Genomewide insertional mutagenesis in Streptomyces coelicolor reveals additional genes involved in morphological differentiation

Transcriptionally induced nucleoid-associated protein-like ccr1 in combined-culture serves as a global effector of Streptomyces secondary metabolism

Combined-cultures involving mycolic acid-containing bacteria (MACB) can stimulate secondary metabolite (SM) production in actinomycetes. In a prior investigation, we screened Streptomyces coelicolor JCM4020 mutants with diminished production of SMs, specifically undecylprodigiosin (RED), which was enhanced by introducing the MACB Tsukamurella pulmonis TP-B0596. In this study, we conducted mutational analysis that pinpointed the sco1842 gene, which we assigned the gene name ccr1 (combined-culture related regulatory protein no. 1), as a crucial factor in the deficient phenotype observed in the production of various major SMs in S. coelicolor A3(2). Notably, the Ccr1 (SCO1842) homolog was found to be highly conserved throughout the Streptomyces genome. Although Ccr1 lacked conserved motifs, in-depth examination revealed the presence of a helix-turn-helix (HTH) motif in the N-terminal region and a helicase C-terminal domain (HCTD) motif in the C-terminal region in some of its homologs. Ccr1 was predicted to be a nucleoid-associated protein (NAP), and its impact on gene transcription was validated by RNA-seq analysis that revealed genome-wide variations. Furthermore, RT-qPCR demonstrated that ccr1 was transcriptionally activated in combined-culture with T. pulmonis, which indicated that Ccr1 is involved in the response to bacterial interaction. We then investigated Streptomyces nigrescens HEK616 in combined-culture, and the knockout mutant of the ccr1 homolog displayed reduced production of streptoaminals and 5aTHQs. This finding reveals that the Ccr1 homolog in Streptomyces species is associated with SM production. Our study elucidates the existence of a new family of NAP-like proteins that evolved in Streptomyces species and play a pivotal role in SM production.

Transposon-based identification of genes involved in the rimocidin biosynthesis in Streptomyces rimosus M527

The transposon mutagenesis strategy has been employed to generate random insertion mutants and analyze the correlation between genes and secondary metabolites in the genus Streptomyces. In this study, our primary objective was to identify an unknown gene involved in rimocidin biosynthesis and elucidate its role in rimocidin production in Streptomyces rimosus M527. To achieve this, we established a random mutant library of S. rimosus M527 using a Tn5 transposon-mediated random mutagenesis strategy. Among the 137 isolated mutants, M527-G10 and M527-W5 exhibited the most significant variations in antagonistic activity against the plant pathogenic fungus Fusarium oxysporum f. sp. cucumerinum. Specifically, M527-G10 displayed a 72.93% reduction, while M527-W5 showed a 49.8% increase in rimocidin production compared to the wild-type (WT) strain S. rimosus M527. Subsequently, we employed a plasmid rescue strategy to identify the insertion loci of the transposon in the genomes of mutants M527-G10 and M527-W5, revealing a response regulator transcription factor (rrt) and a hypothetical protein (hyp), respectively. The roles of rrt and hyp in rimocidin biosynthesis were determined through gene deletion, overexpression in the WT strain, and complemented expression in the transposon mutants. Notably, the gene-deletion mutants M527-ΔRRT and M527-ΔHYP exhibited similar behavior in rimocidin production compared to the corresponding transposon mutants M527-G10 and M527-W5, suggesting that transposon insertions in genes rrt and hyp led to alterations in rimocidin production. Furthermore, both gene deletion and overexpression of rrt and hyp had no discernible effects on cell growth. These results reveal that genes rrt and hyp have positive and negative impacts on rimocidin production in S. rimosus M527, respectively.

Global Effects of the Developmental Regulator BldB in Streptomyces venezuelae

In Streptomyces, the Bld (Bald) regulators control formation of the reproductive aerial hyphae. The functions of some of these regulators have been well characterized, but BldB has remained enigmatic. In addition to the bldB gene itself, Streptomyces venezuelae has 10 paralogs of bldB that sit next to paralogs of whiJ and abaA. Transcriptome sequencing (RNA-seq) revealed that loss of BldB function causes the dramatic transcriptional upregulation of the abaA paralogs and a novel inhibitor of sporulation, iosA, and that cooverexpression of just two of these genes, iosA and abaA6, was sufficient to recapitulate the bldB mutant phenotype. Further RNA-seq analysis showed that the transcription factor WhiJ9 is required for the activation of iosA seen in the bldB mutant, and biochemical studies showed that WhiJ9 mediates the activation of iosA expression by binding to direct repeats in the iosA-whiJ9 intergenic region. BldB and BldB9 hetero-oligomerize, providing a potential link between BldB and the iosA-whiJ9-bldB9 locus. This work greatly expands our overall understanding of the global effects of the BldB developmental regulator. IMPORTANCE To reproduce and disperse, the filamentous bacterium Streptomyces develops specialized reproductive structures called aerial hyphae. The formation of these structures is controlled by the bld (bald) genes, many of which encode transcription factors whose functions have been characterized. An exception is BldB, a protein whose biochemical function is unknown. In this study, we gain insight into the global effects of BldB function by examining the genome-wide transcriptional effects of deleting bldB. We identify a small set of genes that are dramatically upregulated in the absence of BldB. We show that their overexpression causes the bldB phenotype and characterize a transcription factor that mediates the upregulation of one of these target genes. Our results provide new insight into how BldB influences Streptomyces development.

Current perspective on production and applications of microbial cellulases: a review

The potential of cellulolytic enzymes has been widely studied and explored for bioconversion processes and plays a key role in various industrial applications. Cellulase, a key enzyme for cellulose-rich waste feedstock-based biorefinery, has increasing demand in various industries, e.g., paper and pulp, juice clarification, etc. Also, there has been constant progress in developing new strategies to enhance its production, such as the application of waste feedstock as the substrate for the production of individual or enzyme cocktails, process parameters control, and genetic manipulations for enzyme production with enhanced yield, efficiency, and specificity. Further, an insight into immobilization techniques has also been presented for improved reusability of cellulase, a critical factor that controls the cost of the enzyme at an industrial scale. In addition, the review also gives an insight into the status of the significant application of cellulase in the industrial sector, with its techno-economic analysis for future applications. The present review gives a complete overview of current perspectives on the production of microbial cellulases as a promising tool to develop a sustainable and greener concept for industrial applications.

