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September 22, 2019

Genome mining of the marine actinomycete Streptomyces sp. DUT11 and discovery of tunicamycins as anti-complement agents.

Marine actinobacteria are potential producers of various secondary metabolites with diverse bioactivities. Among various bioactive compounds, anti-complement agents have received great interest for drug discovery to treat numerous diseases caused by inappropriate activation of the human complement system. However, marine streptomycetes producing anti-complement agents are still poorly explored. In this study, a marine-derived strain Streptomyces sp. DUT11 showing superior anti-complement activity was focused, and its genome sequence was analyzed. Gene clusters showing high similarities to that of tunicamycin and nonactin were identified, and their corresponding metabolites were also detected. Subsequently, tunicamycin I, V, and VII were isolated from Streptomyces sp. DUT11. Anti-complement assay showed that tunicamycin I, V, VII inhibited complement activation through the classic pathway, whereas no anti-complement activity of nonactin was detected. This is the first time that tunicamycins are reported to have such activity. In addition, genome analysis indicates that Streptomyces sp. DUT11 has the potential to produce novel lassopeptides and lantibiotics. These results suggest that marine Streptomyces are rich sources of anti-complement agents for drug discovery.


September 22, 2019

A comprehensive understanding of the biocontrol potential of Bacillus velezensis LM2303 against Fusarium head blight.

Fusarium head blight (FHB) mainly caused by F. graminearum, always brings serious damage to wheat production worldwide. In this study, we found that strain LM2303 had strong antagonist activity against F. graminearum and significantly reduced disease severity of FHB with the control efficiency of 72.3% under field conditions. To gain a comprehensive understanding of the biocontrol potential of strain LM2303 against FHB, an integrated approach of genome mining and chemical analysis was employed. The whole genome of strain LM2303 was obtained and analyzed, showing the largest number of genes/gene clusters associated with biocontrol functions as compared with the known biocontrol strains (FZB42, M75, CAU B946). And strain LM2303 was accurately determined as a member of the B. velezensis clade using the phylogenomic analysis of single-copy core genes. Through genome mining, 13 biosynthetic gene clusters(BGCs) encoding secondary metabolites with biocontrol functions were identified, which were further confirmed through chemical analyses such as UHPLC-ESI-MS, including three antifungal metabolites (fengycin B, iturin A, and surfactin A), eight antibacterial metabolites (surfactin A, butirosin, plantazolicin and hydrolyzed plantazolicin, kijanimicin, bacilysin, difficidin, bacillaene A and bacillaene B, 7-o-malonyl macrolactin A and 7-o-succinyl macrolactin A), the siderophore bacillibactin, molybdenum cofactor and teichuronic acid. In addition, genes/gene clusters involved in plant colonization, plant growth promotion and induced systemic resistance were also found and analyzed, along with the corresponding metabolites. Finally, four different mechanisms of strain LM2303 involved in the biocontrol of FHB were putatively obtained. This work provides better insights into a mechanistic understanding of strain LM2303 in control of FHB, reinforcing the higher potential of this strain as a powerful biocontrol strain agent (BCA) for FHB control. The results also provide scientific reference and comparison for other biocontrol strains.


September 22, 2019

Characteristics of carbapenem-resistant Enterobacteriaceae in ready-to-eat vegetables in China.

