Intergeneric conjugation in Streptomyces peucetius and Streptomyces sp. strain C5: chromosomal integration and expression of recombinant plasmids carrying the chiC gene

A previously unidentified sugar transporter for engineering of high-yield Streptomyces

Sugar transporters have significant contributions to regulate metabolic flux towards products and they are general potential targets for engineering of high-yield microbial cell factories. Streptomyces, well-known producers of natural product pharmaceuticals, contain an abundance of sugar transporters, while few of them are well characterized and applied. Here, we report a previously unidentified ATP-binding cassette (ABC) sugar transporter TP6568 found within a Streptomyces avermitilis transposon library, along with its key regulator GM006564. Subsequent in silico molecular docking and genetic experiments demonstrated that TP6568 possessed a broad substrate specificity. It could not only promote uptake of diverse monosaccharides and disaccharides, but also enhance the utilization of industrial carbon sources such as starch, sucrose, and dextrin. Constitutive overexpression of TP6568 resulted in decrease of residual total sugar by 36.16%, 39.04%, 38.40%, and 30.21% in engineered S. avermitilis S0, Streptomyces caniferus NEAU6, Streptomyces bingchenggensis BC-101-4, and Streptomyces roseosporus NRRL 11379 than their individual parent strain, respectively. Production of avermectin B1a, guvermectin, and milbemycin A3/A4 increased by 75.61%, 56.89%, and 41.13%, respectively. We then overexpressed TP6568 in combination with the regulator GM006564 in a high-yield strain S. avermitilis S45, and further fine-tuning of their overexpression levels boosted production of avermectin B1a by 50.97% to 7.02 g/L in the engineering strain. Our work demonstrates that TP6568 as a promising sugar transporter may have broad applications in construction of high-yield Streptomyces microbial cell factories for desirable natural product pharmaceuticals. KEY POINTS: • TP6568 from Streptomyces avermitilis was identified as a sugar transporter • TP6568 enhanced utilization of diverse industrially used sugars in Streptomyces • TP6568 is a useful transporter to construct high-yield Streptomyces cell factories.

The Impact of Heterologous Regulatory Genes from Lipodepsipeptide Biosynthetic Gene Clusters on the Production of Teicoplanin and A40926

StrR-like pathway-specific transcriptional regulators (PSRs) function as activators in the biosynthesis of various antibiotics, including glycopeptides (GPAs), aminoglycosides, aminocoumarins, and ramoplanin-like lipodepsipeptides (LDPs). In particular, the roles of StrR-like PSRs have been previously investigated in the biosynthesis of streptomycin, novobiocin, GPAs like balhimycin, teicoplanin, and A40926, as well as LDP enduracidin. In the current study, we focused on StrR-like PSRs from the ramoplanin biosynthetic gene cluster (BGC) in Actinoplanes ramoplaninifer ATCC 33076 (Ramo5) and the chersinamycin BGC in Micromonospora chersina DSM 44151 (Chers28). Through the analysis of the amino acid sequences of Ramo5 and Chers28, we discovered that these proteins are phylogenetically distant from other experimentally investigated StrR PSRs, although all StrR-like PSRs found in BGCs for different antibiotics share a conserved secondary structure. To investigate whether Ramo5 and Chers28, given their phylogenetic positions, might influence the biosynthesis of other antibiotic pathways governed by StrR-like PSRs, the corresponding genes (ramo5 and chers28) were heterologously expressed in Actinoplanes teichomyceticus NRRL B-16726 and Nonomuraea gerenzanensis ATCC 39727, which produce the clinically-relevant GPAs teicoplanin and A40926, respectively. Recombinant strains of NRRL B-16726 and ATCC 39727 expressing chers28 exhibited improved antibiotic production, although the expression of ramo5 did not yield the same effect. These results demonstrate that some StrR-like PSRs can "cross-talk" between distant biosynthetic pathways and might be utilized as tools for the activation of silent BGCs regulated by StrR-like PSRs.

Characterization of a TetR-type positive regulator AtrA for lincomycin production in Streptomyces lincolnensis

AtrA belongs to the TetR family and has been well characterized for its roles in antibiotic biosynthesis regulation. Here, we identified an AtrA homolog (AtrA-lin) in Streptomyces lincolnensis. Disruption of atrA-lin resulted in reduced lincomycin production, whereas the complement restored the lincomycin production level to that of the wild-type. In addition, atrA-lin disruption did not affect cell growth and morphological differentiation. Furthermore, atrA-lin disruption hindered the transcription of regulatory gene lmbU, structural genes lmbA and lmbW inside the lincomycin biosynthesis gene cluster, and 2 other regulatory genes, adpA and bldA. Completement of atrA-lin restored the transcription of these genes to varying degrees. Notably, we found that AtrA-lin directly binds to the promoter region of lmbU. Collectively, AtrA-lin positively modulated lincomycin production via both pathway-specific and global regulators. This study offers further insights into the functional diversity of AtrA homologs and the mechanism of lincomycin biosynthesis regulation.