Systems and synthetic biology to elucidate secondary metabolite biosynthetic gene clusters encoded in Streptomyces genomes

Covering: 2010 to 2020 Over the last few decades, Streptomyces have been extensively investigated for their ability to produce diverse bioactive secondary metabolites. Recent advances in Streptomyces research have been largely supported by improvements in high-throughput technology 'omics'. From genomics, numerous secondary metabolite biosynthetic gene clusters were predicted, increasing their genomic potential for novel bioactive compound discovery. Additional omics, including transcriptomics, translatomics, interactomics, proteomics and metabolomics, have been applied to obtain a system-level understanding spanning entire bioprocesses of Streptomyces, revealing highly interconnected and multi-layered regulatory networks for secondary metabolism. The comprehensive understanding derived from this systematic information accelerates the rational engineering of Streptomyces to enhance secondary metabolite production, integrated with the exploitation of the highly efficient 'Design-Build-Test-Learn' cycle in synthetic biology. In this review, we describe the current status of omics applications in Streptomyces research to better understand the organism and exploit its genetic potential for higher production of valuable secondary metabolites and novel secondary metabolite discovery.

Genome-Wide Mutagenesis Links Multiple Metabolic Pathways with Actinorhodin Production in Streptomyces coelicolor

Streptomyces species are important antibiotic-producing organisms that tightly regulate their antibiotic production. Actinorhodin is a typical antibiotic produced by the model actinomycete Streptomyces coelicolor To discover the regulators of actinorhodin production, we constructed a library of 50,000 independent mutants with hyperactive Tn5 transposase-based transposition systems. Five hundred fifty-one genes were found to influence actinorhodin production in 988 individual mutants. Genetic complementation suggested that most of the insertions (76%) were responsible for the changes in antibiotic production. Genes involved in diverse cellular processes such as amino acid biosynthesis, carbohydrate metabolism, cell wall homeostasis, and DNA metabolism affected actinorhodin production. Genome-wide mutagenesis can identify novel genes and pathways that impact antibiotic levels, potentially aiding in engineering strains to optimize the production of antibiotics in Streptomyces IMPORTANCE Previous studies have shown that various genes can influence antibiotic production in Streptomyces and that intercommunication between regulators can complicate antibiotic production. Therefore, to gain a better understanding of antibiotic regulation, a genome-wide perspective on genes that influence antibiotic production was needed. We searched for genes that affected production of the antibiotic actinorhodin using a genome-wide gene disruption system. We identified 551 genes that altered actinorhodin levels, and more than half of these genes were newly identified effectors. Some of these genes may be candidates for engineering Streptomyces strains to improve antibiotic production levels.

Visual and Microscopic Evaluation of Streptomyces Developmental Mutants

Streptomycetes are filamentous soil bacteria belonging to the phylum Actinobacteria that are found throughout the world and produce a wide array of antibiotics and other secondary metabolites. Streptomyces coelicolor is a well-characterized, non-pathogenic species that is amenable to a variety of analyses in the lab. The phenotyping methods described here use S. coelicolor as a model streptomycete; however, the methods are applicable to all members of this large genus as well as some closely related actinomycetes. Phenotyping is necessary to characterize new species of Streptomyces identified in the environment, and it is also a vital first step in characterizing newly isolated mutant strains of Streptomyces. Proficiency in phenotyping is important for the many new researchers who are entering the field of Streptomyces research, which includes the study of bacterial development, cell division, chromosome segregation, and second messenger signaling. The recent crowdsourcing of antibiotic discovery through the isolation of new soil microbes has resulted in an increased need for training in phenotyping for instructors new to the field of Streptomyces research and their college or high school students. This manuscript describes methods for bacterial strain propagation, storage, and characterization through visual and microscopic examination. After reading this article, new researchers (microbiology education laboratories and citizen scientists) should be able to manipulate Streptomyces strains and begin visual characterization experiments.

Large-Scale Transposition Mutagenesis of Streptomyces coelicolor Identifies Hundreds of Genes Influencing Antibiotic Biosynthesis

Gram-positive Streptomyces bacteria produce thousands of bioactive secondary metabolites, including antibiotics. To systematically investigate genes affecting secondary metabolism, we developed a hyperactive transposase-based Tn5 transposition system and employed it to mutagenize the model species Streptomyces coelicolor, leading to the identification of 51,443 transposition insertions. These insertions were distributed randomly along the chromosome except for some preferred regions associated with relatively low GC content in the chromosomal core. The base composition of the insertion site and its flanking sequences compiled from the 51,443 insertions implied a 19-bp expanded target site surrounding the insertion site, with a slight nucleic acid base preference in some positions, suggesting a relative randomness of Tn5 transposition targeting in the high-GC Streptomyces genome. From the mutagenesis library, 724 mutants involving 365 genes had altered levels of production of the tripyrrole antibiotic undecylprodigiosin (RED), including 17 genes in the RED biosynthetic gene cluster. Genetic complementation revealed that most of the insertions (more than two-thirds) were responsible for the changed antibiotic production. Genes associated with branched-chain amino acid biosynthesis, DNA metabolism, and protein modification affected RED production, and genes involved in signaling, stress, and transcriptional regulation were overrepresented. Some insertions caused dramatic changes in RED production, identifying future targets for strain improvement.IMPORTANCE High-GC Gram-positive streptomycetes and related actinomycetes have provided more than 100 clinical drugs used as antibiotics, immunosuppressants, and antitumor drugs. Their genomes harbor biosynthetic genes for many more unknown compounds with potential as future drugs. Here we developed a useful genome-wide mutagenesis tool based on the transposon Tn5 for the study of secondary metabolism and its regulation. Using Streptomyces coelicolor as a model strain, we found that chromosomal insertion was relatively random, except at some hot spots, though there was evidence of a slightly preferred 19-bp target site. We then used prodiginine production as a model to systematically survey genes affecting antibiotic biosynthesis, providing a global view of antibiotic regulation. The analysis revealed 348 genes that modulate antibiotic production, among which more than half act to reduce production. These might be valuable targets in future investigations of regulatory mechanisms, for strain improvement, and for the activation of silent biosynthetic gene clusters.

Recent advances in genetic modification systems for Actinobacteria

Actinobacteria are extremely important to human health, agriculture, and forests. Because of the vast differences of the characteristics of Actinobacteria, a lot of genetic tools have been developed for efficiently manipulating the genetics. Although there are a lot of successful examples of engineering Actinobacteria, they are still more difficult to be genetically manipulated than other model microorganisms such as Saccharomyces cerevisiae, Escherichia coli, and Bacillus subtilis etc. due to the diverse genomics and biochemical machinery. Here, we review the methods to introduce heterologous DNA into Actinobacteria and the available genetic modification tools. The trends and problems existing in engineering Actinobacteria are also covered.