Vegetables harboring bacteria resistant to antibiotics are a growing food safety issue. However, data concerning carbapenem-resistant Enterobacteriaceae (CRE) in ready-to-eat fresh vegetables is still rare. In this study, 411 vegetable samples from 36 supermarkets or farmer’s markets in 18 cities in China, were analyzed for CRE. Carbapenemase-encoding genes and other resistance genes were analyzed among the CRE isolates. Plasmids carrying carbapenemase genes were studied by conjugation, replicon typing, S1-PFGE southern blot, restriction fragment length polymorphism (RFLP), and sequencing. CRE isolates were also analyzed by pulsed-field gel electrophoresis (PFGE). Ten vegetable samples yielded one or more CRE isolates. The highest detection rate of CRE (14.3%, 4/28) was found in curly endive. Twelve CRE isolates were obtained and all showed multidrug resistance: Escherichia coli, 5; Citrobacter freundii, 5; and Klebsiella pneumoniae, 2. All E. coli and C. freundii carried blaNDM, while K. pneumoniae harbored blaKPC-2. Notably, E. coli with blaNDM and ST23 hypervirulent Klebsiella pneumoniae (hvKP) carrying blaKPC-2 were found in the same cucumber sample and clonal spread of E. coli, C. freundii, and K. pneumoniae isolates were all observed between vegetable types and/or cities. IncX3 plasmids carrying blaNDM from E. coli and C. freundii showed identical or highly similar RFLP patterns, and the sequenced IncX3 plasmid from cucumber was also identical or highly similar (99%) to the IncX3 plasmids from clinical patients reported in other countries, while blaKPC-2 in K. pneumoniae was mediated by similar F35:A-:B1 plasmids. Our results suggest that both clonal expansion and horizontal transmission of IncX3- or F35:A-:B1-type plasmids may mediate the spread of CRE in ready-to-eat vegetables in China. The presence of CRE in ready-to-eat vegetables is alarming and constitutes a food safety issue. To our knowledge, this is the first report of either the C. freundii carrying blaNDM, or K. pneumoniae harboring blaKPC-2 in vegetables. This is also the first report of ST23 carbapenem-resistant hvKP strain in vegetables.


September 22, 2019

The complete genome sequence of Vibrio aestuarianus W-40 reveals virulence factor genes.

Vibrio aestuarianus is an opportunistic environmental pathogen that has been associated with epidemics in cultured shrimp Penaeus vannamei. Hepatopancreas microsporidian (HPM) and monodon slow growth syndrome (MSGS) have been reported in cultured P. vannamei. In this study, we sequenced and assembled the whole genome of V. aestuarianus strain W-40, a strain that was originally isolated from the intestines of an infected P. vannamei. The genome of V. aestuarianus strain W-40 contains two circular chromosomes of 483,7307 bp with a 46.23% GC content. We identified 4,457 open reading frames (ORFs) that occupy 86.35% of the genome. Vibrio aestuarianus strain W-40 consists primarily of the ATP-binding cassette (ABC) transporter system and the phosphotransferase system (PTS). CagA is a metabolism system that includes bacterial extracellular solute-binding protein. Glutathione reductase can purge superoxide radicals (O22-) and hydrogen peroxide (H2 O2 ) damage in V. aestuarianus strain W-40. The presence of two compete type I restriction-modification systems was confirmed. A total of 42 insertion sequences (IS) elements and 16 IS elements were identified. Our results revealed a host of virulence factors that likely contribute to the pathogenicity of V. aestuarianus strain W-40, including the virulence factor genes vacA, clpC, and bvgA, which are important for biofilm dispersion. Several bacitracin and tetracycline antibiotic resistance-encoding genes and type VI secretion systems were also identified in the genome. The complete genome sequence will aid future studies of the pathogenesis of V. aestuarianus strain W-40 and allow for new strategies to control disease to be developed.© 2018 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.


September 22, 2019

Draft genome sequence of Annulohypoxylon stygium, Aspergillus mulundensis, Berkeleyomyces basicola (syn. Thielaviopsis basicola), Ceratocystis smalleyi, two Cercospora beticola strains, Coleophoma cylindrospora, Fusarium fracticaudum, Phialophora cf. hyalina, and Morchella septimelata.

Draft genomes of the species Annulohypoxylon stygium, Aspergillus mulundensis, Berkeleyomyces basicola (syn. Thielaviopsis basicola), Ceratocystis smalleyi, two Cercospora beticola strains, Coleophoma cylindrospora, Fusarium fracticaudum, Phialophora cf. hyalina and Morchella septimelata are presented. Both mating types (MAT1-1 and MAT1-2) of Cercospora beticola are included. Two strains of Coleophoma cylindrospora that produce sulfated homotyrosine echinocandin variants, FR209602, FR220897 and FR220899 are presented. The sequencing of Aspergillus mulundensis, Coleophoma cylindrospora and Phialophora cf. hyalina has enabled mapping of the gene clusters encoding the chemical diversity from the echinocandin pathways, providing data that reveals the complexity of secondary metabolism in these different species. Overall these genomes provide a valuable resource for understanding the molecular processes underlying pathogenicity (in some cases), biology and toxin production of these economically important fungi.