Cross-Talking of Pathway-Specific Regulators in Glycopeptide Antibiotics (Teicoplanin and A40926) Production

Teicoplanin and A40926 (natural precursor of dalbavancin) are clinically relevant glycopeptide antibiotics (GPAs) produced by Actinoplanes teichomyceticus NRRL B-16726 and Nonomuraea gerenzanensis ATCC 39727. Their biosynthetic enzymes are coded within large biosynthetic gene clusters (BGCs), named tei for teicoplanin and dbv for A40926, whose expression is strictly regulated by pathway-specific transcriptional regulators (PSRs), coded by cluster-situated regulatory genes (CSRGs). Herein, we investigated the "cross-talk" between the CSRGs from tei and dbv, through the analysis of GPA production levels in A. teichomyceticus and N. gerenzanensis strains, with knockouts of CSRGs cross-complemented by the expression of heterologous CSRGs. We demonstrated that Tei15* and Dbv4 StrR-like PSRs, although orthologous, were not completely interchangeable: tei15* and dbv4 were only partially able or unable to cross-complement N. gerenzanensis knocked out in dbv4 and A. teichomyceticus knocked out in tei15*, implying that the DNA-binding properties of these PSRs are more different in vivo than it was believed before. At the same time, the unrelated LuxR-like PSRs Tei16* and Dbv3 were able to cross-complement corresponding N. gerenzanensis knocked out in dbv3 and A. teichomyceticus knocked out in tei16*. Moreover, the heterologous expression of dbv3 in A. teichomyceticus led to a significant increase in teicoplanin production. Although the molecular background of these events merits further investigations, our results contribute to a deeper understanding of GPA biosynthesis regulation and offer novel biotechnological tools to improve their production.

A Study of Type II ɛ-PL Degrading Enzyme (pldII) in Streptomyces albulus through the CRISPRi System

ε-Poly-L-lysine (ε-PL) is a widely used antibacterial peptide polymerized of 25–35 L-lysine residues. The antibacterial effect of ε-PL is closely related to the polymerization degree. However, the mechanism of ε-PL degradation in S. albulus remains unclear. This study utilized the integrative plasmid pSET152-based CRISPRi system to transcriptionally repress the ε-PL degrading enzyme (pldII). The expression of pldII is regulated by changing the recognition site of dCas9. Through the ε-PL bacteriostatic experiments of repression strains, it was found that the repression of pldII improves the antibacterial effect of the ε-PL product. The consecutive MALDI-TOF-MS results confirmed that the molecular weight distribution of the ε-PL was changed after repression. The repression strain S1 showed a particular peak with a polymerization degree of 44, and other repression strains also generated ε-PL with a polymerization degree of over 40. Furthermore, the homology modeling and substrate docking of pldII, a typical endo-type metallopeptidase, were performed to resolve the degradation mechanism of ε-PL in S. albulus. The hydrolysis of ε-PL within pldII, initiated from the N-terminus by two amino acid-binding residues, Thr194 and Glu281, led to varying levels of polymerization of ε-PL.

Characterization of Antibacterial Strains against Kiwifruit Bacterial Canker Pathogen

Kiwifruit (Actinidia spp.) is an economically important crop and a bacterial canker disease, caused by Pseudomonas syringae pv. actinidiae (Psa), is the most destructive disease in kiwifruit production. Therefore, prevent and control of the disease is a critical issue in kiwifruit industry worldwide. Unfortunately, there is no reliable control methods have been developed. Recently, interest in disease control using microbial agents is growing. However, kiwifruit microbiota and their roles in the disease control is mainly remaining unknown. In this study, we secured bacterial libraries from kiwifruit ecospheres (rhizosphere, endospere, and phyllosphere) and screened reliable biocontrol strains against Psa. As the results, Streptomyces racemochromogenes W1SF4, Streptomyces sp. W3SF9 and S. parvulus KPB2 were selected as anti-Psa agents from the libraries. The strains showed forcible antibacterial activity as well as exceptional colonization ability on rhizosphere or phyllosphere of kiwifruit. Genome analyses of the strains suggested that the strains may produce several anti-Psa secondary metabolites. Our results will contribute to develop biocontrol strains against the kiwifruit canker pathogen and the disease management strategies.

