Regulation of the phosphate metabolism in Streptomyces genus: impact on the secondary metabolites

An overview of the two-component system GarR/GarS role on antibiotic production in Streptomyces coelicolor

The Streptomyces genus comprises Gram-positive bacteria known to produce over two-thirds of the antibiotics used in medical practice. The biosynthesis of these secondary metabolites is highly regulated and influenced by a range of nutrients present in the growth medium. In Streptomyces coelicolor, glucose inhibits the production of actinorhodin (ACT) and undecylprodigiosin (RED) by a process known as carbon catabolite repression (CCR). However, the mechanism mediated by this carbon source still needs to be understood. It has been observed that glucose alters the transcriptomic profile of this actinobacteria, modifying different transcriptional regulators, including some of the one- and two-component systems (TCSs). Under glucose repression, the expression of one of these TCSs SCO6162/SCO6163 was negatively affected. We aimed to study the role of this TCS on secondary metabolite formation to define its influence in this general regulatory process and likely establish its relationship with other transcriptional regulators affecting antibiotic biosynthesis in the Streptomyces genus. In this work, in silico predictions suggested that this TCS can regulate the production of the secondary metabolites ACT and RED by transcriptional regulation and protein-protein interactions of the transcriptional factors (TFs) with other TCSs. These predictions were supported by experimental procedures such as deletion and complementation of the TFs and qPCR experiments. Our results suggest that in the presence of glucose, the TCS SCO6162/SCO6163, named GarR/GarS, is an important negative regulator of the ACT and RED production in S. coelicolor. KEY POINTS: • GarR/GarS is a TCS with domains for signal transduction and response regulation • GarR/GarS is an essential negative regulator of the ACT and RED production • GarR/GarS putatively interacts with and regulates activators of ACT and RED.

Genomics Analysis Reveals the Potential Biocontrol Mechanism of Pseudomonas aeruginosa QY43 against Fusarium pseudograminearum

Fusarium crown rot (FCR) in wheat is a prevalent soil-borne disease worldwide and poses a significant threat to the production of wheat (Triticum aestivum) in China, with F. pseudograminearum being the dominant pathogen. Currently, there is a shortage of biocontrol resources to control FCR induced by F. pseudograminearum, along with biocontrol mechanisms. In this study, we have identified 37 strains of biocontrol bacteria displaying antagonistic effects against F. pseudograminearum from over 8000 single colonies isolated from soil samples with a high incidence of FCR. Among them, QY43 exhibited remarkable efficacy in controlling FCR. Further analysis identified the isolate QY43 as Pseudomonas aeruginosa, based on its colony morphology and molecular biology. In vitro, QY43 significantly inhibited the growth, conidial germination, and the pathogenicity of F. pseudograminearum. In addition, QY43 exhibited a broad spectrum of antagonistic activities against several plant pathogens. The genomics analysis revealed that there are genes encoding potential biocontrol factors in the genome of QY43. The experimental results confirmed that QY43 secretes biocontrol factor siderophores and pyocyanin. In summary, QY43 exhibits a broad spectrum of antagonistic activities and the capacity to produce diverse biocontrol factors, thereby showing substantial potential for biocontrol applications to plant disease.

Functional expansion of the natural inorganic phosphorus starvation response system in Escherichia coli

Phosphorus, an indispensable nutrient, plays an essential role in cell composition, metabolism, and signal transduction. When inorganic phosphorus (Pi) is scarce, the Pi starvation response in E. coli is activated to increase phosphorus acquisition and drive the cells into a non-growing state to reduce phosphorus consumption. In the six decades of research history, the initiation, output, and shutdown processes of the Pi starvation response have been extensively studied. Simultaneously, Pi starvation has been used in biosensor development, recombinant protein production, and natural product biosynthesis. In this review, we focus on the output process and the applications of the Pi starvation response that have not been summarized before. Meanwhile, based on the current status of mechanistic studies and applications, we propose practical strategies to develop the natural Pi starvation response into a multifunctional and standardized regulatory system in four aspects, including response threshold, temporal expression, intensity range, and bifunctional regulation, which will contribute to its broader application in more fields such as industrial production, medical analysis, and environmental protection.

