The evolution of development inStreptomycesanalysed by genome comparisons

Genomic Diversity of Streptomyces clavuligerus: Implications for Clavulanic Acid Biosynthesis and Industrial Hyperproduction

Streptomyces clavuligerus is a species used worldwide to industrially produce clavulanic acid (CA), a molecule that enhances antibiotic effectiveness against β-lactamase-producing bacterial strains. Despite its low inherent CA production, hyper-producing strains have been developed. However, genomic analyses specific to S. clavuligerus and CA biosynthesis are limited. Genomic variations that may influence CA yield were explored using S. clavuligerus strain genomes from diverse sources. Despite the slight differences obtained by similarity index calculation, pan-genome estimation revealed that only half of the genes identified were present in all strains. As expected, core genes were associated with primary metabolism, while the remaining genes were linked to secondary metabolism. Differences at the sequence level were more likely to be found in regions close to the tips of the linear chromosome. Wild-type strains preserved larger chromosomal and plasmid regions compared to industrial and/or hyper-producing strains; such a grouping pattern was also found through refined phylogenetic analyses. These results provide essential insights for the development of hyper-producing S. clavuligerus strains, attending to the critical demand for this antibiotic enhancer and contributing to future strategies for CA production optimization.

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.

A panoramic view of the genomic landscape of the genus Streptomyces

We delineate the evolutionary plasticity of the ecologically and biotechnologically important genus Streptomyces, by analysing the genomes of 213 species. Streptomycetes genomes demonstrate high levels of internal homology, whereas the genome of their last common ancestor was already complex. Importantly, we identify the species-specific fingerprint proteins that characterize each species. Even among closely related species, we observed high interspecies variability of chromosomal protein-coding genes, species-level core genes, accessory genes and fingerprints. Notably, secondary metabolite biosynthetic gene clusters (smBGCs), carbohydrate-active enzymes (CAZymes) and protein-coding genes bearing the rare TTA codon demonstrate high intraspecies and interspecies variability, which emphasizes the need for strain-specific genomic mining. Highly conserved genes, such as those specifying genus-level core proteins, tend to occur in the central region of the chromosome, whereas those encoding proteins with evolutionarily volatile species-level fingerprints, smBGCs, CAZymes and TTA-codon-bearing genes are often found towards the ends of the linear chromosome. Thus, the chromosomal arms emerge as the part of the genome that is mainly responsible for rapid adaptation at the species and strain level. Finally, we observed a moderate, but statistically significant, correlation between the total number of CAZymes and three categories of smBGCs (siderophores, e-Polylysin and type III lanthipeptides) that are related to competition among bacteria.

The evolution of morphological development is congruent with the species phylogeny in the genus Streptomyces

As the canonical model organism to dissect bacterial morphological development, Streptomyces species has attracted much attention from the microbiological society. However, the evolution of development-related genes in Streptomyces remains elusive. Here, we evaluated the distribution of development-related genes, thus indicating that the majority of these genes were ubiquitous in Streptomyces genomes. Furthermore, the phylogenetic topologies of related strict orthologous genes were compared to the species tree of Streptomyces from both concatenation and single-gene tree analyses. Meanwhile, the reconciled gene tree and normalization based on the number of parsimony-informative sites were also employed to reduce the impact of phylogenetic conflicts, which was induced by uncertainty in single-gene tree inference based merely on the sequence and the bias in the amount of phylogenetic information caused by variable numbers of parsimony-informative sites. We found that the development-related genes had higher congruence to the species tree than other strict orthologous genes. Considering that the development-related genes could also be tracked back to the common ancestor of Streptomyces, these results suggest that morphological development follows the same pattern as species divergence.

Streptomyces rare codon UUA: from features associated with 2 adpA related locations to candidate phage regulatory translational bypassing

In Streptomyces species, the cell cycle involves a switch from an early and vegetative state to a later phase where secondary products including antibiotics are synthesized, aerial hyphae form and sporulation occurs. AdpA, which has two domains, activates the expression of numerous genes involved in the switch from the vegetative growth phase. The adpA mRNA of many Streptomyces species has a UUA codon in a linker region between 5' sequence encoding one domain and 3' sequence encoding its other and C-terminal domain. UUA codons are exceptionally rare in Streptomyces, and its functional cognate tRNA is not present in a fully modified and acylated form, in the early and vegetative phase of the cell cycle though it is aminoacylated later. Here, we report candidate recoding signals that may influence decoding of the linker region UUA. Additionally, a short ORF 5' of the main ORF has been identified with a GUG at, or near, its 5' end and an in-frame UUA near its 3' end. The latter is commonly 5 nucleotides 5' of the main ORF start. Ribosome profiling data show translation of that 5' region. Ten years ago, UUA-mediated translational bypassing was proposed as a sensor by a Streptomyces phage of its host's cell cycle stage and an effector of its lytic/lysogeny switch. We provide the first experimental evidence supportive of this proposal.