Challenges and advances in genetic manipulation of filamentous actinomycetes - the remarkable producers of specialized metabolites

Covering: up to February 2019Actinomycetes are Gram positive bacteria of the phylum Actinobacteria. These organisms are one of the most important sources of structurally diverse, clinically used antibiotics and other valuable bioactive products, as well as biotechnologically relevant enzymes. Most strains were discovered by their ability to produce a given molecule and were often poorly characterized, physiologically and genetically. The development of genetic methods for Streptomyces and related filamentous actinomycetes has led to the successful manipulation of antibiotic biosynthesis to attain structural modification of microbial metabolites that would have been inaccessible by chemical means and improved production yields. Moreover, genome mining reveals that actinomycete genomes contain multiple biosynthetic gene clusters (BGCs), however only a few of them are expressed under standard laboratory conditions, leading to the production of the respective compound(s). Thus, to access and activate the so-called "silent" BGCs, to improve their biosynthetic potential and to discover novel natural products methodologies for genetic manipulation are required. Although different methods have been applied for many actinomycete strains, genetic engineering is still remaining very challenging for some "underexplored" and poorly characterized actinomycetes. This review summarizes the strategies developed to overcome the obstacles to genetic manipulation of actinomycetes and allowing thereby rational genetic engineering of this industrially relevant group of microorganisms. At the end of this review we give some tips to researchers with limited or no previous experience in genetic manipulation of actinomycetes. The article covers the most relevant literature published until February 2019.

Characterization of the Jomthonic Acids Biosynthesis Pathway and Isolation of Novel Analogues in Streptomyces caniferus GUA-06-05-006A

Jomthonic acids (JAs) are a group of natural products (NPs) with adipogenic activity. Structurally, JAs are formed by a modified β-methylphenylalanine residue, whose biosynthesis involves a methyltransferase that in Streptomyces hygroscopicus has been identified as MppJ. Up to date, three JA members (A–C) and a few other natural products containing β-methylphenylalanine have been discovered from soil-derived microorganisms. Herein, we report the identification of a gene (jomM) coding for a putative methyltransferase highly identical to MppJ in the chromosome of the marine actinobacteria Streptomyces caniferus GUA-06-05-006A. In its 5’ region, jomM clusters with two polyketide synthases (PKS) (jomP1, jomP2), a nonribosomal peptide synthetase (NRPS) (jomN) and a thioesterase gene (jomT), possibly conforming a single transcriptional unit. Insertion of a strong constitutive promoter upstream of jomP1 led to the detection of JA A, along with at least two novel JA family members (D and E). Independent inactivation of jomP1, jomN and jomM abolished production of JA A, JA D and JA E, indicating the involvement of these genes in JA biosynthesis. Heterologous expression of the JA biosynthesis cluster in Streptomyces coelicolor M1152 and in Streptomyces albus J1074 led to the production of JA A, B, C and F. We propose a pathway for JAs biosynthesis based on the findings here described.

Comparative Genomic and Regulatory Analyses of Natamycin Production of Streptomyces lydicus A02

Streptomyces lydicus A02 is used by industry because it has a higher natamycin-producing capacity than the reference strain S. natalensis ATCC 27448. We sequenced the complete genome of A02 using next-generation sequencing platforms, and to achieve better sequence coverage and genome assembly, we utilized single-molecule real-time (SMRT) sequencing. The assembled genome comprises a 9,307,519-bp linear chromosome with a GC content of 70.67%, and contained 8,888 predicted genes. Comparative genomics and natamycin biosynthetic gene cluster (BGC) analysis showed that BGC are highly conserved among evolutionarily diverse strains, and they also shared closer genome evolution compared with other Streptomyces species. Forty gene clusters were predicted to involve in the secondary metabolism of A02, and it was richly displayed in two-component signal transduction systems (TCS) in the genome, indicating a complex regulatory systems and high diversity of metabolites. Disruption of the phoP gene of the phoR-phoP TCS and nsdA gene confirmed phosphate sensitivity and global negative regulation of natamycin production. The genome sequence and analyses presented in this study provide an important molecular basis for research on natamycin production in Streptomyces, which could facilitate rational genome modification to improve the industrial use of A02.