Characterization of 5'-nucleotidases secreted from Streptomyces

To study the ability of Streptomyces to utilize environmental nucleotides, we screened for strains exhibiting extracellular 5'-inosine monophosphate (IMP)-dephosphorylating activity in our collection of soil isolates and obtained two producers: NE5-10 and Y2F8-2. The enzyme responsible for the activity was purified from the culture supernatant of each strain, and its mass spectral data were used to identify the coding sequence. The gene was successfully identified in the whole genome sequence of each strain; it was located in a conserved gene cluster of phosphate-related functions and encoded an approximately 600-amino acid long protein containing an N-terminal secretion signal. The mature part of the protein exhibited similarity to a known bacterial 5'-nucleotidase. The locus of the 5'-nucleotidase gene contained genes encoding proteins involved in phosphate utilization. The conserved gene arrangement of the locus in various Streptomyces genomes suggested the genetic region to be involved in phosphate-scavenging in this group of bacteria. Phylogenetic analysis demonstrated that the isolated Streptomyces enzymes represent an uncharacterized group of bacterial 5'-nucleotidases. Enzymatic characterization of the two Streptomyces enzymes demonstrated that both enzymes exhibited 5'-nucleotidase activity but differed in terms of optimal temperature and pH, dependence on divalent cations, and substrate specificity. The Km and Vmax values of the 5'-IMP-dephosphorylating activity were 0.239 mM and 9.47 U/mg, respectively, for NE5-10 and 0.221 mM and 38.17 U/mg, respectively, for Y2F8-2. Enzyme activity in the culture broth of the two Streptomyces producers occurred in a phosphate-limitation-dependent manner, supporting their involvement in the acquisition of phosphorus. KEY POINTS: • We purified and characterized nucleotidases from two Streptomyces. • Two nucleotidases were presumed to be involved in phosphate acquisition. • It showed diversity in phosphate acquisition among microorganisms.

An overview on the two-component systems of Streptomyces coelicolor

The two-component system (TCS) found in various organisms is a regulatory system, which is involved in the response by the organism to stimuli, thereby regulating the internal behavior of the cell. It is commonly found in prokaryotes and is an important signaling system in bacteria. TCSs are involved in the regulation of physiological and morphological differentiation of the industrially important microbes from the genus Streptomyces, which produce a vast array of bioactive secondary metabolites (SMs). Genetic engineering of TCSs can substantially increase the yield of target SMs, which is valuable for industrial-scale production. Research on TCS has mainly been completed in the model strain Streptomyces coelicolor. In this review, we summarize the recent advances in the functional identification and elucidation of the regulatory mechanisms of various TCSs in S. coelicolor, with a focus on their roles in the biosynthesis of important SMs.

Two-Component Systems of Streptomyces coelicolor: An Intricate Network to Be Unraveled

Bacteria of the Streptomyces genus constitute an authentic biotech gold mine thanks to their ability to produce a myriad of compounds and enzymes of great interest at various clinical, agricultural, and industrial levels. Understanding the physiology of these organisms and revealing their regulatory mechanisms is essential for their manipulation and application. Two-component systems (TCSs) constitute the predominant signal transduction mechanism in prokaryotes, and can detect a multitude of external and internal stimuli and trigger the appropriate cellular responses for adapting to diverse environmental conditions. These global regulatory systems usually coordinate various biological processes for the maintenance of homeostasis and proper cell function. Here, we review the multiple TCSs described and characterized in Streptomyces coelicolor, one of the most studied and important model species within this bacterial group. TCSs are involved in all cellular processes; hence, unravelling the complex regulatory network they form is essential for their potential biotechnological application.