September 22, 2019

Adaptation of Pseudomonas aeruginosa to phage PaP1 predation via O-antigen polymerase mutation.

Adaptation of bacteria to phage predation poses a major obstacle for phage therapy. Bacteria adopt multiple mechanisms, such as inhibition of phage adsorption and CRISPR/Cas systems, to resist phage infection. Here, a phage-resistant mutant of Pseudomonas aeruginosa strain PA1 under the infection of lytic phage PaP1 was selected for further study. The PaP1-resistant variant, termed PA1RG, showed decreased adsorption to PaP1 and was devoid of long chain O-antigen on its cell envelope. Whole genome sequencing and comparative analysis revealed a single nucleotide mutation in the gene PA1S_08510, which encodes the O-antigen polymerase Wzy that is involved in lipopolysaccharide (LPS) biosynthesis. PA1_Wzy was classified into the O6 serotype based on sequence homology analysis and adopts a transmembrane topology similar to that seem with P. aeruginosa strain PAO1. Complementation of gene wzy in trans enabled the mutant PA1RG to produce the normal LPS pattern with long chain O-antigen and restored the susceptibility of PA1RG to phage PaP1 infection. While wzy mutation did not affect bacterial growth, mutant PA1RG exhibited decreased biofilm production, suggesting a fitness cost of PA1 associated with resistance of phage PaP1 predation. This study uncovered the mechanism responsible for PA1RG resistance to phage PaP1 via wzy mutation and revealed the role of phages in regulating bacterial behavior.


September 22, 2019

Assembly of chromosome-scale contigs by efficiently resolving repetitive sequences with long reads

Due to the large number of repetitive sequences in complex eukaryotic genomes, fragmented and incompletely assembled genomes lose value as reference sequences, often due to short contigs that cannot be anchored or mispositioned onto chromosomes. Here we report a novel method Highly Efficient Repeat Assembly (HERA), which includes a new concept called a connection graph as well as algorithms for constructing the graph. HERA resolves repeats at high efficiency with single-molecule sequencing data, and enables the assembly of chromosome-scale contigs by further integrating genome maps and Hi-C data. We tested HERA with the genomes of rice R498, maize B73, human HX1 and Tartary buckwheat Pinku1. HERA can correctly assemble most of the tandemly repetitive sequences in rice using single-molecule sequencing data only. Using the same maize and human sequencing data published by Jiao et al. (2017) and Shi et al. (2016), respectively, we dramatically improved on the sequence contiguity compared with the published assemblies, increasing the contig N50 from 1.3 Mb to 61.2 Mb in maize B73 assembly and from 8.3 Mb to 54.4 Mb in human HX1 assembly with HERA. We provided a high-quality maize reference genome with 96.9% of the gaps filled (only 76 gaps left) and several incorrectly positioned sequences fixed compared with the B73 RefGen_v4 assembly. Comparisons between the HERA assembly of HX1 and the human GRCh38 reference genome showed that many gaps in GRCh38 could be filled, and that GRCh38 contained some potential errors that could be fixed. We assembled the Pinku1 genome into 12 scaffolds with a contig N50 size of 27.85 Mb. HERA serves as a new genome assembly/phasing method to generate high quality sequences for complex genomes and as a curation tool to improve the contiguity and completeness of existing reference genomes, including the correction of assembly errors in repetitive regions.


September 22, 2019

C-di-GMP turnover influences motility and biofilm formation in Bacillus amyloliquefaciens PG12.