Taxonomy, Physiology, and Natural Products of Actinobacteria

Actinobacteria are Gram-positive bacteria with high G+C DNA content that constitute one of the largest bacterial phyla, and they are ubiquitously distributed in both aquatic and terrestrial ecosystems. Many Actinobacteria have a mycelial lifestyle and undergo complex morphological differentiation. They also have an extensive secondary metabolism and produce about two-thirds of all naturally derived antibiotics in current clinical use, as well as many anticancer, anthelmintic, and antifungal compounds. Consequently, these bacteria are of major importance for biotechnology, medicine, and agriculture. Actinobacteria play diverse roles in their associations with various higher organisms, since their members have adopted different lifestyles, and the phylum includes pathogens (notably, species of Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, and Tropheryma), soil inhabitants (e.g., Micromonospora and Streptomyces species), plant commensals (e.g., Frankia spp.), and gastrointestinal commensals (Bifidobacterium spp.). Actinobacteria also play an important role as symbionts and as pathogens in plant-associated microbial communities. This review presents an update on the biology of this important bacterial phylum.

Random transposon mutagenesis of the Saccharopolyspora erythraea genome reveals additional genes influencing erythromycin biosynthesis

A single cycle of strain improvement was performed in Saccharopolyspora erythraea mutB and 15 genotypes influencing erythromycin production were found. Genotypes generated by transposon mutagenesis appeared in the screen at a frequency of ~3%. Mutations affecting central metabolism and regulatory genes were found, as well as hydrolases, peptidases, glycosyl transferases and unknown genes. Only one mutant retained high erythromycin production when scaled-up from micro-agar plug fermentations to shake flasks. This mutant had a knockout of the cwh1 gene (SACE_1598), encoding a cell-wall-associated hydrolase. The cwh1 knockout produced visible growth and morphological defects on solid medium. This study demonstrated that random transposon mutagenesis uncovers strain improvement-related genes potentially useful for strain engineering.

Developmental biology of Streptomyces from the perspective of 100 actinobacterial genome sequences

To illuminate the evolution and mechanisms of actinobacterial complexity, we evaluate the distribution and origins of known Streptomyces developmental genes and the developmental significance of actinobacteria-specific genes. As an aid, we developed the Actinoblast database of reciprocal blastp best hits between the Streptomyces coelicolor genome and more than 100 other actinobacterial genomes (http://streptomyces.org.uk/actinoblast/). We suggest that the emergence of morphological complexity was underpinned by special features of early actinobacteria, such as polar growth and the coupled participation of regulatory Wbl proteins and the redox-protecting thiol mycothiol in transducing a transient nitric oxide signal generated during physiologically stressful growth transitions. It seems that some cell growth and division proteins of early actinobacteria have acquired greater importance for sporulation of complex actinobacteria than for mycelial growth, in which septa are infrequent and not associated with complete cell separation. The acquisition of extracellular proteins with structural roles, a highly regulated extracellular protease cascade, and additional regulatory genes allowed early actinobacterial stationary phase processes to be redeployed in the emergence of aerial hyphae from mycelial mats and in the formation of spore chains. These extracellular proteins may have contributed to speciation. Simpler members of morphologically diverse clades have lost some developmental genes.

An insight into the "-omics" based engineering of streptomycetes for secondary metabolite overproduction

Microorganisms produce a range of chemical substances representing a vast diversity of fascinating molecular architectures not available in any other system. Among them, Streptomyces are frequently used to produce useful enzymes and a wide variety of secondary metabolites with potential biological activities. Streptomyces are preferred over other microorganisms for producing more than half of the clinically useful naturally originating pharmaceuticals. However, these compounds are usually produced in very low amounts (or not at all) under typical laboratory conditions. Despite the superiority of Streptomyces, they still lack well documented genetic information and a large number of in-depth molecular biological tools for strain improvement. Previous attempts to produce high yielding strains required selection of the genetic material through classical mutagenesis for commercial production of secondary metabolites, optimizing culture conditions, and random selection. However, a profound effect on the strategy for strain development has occurred with the recent advancement of whole-genome sequencing, systems biology, and genetic engineering. In this review, we demonstrate a few of the major issues related to the potential of "-omics" technology (genomics, transcriptomics, proteomics, and metabolomics) for improving streptomycetes as an intelligent chemical factory for enhancing the production of useful bioactive compounds.

Application of T-DNA insertional mutagenesis for improving cellulase production in the filamentous fungus Trichoderma reesei

A T-DNA-tagged mutant library created by Agrobacterium-mediated transformation (AMT) was assayed for improvement of cellulase production. After 96-well plate screening for rapid growth on cellulose substrates followed by plate-clearing zone assay, three putative mutants, TA-32, TB-87 and TE-6, with enhanced cellulolytic ability were isolated, exhibiting 38%, 51% and 31% increase in total cellulase activity than the parental strain QM9414, respectively. Endoglucanase, cellobiohydrolase and β-glucosidase activities as well as the hydrolysis efficiencies of the mutants were also improved. Moreover, T-DNA was shown to be integrated at a single site in the genomes of TA-32 and TE-6 while inserted at two copies into the genome of TB-87. Further, the sequences flanking the T-DNA insertion sites were successfully rescued, demonstrating the increased utility of T-DNA insertional mutagenesis for improvement of cellulase production as well as subsequent identification of the tagged genes relevant to cellulolytic ability.

Signals and regulators that govern Streptomyces development

Streptomyces coelicolor is the genetically best characterized species of a populous genus belonging to the gram-positive Actinobacteria. Streptomycetes are filamentous soil organisms, well known for the production of a plethora of biologically active secondary metabolic compounds. The Streptomyces developmental life cycle is uniquely complex and involves coordinated multicellular development with both physiological and morphological differentiation of several cell types, culminating in the production of secondary metabolites and dispersal of mature spores. This review presents a current appreciation of the signaling mechanisms used to orchestrate the decision to undergo morphological differentiation, and the regulators and regulatory networks that direct the intriguing development of multigenomic hyphae first to form specialized aerial hyphae and then to convert them into chains of dormant spores. This current view of S. coelicolor development is destined for rapid evolution as data from '-omics' studies shed light on gene regulatory networks, new genetic screens identify hitherto unknown players, and the resolution of our insights into the underlying cell biological processes steadily improve.