Comparative Proteomic Analysis of Transcriptional and Regulatory Proteins Abundances in S. lividans and S. coelicolor Suggests a Link between Various Stresses and Antibiotic Production

Streptomyces coelicolor and Streptomyces lividans constitute model strains to study the regulation of antibiotics biosynthesis in Streptomyces species since these closely related strains possess the same pathways directing the biosynthesis of various antibiotics but only S. coelicolor produces them. To get a better understanding of the origin of the contrasted abilities of these strains to produce bioactive specialized metabolites, these strains were grown in conditions of phosphate limitation or proficiency and a comparative analysis of their transcriptional/regulatory proteins was carried out. The abundance of the vast majority of the 355 proteins detected greatly differed between these two strains and responded differently to phosphate availability. This study confirmed, consistently with previous studies, that S. coelicolor suffers from nitrogen stress. This stress likely triggers the degradation of the nitrogen-rich peptidoglycan cell wall in order to recycle nitrogen present in its constituents, resulting in cell wall stress. When an altered cell wall is unable to fulfill its osmo-protective function, the bacteria also suffer from osmotic stress. This study thus revealed that these three stresses are intimately linked in S. coelicolor. The aggravation of these stresses leading to an increase of antibiotic biosynthesis, the connection between these stresses, and antibiotic production are discussed.

The Global Regulator PhoU Positively Controls Growth and Butenyl-Spinosyn Biosynthesis in Saccharopolyspora pogona

Butenyl-spinosyn, a highly effective biological insecticide, is produced by Saccharopolyspora pogona. However, its application has been severely hampered by its low yield. Recent studies have shown that PhoU plays a pivotal role in regulating cell growth, secondary metabolite biosynthesis and intracellular phosphate levels. Nevertheless, the function of PhoU remains ambiguous in S. pogona. In this study, we investigated the effects of PhoU on the growth and the butenyl-spinosyn biosynthesis of S. pogona by constructing the mutants. Overexpression of phoU increased the production of butenyl-spinosyn to 2.2-fold that of the wild-type strain. However, the phoU deletion resulted in a severe imbalance of intracellular phosphate levels, and suppression of the growth and butenyl-spinosyn biosynthesis. Quantitative Real-time PCR (qRT-PCR) analysis, distinctive protein detection and mass spectrometry revealed that PhoU widely regulated primary metabolism, energy metabolism and DNA repair, which implied that PhoU influences the growth and butenyl-spinosyn biosynthesis of S. pogona as a global regulator.

A TetR family transcriptional regulator, SP_2854 can affect the butenyl-spinosyn biosynthesis by regulating glucose metabolism in Saccharopolyspora pogona

Background

Butenyl-spinosyn produced by Saccharopolyspora pogona exhibits strong insecticidal activity and a broad pesticidal spectrum. Currently, important functional genes involve in butenyl-spinosyn biosynthesis remain unknown, which leads to difficulty in efficiently understanding its regulatory mechanism, and improving its production by metabolic engineering.

Results

Here, we identified a TetR family transcriptional regulator, SP_2854, that can positively regulate butenyl-spinosyn biosynthesis and affect strain growth, glucose consumption, and mycelial morphology in S. pogona. Using targeted metabolomic analyses, we found that SP_2854 overexpression enhanced glucose metabolism, while SP_2854 deletion had the opposite effect. To decipher the overproduction mechanism in detail, comparative proteomic analysis was carried out in the SP-2854 overexpressing mutant and the original strain, and we found that SP_2854 overexpression promoted the expression of proteins involved in glucose metabolism.

Conclusion

Our findings suggest that SP_2854 can affect strain growth and development and butenyl-spinosyn biosynthesis in S. pogona by controlling glucose metabolism. The strategy reported here will be valuable in paving the way for genetic engineering of regulatory elements in actinomycetes to improve important natural products production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01808-2.

Strategies of organic phosphorus recycling by soil bacteria: acquisition, metabolism, and regulation

Critical to meeting cellular phosphorus (P) demand, soil bacteria deploy a number of strategies to overcome limitation in inorganic P (P_i ) in soils. As a significant contributor to P recycling, soil bacteria secrete extracellular enzymes to degrade organic P (P_o ) in soils into the readily bioavailable P_i . In addition, several P_o compounds can be transported directly via specific transporters and subsequently enter intracellular metabolic pathways. In this review, we highlight the strategies that soil bacteria employ to recycle P_o from the soil environment. We discuss the diversity of extracellular phosphatases in soils, the selectivity of these enzymes towards various P_o biomolecules and the influence of the soil environmental conditions on the enzyme's activities. Moreover, we outline the intracellular metabolic pathways for P_o biosynthesis and transporter-assisted P_o and P_i uptake at different P_i availabilities. We further highlight the regulatory mechanisms that govern the production of phosphatases, the expression of P_o transporters and the key metabolic changes in P metabolism in response to environmental P_i availability. Due to the depletion of natural resources for P_i , we propose future studies needed to leverage bacteria-mediated P recycling from the large pools of P_o in soils or organic wastes to benefit agricultural productivity.

