liquid phase was collected for product analysis. Cells were collected for the determination of gene expression levels and then used in bioconversion using resting cells for another period of 2 days. The liquid phase was measured to determine the output of the target products and the expression levels of the key genes related to the biosynthesis of these compounds. Consequently, co-culture with Alternaria MG1 and addition of Tu-chung bark in the medium efficiently increased Pin, PMG, and PDG production yield in the biosynthesis systems using potato dextrose broth medium and resting cells of Phomopsis sp. XP-8. The key genes related to the biosynthesis of these compounds were significantly upregulated. However, in the majority of cases, the addition of ethanol and sodium butyrate, and ultrasound treatment decreased the production yield of Pin, PMG, and PDG. The change in production yield was not consistently accompanied by a change in gene expression.

Enhanced production of total flavones from Inonotus baumii by multiple strategies

As one kind of important secondary metabolites produced by Inonotus baumii, flavones can be applied in food, medicine, and other industries due to their biological activities such as antioxidant, anticancer, and antibacterial activity. To enhance total flavone production in submerged fermentation of I. baumii, three different strategies, optimization of fermentation parameters by statistical designs including Plackett-Burman design and response surface methodology, addition of precursors and elicitors, and two-phase culture, were used. The production of total flavones (PTF) reached 1532.83 mg/L when the optimized medium was used. All precursors and elicitors can increase the PTF. The maximum PTF (2184.06 mg/L, up to 1.57-fold) was obtained with the addition of both AgNO₃ and glutathione in fermentation media. Interestingly, when 0.5% (w/v) DM130 macroporous resin as adsorbent was added to fermentation broth on day 4 of culture, the highest production reached 2407.79 mg/L with this two-phase culture strategy. These methods can be further applied to large-scale industrial production and broaden the application of flavones.

Scaling up a virginiamycin production by a high-yield Streptomyces virginiae VKM Ac-2738D strain using adsorbing resin addition and fed-batch fermentation under controlled conditions

Virginiamycin produced by Streptomyces virginiae as a natural mix of macrocyclic peptidolactones M and S is widely used in the industrial production of ethanol fuel and as an antibiotic feed additive for cattle and poultry. Its main antimicrobial components, M1 and S1 factors, act synergistically if the M1:S1 ratio in the final product is 70-75:25-30. This fact significantly complicates the development of stable high-yield strains suitable for industrial application. In the previous work, authors obtained a mutant S. virginiae VKM Ac-2738D strain, characterized by a high productivity in flasks and the optimum M1:S1 ratio (75:25) in the final product. In this study, the scale-up of the virginiamycin production by VKM AC-2738D from shake flasks to a pilot-scale (100 L) stirred fermentor was carried out and the possibility of the in situ use of synthetic adsorbing resins to remove virginiamycin from culture broth was assessed. After the optimization of pH and dissolved oxygen concentration (6.8-7.0 and 50%, respectively), the fed-batch fermentation of VKM Ac-2738D with continuous addition of 50% sucrose solution (5 g/L/day starting from 48 h of fermentation) resulted in a final virginiamycin titer of 4.9 g/L. Among four tested resins, Diaion® HP21 added to fermentation medium prior to sterilization absorbed 98.5% of the total virginiamycin that simplifies its further recovery procedure and increased its total titer to 5.6 g/L at the M1:S1 ratio of 74:26. The developed technology has several important advantages, which include (1) the optimum M1:S1 ratio in the final product, (2) the possibility to use sucrose as a carbon source instead of traditionally used and more expensive glucose or D-maltose, and (3) selective binding of up to 98.5% of produced virginiamycin on the adsorbing resin.

Interspecific metabolic diversity of root-colonizing endophytic fungi revealed by enzyme activity tests

Although dark septate endophytes (DSE) represent a worldwide dispersed form group of root-colonizing endophytic fungi, our knowledge on their role in ecosystem functioning is far limited. In this study, we aimed to test if functional diversity exists among DSE fungi representing different lineages of root endophytic fungal community of semiarid sandy grasslands. To address this question and to gain general information on function of DSE fungi, we adopted api-ZYM and BioLog FF assays to study those non-sporulating filamentous fungi and characterized the metabolic activity of 15 different DSE species. Although there were striking differences among the species, all of the substrates tested were utilized by the DSE fungi. When endophytes characteristic to grasses and non-grass host plants were separately considered, we found that the whole substrate repertoire was used by both groups. This might illustrate the complementary functional diversity of the communities root endophytic plant-associated fungi. The broad spectra of substrates utilized by these root endophytes illustrate the functional importance of their diversity, which can play role not only in nutrient mobilization and uptake of plants from with nutrient poor soils, but also in general plant performance and ecosystem functioning.