Constitutive expression of ftsZ overrides the whi developmental genes to initiate sporulation of Streptomyces coelicolor

The filamentous soil bacteria Streptomyces undergo a highly complex developmental programme. Before streptomycetes commit themselves to sporulation, distinct morphological checkpoints are passed in the aerial hyphae that are subject to multi-level control by the whi sporulation genes. Here we show that whi-independent expression of FtsZ restores sporulation to the early sporulation mutants whiA, whiB, whiG, whiH, whiI and whiJ. Viability, stress resistance and high-resolution electron microscopy underlined that viable spores were formed. However, spores from sporulation-restored whiA and whiG mutants showed defects in DNA segregation/condensation, while spores from the complemented whiB mutant had increased stress sensitivity, perhaps as a result of changes in the spore sheath. In contrast to the whi mutants, normal sporulation of ssgB null mutants—which fail to properly localise FtsZ—could not be restored by enhancing FtsZ protein levels, forming spore-like bodies that lack spore walls. Our data strongly suggest that the whi genes control a decisive event towards sporulation of streptomycetes, namely the correct timing of developmental ftsZ transcription. The biological significance may be to ensure that sporulation-specific cell division will only start once sufficient aerial mycelium biomass has been generated. Our data shed new light on the longstanding question as to how whi genes control sporulation, which has intrigued scientists for four decades.

Efficient transposition of IS204-derived plasmids in Streptomyces coelicolor

In order to study functional gene expression in Streptomyces coelicolor, a mini-transposon encoding the apramycin resistance gene aac(3)IV within its inverted repeat (IR) boundaries was constructed based on IS204, which was previously identified in the genome of Nocardia asteroides YP21. The mini-transposon and IS204 transposase gene were then put on a kanamycin-resistant conjugative plasmid pDZY101 that can only replicate in Escherichia coli. After mating with S. coelicolor A3(2) M145, resistant colonies arose efficiently on both apramycin and kanamycin plates. Plasmid rescue indicated that entire plasmids were inserted into the M145 genome with cleavage at an inverted repeat junction formed by the right inverted repeat (IRR) and the last 18bp of the transposase gene, while the left inverted repeat (IRL) was untouched. Southern blot analysis of the mutants using an aac(3)IV gene probe showed that transposition of plasmid pDZY101 was genetically stable, with a single-copy insertion within the S. coelicolor M145 genome. Several mutagenesis libraries of S. coelicolor M145 were constructed using plasmid pDZY101 derivatives and the transposon insertion site was determined. The correlation between novel mutant phenotypes and previously uncharacterized genes was established and these transposon locations were widely scattered around the genome.

Streptomyces scopuliridis sp. nov., a bacteriocin-producing soil streptomycete

Actinomycete strain RB72(T) was isolated from woodland bluff soil in northern Alabama, USA, and shown to produce a broad spectrum bacteriocin. Based on morphological and chemotaxonomic characteristics, the strain was determined to belong to the genus Streptomyces. Phylogenetic analysis of the near-complete 16S rRNA gene sequence indicated that it differed from those of the described streptomycetes available in public databases. The distinctive white aerial hyphae and lack of sporulation suggest a deficiency in the whi pathway of the organism. A combination of substrate utilization patterns, morphological and chemotaxonomic characteristics and DNA-DNA hybridization results supported the affiliation of strain RB72(T) to the genus Streptomyces and enabled the genotypic and phenotypic differentiation of strain RB72(T) from closely related reference strains. Strain RB72(T) therefore represents a novel species of the genus Streptomyces, for which the name Streptomyces scopuliridis sp. nov. is proposed. The type strain is RB72(T) ( = DSM 41917(T)  = NRRL B-24574(T)).

The complex whiJ locus mediates environmentally sensitive repression of development of Streptomyces coelicolor A3(2)

A segment of DNA was isolated that complemented several poorly characterised sporulation-defective white-colony mutants of Streptomyces coelicolor A3(2) from an early collection (Hopwood et al., J Gen Microbiol 61: 397-408, 1970). Complementation was attributable to a gene, SCO4543, named whiJ, encoding a likely DNA-binding protein. Surprisingly, although some mutations in whiJ had a white colony phenotype, complete deletion of the wild-type or mutant gene gave a wild-type morphology. The whiJ gene is a member of a large paralogous set of S. coelicolor genes including abaAorfA, which regulates antibiotic production; and genes flanking whiJ are paralogues of other gene classes that are often associated with whiJ-like genes (Gehring et al., Proc Natl Acad Sci USA 97: 9642-9647, 2000). Thus, the small gene SCO4542 encodes a paralogue of the abaAorfD gene product, and SCO4544 encodes a paralogue of a family of likely anti-sigma factors (including the product of abaAorfB). Deletion of SCO4542 resulted in a medium-dependent bald- or white-colony phenotype, which could be completely suppressed by the simultaneous deletion of whiJ. A model is proposed in which WhiJ binds to operator sequences to repress developmental genes, with repression being released by interaction with the WhiJ-associated SCO4542 protein. It is suggested that this activity of SCO4542 protein is prevented by an unknown signal.

In vivo Tn5-based transposon mutagenesis of Streptomycetes

This paper reports the in vivo expression of the synthetic transposase gene tnp(a) from a hyperactive Tn5 tnp gene mutant in Streptomyces coelicolor. Using the synthetic tnp(a) gene adapted for Streptomyces codon usage, we showed random insertion of the transposon into the Streptomycetes genome. The insertion frequency for the hyperactive Tn5 derivative is 98% of transformed S. coelicolor cells. The random transposition has been confirmed by the recovery of ~1.1% of auxotrophs. The Tn5 insertions are stably inherited in the absence of apramycin selection. The transposon contains an apramycin resistance selection marker and an R6Kgamma origin of replication for transposon rescue. We identified the transposon insertion loci by random sequencing of 14 rescue plasmids. The majority of insertions (12 of 14) were mapped to putative open-reading frames on the S. coelicolor chromosome. These included two new regulatory genes affecting S. coelicolor growth and actinorhodin biosynthesis.