Impact of MtrA on phosphate metabolism genes and the response to altered phosphate conditions in Streptomyces

Phosphate metabolism is known to be regulated by the PhoPR regulatory system in Streptomyces and some other bacteria. In this study, we report that MtrA also regulates phosphate metabolism in Streptomyces. Our data showed that, in Streptomyces coelicolor, MtrA regulates not only phosphate metabolism genes such as phoA but also phoP under different phosphate conditions, including growth on rich complex media without added inorganic phosphate and on defined media with low or high concentrations of inorganic phosphate. Cross-regulation was also observed among mtrA, phoP and glnR under these conditions. We demonstrated both in vitro and in vivo binding of MtrA to the promoter regions of genes associated with phosphate metabolism and to the intergenic region between phoR and phoU, indicating that these phosphate metabolism genes are targets of MtrA. We further showed that MtrA in S. lividans and S. venezuelae has detectable regulatory effects on expression of phosphate metabolism genes. Additionally, the MtrA homologue from Corynebacterium glutamicum bound predicted MtrA sites of multiple phosphate metabolism genes, implying its potential for regulating phosphate metabolism in this species. Overall, our findings support MtrA as a major regulator for phosphate metabolism in Streptomyces and also potentially in other actinobacteria.

Anhydroexfoliamycin, a Streptomyces Secondary Metabolite, Mitigates Microglia-Driven Inflammation

Anhydroexfoliamycin, a secondary metabolite from Streptomyces, has shown antioxidant properties in primary cortical neurons reducing neurodegenerative hallmarks diseases, both in vitro and in vivo models. Activated microglia, in the central nervous system, plays a crucial role in neuroinflammation and is associated with neurodegeneration. Therefore, the aim of the present study was to determine the anti-inflammatory and antioxidant potential of the anhydroexfoliamycin over microglia BV2 cells. Neuroinflammation was simulated by incubation of microglia cells in the presence of lipopolysaccharide to activate proinflammatory transduction pathways. Moreover, a coculture of neuron SH-SY5Y and microglia BV2 cells was used to evaluate the neuroprotective properties of the Streptomyces metabolite. When microglia cells were preincubated with anhydroexfoliamycin, proinflammatory pathways, such as the translocation of the nuclear factor κB, the phosphorylation of c-Jun N-terminal kinase, and the inducible nitric oxide synthase expression, were inhibited. In addition, intracellular reactive oxygen species generation and the liberation of nitric oxide, interleukin 6, and tumor necrosis factor α were also decreased. Besides, the Streptomyces-derived compound showed antioxidant properties promoting the translocation of the factor erythroid 2-related factor 2 and protecting the SH-SY5Y cells from the neurotoxic mediators released by activated microglia. The effects of this compound were at the same level as the immunosuppressive drug cyclosporine A. Therefore, these results indicate that anhydroexfoliamycin is a promising tool to control microglia-driven inflammation with therapeutic potential in neuroinflammation.

N-oxygenation of amino compounds: Early stages in its application to the biocatalyzed preparation of bioactive compounds

Among the compounds that contain unusual functional groups, nitro is perhaps one of the most interesting due to the valuable properties it confers on pharmaceuticals and explosives. Traditional chemistry has for many years used environmentally unfriendly strategies; in contrast, the biocatalyzed production of this type of products offers a promising alternative. The small family of enzymes formed by N-oxygenases allows the conversion of an amino group to a nitro through the sequential addition of oxygen. These enzymes also make it possible to obtain other less oxidized N-O functions, such as hydroxylamine or nitroso, present in intermediate or final products. The current substrates on which these enzymes are reported to work encompass a few aromatic molecules and sugars. The unique characteristics of N-oxygenases and the great economic value of the products that they could generate, place them in a position of very high scientific and industrial interest. The most important and best studied N-oxygenases will be presented here.