Identification and characterization of a bacterial cytochrome P450 monooxygenase catalyzing the 3-nitration of tyrosine in rufomycin biosynthesis

Rufomycin is a circular heptapeptide with anti-mycobacterial activity and is produced by Streptomyces atratus ATCC 14046. Its structure contains three non-proteinogenic amino acids, N-dimethylallyltryptophan, trans-2-crotylglycine, and 3-nitrotyrosine (3NTyr). Although the rufomycin structure was already reported in the 1960s, its biosynthesis, including 3NTyr generation, remains unclear. To elucidate the rufomycin biosynthetic pathway, we assembled a draft genome sequence of S. atratus and identified the rufomycin biosynthetic gene cluster (ruf cluster), consisting of 20 ORFs (rufA-rufT). We found a putative heptamodular nonribosomal peptide synthetase encoded by rufT, a putative tryptophan N-dimethylallyltransferase encoded by rufP, and a putative trimodular type I polyketide synthase encoded by rufEF Moreover, the ruf cluster contains an apparent operon harboring putative cytochrome P450 (rufO) and nitric oxide synthase (rufN) genes. A similar operon, txtDE, is responsible for the formation of 4-nitrotryptophan in thaxtomin biosynthesis; the cytochrome P450 TxtE catalyzes the 4-nitration of Trp. Therefore, we hypothesized that RufO should catalyze the Tyr 3-nitration. Disruption of rufO abolished rufomycin production by S. atratus, which was restored when 3NTyr was added to the culture medium of the disruptant. Recombinant RufO protein exhibited Tyr 3-nitration activity both in vitro and in vivo Spectroscopic analysis further revealed that RufO recognizes Tyr as the substrate with a dissociation constant of ∼0.1 μm These results indicate that RufO is an unprecedented cytochrome P450 that catalyzes Tyr nitration. Taken together with the results of an in silico analysis of the ruf cluster, we propose a rufomycin biosynthetic pathway in S. atratus.

An Efficient Method To Generate Gene Deletion Mutants of the Rapamycin-Producing Bacterium Streptomyces iranensis HM 35

Streptomyces iranensis HM 35 is an alternative rapamycin producer to Streptomyces rapamycinicus Targeted genetic modification of rapamycin-producing actinomycetes is a powerful tool for the directed production of rapamycin derivatives, and it has also revealed some key features of the molecular biology of rapamycin formation in S. rapamycinicus. The approach depends upon efficient conjugational plasmid transfer from Escherichia coli to Streptomyces, and the failure of this step has frustrated its application to Streptomyces iranensis HM 35. Here, by systematically optimizing the process of conjugational plasmid transfer, including screening of various media, and by defining optimal temperatures and concentrations of antibiotics and Ca(2+) ions in the conjugation media, we have achieved exconjugant formation for each of a series of gene deletions in S. iranensis HM 35. Among them were rapK, which generates the starter unit for rapamycin biosynthesis, and hutF, encoding a histidine catabolizing enzyme. The protocol that we have developed may allow efficient generation of targeted gene knockout mutants of Streptomyces species that are genetically difficult to manipulate.

IMPORTANCE

The developed protocol of conjugational plasmid transfer from Escherichia coli to Streptomyces iranensis may allow efficient generation of targeted gene knockout mutants of other genetically difficult to manipulate, but valuable, Streptomyces species.

Tools for metabolic engineering in Streptomyces

During the last few decades, Streptomycetes have shown to be a very important and adaptable group of bacteria for the production of various beneficial secondary metabolites. These secondary metabolites have been of great interest in academia and the pharmaceutical industries. To date, a vast variety of techniques and tools for metabolic engineering of relevant structural biosynthetic gene clusters have been developed. The main aim of this review is to summarize and discuss the published literature on tools for metabolic engineering of Streptomyces over the last decade. These strategies involve precursor engineering, structural and regulatory gene engineering, and the up or downregulation of genes, as well as genome shuffling and the use of genome scale metabolic models, which can reconstruct bacterial metabolic pathways to predict phenotypic changes and hence rationalize engineering strategies. These tools are continuously being developed to simplify the engineering strategies for this vital group of bacteria.