Phosphomannose isomerase and phosphomannomutase gene disruptions in Streptomyces nodosus: impact on amphotericin biosynthesis and implications for glycosylation engineering

Streptomycetes synthesise several bioactive natural products that are modified with sugar residues derived from GDP-mannose. These include the antifungal polyenes, the antibacterial antibiotics hygromycin A and mannopeptimycins, and the anticancer agent bleomycin. Three enzymes function in biosynthesis of GDP-mannose from the glycolytic intermediate fructose 6-phosphate: phosphomannose isomerase (PMI), phosphomannomutase (PMM) and GDP-mannose pyrophosphorylase (GMPP). Synthesis of GDP-mannose from exogenous mannose requires hexokinase or phosphotransferase enzymes together with PMM and GMPP. In this study, a region containing genes for PMI, PMM and GMPP was cloned from Streptomyces nodosus, producer of the polyenes amphotericins A and B. Inactivation of the manA gene for PMI resulted in production of amphotericins and their aglycones, 8-deoxyamphoteronolides. A double mutant lacking the PMI and PMM genes produced 8-deoxyamphoteronolides in good yields along with trace levels of glycosylated amphotericins. With further genetic engineering these mutants may activate alternative hexoses as GDP-sugars for transfer to aglycones in vivo.

Change in colony morphology and kinetics of tylosin production after UV and gamma irradiation mutagenesis of Streptomyces fradiae NRRL-2702

Tylosin is a macrolide antibiotic used as veterinary drug and growth promoter. Attempts were made for hyper production of tylosin by a strain of Streptomyces fradiae NRRL-2702 through irradiation mutagenesis. Ultraviolet (UV) irradiation of wild-type strain caused development of six morphologically altered colony types on agar plates. After screening using Bacillus subtilis bioassay only morphological mutants indicated the production of tylosin. An increase of 2.7+/-0.22-fold in tylosin production (1500mg/l) in case of mutant UV-2 in complex medium was achieved as compared to wild-type strain (550mg/l). Gamma irradiation of mutant UV-2 using (60)Co gave one morphologically altered colony type gamma-1, which gave 2500mg/l tylosin yield in complex medium. Chemically defined media promoted tylosin production upto 3800mg/l. Maximum value of q(p) (3.34mg/gh) was observed by mutant gamma-1 as compared to wild strain (0.81mg/gh). Moreover, UV irradiation associated changes were unstable with loss of tylosin activity whereas mutant gamma-1 displayed high stability on subsequent culturing.

The evolution of development inStreptomycesanalysed by genome comparisons

There is considerable information about the genetic control of the processes by which mycelial Streptomyces bacteria form spore-bearing aerial hyphae. The recent acquisition of genome sequences for 16 species of actinobacteria, including two streptomycetes, makes it possible to try to reconstruct the evolution of Streptomyces differentiation by a comparative genomic approach, and to place the results in the context of current views on the evolution of bacteria. Most of the developmental genes evaluated are found only in actinobacteria that form sporulating aerial hyphae, with several being peculiar to streptomycetes. Only four (whiA, whiB, whiD, crgA) are generally present in nondifferentiating actinobacteria, and only two (whiA, whiG) are found in other bacteria, where they are widespread. Thus, the evolution of Streptomyces development has probably involved the stepwise acquisition of laterally transferred DNA, each successive acquisition giving rise either to regulatory changes that affect the conditions under which development is initiated, or to changes in cellular structure or morphology.

Identification and characterization of bacterial cysteine dioxygenases: a new route of cysteine degradation for eubacteria

In metazoa and fungi, the catabolic dissimilation of cysteine begins with its sulfoxidation to cysteine sulfinic acid by the enzyme cysteine dioxygenase (CDO). In these organisms, CDO plays an important role in the homeostatic regulation of steady-state cysteine levels and provides important oxidized metabolites of cysteine such as sulfate and taurine. To date, there has been no experimental evidence for the presence of CDO in prokaryotes. Using PSI-BLAST searches and crystallographic information about the active-site geometry of mammalian CDOs, we identified a total of four proteins from Bacillus subtilis, Bacillus cereus, and Streptomyces coelicolor A3(2) that shared low overall identity to CDO (13 to 21%) but nevertheless conserved important active-site residues. These four proteins were heterologously expressed and purified to homogeneity by a single-step immobilized metal affinity chromatography procedure. The ability of these proteins to oxidize cysteine to cysteine sulfinic acid was then compared against recombinant rat CDO. The kinetic data strongly indicate that these proteins are indeed bona fide CDOs. Phylogenetic analyses of putative bacterial CDO homologs also indicate that CDO is distributed among species within the phyla of Actinobacteria, Firmicutes, and Proteobacteria. Collectively, these data suggest that a large subset of eubacteria is capable of cysteine sulfoxidation. Suggestions are made for how this novel pathway of cysteine metabolism may play a role in the life cycle of the eubacteria that have it.

DevA, a GntR-like transcriptional regulator required for development in Streptomyces coelicolor

The gram-positive filamentous bacterium Streptomyces coelicolor has a complex developmental cycle with three distinct phases: growth of the substrate mycelium, development of reproductive structures called aerial hyphae, and differentiation of these aerial filaments into long chains of exospores. During a transposon mutagenesis screen, we identified a novel gene (devA) required for proper development. The devA mutant produced only rare aerial hyphae, and those that were produced developed aberrant spore chains that were much shorter than wild-type chains and had misplaced septa. devA encodes a member of the GntR superfamily, a class of transcriptional regulators that typically respond to metabolite effector molecules. devA forms an operon with the downstream gene devB, which encodes a putative hydrolase that is also required for aerial mycelium formation on R5 medium. S1 nuclease protection analysis showed that transcription from the single devA promoter was temporally associated with vegetative growth, and enhanced green fluorescent protein transcriptional fusions showed that transcription was spatially confined to the substrate hyphae in the wild type. In contrast, devAB transcript levels were dramatically upregulated in a devA mutant and the devA promoter was also active in aerial hyphae and spores in this background, suggesting that DevA might negatively regulate its own production. This suggestion was confirmed by gel mobility shift assays that showed that DevA binds its own promoter region in vitro.

Effects of methylmalonyl-CoA mutase gene knockouts on erythromycin production in carbohydrate-based and oil-based fermentations of Saccharopolyspora erythraea

In carbohydrate-based fermentations of Saccharopolyspora erythraea, a polar knockout of the methylmalonyl-CoA mutase (MCM) gene, mutB, improved erythromycin production an average of 126% (within the range of 102-153% for a 0.95 confidence interval). In oil-based fermentations, where erythromycin production by the wild-type strain averages 184% higher (141-236%, 0.95 CI) than in carbohydrate-based fermentations, the same polar knockout in mutB surprisingly reduced erythromycin production by 66% (53-76%, 0.95 CI). A metabolic model is proposed where in carbohydrate-based fermentations MCM acts as a drain on the methylmalonyl-CoA metabolite pool, and in oil-based fermentations, MCM acts in the reverse direction to fill the methylmalonyl-CoA pool. Therefore, the model explains, in part, how the well-known oil-based process improvement for erythromycin production operates at the biochemical level; furthermore, it illustrates how the mutB erythromycin strain improvement mutation operates at the genetic level in carbohydrate-based fermentations.