Bis-(3′?5′) cyclic dimeric guanosine monophosphate (c-di-GMP) is defined as a highly versatile secondary messenger in bacteria, coordinating diverse aspects of bacterial growth and behavior, including motility and biofilm formation. Bacillus amyloliquefaciens PG12 is an effective biocontrol agent against apple ring rot caused by Botryosphaeria dothidea. In this study, we characterized the core regulators of c-di-GMP turnover in B. amyloliquefaciens PG12. Using bioinformatic analysis, heterologous expression and biochemical characterization of knockout and overexpression derivatives, we identified and characterized two active diguanylate cyclases (which catalyze c-di-GMP biosynthesis), YhcK and YtrP and one active c-di-GMP phosphodiesterase (which degrades c-di-GMP), YuxH. Furthermore, we showed that elevating c-di-GMP levels up to a certain threshold inhibited the swimming motility of B. amyloliquefaciens PG12. Although yhcK, ytrP and yuxH knockout mutants did not display defects in biofilm formation, significant increases in c-di-GMP levels induced by YtrP or YuxH overexpression stimulated biofilm formation in B. amyloliquefaciens PG12. Our results indicate that B. amyloliquefaciens possesses a functional c-di-GMP signaling system that influences the bacterium’s motility and ability to form biofilms. Since motility and biofilm formation influence the efficacy of biological control agent, our work provides a basis for engineering a more effective strain of B. amyloliquefaciens PG12. Copyright © 2018 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.


September 22, 2019

Saliniramus fredricksonii gen. nov., sp. nov., a heterotrophic halophile isolated from Hot Lake, Washington, a member of a novel lineage (Salinarimonadaceae fam. nov.) within the order Rhizobiales, and reclassification of the genus Salinarimonas Liu et al. 2010 into Salinarimonadaceae.

There was an error in the proposed genus name in the published article, in that the genus ‘Salinivirga’ was effectively published while this article was in review. Therefore, the genus ‘Salinivirga’ should be replaced with ‘Saliniramus’. For the convenience of future readers, we have included the complete corrected article below, in which all occurrences of the incorrect genus name have been amended: A halophilic bacterial strain, HL-109T, was isolated from the unicyanobacterial consortium UCC-O, which was obtained from the photosynthetic mat of Hot Lake (Washington, USA). A polyphasic approach using phenotypic, genotypic and chemotaxonomic data was used to classify the strain within the order Rhizobiales. The organism stained Gram-negative and was a moderate thermophile with a growth optimum of 45?°C. It was obligately aerobic, heterotrophic and halophilic, growing in both NaCl and MgSO4 brines. The novel isolate had a polymorphic cellular morphology of short rods with occasional branching, and cells were monotrichous. The major fatty acids detected were C18?:?1, C18?:?0, C16?:?0 and C18?:?cyc. Phylogenetic analysis of the 16S rRNA gene placed the strain in the order Rhizobiales and it shared 94?% identity with the type strain of its nearest relative, Salinarimonas ramus. Morphological, chemotaxonomic and phylogenetic results did not affiliate the novel organism with any of the families in the Rhizobiales; therefore, HL-109T is representative of a new lineage, for which the name Saliniramus fredricksonii gen. nov., sp. nov. is proposed, with the type strain HL-109T (=JCM 31876T=DSM 102886T). In addition, examination of the phylogenetics of strain HL-109T and its nearest relatives, Salinarimonas ramus and Salinarimonasrosea, demonstrates that these halophiles form a clade distinct from the described families of the Rhizobiales. We further propose the establishment of a new family, Salinarimonadaceae fam. nov., to accommodate the genera Saliniramus and Salinarimonas (the type genus of the family).


September 22, 2019

Genome-wide DNA methylation and transcriptome changes in Mycobacterium tuberculosis with rifampicin and isoniazid resistance

We investigated the genome-wide DNA methylation and transcriptome changes in M. tuberculosis with rifampicin or isoniazid resistance. Single-molecule real-time (SMRT) sequencing and microarray technology were performed to expound DNA methylation profiles and differentially expressed genes in rifampicin or isoniazid resis- tant M. tuberculosis. Kyoto Encyclopedia of Genes and Genomes (KEGG) biological pathway analysis and meth- ylated regulatory network analysis were conducted by online forecasting databases. Integrated analysis of DNA methylation and transcriptome revealed that 335 differentially methylated genes (175 hypermethylated and 160 hypomethylated) and 132 significant differentially expressed genes (68 up-regulated and 63 down-regulated) were found to be regulated by both rifampicin and isoniazid in M. tuberculosis H37Rv. Correlation analysis showed that differential methylated genes were negatively correlated with their transcriptional levels in rifampicin or isoniazid resistant strains. KEGG pathway analysis indicated that nitrogen metabolism pathway is closely related to differ- entially methylated genes induced by rifampicin and isoniazid. KEGG also suggested that differentially expressed genes in rifampicin or isoniazid-resistant strains may play different roles in regulating signal transduction events. Furthermore, five differentially methylated candidate genes (Rv0840c, Rv2243, Rv0644c, Rv2386c and Rv1130) in rifampicin resistant strains and three genes (Rv0405, Rv0252 and Rv0908) in isoniazid-resistant strains were verified the existence of protein-protein interaction in STRING database. Integrated DNA methylation and transcrip- tome analyses provide an epigenetic overview of rifampicin and isoniazid-induced antibiotic resistance in M. tuber- culosis H37Rv. Several interesting genes and regulatory pathways may provide valuable resources for epigenetic studies in M. tuberculosis antibiotic resistance.