Heterologous coexpression of Vitreoscilla hemoglobin and Bacillus megaterium glucanase in Streptomyces lydicus A02 enhanced its production of antifungal metabolites

Streptomyces lydicus A02 is a novel producer of commercially important polyene macrocyclic antibiotic natamycin and a potential biocontrol agent to several plant fungal diseases, including wilt caused by Fusarium oxysporum f. spp. To improve the natamycin production and the antifungal activity of S. lydicus A02, we coexpressed gene vgb encoding Vitreoscilla hemoglobin (VHb) and bglC encoding Bacillus megaterium L103 glucanase, both under the control of the strong constitutive ermE* promoter, in S. lydicus A02. Our results showed that coexpressing VHb and glucanase improved cell growth, and the engineered strain produced 26.90% more biomass than the wild-type strain after 72h fermentation in YSG medium. In addition, coexpressing genes encoding VHb and glucanase led to increased natamycin production, higher endogenous chitinase activity and exogenous glucanase activity, as well as enhanced antifungal activity in the engineered S. lydicus AVG02 and AGV02, regardless of the position of the two genes on the plasmids. Compared with model strains, few reports have successfully coexpressed VHb and other foreign proteins in industrial strains. Our results illustrated an effective approach for improving antifungal activity in an industrial strain by the rational engineering of combined favorable factors.

ChiS histidine kinase negatively regulates the production of chitinase ChiC in Streptomyces peucetius

Computational analysis of sequence homology of the chiSRC gene cluster, encoding a chitinase in Streptomyces peucetius, showed that the gene cluster could be a two-component regulon comprising a sensor kinase (chiS) and a response regulator (chiR). To prove that the ChiSRC is an authentic two-component system, the chiS gene was cloned and expressed in E.coli and the purified protein was used for biochemical analysis. In this report, we provide biochemical evidence to show that the sensor kinase encoded by chiS gene indeed is a histidine kinase capable of autophosphorylation and the histidine 144 residue of the ChiS protein is the phosphate acceptor. An insertion mutation at the chiS locus led to overproduction chitinase protein in S. peucetius implying that the chiC gene is negatively regulated by the two-component system.

SlnM gene overexpression with different promoters on natamycin production in Streptomyces lydicus A02

Natamycin is an important polyene macrolide antifungal agent produced by several Streptomyces strains and is widely used as a food preservative and fungicide in food, medicinal and veterinary products. In order to increase the yield of natamycin, this study aimed at cloning and overexpressing a natamycin-positive regulator, slnM2, with different promoters in the newly isolated strain Streptomyces lydicus A02, which is capable of producing natamycin. The slnM gene in S. lydicus is highly similar to gene pimM (scnRII), the pathway-specific positive regulator of natamycin biosynthesis in S. natalensis and S. chattanoogensis, which are PAS-LuxR regulators. Three engineered strains of S. lydicus, AM01, AM02 and AM03, were generated by inserting an additional copy of slnM2 with an ermEp* promoter, inserting an additional copy of slnM2 with dual promoters, ermEp* and its own promoter, and inserting an additional copy of slnM2 with its own promoter, respectively. No obvious changes in growth were observed between the engineered and wild-type strains. However, natamycin production in the engineered strains was significantly enhanced, by 2.4-fold in strain AM01, 3.0-fold in strain AM02 and 1.9-fold in strain AM03 when compared to the strain A02 in YEME medium without sucrose. These results indicated that the ermEp* promoter was more active than the native promoter of slnM2. Overall, dual promoters displayed the highest transcription of biosynthetic genes and yield of natamycin.

Genome engineering in actinomycetes using site-specific recombinases

The rational modification of the actinomycetes genomes has a variety of applications in research, medicine, and biotechnology. The use of site-specific recombinases allows generation of multiple mutations, large DNA deletions, integrations, and inversions and may lead to significant progress in all of these fields. Despite their huge potential, site-specific recombinase-based technologies have primarily been used for simple marker removal from a chromosome. In this review, we summarise the site-specific recombination approaches for genome engineering in various actinomycetes.

Protective role of Mycobacterium leprae small heat-shock protein in heterologous hosts, Escherichia coli and Mycobacterium smegmatis, grown under stress

The aim of this study is to examine the in vivo role of a small heat-shock protein (sHsp18) from Mycobacterium leprae in the survival of heterologous recombinant hosts carrying the gene encoding this protein under different environmental conditions that are normally encountered by M. leprae during its infection of the human host. Using an Escherichia coli system where shsp18 expression is controlled by its native promoter, we show that expression of shsp18 is induced under low oxygen tension, nutrient depletion and oxidative stress, all of which reflect the natural internal environment of the granulomas where the pathogen resides for long periods. We demonstrate the in vivo chaperone activity of sHsp18 through its ability to confer survival advantage to recombinant E. coli at heat-shock temperatures. Additional evidence for the protective role of sHsp18 was obtained when Mycobacterium smegmatis harbouring a copy of shsp18 was found to multiply better in human macrophages. Furthermore, the autokinase activity of sHsp18 protein demonstrated for what is believed to be the first time in this study implies that some of the functions of sHsp18 might be controlled by the phosphorylation state of this protein. Results from this study suggest that shsp18 might be one of the factors that facilitate the survival and persistence of M. leprae under stress and autophosphorylation of sHsp18 protein could be a mechanism used by this protein to sense changes in the external environment.