Genomic Investigation of Desert Streptomyces huasconensis D23 Reveals Its Environmental Adaptability and Antimicrobial Activity

The harsh climatic conditions of deserts may lead to unique adaptations of microbes, which could serve as potential sources of new metabolites to cope with environmental stresses. However, the mechanisms governing the environmental adaptability and antimicrobial activity of desert Streptomyces remain inadequate, especially in extreme temperature differences, drought conditions, and strong radiation. Here, we isolated a Streptomyces strain from rocks in the Kumtagh Desert in Northwest China and tested its antibacterial activity, resistance to UV-C irradiation, and tolerance to hydrogen peroxide (H2O2). The whole-genome sequencing was carried out to study the mechanisms underlying physiological characteristics and ecological adaptation from a genomic perspective. This strain has a growth inhibitory effect against a variety of indicator bacteria, and the highest antibacterial activity recorded was against Bacillus cereus. Moreover, strain D23 can withstand UV-C irradiation up to 100 J/m2 (D10 = 80 J/m2) and tolerate stress up to 70 mM H2O2. The genome prediction of strain D23 revealed the mechanisms associated with its adaptation to extreme environmental and stressful conditions. In total, 33 biosynthetic gene clusters (BGCs) were predicted based on anti-SMASH. Gene annotation found that S. huasconensis D23 contains several genes and proteins associated with the biosynthesis of factors required to cope with environmental stress of temperature, UV radiation, and osmotic pressure. The results of this study provide information about the genome and BGCs of the strain S. huasconensis D23. The experimental results combined with the genome sequencing data show that antimicrobial activity and stress resistance of S. huasconensis D23 was due to the rich and diverse secondary metabolite production capacity and the induction of stress-responsive genes. The environmental adaptability and antimicrobial activity information presented here will be valuable for subsequent work regarding the isolation of bioactive compounds and provide insight into the ecological adaptation mechanism of microbes to extreme desert environments.

Bioprospecting of Soil-Derived Actinobacteria Along the Alar-Hotan Desert Highway in the Taklamakan Desert

Taklamakan desert is known as the largest dunefield in China and as the second largest shifting sand desert in the world. Although with long history and glorious culture, the Taklamakan desert remains largely unexplored and numerous microorganisms have not been harvested in culture or taxonomically identified yet. The main objective of this study is to explore the diversity, novelty, and pharmacological potential of the cultivable actinomycetes from soil samples at various sites along the Alar-Hotan desert highway in the Taklamakan desert. A total of 590 actinobacterial strains were recovered by the culture-dependent approach. Phylogenetic analysis based on 16S ribosomal RNA (rRNA) gene sequences unveiled a significant level of actinobacterial diversity with 55 genera distributed in 27 families of 12 orders. Thirty-six strains showed relatively low 16S rRNA similarities (<98.65%) with validly described species, among which four strains had already been characterized as novel taxa by our previous research. One hundred and forty-six actinobacterial isolates were selected as representatives to evaluate the antibacterial activities and mechanism of action by the paper-disk diffusion method and a double fluorescent protein reporter "pDualrep2" system, respectively. A total of 61 isolates exhibited antagonistic activity against the tested "ESKAPE" pathogens, among which seven strains could produce bioactive metabolites either to be able to block translation machinery or to induce SOS-response in the pDualrep2 system. Notably, Saccharothrix sp. 16Sb2-4, harboring a promising antibacterial potential with the mechanism of interfering with protein translation, was analyzed in detail to gain deeper insights into its bioactive metabolites. Through ultra-performance liquid chromatography (UPLC)-quadrupole time-of-flight (QToF)-MS/MS based molecular networking analysis and databases identification, four families of compounds (1-16) were putatively identified. Subsequent bioassay-guided separation resulted in purification of four 16-membered macrolide antibiotics, aldgamycin H (8), aldgamycin K (9), aldgamycin G (10), and swalpamycin B (11), and their structures were elucidated by HR-electrospray ionization source (ESI)-MS and NMR spectroscopy. All compounds 8-11 displayed antibacterial activities by inhibiting protein synthesis in the pDualrep2 system. In conclusion, this work demonstrates that Taklamakan desert is a potentially unique reservoir of versatile actinobacteria, which can be a promising source for discovery of novel species and diverse bioactive compounds.

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 Mining of the Genus Streptacidiphilus for Biosynthetic and Biodegradation Potential

The genus Streptacidiphilus represents a group of acidophilic actinobacteria within the family Streptomycetaceae, and currently encompasses 15 validly named species, which include five recent additions within the last two years. Considering the potential of the related genera within the family, namely Streptomyces and Kitasatospora, these relatively new members of the family can also be a promising source for novel secondary metabolites. At present, 15 genome data for 11 species from this genus are available, which can provide valuable information on their biology including the potential for metabolite production as well as enzymatic activities in comparison to the neighboring taxa. In this study, the genome sequences of 11 Streptacidiphilus species were subjected to the comparative analysis together with selected Streptomyces and Kitasatospora genomes. This study represents the first comprehensive comparative genomic analysis of the genus Streptacidiphilus. The results indicate that the genomes of Streptacidiphilus contained various secondary metabolite (SM) producing biosynthetic gene clusters (BGCs), some of them exclusively identified in Streptacidiphilus only. Several of these clusters may potentially code for SMs that may have a broad range of bioactivities, such as antibacterial, antifungal, antimalarial and antitumor activities. The biodegradation capabilities of Streptacidiphilus were also explored by investigating the hydrolytic enzymes for complex carbohydrates. Although all genomes were enriched with carbohydrate-active enzymes (CAZymes), their numbers in the genomes of some strains such as Streptacidiphilus carbonis NBRC 100919^T were higher as compared to well-known carbohydrate degrading organisms. These distinctive features of each Streptacidiphilus species make them interesting candidates for future studies with respect to their potential for SM production and enzymatic activities.