September 22, 2019

Comparative genomics provides insights into the marine adaptation in sponge-derived Kocuriaflava S43.

Sponge-derived actinomycetes represent a significant component of marine actinomycetes. Members of the genus Kocuria are distributed in various habitats such as soil, rhizosphere, clinical specimens, marine sediments, and sponges, however, to date, little is known about the mechanism of their environmental adaptation. Kocuria flava S43 was isolated from a coastal sponge. Phylogenetic analysis revealed that it was closely related to the terrestrial airborne K. flava HO-9041. In this study, to gain insights into the marine adaptation in K. flava S43 we sequenced the draft genome for K. flava S43 by third generation sequencing (TGS) and compared it with those of K. flava HO-9041 and some other Kocuria relatives. Comparative genomics and phylogenetic analyses revealed that K. flava S43 might adapt to the marine environment mainly by increasing the number of the genes linked to potassium homeostasis, resistance to heavy metals and phosphate metabolism, and acquiring the genes associated with electron transport and the genes encoding ATP-binding cassette (ABC) transporter, aquaporin, and thiol/disulfide interchange protein. Notably, gene acquisition was probably a primary mechanism of environmental adaptation in K. flava S43. Furthermore, this study also indicated that the Kocuria isolates from various marine and hyperosmotic environments possessed common genetic basis for environmental adaptation.


September 22, 2019

Genome sequencing of Streptomyces atratus SCSIOZH16 and activation production of nocardamine via metabolic engineering.

The Actinomycetes are metabolically flexible microorganisms capable of producing a wide range of interesting compounds, including but by no means limited to, siderophores which have high affinity for ferric iron. In this study, we report the complete genome sequence of marine-derived Streptomyces atratus ZH16 and the activation of an embedded siderophore gene cluster via the application of metabolic engineering methods. The S. atratus ZH16 genome reveals that this strain has the potential to produce 26 categories of natural products (NPs) barring the ilamycins. Our activation studies revealed S. atratus SCSIO ZH16 to be a promising source of the production of nocardamine-type (desferrioxamine) compounds which are important in treating acute iron intoxication and performing ecological remediation. We conclude that metabolic engineering provides a highly effective strategy by which to discover drug-like compounds and new NPs in the genomic era.


September 22, 2019

Long-read whole genome sequencing and comparative analysis of six strains of the human pathogen Orientia tsutsugamushi.

Orientia tsutsugamushi is a clinically important but neglected obligate intracellular bacterial pathogen of the Rickettsiaceae family that causes the potentially life-threatening human disease scrub typhus. In contrast to the genome reduction seen in many obligate intracellular bacteria, early genetic studies of Orientia have revealed one of the most repetitive bacterial genomes sequenced to date. The dramatic expansion of mobile elements has hampered efforts to generate complete genome sequences using short read sequencing methodologies, and consequently there have been few studies of the comparative genomics of this neglected species.We report new high-quality genomes of O. tsutsugamushi, generated using PacBio single molecule long read sequencing, for six strains: Karp, Kato, Gilliam, TA686, UT76 and UT176. In comparative genomics analyses of these strains together with existing reference genomes from Ikeda and Boryong strains, we identify a relatively small core genome of 657 genes, grouped into core gene islands and separated by repeat regions, and use the core genes to infer the first whole-genome phylogeny of Orientia.Complete assemblies of multiple Orientia genomes verify initial suggestions that these are remarkable organisms. They have larger genomes compared with most other Rickettsiaceae, with widespread amplification of repeat elements and massive chromosomal rearrangements between strains. At the gene level, Orientia has a relatively small set of universally conserved genes, similar to other obligate intracellular bacteria, and the relative expansion in genome size can be accounted for by gene duplication and repeat amplification. Our study demonstrates the utility of long read sequencing to investigate complex bacterial genomes and characterise genomic variation.