Efficient production of nonactin by Streptomyces griseus subsp. griseus

Here we report the production of the cyclic macrotetrolide nonactin from the fermentation culture of Streptomyces griseus subsp. griseus. Nonactin is a member of a family of naturally occurring cyclic ionophores known as the macrotetrolide antibiotics. Our fermentation procedure of Streptomyces griseus was performed at 30 °C and 200 rev·min−1 for 5 days on a rotary shaker. Diaion HP-20 and Amberlite XAD-16 were added to the fermentation medium. Isolated yield of nonactin was up to 80 mg·L−1 using our methodology. Nonactin is commonly known as an ammonium ionophore and also exhibits antibacterial, antiviral, and antitumor activities. It is also widely used for the preparation of ion-selective electrodes and sensors. Chemical synthesis of nonactin has been achieved by some groups; however, overall yields are very low, making efficient biosynthesis an attractive means of production.

Endophytes as in vitro production platforms of high value plant secondary metabolites

Many reports have been published on bioprospecting of endophytic fungi capable of producing high value bioactive molecules like, paclitaxel, vincristine, vinblastine, camptothecin and podophyllotoxin. However, commercial exploitation of endophytes for high value-low volume plant secondary metabolites remains elusive due to widely reported genomic instability of endophytes in the axenic culture. While most of the endophyte research focuses on screening endophytes for novel or existing high value biomolecules, very few reports seek to explore the possible mechanisms of production of host-plant associated or novel secondary metabolites in these organisms. With an overview of host-endophyte relationship and its possible impact on the secondary metabolite production potential of endophytes, the review highlights the evidence reported for and against the presence of host-independent biosynthetic machinery in endophytes. The review aims to address the question, why should and how can endophytes be exploited for large scale in vitro production of high value phytochemicals? In this regard, various bioprocess optimization strategies that have been applied to sustain and enhance the product yield from the endophytes have also been described in detail. Further, techniques like mixed fermentation/co-cultivation and use of epigenetic modifiers have also been discussed as potential strategies to activate cryptic gene clusters in endophytes, thereby aiding in novel metabolite discovery and overcoming the limitations associated with axenic culture of endophytes.

Nitrogen recycling from fuel-extracted algal biomass: residuals as the sole nitrogen source for culturing Scenedesmus acutus

In this study, the reuse of nitrogen from fuel-extracted algal residues was investigated. The alga Scenedesmus acutus was found to be able to assimilate nitrogen contained in amino acids, yeast extracts, and proteinaceous alga residuals. Moreover, these alternative nitrogen resources could replace nitrate in culturing media. The ability of S. acutus to utilize the nitrogen remaining in processed algal biomass was unique among the promising biofuel strains tested. This alga was leveraged in a recycling approach where nitrogen is recovered from algal biomass residuals that remain after lipids are extracted and carbohydrates are fermented to ethanol. The protein-rich residuals not only provided an effective nitrogen resource, but also contributed to a carbon "heterotrophic boost" in subsequent culturing, improving overall biomass and lipid yields relative to the control medium with only nitrate. Prior treatment of the algal residues with Diaion HP20 resin was required to remove compounds inhibitory to algal growth.

Enhanced production of botrallin and TMC-264 with in situ macroporous resin adsorption in mycelial liquid culture of the endophytic fungus Hyalodendriella sp. Ponipodef12

Hyalodendriella sp. Ponipodef12, an endophytic fungus from the hybrid "Neva" of Populus deltoides × P. nigra, is a high producer of the bioactive dibenzo-α-pyrones botrallin and TMC-264. However, both the botrallin and TMC-264 produced by Hyalodendriella sp. Ponipodef12 were retained as both intracellular and extracellular products. The aim of this study was to evaluate an in situ macroporous resin adsorption for enhancement of botrallin and TMC-264 production in mycelial liquid culture of Hyalodendriella sp. Ponipodef12. Production of botrallin and TMC-264 was most effectively enhanced by macroporous resin DM-301 among the thirteen nonionic macroporous resins tested. The highest botrallin yield (51.47 mg/L, which was 2.29-fold higher than the control at 22.49 mg/L) was obtained by adding resin DM-301 at 4.38% (g/mL) to the culture broth on day 24 and allowing a period of 4 days for adsorption. The highest TMC-264 yield reached 47.74 mg/L, which was 11.76-fold higher than that of the control (4.06 mg/L), and was achieved by adding DM-301 resin at 4.38% (w/v) in the culture broth on day 24 and allowing a period of 6 days for adsorption. The results show that in situ resin adsorption is an effective strategy for enhancing production of botrallin and TMC-264, and also for facilitating their recovery from mycelial liquid culture of Hyalodendriella sp. Ponipodef12.

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.

Assessing the effects of adsorptive polymeric resin additions on fungal secondary metabolite chemical diversity

Adsorptive polymeric resins have been occasionally described to enhance the production of specific secondary metabolites (SMs) of interest. Methods that induce the expression of new chemical entities in fungal fermentations may lead to the discovery of new bioactive molecules and should be addressed as possible tools for the creation of new microbial chemical libraries for drug lead discovery. Herein, we apply both biological activity and chemical evaluations to assess the use of adsorptive resins as tools for the differential expression of SMs in fungal strain sets. Data automation approaches were applied to ultra high performance liquid chromatography analysis of extracts to evaluate the general influence in generating new chemical entities or in changing the production of specific SMs by fungi grown in the presence of resins and different base media.