Thiol-specific oxidant diamide downregulates whiA gene of Corynebacterium glutamicum, thereby suppressing cell division and metabolism

The whiA (NCgl1527) gene from Corynebacterium glutamicum plays a crucial role during cell growth, and WhiA is recognized as the transcription factor for genes involved in cell division. In this study, we assessed the regulatory role of the gene in cell physiology. Transcription of the gene was specifically downregulated by the thiol-specific oxidant, diamide, and by heat stress. Cells exposed to diamide showed decreased transcription of genes involved in cell division and these effects were more profound in ΔwhiA cells. In addition, the ΔwhiA cells showed sensitivity to thiol-specific oxidants, DNA-damaging agents, and high temperature. Further, downregulation of sigH (NCgl0733), the central regulator in stress responses, along with master regulatory genes in cell metabolism, was observed in the ΔwhiA strain. Moreover, the amount of cAMP in the ΔwhiA cells in the early stationary phase was only at 30% level of that for the wild-type strain. Collectively, our data indicate that the role of whiA is to downregulate genes associated with cell division in response to heat or thiol-specific oxidative stress, and may suggest a role for the gene in downshifting cell metabolism by downregulating global regulatory genes when growth condition is not optimal for cells.

Construction of Inducible Genetic Switch for the Global Regulator WblA To Sustain Both Overproduction of Tiancimycins and On-Demand Sporulation in Streptomyces sp. CB03234

The complex life cycle of streptomycetes is closely related to their secondary metabolisms, all controlled by cascade regulations. Tiancimycins (TNMs) are ten-membered enediynes possessing great potential for antitumor drug development. However, their low yields in Streptomyces sp. CB03234 have greatly limited subsequent studies. Through transcriptome analysis and genetic characterization, we proved that WblA is one pivotal global regulator to repress the biosynthesis of TNMs. The deletion of wblA could significantly enhance the production of TNMs, but also abolish the sporulation in CB03234. By constructing the NitR-ε-caprolactam inducible genetic switch, the expression of wblA was governed in CB03234-NRW, thereby sustaining the overproduction of TNMs and recovering the normal sporulation upon induction, which were practical for the scaled-up production of TNMs. Considering the prevalence and conserved regulatory roles of WblA in streptomycetes, our developed strategy shall provide an effective and practical approach to facilitate titer improvement and discovery of natural products.

Differential transcription of expanded gene families in central carbon metabolism of Streptomyces coelicolor A3(2)

Background

Streptomycete bacteria are prolific producers of specialized metabolites, many of which have clinically relevant bioactivity. A striking feature of their genomes is the expansion of gene families that encode the same enzymatic function. Genes that undergo expansion events, either by horizontal gene transfer or duplication, can have a range of fates: genes can be lost, or they can undergo neo-functionalization or sub-functionalization. To test whether expanded gene families in Streptomyces exhibit differential expression, an RNA-Seq approach was used to examine cultures of wild-type Streptomyces coelicolor grown with either glucose or tween as the sole carbon source.

Results

RNA-Seq analysis showed that two-thirds of genes within expanded gene families show transcriptional differences when strains were grown on tween compared to glucose. In addition, expression of specialized metabolite gene clusters (actinorhodin, isorenieratane, coelichelin and a cryptic NRPS) was also influenced by carbon source.

Conclusions

Expression of genes encoding the same enzymatic function had transcriptional differences when grown on different carbon sources. This transcriptional divergence enables partitioning to function under different physiological conditions. These approaches can inform metabolic engineering of industrial Streptomyces strains and may help develop cultivation conditions to activate the so-called silent biosynthetic gene clusters.

Genome Features and Secondary Metabolites Biosynthetic Potential of the Class Ktedonobacteria

The prevalence of antibiotic resistance and the decrease in novel antibiotic discovery in recent years necessitates the identification of potentially novel microbial resources to produce natural products. Ktedonobacteria, a class of deeply branched bacterial lineage in the ancient phylum Chloroflexi, are ubiquitous in terrestrial environments and characterized by their large genome size and complex life cycle. These characteristics indicate Ktedonobacteria as a potential active producer of bioactive compounds. In this study, we observed the existence of a putative "megaplasmid," multiple copies of ribosomal RNA operons, and high ratio of hypothetical proteins with unknown functions in the class Ktedonobacteria. Furthermore, a total of 104 antiSMASH-predicted putative biosynthetic gene clusters (BGCs) for secondary metabolites with high novelty and diversity were identified in nine Ktedonobacteria genomes. Our investigation of domain composition and organization of the non-ribosomal peptide synthetase and polyketide synthase BGCs further supports the concept that class Ktedonobacteria may produce compounds structurally different from known natural products. Furthermore, screening of bioactive compounds from representative Ktedonobacteria strains resulted in the identification of broad antimicrobial activities against both Gram-positive and Gram-negative tested bacterial strains. Based on these findings, we propose the ancient, ubiquitous, and spore-forming Ktedonobacteria as a versatile and promising microbial resource for natural product discovery.

Regulation of antibiotic production in Actinobacteria: new perspectives from the post-genomic era

Covering: 2000 to 2018 The antimicrobial activity of many of their natural products has brought prominence to the Streptomycetaceae, a family of Gram-positive bacteria that inhabit both soil and aquatic sediments. In the natural environment, antimicrobial compounds are likely to limit the growth of competitors, thereby offering a selective advantage to the producer, in particular when nutrients become limited and the developmental programme leading to spores commences. The study of the control of this secondary metabolism continues to offer insights into its integration with a complex lifecycle that takes multiple cues from the environment and primary metabolism. Such information can then be harnessed to devise laboratory screening conditions to discover compounds with new or improved clinical value. Here we provide an update of the review we published in NPR in 2011. Besides providing the essential background, we focus on recent developments in our understanding of the underlying regulatory networks, ecological triggers of natural product biosynthesis, contributions from comparative genomics and approaches to awaken the biosynthesis of otherwise silent or cryptic natural products. In addition, we highlight recent discoveries on the control of antibiotic production in other Actinobacteria, which have gained considerable attention since the start of the genomics revolution. New technologies that have the potential to produce a step change in our understanding of the regulation of secondary metabolism are also described.