An ordered, nonredundant library of Pseudomonas aeruginosa strain PA14 transposon insertion mutants

Random transposon insertion libraries have proven invaluable in studying bacterial genomes. Libraries that approach saturation must be large, with multiple insertions per gene, making comprehensive genome-wide scanning difficult. To facilitate genome-scale study of the opportunistic human pathogen Pseudomonas aeruginosa strain PA14, we constructed a nonredundant library of PA14 transposon mutants (the PA14NR Set) in which nonessential PA14 genes are represented by a single transposon insertion chosen from a comprehensive library of insertion mutants. The parental library of PA14 transposon insertion mutants was generated by using MAR2xT7, a transposon compatible with transposon-site hybridization and based on mariner. The transposon-site hybridization genetic footprinting feature broadens the utility of the library by allowing pooled MAR2xT7 mutants to be individually tracked under different experimental conditions. A public, internet-accessible database (the PA14 Transposon Insertion Mutant Database, http://ausubellab.mgh.harvard.edu/cgi-bin/pa14/home.cgi) was developed to facilitate construction, distribution, and use of the PA14NR Set. The usefulness of the PA14NR Set in genome-wide scanning for phenotypic mutants was validated in a screen for attachment to abiotic surfaces. Comparison of the genes disrupted in the PA14 transposon insertion library with an independently constructed insertion library in P. aeruginosa strain PAO1 provides an estimate of the number of P. aeruginosa essential genes.

Mycelium development in Streptomyces antibioticus ATCC11891 occurs in an orderly pattern which determines multiphase growth curves

Background

The current model for the developmental cycle of Streptomyces confluent cultures on agar surface is based on the assumption that the only differentiation takes place along the transverse axis (bottom-up): a vegetative (substrate) mycelium grows completely live and viable on the surface and inside the agar until it undergoes a death process and differentiates to a reproductive (aerial) mycelium which grows into the air. Hence, this vertical description assumes that the development in the pre-sporulating phases is more or less homogeneous in all zones of the plate surface.

Results

The work presents a detailed analysis of the differentiation cycle in Streptomyces antibioticus ATCC11891 considering a different spatial dimension: the longitudinal axes, represented by the plate surface. A previously unsuspected complexity during the substrate mycelial phase was detected. We have demonstrated that the young substrate hyphae suffer an early death round that has not been previously described. Subsequently, the remaining mycelium grows in successive waves which vary according to the density of the spore inoculum. In the presence of dense inocula (1.5 × 10⁶ spores per plate), the hyphae develop in regular circles, approximately 0.5 cm in diameter. By contrast, with highly diluted inocula (6 × 10³ spores per plate), aerial mycelium develops initially in the form of islands measuring 0.9 mm in diameter. Further mycelial development occurs between the circles or islands until the plate surface is totally covered. This pattern persists throughout the entire developmental cycle including the sporulation phases.

Conclusion

An early death round during the substrate mycelial phase of Streptomyces antibioticus ATCC11891 takes place prior to successive growth periods in surface cultures. These developmental periods in turn, determine the shape of the complex multiphase growth curves observed. As shown here, these results also apply to other Streptomyces strains and species. Understanding these peculiarities of the Streptomyces developmental cycle is essential in order to properly interpret the morphological/biochemical data obtained from solid cultures and will expand the number of potential phenotypes subject to study.

Sigma factor WhiG and its regulation constitute a target of a mutational phenomenon occurring during aerial mycelium growth in Streptomyces ambofaciens ATCC23877

The genetic instability of Streptomyces ambofaciens affects the pigmentation of colonies and generates a variety of mutants the majority of which display large genome rearrangements. Among them, the Pig-pap mutants, which probably result from a mutational event occurring during aerial mycelium growth, display specific features, since they are unable to sporulate and do not harbor any large detectable genome rearrangements. To identify the mutational event causing their phenotype, three Pig-pap mutants originating from three independent mutational events were characterized. These mutants exhibited a whiG-like phenotype which was suppressed by the introduction of one copy of Streptomyces coelicolor whiG. Their own whiG gene was devoid of mutations and appeared to be transcribed at a level similar to that of the WT. However, whiH, the expression of which depends on sigma(WhiG), was not transcribed in any of the three Pig-pap mutants, suggesting that the sigma(WhiG) was absent or inactive. This suggests that in these Pig-pap mutants, the regulation of sigma(WhiG) might be affected. Finally, the introduction of S. coelicolor whiG in one of these Pig-pap mutants restored not only pigmentation and sporulation, but also the ability to once again form white papillae. Analyses of transgene whiG in these papillae revealed that it constitutes a mutational target during aerial mycelium formation when integrated into the genome of this Pig-pap mutant.

Engineering precursor flow for increased erythromycin production in Aeromicrobium erythreum

Metabolic engineering technology for industrial microorganisms is under development to create rational, more reliable, and more cost-effective approaches to strain improvement. Strain improvement is a critical component of the drug development process, yet the genetic basis for high production by industrial microorganisms is still a mystery. In this study, a search was begun for genetic modifications critical for high-level antibiotic production. The model system used was erythromycin production studied in the unicellular actinomycete, Aeromicrobium erythreum. A tagged-mutagenesis approach allowed reverse engineering of improved strains, revealing two genes, mutB and cobA, in the primary metabolic branch for methylmalonyl-CoA utilization. Knockouts in these genes created a permanent metabolic switch in the flow of methylmalonyl-CoA, from the primary branch into a secondary metabolic branch, driving erythromycin overproduction. The model provides insights into the regulation and evolution of secondary metabolism.

Alternatives to binary fission in bacteria

Whereas most prokaryotes rely on binary fission for propagation, many species use alternative mechanisms, which include multiple offspring formation and budding, to reproduce. In some bacterial species, these eccentric reproductive strategies are essential for propagation, whereas in others the programmes are used conditionally. Although there are tantalizing images and morphological descriptions of these atypical developmental processes, none of these reproductive structures are characterized at the molecular genetic level. Now, with newly available analytical techniques, model systems to study these alternative reproductive programmes are being developed.