Engineering Streptomyces tenebrarius to synthesize single component of carbamoyl tobramycin

AIMS

To engineer Streptomyces tenebrarius for producing carbamoyl tobramycin as a main component.

METHODS AND RESULTS

The aprH-M gene fragment (apramycin biosynthetic gene from GenBank) in S. tenebrarius Tt49 was knocked out by genetic engineering to form S. tenebrarius T106 (ΔaprH-M). Compared to the wild-type strain, mutant strain T106 (ΔaprH-M) no longer produced apramycin, while mainly synthesize carbamoyl tobramycin. TLC and HPLC-MS analyses indicated that the mutant strain significantly increased the production of carbamoyl tobramycin.

CONCLUSIONS

The metabolic flow for the apramycin and its analogues biosynthesis was blocked by disrupting the aprH-M gene clusters. The aprH-M gene clusters might be essential for the biosynthesis of apramycin. The mutant strain T106 mainly synthesized carbamoyl tobramycin.

SIGNIFICANCE AND IMPACT OF STUDY

The mutant T106 mainly produces carbamoyl tobramycin without synthesizing apramycin, which will reduce cost of postextraction from fermentation products. Therefore, it has good prospects for industrial application.

An efficient intergeneric conjugation of DNA from Escherichia coli to mycelia of the lincomycin-producer Streptomyces lincolnensis

Streptomyces lincolnensis is a producer of lincomycin, which is a lincosamide antibiotic for the treatment of infective diseases caused by Gram-positive bacteria. S. lincolnensis is refractory to introducing plasmid DNA into cells because of resistance of foreign DNAs and poor sporulation. In this study, a simple and efficient method of transferring plasmids into S. lincolnensis through the intergeneric Escherichia coli-mycelia conjugation was established and optimized for the first time. The recipient mycelia of S. lincolnensis were prepared in liquid SM medium containing 10.3% sucrose for three days. The dispersed mycelia were conjugated with competent E. coli donor cells. The exconjugants were regenerated efficiently on solid mannitol soya flour (MS) medium containing 20 mM MgCl₂. The average conjugation frequency was observed at 1.1 × 10⁻⁴ per input donor cell and validated functionally by transferring two types of vectors containing lincomycin resistance genes lmrA, lmrB and lmrC into S. lincolnensis mycelia. The data of fermentation in shaking flasks showed the lincomycin yield of the exconjugants increased by 52.9% for the multiple copy vector and 38.3% for the integrative one, compared with the parental strain. The efficient and convenient method of intergeneric E. coli-mycelia conjugation in this study provides a promising procedure to introduce plasmid DNA into other refractory streptomycetes.

Conjugal transferring of resistance gene ptr for improvement of pristinamycin-producing Streptomyces pristinaespiralis

Improving pristinamycin production from Streptomyces pristinaespiralis was performed by introducing the resistance gene ptr followed by selection for enhanced tolerance to pristinamycin and fermentation test. To transfer ptr into S. pristinaespiralis, an effective method was established for the first time by using the intergeneric conjugation of DNA from Escherichia coli to S. pristinaespiralis. The procedure was optimized with heat treatment, spore concentration, optimum medium used in conjugation, concentration of MgCl(2), etc. With the optimized conditions, the conjugation frequency was up to 1.36 x 10(-3) exconjugants per recipient. The procedure was used to transfer the ptr gene into S. pristinaespiralis, resulting in 146 exconjugants. These exconjugants were screened on the pristinamycin-resistant plates, and then the fermentation test subsequently. Finally, two strains (SPR1 and SPR2) were obtained with a high yield of 0.11 and 0.15 g/l, respectively, which is about six to eight times more than that of wild-strain ATCC25486. The subculture experiments indicated that the hereditary character of the high-producing S. pristinaespiralis SPR1 and SPR2 was stable. Our work suggests that introducing resistance gene ptr into S. pristinaespiralis could be the way to improve the production of pristinamycin through the enhancement of antibiotic tolerance.