Recent advances in natural products exploitation in Streptomyces via synthetic biology

Natural products of microbial origin have proven to be the wellspring of clinically useful compounds for human therapeutics. Streptomyces species are predominant sources of bioactive compounds, most of which serve as potential drug candidates. While the exploitation of natural products has been severely reduced over the past two decades, the growing crisis of evolution and dissemination of drug resistant pathogens have again attracted great interest in this field. The emerging synthetic biology has been heralded as a new bioengineering platform to discover novel bioactive compounds and expand bioactive natural products diversity and production. Herein, we review recent advances in the natural products exploitation of Streptomyces with the applications of synthetic biology from three major aspects, including recently developed synthetic biology tools, natural products biosynthetic pathway engineering strategies as well as chassis host modifications.

Streptomyces Cytochrome P450 Enzymes and Their Roles in the Biosynthesis of Macrolide Therapeutic Agents

The study of the genus Streptomyces is of particular interest because it produces a wide array of clinically important bioactive molecules. The genomic sequencing of many Streptomyces species has revealed unusually large numbers of cytochrome P450 genes, which are involved in the biosynthesis of secondary metabolites. Many macrolide biosynthetic pathways are catalyzed by a series of enzymes in gene clusters including polyketide and non-ribosomal peptide synthesis. In general, Streptomyces P450 enzymes accelerate the final, post-polyketide synthesis steps to enhance the structural architecture of macrolide chemistry. In this review, we discuss the major Streptomyces P450 enzymes research focused on the biosynthetic processing of macrolide therapeutic agents, with an emphasis on their biochemical mechanisms and structural insights.

Soil bacterial communities of Sahara and Gibson deserts: Physiological and taxonomical characteristics

The purpose of this research was to investigate the structure of soil bacteria communities present in the Gibson (Australia) and the Sahara (Egypt) deserts, as well as to estimate strain survivability under different environmental factors. It should be noticed that the screening of bacterial resistance to wide spectra of principally different stress conditions was performed for the first time. Experiments were conducted with culturable bacterial communities. Strains were identified using 16S rRNA sequencing, and stress-tolerance was estimated by growing strains in various nutrient media. In order to characterize the community the epifluorescent microscopy and multisubstrate testing were also performed. High bacterial abundance in the desert soils was detected, and there was seen a significant proportion of culturable cells. The close numbers of psychotropic and mesophilic bacteria in arid ecosystems were revealed. The representatives of the Actinobacteria phylum were dominant in the microbial communities, and Firmicutes, Proteobacteria, and Bacteroidetes phyla representatives were also identified. Tolerance of the axenic bacterial cultures, isolated from arid desert ecotopes, to temperature, pH, salts (KCl, NaCl, MgSO4, NaHCO3), strong oxidizers (Mg(ClO4)2), and antibiotics (ampicillin, cephalexin, chloramphenicol, tetracycline, doxycycline, kanamycin, rifampicin) was studied. The bacterial isolates were characterized by polyextremotolerance and by the ability to maintain metabolic activity in vitro while influenced by a wide range of physicochemical and biotic factors.

Molecular Characterization of Plasmids Harbored by Actinomycetes Isolated From the Great Salt Plains of Oklahoma Using PFGE and Next Generation Whole Genome Sequencing

One of the unique features of actinomycetes, especially the genus Streptomyces, is the presence of linear plasmids. These range in size from 12 to 600 kb, and are often termed mega-plasmids. While many of the genes involved in secondary metabolite production reside in clusters on the chromosome, several studies have identified biosynthetic clusters on large linear plasmids that produce important secondary metabolites, including antibiotics. In this study, Pulse Field Gel Electrophoresis (PFGE) was used to screen 176 actinomycete isolates for the presence of plasmids; these bacterial strains were previously isolated from the Great Salt Plains of Oklahoma. Seventy-eight of the 176 actinomycete isolates (44%) contained plasmids. Several strains contained more than one plasmid, accounting for a total of 109 plasmids. Ten isolates showed extrachromosomal DNA larger than 200 kb, thus falling into the category of mega-plasmids. A subset of plasmids from 55 isolates was treated with S1 nuclease to determine topology; all plasmids examined appeared to be linear and ranged from ~55 to 400 kb. Eleven isolates were chosen for Whole Genome Next Generation Sequencing. From the 11 sequenced isolates, seven plasmids were partially assembled. While the majority of the genes identified on the plasmids coded for hypothetical proteins, others coded for general functions, stress response, and antibiotic and heavy metal resistance. Draft genome sequences of two mega-plasmid-bearing Streptomyces sp. strains, BF-3 and 4F, revealed the presence of genes involved in antibiotic production, antibiotic, and heavy metal resistance, osmoregulation, and stress response, which likely facilitate their survival in this extreme halophilic environment. To our knowledge, this is the first study to explore plasmids harbored by actinomycetes isolated from the Great Salt Plains of Oklahoma.