Use of in situ solid-phase adsorption in microbial natural product fermentation development

It has been half a century since investigators first began experimenting with adding ion exchange resins during the fermentation of microbial natural products. With the development of nonionic polymeric adsorbents in the 1970s, the application of in situ product adsorption in bioprocessing has grown slowly, but steadily. To date, in situ product adsorption strategies have been used in biotransformations, plant cell culture, the production of biofuels, and selected bulk chemicals, such as butanol and lactic acid, as well as in more traditional natural product fermentation within the pharmaceutical industry. Apart from the operational gains in efficiency from the integration of fermentation and primary recovery, the addition of adsorbents during fermentation has repeatedly demonstrated the capacity to significantly increase titers by sequestering the product and preventing or mitigating degradation, feedback inhibition and/or cytotoxic effects. Adoption of in situ product adsorption has been particularly valuable in the early stages of natural product-based drug discovery programs, where quickly and cost-effectively generating multigram quantities of a lead compound can be challenging when using a wild-type strain and fermentation conditions that have not been optimized. While much of the literature involving in situ adsorption describes its application early in the drug development process, this does not imply that the potential for scale-up is limited. To date, commercial-scale processes utilizing in situ product adsorption have reached batch sizes of at least 30,000 l. Here we present examples where in situ product adsorption has been used to improve product titers or alter the ratios among biosynthetically related natural products, examine some of the relevant variables to consider, and discuss the mechanisms by which in situ adsorption may impact the biosynthesis of microbial natural products.

Chemical and physical modulation of antibiotic activity in emericella species

The addition of epigenetic modifying agents and ion-exchange resins to culture media and solid-state fermentations have been promoted as ways to stimulate expression of latent biosynthetic gene clusters and to modulate secondary metabolite biosynthesis. We asked how combination of these treatments would affect a population of screening isolates and their patterns of antibiosis relative to fermentation controls. A set of 43 Emericella strains, representing 25 species and varieties, were grown on a nutrient-rich medium comprising glucose, casein hydrolysate, urea, and mineral salts. Each strain was grown in untreated agitated liquid medium, a medium treated with suberoylanilide hydroxamic acid, a histone deacetylase inhibitor, 5-azacytidine, a DNA methylation inhibitor, an Amberlite non-ionic polyacrylate resin, and the same medium incorporated into an inert static vermiculite matrix. Species-inherent metabolic differences more strongly influenced patterns of antibiosis than medium treatments. The antibacterial siderophore, desferritriacetylfusigen, was detected in most species in liquid media, but not in the vermiculite medium. The predominant antifungal component detected was echinocandin B. Some species produced this antifungal regardless of treatment, although higher quantities were often produced in vermiculite. Several species are reported for the first time to produce echinocandin B. A new echinocandin analog, echinocandin E, was identified from E. quadrilineata.

Targeting Mnks for cancer therapy

Deregulation of protein synthesis is a common event in human cancer and a key player in translational control is eIF4E. Elevated expression levels of eIF4E promote cancer development and progression. Recent findings suggest that eIF4E activity is a key determinant of the PI3K/Akt/mTOR and Ras/Raf/MEK/ERK mediated tumorigenic activity and targeting eIF4E should have a major impact on these pathways in human cancer. The function of eIF4E is modulated through phosphorylation of a conserved serine (Ser209) by Mnk1 and Mnk2 downstream of ERK. While the phosphorylation event is necessary for oncogenic transformation, it seems to be dispensable for normal development. Hence, pharmacologic Mnk inhibitors may provide non-toxic and effective anti-cancer strategy. Strong circumstantial evidence indicates that Mnk inhibition presents attractive therapeutic potential, but the lack of selective Mnk inhibitors has so far confounded pharmacological target validation and clinical development.

Extractive fermentation for enhanced production of thailandepsin A from Burkholderia thailandensis E264 using polyaromatic adsorbent resin Diaion HP-20

Thailandepsin A is natural product of Burkholderia thailandensis E264 with potent histone deacetylase inhibitory activities and promising anticancer activities. The titer of thailandepsin A is very low (less than 10 mg/l) from limited empirical fermentation. To facilitate preclinical evaluations and potentially clinical development of thailandepsin A, systematic optimization and extractive fermentation of thailandepsin A from B. thailandensis E264 culture in flasks were investigated in this pilot study. The main fermentation parameters—28°C, pH 7.0, inoculum ratio 1% (v/v), incubation duration 60 h, medium volume 26%, shaking speed 170 rpm, and chloroform as extracting solvent—were determined by single factor experiments. Polyaromatic adsorbent resin Diaion HP-20, when added at a concentration of 4% (w/v), was most effective to reduce feedback inhibition of thailandepsin A and to significantly increase the titer of target product. Central composite design was used to further optimize the fermentation medium for B. thailandensis E264. The optimized medium contains glucose 17.89 g/l, tryptone 34.98 g/l, potassium phosphate 24.84 g/l, and sodium citrate 0.01 g/l, which resulted in a large increase of the titer of thailandepsin A to 236.7 mg/l. Finally kinetic models based on the modified logistic and Luedeking–Piret equations were developed, delivering a good description of temporal variations of biomass, product, and substrate in the fermentation process, which could be used as references for developing large-scale fermentation.