Identification by gene deletion analysis of barS2, a gene involved in the biosynthesis of gamma-butyrolactone autoregulator in Streptomyces virginiae

Virginiae butanolide (VB) is a member of the gamma-butyrolactone autoregulators and triggers the production of streptogramin antibiotics virginiamycin M1 and S in Streptomyces virginiae. A VB biosynthetic gene (barS2) was localized in a 10-kb regulatory island which controls the virginiamycin biosynthesis/resistance of S. virginiae, and analyzed by gene disruption/complementation. The barS2 gene is flanked by barS1, another VB biosynthetic gene catalyzing stereospecific reduction of an A-factor-type precursor into a VB-type compound, and barX encoding a pleiotropic regulator for virginiamycin biosynthesis. The deduced product of barS2 possessed moderate similarity to a putative dehydrogenase of Streptomyces venezuelae, encoded by jadW2 located in similar gene arrangement to that in the regulatory island of S. virginiae. A barS2-disruptant (strain IC152), created by means of homologous recombination, showed no differences in growth in liquid medium or morphology on solid medium compared to a wild-type strain, suggesting that BarS2 does not play any role in primary metabolism or morphological differentiation of S. virginiae. In contrast, no initiation of virginiamycin production or VB production was detected with the strain IC152 until 18 h of cultivation, at which time full production of virginiamycin occurs in the wild-type strain. The delayed virginiamycin production of the strain IC152 was fully restored to the level of the wild-type strain either by the exogenous addition of VB or by complementation of the intact barS2 gene, indicating that the lack of VB production at the initiation phase of virginiamycin production is the sole reason for the defect of virginiamycin production, and the barS2 gene is of primary importance for VB biosynthesis in S. virginiae.

Intergeneric conjugation in holomycin-producing marine Streptomyces sp. strain M095

Marine Streptomyces are potential candidates for novel natural products and industrial catalysts. In order to set up biosynthesis approach for a holomycin-producing strain M095 isolated from Jiaozhou Bay, China, a genetic transformation system was established using intergeneric conjugation. The plasmid pIJ8600 consists of an origin of replication for Escherichia coli, a phage integrase directing efficient site-specific integration in bacterial chromosome, thiostrepton-induced promoter and an attP sequence. Using E. coli ET12567 (pUZ8002) carrying pIJ8600 as a conjugal donor, while it was mated with strain M095, pIJ8600 was mobilized to the recipient and the transferred DNA was also integrated into the recipient chromosome. The frequency of exconjugants was 1.9+/-0.13x10(-4) per recipient cell. Analysis of eight exconjugants showed pIJ8600 was stable integrated at a single chromosomal site (attB) of the Streptomyces genome. The DNA sequence of the attB was cloned and shown to be conserved. The results of growth and antimicrobial activity analysis indicated that the integration of pIJ8600 did not seem to affect the biosynthesis of antibiotics or other essential amino acids. To demonstrate the feasibility of above gene transfer system, the allophycocyanin gene (apc) from cyanobacterium Anacystis nidulans UTEX625 was expressed in strain M095, and the results indicated heterologous allophycocyanin could be expressed and folded effectively.

The Structural Basis for Docking in Modular Polyketide Biosynthesis

Polyketide natural products such as erythromycin and rapamycin are assembled on polyketide synthases (PKSs), which consist of modular sets of catalytic activities distributed across multiple protein subunits. Correct protein-protein interactions among the PKS subunits which are critical to the fidelity of biosynthesis are mediated in part by "docking domains" at the termini of the proteins. The NMR solution structure of a representative docking domain complex from the erythromycin PKS (DEBS) was recently solved, and on this basis it has been proposed that PKS docking is mediated by the formation of an intermolecular four-alpha-helix bundle. Herein, we report the genetic engineering of such a docking domain complex by replacement of specific helical segments and analysis of triketide synthesis by mutant PKSs in vivo. The results of these helix swaps are fully consistent with the model and highlight residues in the docking domains that may be targeted to alter the efficiency or specificity of subunit-subunit docking in hybrid PKSs.

Development of gene delivery systems for the epsilon-poly-L-lysine producer, Streptomyces albulus

Streptomyces albulus IFO14147 produces epsilon-poly-L-lysine (epsilon-PL), an amino acid homopolymer antibiotic that is used as a food preservative in many countries, including Japan, South Korea, and the United States. To construct an overproducer of the industrially important epsilon-PL and to develop a deeper understanding of its biosynthetic mechanism, we developed systems for DNA delivery into the S. albulus strain based on both polyethylene glycol-mediated protoplast transformation and intergeneric conjugation from Escherichia coli. The successes of these transformations in particular were accomplished by employing the new cryptic-plasmid-based shuttle vectors constructed in this study. The genetic systems developed here should facilitate a molecular genetic approach to S. albulus.