Biosynthetic Potential of Bioactive Streptomycetes Isolated From Arid Region of the Thar Desert, Rajasthan (India)

Acquisition of Actinobacteria, especially Streptomyces from previously underexplored habitats and the exploration of their biosynthetic potential have gained much attention in the rejuvenated antibiotics search programs. Herein, we isolated some Streptomyces strains, from an arid region of the Great Indian Thar Desert, which possess an ability to produce novel bioactive compounds. Twenty-one morphologically distinctive strains differing in their aerial and substrate mycelium were isolated by employing a stamping method. Among them, 12 strains were identified by a two-level antimicrobial screening method, exerting antimicrobial effects against a panel of indicator strains including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus species. Based on their potent antimicrobial activity, four isolates were further explored by 16S rRNA gene-based identification, genetic screening, and metabolomic analysis; and it was found that these strains belong to the genus Streptomyces. The selected strains were found to have polyketide synthase and non-ribosomal peptide synthetase systems. In addition, extracellular metabolomic screening revealed that the isolates produced analogs of doxorubicinol, pyrromycin, erythromycin, and 6-13 other putative novel metabolites. These results demonstrate the significance of Streptomyces inhabiting the arid region of Thar Desert, suggesting that similar arid environments can be considered as the reservoirs of novel Streptomyces strains that could have biotechnological significance.

Global regulator BldA regulates morphological differentiation and lincomycin production in Streptomyces lincolnensis

Global regulator BldA, the only tRNA for a rare leucine codon UUA, is best known for its ability to affect morphological differentiation and secondary metabolism in the genus Streptomyces. In this study, we confirmed the regulatory function of the bldA gene (Genbank accession no. EU124663.1) in Streptomyces lincolnensis. Disruption of bldA hinders the sporulation and lincomycin production, that can recur when complemented with a functional bldA gene. Western blotting assays demonstrate that translation of the lmbB2 gene which encodes a L-tyrosine hydroxylase is absolutely dependent on BldA; however, mistranslation of the lmbU gene which encodes a cluster-situated regulator (CSR) is observed in a bldA mutant. Intriguingly, when the preferential cognate codon CTG was used, the expression level of LmbU was not the highest compared to the usage of rare codon TTA or CTA, indicating the rare codon in this position is significant for the regulation of lmbU expression. Moreover, replacement of TTA codons in both genes with another leucin codon in the bldA mutant did not restore lincomycin production. Thus, we believe that the bldA gene regulates lincomycin production via controlling the translation of not only lmbB2 and lmbU, but also the other TTA-containing genes. In conclusion, the present study demonstrated the importance of the bldA gene in morphological differentiation and lincomycin production in S. lincolnensis.

Diversity and Contributions to Nitrogen Cycling and Carbon Fixation of Soil Salinity Shaped Microbial Communities in Tarim Basin

Arid and semi-arid regions comprise nearly one-fifth of the earth's terrestrial surface. However, the diversities and functions of their soil microbial communities are not well understood, despite microbial ecological importance in driving biogeochemical cycling. Here, we analyzed the geochemistry and microbial communities of the desert soils from Tarim Basin, northwestern China. Our geochemical data indicated half of these soils are saline. Metagenomic analysis showed that bacterial phylotypes (89.72% on average) dominated the community, with relatively small proportions of Archaea (7.36%) and Eukaryota (2.21%). Proteobacteria, Firmicutes, Actinobacteria, and Euryarchaeota were most abundant based on metagenomic data, whereas genes attributed to Proteobacteria, Actinobacteria, Euryarchaeota, and Thaumarchaeota most actively transcribed. The most abundant phylotypes (Halobacterium, Halomonas, Burkholderia, Lactococcus, Clavibacter, Cellulomonas, Actinomycetospora, Beutenbergia, Pseudomonas, and Marinobacter) in each soil sample, based on metagenomic data, contributed marginally to the population of all microbial communities, whereas the putative halophiles, which contributed the most abundant transcripts, were in the majority of the active microbial population and is consistent with the soil salinity. Sample correlation analyses according to the detected and active genotypes showed significant differences, indicating high diversity of microbial communities among the Tarim soil samples. Regarding ecological functions based on the metatranscriptomic data, transcription of genes involved in various steps of nitrogen cycling, as well as carbon fixation, were observed in the tested soil samples. Metatranscriptomic data also indicated that Thaumarchaeota are crucial for ammonia oxidation and Proteobacteria play the most important role in other steps of nitrogen cycle. The reductive TCA pathway and dicarboxylate-hydroxybutyrate cycle attributed to Proteobacteria and Crenarchaeota, respectively, were highly represented in carbon fixation. Our study reveals that the microbial communities could provide carbon and nitrogen nutrients for higher plants in the sandy saline soils of Tarim Basin.

Expanding Primary Metabolism Helps Generate the Metabolic Robustness To Facilitate Antibiotic Biosynthesis in Streptomyces

The expansion of the genetic repertoire of an organism by gene duplication or horizontal gene transfer (HGT) can aid adaptation. Streptomyces bacteria are prolific producers of bioactive specialized metabolites that have adaptive functions in nature and have found extensive utility in human medicine. While the biosynthesis of these specialized metabolites is directed by dedicated biosynthetic gene clusters, little attention has been focused on how these organisms have evolved robustness in their genomes to facilitate the metabolic plasticity required to provide chemical precursors for biosynthesis during the complex metabolic transitions from vegetative growth to specialized metabolite production and sporulation. Here, we examine genetic redundancy in actinobacteria and show that specialized metabolite-producing bacterial families exhibit gene family expansion in primary metabolism. Focusing on a gene duplication event, we show that the two pyruvate kinases in the genome of Streptomyces coelicolor arose by an ancient duplication event and that each has evolved altered enzymatic kinetics, with Pyk1 having a 20-fold-higher kcat than Pyk2 (4,703 s-1 compared to 215 s-1, respectively), and yet both are constitutively expressed. The pyruvate kinase mutants were also found to be compromised in terms of fitness compared to wild-type Streptomyces These data suggest that expanding gene families can help maintain cell functionality during metabolic perturbation such as nutrient limitation and/or specialized metabolite production.IMPORTANCE The rise of antimicrobial-resistant infections has prompted a resurgence in interest in understanding the production of specialized metabolites, such as antibiotics, by Streptomyces The presence of multiple genes encoding the same enzymatic function is an aspect of Streptomyces biology that has received little attention; however, understanding how the metabolic expansion influences these organisms can help enhance production of clinically useful molecules. Here, we show that expanding the number of pyruvate kinases enables metabolic adaptation, increases strain fitness, and represents an excellent target for metabolic engineering of industrial specialized metabolite-producing bacteria and the activation of cryptic specialized metabolites.