A novel derivatization strategy for profiling phosphate ester/anhydride metabolic network and application on glioma rats using HILIC-MS/MS

Phosphate esters and anhydrides have great significance in the field of biochemical research and medical therapy. The genetic materials (DNA or RNA), most of the coenzymes, many intermediary metabolites, such as nucleotides and glycosyl phosphates in vivo are phosphodiesters, phosphoric acid or phosphates, respectively. It is important to monitor endogenous active phosphate metabolites for investigating many biological processes or drug mechanism. However, the detection and determination of those free active phosphate metabolites are challenged due to their unstable and easily hydrolyzed property and relatively low sensitivity, especially diphosphates and triphosphates. In the current study, we successfully developed a strategy by 3-aminomethyl pyridine (AMPy) derivatization coupled with hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) for simultaneous determination of multiple types of phosphate metabolites with good stability in 48 h and 29 to 126-fold improvement of the limit of detection (LOD). Based on the diagnostic fragment ions of different types of AMPy-derivatized phosphate metabolites, characteristic MRM ion pairs were successfully performed for global profiling of the phosphate metabolites in phosphate ester/anhydride metabolic network, including nucleotide/deoxynucleotide mono/di/triphosphates, glycosyl mono/diphosphates, and other key phosphates, such as 5-phosphoribosyl-1-pyrophosphate (PRPP), SAICARP and FAICARP in HPF, HUVEC and PBMCs cells without standards. The developed strategy greatly expanded the coverage of applying a single derivatization reaction to analyze active phosphate metabolites. Finally, the established method was performed to investigate the phosphate esters and anhydrides based on a glioma rat model. For the first time, phosphate metabolites were comprehensively characterized based on phosphate ester and anhydride metabolic network, covering nucleotide metabolism, glycolysis and pentose phosphate pathways, etc. The results demonstrated that the applicability of the method could be extended to a wider range of active phosphate compounds and could facilitate to related applications in the future studies.

Interactive effects of ozone exposure and nitrogen addition on the rhizosphere bacterial community of poplar saplings

It is widely documented that elevated ground-level ozone (O₃) has negative effects on tree physiological characteristics, and in return, affects forest ecosystem function. However, the effect may be modified by soil nitrogen (N) availability. Numerous studies have focused on the aboveground part of trees under elevated O₃ alone or in combination with soil N; however, little is known about the response of soil bacterial communities. Here, we investigated the effects of O₃ (charcoal-filtered air, CF, versus ambient air +40 ppb of O₃, E-O₃), N addition (0 kg ha^-1 yr^-1, N0, versus 200 kg ha^-1 yr^-1, N200), and their combination on rhizosphere soil bacterial communities of hybrid poplar, using an MiSeq targeted amplicon sequencing of the bacterial 16S rRNA gene. E-O₃ significantly decreased bacterial abundance, and N200 significantly decreased the α-diversity. The negative impacts of N200 on α-diversity were alleviated by E-O₃. Nitrogen and E-O₃-N200 combination altered bacterial community composition, with a significant increase in the relative abundance of Proteobacteria and Bacteroidetes and a decrease in the abundance of Firmicutes. From an ecological network analysis, E-O₃, alone and in combination with N200, complicated the co-occurrence network of bacterial communities by inducing a microbial survival strategy, shifting the hub species from RB41 to Bacillus and Blastococcus. Conversely, N200 led to simplification and decentralization of the co-occurrence network. These findings demonstrate that the rhizosphere bacterial communities exhibit divergent responses to E-O₃ and N200, suggesting the need to consider the stability of the belowground ecosystem to optimize plantation management in response to environmental changes.

A Genome-Scale Insight into the Effect of Shear Stress During the Fed-Batch Production of Clavulanic Acid by Streptomyces Clavuligerus

Streptomyces clavuligerus is a filamentous Gram-positive bacterial producer of the β-lactamase inhibitor clavulanic acid. Antibiotics biosynthesis in the Streptomyces genus is usually triggered by nutritional and environmental perturbations. In this work, a new genome scale metabolic network of Streptomyces clavuligerus was reconstructed and used to study the experimentally observed effect of oxygen and phosphate concentrations on clavulanic acid biosynthesis under high and low shear stress. A flux balance analysis based on experimental evidence revealed that clavulanic acid biosynthetic reaction fluxes are favored in conditions of phosphate limitation, and this is correlated with enhanced activity of central and amino acid metabolism, as well as with enhanced oxygen uptake. In silico and experimental results show a possible slowing down of tricarboxylic acid (TCA) due to reduced oxygen availability in low shear stress conditions. In contrast, high shear stress conditions are connected with high intracellular oxygen availability favoring TCA activity, precursors availability and clavulanic acid (CA) production.