September 22, 2019

Homogenization of sub-genome secretome gene expression patterns in the allodiploid fungus Verticillium longisporum

Allopolyploidization, genome duplication through interspecific hybridization, is an important evolutionary mechanism that can enable organisms to adapt to environmental changes or stresses. The increased adaptive potential of allopolyploids can be particularly relevant for plant pathogens in their ongoing quest for host immune response evasion. To this end, plant pathogens secrete a plethora of molecules that enable host colonization. Allodiploidization has resulted in the new plant pathogen Verticillium longisporum that infects different hosts than haploid Verticillium species. To reveal the impact of allodiploidization on plant pathogen evolution, we studied the genome and transcriptome dynamics of V. longisporum using next-generation sequencing. V. longisporum genome evolution is characterized by extensive chromosomal rearrangements, between as well as within parental chromosome sets, leading to a mosaic genome structure. In comparison to haploid Verticillium species, V. longisporum genes display stronger signs of positive selection. The expression patterns of the two sub-genomes show remarkable resemblance, suggesting that the parental gene expression patterns homogenized upon hybridization. Moreover, whereas V. longisporum genes encoding secreted proteins frequently display differential expression between the parental sub-genomes in culture medium, expression patterns homogenize upon plant colonization. Collectively, our results illustrate of the adaptive potential of allodiploidy mediated by the interplay of two sub-genomes. Author summary Hybridization followed by whole-genome duplication, so-called allopolyploidization, provides genomic flexibility that is beneficial for survival under stressful conditions or invasiveness into new habitats. Allopolyploidization has mainly been studied in plants, but also occurs in other organisms, including fungi. Verticillium longisporum, an emerging fungal pathogen on brassicaceous plants, arose by allodiploidization between two Verticillium spp. We used comparative genomics to reveal the plastic nature of the V. longisporum genomes, showing that parental chromosome sets recombined extensively, resulting in a mosaic genome pattern. Furthermore, we show that non-synonymous substitutions frequently occurred in V. longisporum. Moreover, we reveal that expression patterns of genes encoding secreted proteins homogenized between the V. longisporum sub-genomes upon plant colonization. In conclusion, our results illustrate the large adaptive potential upon genome hybridization for fungi mediated by genomic plasticity and interaction between sub-genomes.


September 22, 2019

Improved de novo genome assembly and analysis of the Chinese cucurbit Siraitia grosvenorii, also known as monk fruit or luo-han-guo.

Luo-han-guo (Siraitia grosvenorii), also called monk fruit, is a member of the Cucurbitaceae family. Monk fruit has become an important area for research because of the pharmacological and economic potential of its noncaloric, extremely sweet components (mogrosides). It is also commonly used in traditional Chinese medicine for the treatment of lung congestion, sore throat, and constipation. Recently, a single reference genome became available for monk fruit, assembled from 36.9x genome coverage reads via Illumina sequencing platforms. This genome assembly has a relatively short (34.2 kb) contig N50 length and lacks integrated annotations. These drawbacks make it difficult to use as a reference in assembling transcriptomes and discovering novel functional genes.Here, we offer a new high-quality draft of the S. grosvenorii genome assembled using 31 Gb (~73.8x) long single molecule real time sequencing reads and polished with ~50 Gb Illumina paired-end reads. The final genome assembly is approximately 469.5 Mb, with a contig N50 length of 432,384 bp, representing a 12.6-fold improvement. We further annotated 237.3 Mb of repetitive sequence and 30,565 consensus protein coding genes with combined evidence. Phylogenetic analysis showed that S. grosvenorii diverged from members of the Cucurbitaceae family approximately 40.9 million years ago. With comprehensive transcriptomic analysis and differential expression testing, we identified 4,606 up-regulated genes in the early fruit compared to the leaf, a number of which were linked to metabolic pathways regulating fruit development and ripening.The availability of this new monk fruit genome assembly, as well as the annotations, will facilitate the discovery of new functional genes and the genetic improvement of monk fruit.


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