Pleiomorphism in Mycobacterium

Morphological variants in mycobacterial cultures under different growth conditions, including aging of the culture, have been shown to include fibrous aggregates, biofilms, coccoids, and spores. Here we discuss the diversity in shape and size changes demonstrated by bacterial cells with special reference to pleiomorphism observed in Mycobacterium spp. in response to nutritional and other environmental stresses. Inherent asymmetry in cell division and compartmentalization of cell interior under different growth conditions might contribute toward the observed pleiomorphism in mycobacteria. The regulatory genes comprising the bacterial signaling pathway responsible for initiating morphogenesis are speculated upon from bioinformatic identifications of genes for known sensors, kinases, and phosphatases existing in mycobacterial genomes as well as on the basis of what is known in other bacteria.

SpiE interacts with Corynebacterium glutamicum WhcE and is involved in heat and oxidative stress responses

The gene whcE in Corynebacterium glutamicum positively responds to oxidative and heat stress. To search for proteins that interact with WhcE, we employed a two-hybrid system with WhcE as the bait. Sequencing analysis of the isolated clones revealed peptide sequences, one of which showed high sequence identity to a hydrophobe/amphiphile efflux-1 family transporter encoded by NCgl1497. The interaction of the NCgl1497-encoded protein with WhcE in vivo was verified using reporter gene expression by real-time quantitative PCR (RT-qPCR). The WhcE protein strongly interacted with the NCgl1497-encoded protein in the presence of oxidative and heat stress. Furthermore, purified WhcE and NCgl1497-encoded proteins interacted in vitro, especially in the presence of the oxidant diamide, and the protein-protein interaction was disrupted in the presence of the reductant dithiothreitol. In addition, the transcription of NCgl1497 was activated approximately twofold in diamide- or heat-treated cells. To elucidate the function of the NCgl497 gene, an NCgl1497-deleted mutant strain was constructed. The mutant showed decreased viability in the presence of diamide and heat stress. The mutant strain also exhibited reduced transcription of the thioredoxin reductase gene, which is known to be regulated by whcE. Based on the results, NCgl1497 was named spiE (stress protein interacting with WhcE). Collectively, our data suggest that spiE is involved in the whcE-mediated oxidative stress response pathway of C. glutamicum.

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.

Bacterial iron-sulfur cluster sensors in mammalian pathogens

Iron-sulfur clusters act as important cofactors for a number of transcriptional regulators in bacteria, including many mammalian pathogens. The sensitivity of iron-sulfur clusters to iron availability, oxygen tension, and reactive oxygen and nitrogen species enables bacteria to use such regulators to adapt their gene expression profiles rapidly in response to changing environmental conditions. In this review, we discuss how the [4Fe-4S] or [2Fe-2S] cluster-containing regulators FNR, Wbl, aconitase, IscR, NsrR, SoxR, and AirSR contribute to bacterial pathogenesis through control of both metabolism and classical virulence factors. In addition, we briefly review mammalian iron homeostasis as well as oxidative/nitrosative stress to provide context for understanding the function of bacterial iron-sulfur cluster sensors in different niches within the host.

Draft Genome Sequence of Kitasatospora griseola Strain MF730-N6, a Bafilomycin, Terpentecin, and Satosporin Producer

We report here the draft genome sequence of Kitasatospora griseola strain MF730-N6, a known producer of bafilomycin, terpentecin, and satosporins. The current assembly comprises 8 contigs covering 7.97 Mb. Genome annotation revealed 7,225 protein coding sequences, 100 tRNAs, 40 rRNA genes, and 23 secondary metabolite biosynthetic gene clusters.

Analysis of a draft genome sequence of Kitasatospora cheerisanensis KCTC 2395 producing bafilomycin antibiotics

Kitasatospora cheerisanensis KCTC 2395, producing bafilomycin antibiotics belonging to plecomacrolide group, was isolated from a soil sample at Mt. Jiri, Korea. The draft genome sequence contains 8.04 Mb with 73.6% G+C content and 7,810 open reading frames. All the genes for aerial mycelium and spore formations were confirmed in this draft genome. In phylogenetic analysis of MurE proteins (UDP-N-acetylmuramyl-(L)-alanyl-(D)-glutamate:DAP ligase) in a conserved dcw (division of cell wall) locus, MurE proteins of Kitasatospora species were placed in a separate clade between MurEs of Streptomyces species incorporating (LL)-diaminopimelic acid (DAP) and MurEs of Saccharopolyspora erythraea as well as Mycobacterium tuberculosis ligating meso-DAP. From this finding, it was assumed that Kitasatospora MurEs exhibit the substrate specificity for both (LL)-DAP and meso-DAP. The bafilomycin biosynthetic gene cluster was located in the left subtelomeric region. In 71.3 kb-long gene cluster, 17 genes probably involved in the biosynthesis of bafilomycin derivatives were deduced, including 5 polyketide synthase (PKS) genes comprised of 12 PKS modules.