Reverse engineering of industrial pharmaceutical-producing actinomycete strains using DNA microarrays

Transcript levels in production cultures of wildtype and classically improved strains of the actinomycete bacteria Saccharopolyspora erythraea and Streptomyces fradiae were monitored using microarrays of the sequenced actinomycete S. coelicolor. Sac. erythraea and S. fradiae synthesize the polyketide antibiotics erythromycin and tylosin, respectively, and the classically improved strains contain unknown overproduction mutations. The Sac. erythraea overproducer was found to express the entire 56-kb erythromycin gene cluster several days longer than the wildtype strain. In contrast, the S. fradiae wildtype and overproducer strains expressed the 85-kb tylosin biosynthetic gene cluster similarly, while they expressed several tens of other S. fradiae genes and S. coelicolor homologs differently, including the acyl-CoA dehydrogenase gene aco and the S. coelicolor isobutyryl-CoA mutase homolog icmA. These observations indicated that overproduction mechanisms in classically improved strains can affect both the timing and rate of antibiotic synthesis, and alter the regulation of antibiotic biosynthetic enzymes and enzymes involved in precursor metabolism.

Novel genes that influence development in Streptomyces coelicolor

Filamentous soil bacteria of the genus Streptomyces carry out complex developmental cycles that result in sporulation and production of numerous secondary metabolites with pharmaceutically important activities. To further characterize the molecular basis of these developmental events, we screened for mutants of Streptomyces coelicolor that exhibit aberrant morphological differentiation and/or secondary metabolite production. On the basis of this screening analysis and the subsequent complementation analysis of the mutants obtained we assigned developmental roles to a gene involved in methionine biosynthesis (metH) and two previously uncharacterized genes (SCO6938 and SCO2525) and we reidentified two previously described developmental genes (bldA and bldM). In contrast to most previously studied genes involved in development, the genes newly identified in the present study all appear to encode biosynthetic enzymes instead of regulatory proteins. The MetH methionine synthase appears to be required for conversion of aerial hyphae into chains of spores, SCO6938 is a probable acyl coenzyme A dehydrogenase that contributes to the proper timing of aerial mycelium formation and antibiotic production, and SCO2525 is a putative methyltransferase that influences various aspects of colony growth and development.

Systematic insertional mutagenesis of a streptomycete genome: a link between osmoadaptation and antibiotic production

The model organism Streptomyces coelicolor represents a genus that produces a vast range of bioactive secondary metabolites. We describe a versatile procedure for systematic and comprehensive mutagenesis of the S. coelicolor genome. The high-throughput process relies on in vitro transposon mutagenesis of an ordered cosmid library; mutagenized cosmids with fully characterized insertions are then transferred by intergeneric conjugation into Streptomyces, where gene replacement is selected. The procedure can yield insertions in upward of 90% of genes, and its application to the entire genome is underway. The methodology could be applied to many other organisms that can receive DNA via RK2/RP4-mediated intergeneric conjugation. The system permits introduction of mutations into different genetic backgrounds and qualitative measurement of the expression of disrupted genes as demonstrated in the analysis of a hybrid histidine kinase and response regulator gene pair, osaAB, involved in osmoadaptation in Streptomyces. The independently transcribed response regulator gene, osaB, is essential for osmoadaptation; when grown with supplementary osmolyte, an osaB mutant cannot erect aerial hyphae and produces up to fivefold greater antibiotic yields than the wild-type strain.

SCP1, a 356 023 bp linear plasmid adapted to the ecology and developmental biology of its host, Streptomyces coelicolor A3(2)

The sequencing of the entire genetic complement of Streptomyces coelicolor A3(2) has been completed with the determination of the 365,023 bp sequence of the linear plasmid SCP1. Remarkably, the functional distribution of SCP1 genes somewhat resembles that of the chromosome: predicted gene products/functions include ECF sigma factors, antibiotic biosynthesis, a gamma-butyrolactone signalling system, members of the actinomycete-specific Wbl class of regulatory proteins and 14 secreted proteins. Some of these genes are among the 18 that contain a TTA codon, making them targets for the developmentally important tRNA encoded by the bldA gene. RNA analysis and gene fusions showed that one of the TTA-containing genes is part of a large bldA-dependent operon, the gene products of which include three proteins isolated from the spore surface by detergent washing (SapC, D and E), and several probable metabolic enzymes. SCP1 shows much evidence of recombinational interactions with other replicons and transposable elements during its history. For example, it has two sets of partitioning genes (which may explain why an integrated copy of SCP1 partially suppressed the defective partitioning of a parAB-deleted chromosome during sporulation). SCP1 carries a cluster of probable transfer determinants and genes encoding likely DNA polymerase III subunits, but it lacks an obvious candidate gene for the terminal protein associated with its ends. This may be related to atypical features of its end sequences.

Transposon-based strategies for microbial functional genomics and proteomics

Transposons are mobile genetic elements that can relocate from one genomic location to another. As well as modulating gene expression and contributing to genome plasticity and evolution, transposons are remarkably diverse molecular tools for both whole-genome and single-gene studies in bacteria, yeast, and other microorganisms. Efficient but simple in vitro transposition reactions now allow the mutational analysis of previously recalcitrant microorganisms. Transposon-based signature-tagged mutagenesis and genetic footprinting strategies have pinpointed essential genes and genes that are crucial for the infectivity of a variety of human and other pathogens. Individual proteins and protein complexes can be dissected by transposon-mediated scanning linker mutagenesis. These and other transposon-based approaches have reaffirmed the usefulness of these elements as simple yet highly effective mutagens for both functional genomic and proteomic studies of microorganisms.

Identification of three new genes involved in morphogenesis and antibiotic production in Streptomyces coelicolor

We report the isolation and partial characterization of three new mutants of Streptomyces coelicolor that are defective in morphogenesis and antibiotic production. The genes identified by the mutations were located and cloned by using a combination of Tn5 in vitro mutagenesis, cotransformation, and genetic complementation. Mutant SE69 produces lower amounts of antibiotics than the wild type produces, produces spores only after prolonged incubation on rich media, and identifies a gene whose predicted protein product is similar to the GntR family of transcriptional regulators; also, production of aerial mycelia on both rich and poor media is significantly delayed in this mutant. Mutant SE293 is defective in morphogenesis, overproduces antibiotics on rich media, fails to grow on minimal media, and identifies a gene whose predicted protein product is similar to the TetR family of transcriptional regulators. Preliminary evidence suggests that the SE293 gene product may control a molybdopterin binding protein located immediately adjacent to it. Mutant SJ175 sporulates sooner and more abundantly than the wild type and overproduces antibiotics on rich media, and it identifies a gene whose predicted protein product contains regions of predominantly hydrophobic residues similar to those of integral membrane proteins.