Genome sequence and annotation of Streptomyces tendae UTMC 3329, acid and alkaline tolerant actinobacterium

BACKGROUND AND OBJECTIVES

Streptomyces tendae is one of the most prolific actinobacteria with a wide range of biotechnological applications. Genomic data can help in better understanding and exploration of important microorganisms, however, there is a few genomic information available for this species.

MATERIALS AND METHODS

Molecular identification, pH and salt tolerance of an actinobacterium, designated Streptomyces tendae UTMC 3329, isolated from a tea field soil were done. Also, genomic DNA was extracted and sequenced using Illumina platform with MPS (massively parallel sequencing) Illumina technology. Gene annotation and bioinformatic analysis were done using appropriate software and servers.

RESULTS

The draft genome is ∼8.7 megabase pairs, containing 7557 predicted coding sequences. The strain was able to grow at pH 5-12 and 0-10% NaCl. The maximum growth rate of the bacterium was obtained at pH 7. The gene clusters involved in central carbon metabolism, phosphate regulation, transport system, stress responses were revealed. It was shown the presence of gene clusters of polyketides, ribosomally and non-ribosomally synthesized peptides. Various genes were found in xenobiotic degradation pathways and heavy metal resistance.

CONCLUSION

The current genomic information which reveals biological features, as well as the biotechnological potential of this acid and alkaline tolerant actinobacterium, can be implemented for further research on the species.

SenX3-RegX3, an Important Two-Component System, Regulates Strain Growth and Butenyl-spinosyn Biosynthesis in Saccharopolyspora pogona

Butenyl-spinosyn produced by Saccharopolyspora pogona exhibits strong insecticidal activity and a broad pesticidal spectrum. Currently, important functional genes involved in butenyl-spinosyn biosynthesis remain unknown, which leads to difficulty in efficient understanding of its regulatory mechanism and improving its production by metabolic engineering. Here, we present data supporting a role of the SenX3-RegX3 system in regulating the butenyl-spinosyn biosynthesis. EMSAs and qRT-PCR demonstrated that RegX3 positively controls butenyl-spinosyn production in an indirect way. Integrated proteomic and metabolomic analysis, regX3 deletion not only strengthens the basal metabolic ability of S. pogona in the mid-growth phase but also promotes the flow of the acetyl-CoA produced via key metabolic pathways into the TCA cycle rather than the butenyl-spinosyn biosynthetic pathway, which ultimately leads to continued growth but reduced butenyl-spinosyn production. The strategy demonstrated here may be valuable for revealing the regulatory role of the SenX3-RegX3 system in the biosynthesis of other natural products.

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Butenyl-spinosyn biosynthesis is highly sensitive to Pi control

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RegX3 regulates polyP accumulation in S. pogona

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RegX3 may indirectly regulate butenyl-spinosyn production

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RegX3 plays an important role in the normal growth development of S. pogona

Omics Approaches Applied to Penicillium chrysogenum and Penicillin Production: Revealing the Secrets of Improved Productivity

Penicillin biosynthesis by Penicillium chrysogenum is one of the best-characterized biological processes from the genetic, molecular, biochemical, and subcellular points of view. Several omics studies have been carried out in this filamentous fungus during the last decade, which have contributed to gathering a deep knowledge about the molecular mechanisms underlying improved productivity in industrial strains. The information provided by these studies is extremely useful for enhancing the production of penicillin or other bioactive secondary metabolites by means of Biotechnology or Synthetic Biology.