Piericidin A aggravates Tau pathology in P301S transgenic mice

Objective

The P301S mutation in exon 10 of the tau gene causes a hereditary tauopathy. While mitochondrial complex I inhibition has been linked to sporadic tauopathies. Piericidin A is a prototypical member of the group of the piericidins, a class of biologically active natural complex I inhibitors, isolated from streptomyces spp. with global distribution in marine and agricultural habitats. The aim of this study was to determine whether there is a pathogenic interaction of the environmental toxin piericidin A and the P301S mutation.

Methods

Transgenic mice expressing human tau with the P301S-mutation (P301S^+/+) and wild-type mice at 12 weeks of age were treated subcutaneously with vehicle (N = 10 P301S^+/+, N = 7 wild-type) or piericidin A (N = 9 P301S^+/+, N = 9 wild-type mice) at a dose of 0.5 mg/kg/d for a period of 28 days via osmotic minipumps. Tau pathology was measured by stereological counts of cells immunoreative with antibodies against phosphorylated tau (AD2, AT8, AT180, and AT100) and corresponding Western blot analysis.

Results

Piericidin A significantly increased the number of phospho-tau immunoreactive cells in the cerebral cortex in P301S^+/+ mice, but only to a variable and mild extent in wild-type mice. Furthermore, piericidin A led to increased levels of pathologically phosphorylated tau only in P301S^+/+ mice. While we observed no apparent cell loss in the frontal cortex, the synaptic density was reduced by piericidin A treatment in P301S^+/+ mice.

Discussion

This study shows that exposure to piericidin A aggravates the course of genetically determined tau pathology, providing experimental support for the concept of gene-environment interaction in the etiology of tauopathies.

Endospore-enriched sequencing approach reveals unprecedented diversity of Firmicutes in sediments

We present a method for the physical isolation of endospores from environmental samples allowing the specific targeting of endospore-forming bacteria for sequencing (endospore-enriched community). The efficiency of the method was tested on lake sediment samples. After 16S rRNA gene amplicon sequencing, the composition in the endospore-enriched community was compared with the community from untreated control samples (whole community). In the whole community, Firmicutes had a relative abundance of 8% and 19% in the two different lake sediments. In contrast, in the endospore-enriched community, Firmicutes abundance increased to 90.6% and 83.9%, respectively, confirming the efficiency of the endospore enrichment. The relative abundance of other microbial groups that form spore-like resisting states (i.e. actinobacteria, cyanobacteria and myxococcales) was below 2% in the endospore-enriched community, indicating that the method is adapted to true endospores. Representatives from two out of the three known classes of Firmicutes (Bacilli and Clostridia) were detected and supposedly asporogenic groups (e.g. Ethanoligenes and Trichococcus) could be detected. The method presented here is a leap forward for ecological studies of endospore-forming Firmicutes. It can be applied to other types of samples in order to reveal the diversity and metabolic potential of this bacterial group in the environment.

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.

Regulation of the clpP1clpP2 operon by the pleiotropic regulator AdpA in Streptomyces lividans

Insertion of an apramycin resistance cassette in the clpP1clpP2 operon (encoding the ClpP1 and ClpP2 peptidase subunits) affects morphological and physiological differentiation of Streptomyces lividans. Another key factor controlling Streptomyces differentiation is the pleiotropic transcriptional regulator AdpA. We have identified a spontaneous missense mutation (-1 frameshift) in the adpA (bldH) open reading frame in a clpP1clpP2 mutant that led to the synthesis of a non-functional AdpA protein. Electrophoretic mobility shift assays showed that AdpA bound directly to clpP1clpP2 promoter region. Quantitative real-time PCR analysis showed that AdpA regulated the clpP1clpP2 operon expression at specific growth times. In vitro, AdpA and ClgR, a transcriptional activator of clpP1clpP2 operon and other genes, were able to bind simultaneously to clpP1 promoter, which suggests that AdpA binding to clpP1 promoter did not affect that of ClgR. This study allowed to uncover an interplay between the ClpP peptidases and AdpA in S. lividans.

WhiB7, an Fe-S-dependent transcription factor that activates species-specific repertoires of drug resistance determinants in actinobacteria

WhiB-like (Wbl) proteins are well known for their diverse roles in actinobacterial morphogenesis, cell division, virulence, primary and secondary metabolism, and intrinsic antibiotic resistance. Gene disruption experiments showed that three different Actinobacteria (Mycobacterium smegmatis, Streptomyces lividans, and Rhodococcus jostii) each exhibited a different whiB7-dependent resistance profile. Heterologous expression of whiB7 genes showed these resistance profiles reflected the host's repertoire of endogenous whiB7-dependent genes. Transcriptional activation of two resistance genes in the whiB7 regulon, tap (a multidrug transporter) and erm(37) (a ribosomal methyltransferase), required interaction of WhiB7 with their promoters. Furthermore, heterologous expression of tap genes isolated from Mycobacterium species demonstrated that divergencies in drug specificity of homologous structural proteins contribute to the variation of WhiB7-dependent drug resistance. WhiB7 has a specific tryptophan/glycine-rich region and four conserved cysteine residues; it also has a peptide sequence (AT-hook) at its C terminus that binds AT-rich DNA sequence motifs upstream of the promoters it activates. Targeted mutagenesis showed that these motifs were required to provide antibiotic resistance in vivo. Anaerobically purified WhiB7 from S. lividans was dimeric and contained 2.1 ± 0.3 and 2.2 ± 0.3 mol of iron and sulfur, respectively, per protomer (consistent with the presence of a 2Fe-2S cluster). However, the properties of the dimer's absorption spectrum were most consistent with the presence of an oxygen-labile 4Fe-4S cluster, suggesting 50% occupancy. These data provide the first insights into WhiB7 iron-sulfur clusters as they exist in vivo, a major unresolved issue in studies of Wbl proteins.