Structural and genetic analysis of the BldB protein of Streptomyces coelicolor

We have demonstrated that the bldB gene of Streptomyces coelicolor is required for the formation of aerial hyphae and the synthesis of antibiotics. We also found that BldB forms a higher-order complex (most likely a dimer) and that amino acid residues 20 to 78 are important for this interaction. This region is conserved in the BldB family, suggesting that dimer formation may be a common feature of these proteins.

New Mos1 mariner transposons suitable for the recovery of gene fusions in vivo and in vitro

The Drosophila Mos1 element can be mobilized in species ranging from prokaryotes to protozoans and vertebrates, and the purified transposase can be used for in vitro transposition assays. In this report we developed a 'mini-Mos1' element and describe a number of useful derivatives suitable for transposon mutagenesis in vivo or in vitro. Several of these allow the creation and/or selection of tripartite protein fusions to a green fluorescent protein-phleomycin resistance (GFP-PHLEO) reporter/selectable marker. Such X-GFP-PHLEO-X fusions have the advantage of retaining 5' and 3' regulatory information and N- and C-terminal protein targeting domains. A Mos1 derivative suitable for use in transposon-insertion mediated linker insertion (TIMLI) mutagenesis is described, and transposons bearing selectable markers suitable for use in the protozoan parasite Leishmania were made and tested. A novel 'negative selection' approach was developed which permits in vitro assays of transposons lacking bacterial selectable markers. Application of this assay to several Mos1 elements developed for use in insects suggests that the large mariner pM[cn] element used previously in vivo is poorly active in vitro, while the Mos1-Act-EGFP transposon is highly active.

Mutagenesis in the post genomics era: tools for generating insertional mutations in the lactic acid bacteria

The increasing availability of whole genome sequences has increased the demand for effective tools to generate insertional mutations in the lactic acid bacteria (LAB). Several novel approaches, such as shuttle-, transposome- and intron-based mutagenesis methods, are possible additions to the existing repertoire of transposon- and recombination-based tools available for mutagenesis of LAB.

RNA polymerase sigma factor that blocks morphological differentiation by Streptomyces coelicolor

The filamentous bacterium Streptomyces coelicolor undergoes a complicated process of morphological differentiation that begins with the formation of an aerial mycelium and culminates in sporulation. Genes required for the initiation of aerial mycelium formation have been termed bld (bald), describing the smooth, undifferentiated colonies of mutant strains. By using an insertional mutagenesis protocol that relies on in vitro transposition, we have isolated a bld mutant harboring an insertion in a previously uncharacterized gene, SCE59.12c, renamed here rsuA. The insertion mutant exhibited no measurable growth defect but failed to produce an aerial mycelium and showed a significant delay in the production of the polyketide antibiotic actinorhodin. The rsuA gene encodes an apparent anti-sigma factor and is located immediately downstream of SCE59.13c, renamed here sigU, whose product is inferred to be a member of the extracytoplasmic function subfamily of RNA polymerase sigma factors. The absence of rsuA in a strain that contained sigU caused a block in development, and the overexpression of sigU in an otherwise wild-type strain caused a delay in aerial mycelium formation. However, a strain in which both rsuA and sigU had been deleted was able to undergo morphological differentiation normally. We conclude that the rsuA-encoded anti-sigma factor is responsible for antagonizing the function of the sigma factor encoded by sigU. We also conclude that the sigU-encoded sigma factor is not normally required for development but that its uncontrolled activity obstructs morphological differentiation at an early stage.

An eukaryotic-type serine/threonine protein kinase involved in the carbon source-dependent pigment biosynthesis in Amycolatopsis mediterranei U32

The structural gene, pkmA, was cloned and sequenced from a rifamycin SV-producing Amycolatopsis mediterranei U32 strain. The N-terminal portion of the deduced amino acid sequence of pkmA showed significant similarity to the family of serine/threonine protein kinases. It contains all the structural features which are highly conserved in protein kinases, including the Gly-X-Gly-X-X-Gly motif of ATP binding and the essential amino acids known to be important for the recognition of the correct hydroxyamino acid in serine/threonine protein specific kinases. The protein possesses a region rich in Ala and Pro residues around the middle of pkmA open reading frame, which might be involved in the transmembrane function, as suggested by PhoA fusion protein analysis. The pkmA gene was expressed in Escherichia coli as a glutathione S-transferase (GST) fusion protein, and the protein was found to have the activity of autophosphorylation. A double crossover gene replacement was achieved by inserting an aparmycin resistance gene into pkmA in A. mediterranei chromosomal DNA. The phenotypic analysis of the mutant suggested that pkmA gene is involved in carbon source-dependent pigment formation in A. mediterranei U32.

Generalized transduction in Streptomyces coelicolor

We report the isolation of generalized transducing phages for Streptomyces species able to transduce chromosomal markers or plasmids between derivatives of Streptomyces coelicolor, the principal genetic model system for this important bacterial genus. We describe four apparently distinct phages (DAH2, DAH4, DAH5, and DAH6) that are capable of transducing multiple chromosomal markers at frequencies ranging from 10(-5) to 10(-9) per plaque-forming unit. The phages contain DNA ranging in size from 93 to 121 kb and mediate linked transfer of genetic loci at neighboring chromosomal sites sufficiently close to be packaged within the same phage particle. The key to our ability to demonstrate transduction by these phages was the establishment of conditions expected to severely reduce superinfection killing during the selection of transductants. The host range of these phages, as measured by the ability to form plaques, extends to species as distantly related as Streptomyces avermitilis and Streptomyces verticillus, which are among the most commercially important species of this genus. Transduction of plasmid DNA between S. coelicolor and S. verticillus was observed at frequencies of approximately 10(-4) transductants per colony-forming unit.

Recent advances in large-scale transposon mutagenesis

Transposons were identified as mobile genetic elements over fifty years ago and subsequently became powerful tools for molecular-genetic studies. Recently, transposon-mutagenesis strategies have been developed to identify essential and pathogenicity-related genes in pathogenic microorganisms. Also, a number of in vitro transposition systems have been used to facilitate genome sequence analysis. Finally, transposon mutagenesis of yeast and complex eukaryotes has provided valuable functional genomic information to complement genome-sequencing projects.