Cloning and in vivo functional analysis by disruption of a gene encoding the gamma-butyrolactone autoregulator receptor from Streptomyces natalensis

A gene encoding a gamma-butyrolactone autoregulator receptor, which has a common activity as DNA-binding transcriptional repressors controlling secondary metabolism and/or morphological differentiation in Streptomyces, was cloned from a natamycin producer, Streptomyces natalensis. PCR using the primers designed for the two highly conserved regions of Streptomyces autoregulator receptors (BarA, FarA, ScbR, and ArpA) gave a 102-bp band. The sequence of this band had a high similarity to the expected region of a receptor gene. By genomic Southern hybridization with the 102-bp insert as a probe, a 687-bp intact receptor gene (sngR) was obtained from S. natalensis. To clarify the in vivo function of sngR, a sngR-disrupted strain was constructed, and the phenotypes were compared with those of the wild-type strain. The sngR-disruptants started natamycin production 6 h earlier and showed a 4.6-fold higher production of natamycin than the wild-type strain. In addition, the sporulation began earlier and the number of spores was tenfold more abundant than that of the wild-type strain. All the phenotypes were restored back to the original phenotypes of the wild-type strain by complementation with the intact sngR, indicating that the autoregulator receptor protein of S. natalensis acts as a primary negative regulator both on the biosynthesis of natamycin and sporulation.

Cloning of mce1 locus of Mycobacterium leprae in Mycobacterium smegmatis mc2 155 SMR5 and evaluation of expression of mce1 genes in M. smegmatis and M. leprae

Plasmid pSET152 is a broad host range mobilizable vector which integrates into streptomyces chromosome utilizing att site and int function of slashed circleC31. Transformation of this plasmid into Mycobacterium smegmatis mc2 155 SMR5 gave stable transformants carrying the pSET152 as an integrated copy. Integration occurred at the cross over sequence 5'TTG disrupting the gatA gene (Glu-tRNA(Gln) amidotransferase subunitA), which is non-essential under conditions used. Recombinant pSET152 plasmids carrying mce1 locus of Mycobacterium leprae were used to construct M. smegmatis transformants carrying the mce1 locus in their chromosome. RT-PCR analysis revealed specific transcripts of M. leprae mce in M. smegmatis. The transcribed mRNA carried intergenic regions between genes of mce1 locus indicating that mce1 locus is an operon. Examination of M. leprae specific mRNA from lepromatous leprosy patient's biopsy showed that mce locus is transcribed as an operon in the pathogen also.

Cloning and functional analysis by gene disruption of a gene encoding a gamma-butyrolactone autoregulator receptor from Kitasatospora setae

Gamma-butyrolactone autoregulator receptors of the genus Streptomyces have a common activity as DNA-binding transcriptional repressors, controlling secondary metabolism and/or morphological differentiation. A gene encoding a gamma-butyrolactone autoregulator receptor was cloned from a bafilomycin B1 producer, Kitasatospora setae, for the first time from a non-Streptomyces genus of actinomycetes, and its function was evaluated by in vitro and in vivo analyses. The gene fragment was initially cloned by PCR with primers designed from two highly conserved regions of Streptomyces autoregulator receptors (BarA, FarA, ScbR, and ArpA), followed by genomic Southern hybridization yielding a 7-kb BamHI fragment on which a 654-bp receptor gene (ksbA) was identified. The recombinant KsbA protein demonstrated clear binding activity toward 3H-labeled autoregulators, especially toward [3H]SCB1, confirming that ksbA encodes a real autoregulator receptor of K. setae. To clarify the in vivo function of ksbA, a ksbA-disrupted strain was constructed by means of homologous recombination after introducing a ksbA disruption construct via transconjugation from Escherichia coli. No difference in morphology was found between the wild-type strain and the ksbA disruptants. However, the ksbA disruptants started producing bafilomycin 18 h earlier than the wild-type strain and showed a 2.4-fold-higher accumulation of bafilomycin. The phenotype was restored to the original wild-type phenotype by complementation with intact ksbA, indicating that the autoregulator receptor protein of K. setae acts as a primary negative regulator of the biosynthesis of bafilomycin but plays no role in cytodifferentiation of K. setae. This indicates that, unlike the A-factor receptor of Streptomyces griseus, the autoregulator receptor (ksbA) of K. setae belongs to a family of autoregulator receptors which control secondary metabolism but play no role in morphological differentiation.