The mycobacterial antibiotic resistance determinant WhiB7 acts as a transcriptional activator by binding the primary sigma factor SigA (RpoV)

Tuberculosis therapeutic options are limited by the high intrinsic antibiotic resistance of Mycobacterium tuberculosis. The putative transcriptional regulator WhiB7 is crucial for the activation of systems that provide resistance to diverse antibiotic classes. Here, we used in vitro run-off, two-hybrid assays, as well as mutagenic, complementation and protein pull-down experiments, to characterize WhiB7 as an auto-regulatory, redox-sensitive transcriptional activator in Mycobacterium smegmatis. We provide the first direct biochemical proof that a WhiB protein promotes transcription and also demonstrate that this activity is sensitive to oxidation (diamide). Its partner protein for transcriptional activation was identified as SigA, the primary sigma factor subunit of RNA polymerase. Residues required for the interaction mapped to region 4 of SigA (including R515H) or adjacent domains of WhiB7 (including E63D). WhiB7's ability to provide a specific spectrum of antibiotic-resistance was dependent on these residues as well as its C-terminal AT-hook module that binds to an AT-rich motif immediately upstream of the -35 hexamer recognized by SigA. These experimentally established constrains, combined with protein structure predictions, were used to generate a working model of the WhiB7-SigA-promoter complex. Inhibitors preventing WhiB7 interactions could allow the use of previously ineffective antibiotics for treatment of mycobacterial diseases.

A genomic signature and the identification of new sporulation genes

Bacterial endospores are the most resistant cell type known to humans, as they are able to withstand extremes of temperature, pressure, chemical injury, and time. They are also of interest because the endospore is the infective particle in a variety of human and livestock diseases. Endosporulation is characterized by the morphogenesis of an endospore within a mother cell. Based on the genes known to be involved in endosporulation in the model organism Bacillus subtilis, a conserved core of about 100 genes was derived, representing the minimal machinery for endosporulation. The core was used to define a genomic signature of about 50 genes that are able to distinguish endospore-forming organisms, based on complete genome sequences, and we show this 50-gene signature is robust against phylogenetic proximity and other artifacts. This signature includes previously uncharacterized genes that we can now show are important for sporulation in B. subtilis and/or are under developmental control, thus further validating this genomic signature. We also predict that a series of polyextremophylic organisms, as well as several gut bacteria, are able to form endospores, and we identified 3 new loci essential for sporulation in B. subtilis: ytaF, ylmC, and ylzA. In all, the results support the view that endosporulation likely evolved once, at the base of the Firmicutes phylum, and is unrelated to other bacterial cell differentiation programs and that this involved the evolution of new genes and functions, as well as the cooption of ancestral, housekeeping functions.

Mammalian cell entry genes in Streptomyces may provide clues to the evolution of bacterial virulence

Understanding the evolution of virulence is key to appreciating the role specific loci play in pathogenicity. Streptomyces species are generally non-pathogenic soil saprophytes, yet within their genome we can find homologues of virulence loci. One example of this is the mammalian cell entry (mce) locus, which has been characterised in Mycobacterium tuberculosis. To investigate the role in Streptomyces we deleted the mce locus and studied its impact on cell survival, morphology and interaction with other soil organisms. Disruption of the mce cluster resulted in virulence towards amoebae (Acanthamoeba polyphaga) and reduced colonization of plant (Arabidopsis) models, indicating these genes may play an important role in Streptomyces survival in the environment. Our data suggest that loss of mce in Streptomyces spp. may have profound effects on survival in a competitive soil environment, and provides insight in to the evolution and selection of these genes as virulence factors in related pathogenic organisms.

Phylogenetic framework and molecular signatures for the main clades of the phylum Actinobacteria

The phylum Actinobacteria harbors many important human pathogens and also provides one of the richest sources of natural products, including numerous antibiotics and other compounds of biotechnological interest. Thus, a reliable phylogeny of this large phylum and the means to accurately identify its different constituent groups are of much interest. Detailed phylogenetic and comparative analyses of >150 actinobacterial genomes reported here form the basis for achieving these objectives. In phylogenetic trees based upon 35 conserved proteins, most of the main groups of Actinobacteria as well as a number of their superageneric clades are resolved. We also describe large numbers of molecular markers consisting of conserved signature indels in protein sequences and whole proteins that are specific for either all Actinobacteria or their different clades (viz., orders, families, genera, and subgenera) at various taxonomic levels. These signatures independently support the existence of different phylogenetic clades, and based upon them, it is now possible to delimit the phylum Actinobacteria (excluding Coriobacteriia) and most of its major groups in clear molecular terms. The species distribution patterns of these markers also provide important information regarding the interrelationships among different main orders of Actinobacteria. The identified molecular markers, in addition to enabling the development of a stable and reliable phylogenetic framework for this phylum, also provide novel and powerful means for the identification of different groups of Actinobacteria in diverse environments. Genetic and biochemical studies on these Actinobacteria-specific markers should lead to the discovery of novel biochemical and/or other properties that are unique to different groups of Actinobacteria.

SapB and the rodlins are required for development of Streptomyces coelicolor in high osmolarity media

Streptomyces coelicolor produces spore-forming aerial hyphae after a period of vegetative growth. These aerial structures are decorated with a hydrophobic coating of rodlets consisting of chaplins and rodlins. Here, we show that rodlins and the surface-active peptide SapB are essential for development during growth in a medium with high osmolarity. To this end, both vegetative and aerial hyphae secrete SapB, whereas rodlins are only secreted by the spore-forming aerial hyphae.