Expression of genes of the Pho regulon is altered in Streptomyces coelicolor

Most currently used antibiotics originate from Streptomycetes and phosphate limitation is an important trigger of their biosynthesis. Understanding the molecular processes underpinning such regulation is of crucial importance to exploit the great metabolic diversity of these bacteria and get a better understanding of the role of these molecules in the physiology of the producing bacteria. To contribute to this field, a comparative proteomic analysis of two closely related model strains, Streptomyces lividans and Streptomyces coelicolor was carried out. These strains possess identical biosynthetic pathways directing the synthesis of three well-characterized antibiotics (CDA, RED and ACT) but only S. coelicolor expresses them at a high level. Previous studies established that the antibiotic producer, S. coelicolor, is characterized by an oxidative metabolism and a reduced triacylglycerol content compared to the none producer, S. lividans, characterized by a glycolytic metabolism. Our proteomic data support these findings and reveal that these drastically different metabolic features could, at least in part, due to the weaker abundance of proteins of the two component system PhoR/PhoP in S. coelicolor compared to S. lividans. In condition of phosphate limitation, PhoR/PhoP is known to control positively and negatively, respectively, phosphate and nitrogen assimilation and our study revealed that it might also control the expression of some genes of central carbon metabolism. The tuning down of the regulatory role of PhoR/PhoP in S. coelicolor is thus expected to be correlated with low and high phosphate and nitrogen availability, respectively and with changes in central carbon metabolic features. These changes are likely to be responsible for the observed differences between S. coelicolor and S. lividans concerning energetic metabolism, triacylglycerol biosynthesis and antibiotic production. Furthermore, a novel view of the contribution of the bio-active molecules produced in this context, to the regulation of the energetic metabolism of the producing bacteria, is proposed and discussed.

Discovery and evaluation on the antibacterial and cytotoxic activities of a novel antifungalmycin N2 produced from Streptomyces sp. strain N2

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C₆H₇O₂N) was a novel metabolite produced from Streptomyces sp. strain N2, and the present study aimed to evaluate its antibacterial and cytotoxic properties. By using Oxford cup method, the obtained results revealed that antifungalmycin N2 exhibited a significant antibacterial activity against the pathogenic bacteria such as Staphylococcus aureus, Escherichia coli, and Micrococcus kristinae, especially the Gram-positive S. aureus. Meanwhile, the MTT assay showed that antifungalmycin N2 could exert a marked inhibitory action on tumor cell lines, such as the cell lines of BEL-7402 (human hepatocellular carcinoma), Hela (human cervical carcinoma), HCT116 (human colon cancer), and SW620 (human colon cancer). And the IC₅₀ values antifungalmycin N2 against the above cell lines ranged from 11.23 to 15.37 μg/mL. In conclusion, the antibacterial and cytotoxic activities suggested that the novel antifungalmycin N2 was a promising active structure to be developed as new drug for treating infectious diseases and cancers.

Enhanced Natamycin production by Streptomyces natalensis in shake-flasks and stirred tank bioreactor under batch and fed-batch conditions

Background

Natamycin is an antifungal polyene macrolide antibiotic with wide applications in health and food industries. Currently, it is the only antifungal food additive with the GRAS status (Generally Regarded as Safe).

Results

Natamycin production was investigated under the effect of different initial glucose concentrations. Maximal antibiotic production (1.58 ± 0.032 g/L) was achieved at 20 g/L glucose. Under glucose limitation, natamycin production was retarded and the produced antibiotic was degraded. Higher glucose concentrations resulted in carbon catabolite repression. Secondly, intermittent feeding of glucose improved natamycin production due to overcoming glucose catabolite regulation, and moreover it was superior to glucose-beef mixture feeding, which overcomes catabolite regulation, but increased cell growth on the expense of natamycin production. Finally, the process was optimized in 7.5 L stirred tank bioreactor under batch and fed-batch conditions. Continuous glucose feeding for 30 h increased volumetric natamycin production by about 1.6- and 1.72-folds in than the batch cultivation in bioreactor and shake-flasks, respectively.

Conclusions

Glucose is a crucial substrate that significantly affects the production of natamycin, and its slow feeding is recommended to alleviate the effects of carbon catabolite regulation as well as to prevent product degradation under carbon source limitation. Cultivation in bioreactor under glucose feeding increased maximal volumetric enzyme production by about 72% from the initial starting conditions.