Bactericidal Effect of Pseudomonas oryziphila sp. nov., a Novel Pseudomonas Species Against Xanthomonas oryzae Reduces Disease Severity of Bacterial Leaf Streak of Rice

Characterization and identification of Pseudomonas sp. AW4, an arsenic-resistant and plant growth-promoting bacteria isolated from the soybean (Glycine max L.) rhizosphere

Pseudomonas sp. AW4 is a highly arsenic (As) resistant bacterium with plant growth promoting properties, originally isolated from the soybean (Glycine max L.) rhizosphere. In order to safely use this isolate in diverse bioformulations, its characterization needs to be completed and a reliable identification must be provided. In the present work, we analyzed the morpho-physiological, biochemical and genomic characteristics of Pseudomonas sp. AW4. Identification of the isolate varied according to the parameters analyzed, mainly biochemical and physiological tests or individual genes and phylogenetic analyses. In this regard, we performed massive sequencing of its genome, in order to consistently complete its characterization and identification. Pseudomonas sp. AW4 formed a monophyletic clade with P. urmiensis SWRI10, presenting 3.08 % of unique genes against this reference isolate. More than 70 % of AW4 genes were also shared with P. oryziphila strain 1257 NZ and with P. reidholzensis strain CCOS 865. The search for genes related to As resistance evidenced the presence of the operon arsHRBC. Taken together, results of the present work allow identification of this bacterium as Pseudomonas urmiensis AW4 and open up a number of opportunities to study this strain and understand the mechanisms of arsenic resistance and plant growth promotion.

Whole Genome Sequencing and Comparative Genomic Analysis of Pseudomonas aeruginosa SF416, a Potential Broad-Spectrum Biocontrol Agent Against Xanthomonas oryzae pv. oryzae

Rice is one of the most important staple crops worldwide. However, the bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) poses a major threat to the production of rice. In this study, we isolated and identified the strain Pseudomonas aeruginosa SF416, which exhibited significant antagonistic activity against Xoo, from a soil sample collected in a winter wheat field in Shannanzhalang County, Tibet, China. The bacterial solution (BS) and cell-free supernatant (CFS) of SF416 had significant prevention effects for the bacterial blight of rice, with an efficacy of 45.1% and 34.18%, respectively, while they exhibited a slightly lower therapeutic efficiency of 31.64% and 25.09%. The genomic analysis showed that P. aeruginosa SF416 contains genes involved in cell motility, colonization, cold and hot shock proteins, antibiotic resistance, and plant growth promotion. SF416 also harbors two sets of phenazine-1-carboxylic acid (PCA) synthesis gene clusters, phz1 (phzA1-G1) and phz2 (phzA2-G2), and other phenozine product-synthesis--related genes phzS, phzM, and phzH, as well as genes in the SF416 genome that share high similarity with the ones in the genomes of P. aeruginosa M18, suggesting that the two sets of PCA synthesis gene clusters are responsible for the antagonistic effect of SF416 against Xoo. A comparative antiSMASH analysis revealed that P. aeruginosa SF416 contains 17 gene clusters related to secondary metabolite synthesis, 7 of which, encoding for pyochelin, azetidomonamide A/B, L-2-amino-4-methoxy-trans-3-butenoic acid, hydrogen cyanide, pyocyanine, pseudopaline, and bicyclomycin, are conserved in strains of P. aeruginosa. Moreover, SF416 can produce protease and siderophores and display a broad-spectrum antagonistic activity against various major plant pathogenic bacteria and fungi. The results suggest that P. aeruginosa SF416 could be a potential candidate agent for the bacterial blight of rice.

Diversity and function of viral AMGs associated with DNA biosynthesis in the Napahai plateau wetland

Viruses play an important role in microbial community structure and biodiversity by lysing host cells, and can also affect host metabolic pathways by expressing auxiliary metabolic genes (AMGs). As a unique low-latitude, high-altitude seasonal plateau wetland in China, Napahai has high research value. However, studies on the genetic diversity of AMGs and viruses associated with DNA biosynthesis have not been reported. Based on metagenomics, with the phylogenetic tree, PCoA, and α diversity analysis, we found that three DNA biosynthesis-related viral AMGs (cobS, mazG, and purM) in the Napahai plateau wetland were rich in genetic diversity, uniqueness, and differences compared with other habitats and host sources. Through the KEGG metabolic pathway and metabolic flow analysis of Pseudomonas mandelii (SW-3) and phage (VSW-3), the AMGs (cobS, mazG, and purM) genes of the three related viruses involved in DNA biosynthesis were upregulated and their expression increased significantly. In general, we systematically described the genetic diversity of AMGs associated with DNA biosynthesis in plateau wetland ecosystems and clarified the contribution of viral AMGs in the Napahai plateau wetland to DNA biosynthesis, as well as the changes of metabolites and genes. It further expands the understanding of phage-host interactions, which is of great significance for further revealing the role of viral AMGs in the biological evolution and biogeochemical cycle of wetland ecosystems.

The effects of Pseudomonas strains isolated from Achnatherum inebrians on plant growth: A genomic perspective

Achnatherum inebrians is a perennial grass widely distributed in northwest China. Nearly all wild A. inebrians plants are infected by Epichloë endophytes. In this study, bacteria from the phyllosphere were isolated from leaves of both endophyte-free and endophyte-infected A. inebrians and sequenced for identification. Pseudomonas, comprising 48.12% of the culturable bacterial communities, was the most dominant bacterial genus. Thirty-four strains from 12 Pseudomonas species were used to inoculate A. inebrians seeds and plants. Results indicated that Epichloë significantly increased the diversity and richness index of the phyllosphere. Pseudomonas Sp1, Sp3, Sp5 and Sp7 had a significantly positive effect on plant growth and photosynthesis, whereas Sp10, Sp11 and Sp12 had a significantly negative effect. Whole-genome and pan-genome analysis suggested that the variability in the effects of Pseudomonas on A. inebrians was related to differences in genome composition and genomic islands.

A New Biocontrol Agent Bacillus velezensis SF334 against Rubber Tree Fungal Leaf Anthracnose and Its Genome Analysis of Versatile Plant Probiotic Traits

Natural rubber is an important national strategic and industrial raw material. The leaf anthracnose of rubber trees caused by the Colletotrichum species is one of the important factors restricting the yields of natural rubber. In this study, we isolated and identified strain Bacillus velezensis SF334, which exhibited significant antagonistic activity against both C. australisinense and C. siamense, the dominant species of Colletotrichum causing rubber tree leaf anthracnose in the Hainan province of China, from a pool of 223 bacterial strains. The cell suspensions of SF334 had a significant prevention effect for the leaf anthracnose of rubber trees, with an efficacy of 79.67% against C. siamense and 71.8% against C. australisinense. We demonstrated that SF334 can lead to the lysis of C. australisinense and C. siamense mycelia by causing mycelial expansion, resulting in mycelial rupture and subsequent death. B. velezensis SF334 also harbors some plant probiotic traits, such as secreting siderophore, protease, cellulase, pectinase, and the auxin of indole-3-acetic acid (IAA), and it has broad-spectrum antifungal activity against some important plant pathogenic fungi. The genome combined with comparative genomic analyses indicated that SF334 possesses most genes of the central metabolic and gene clusters of secondary metabolites in B. velezensis strains. To our knowledge, this is the first time a Bacillus velezensis strain has been reported as a promising biocontrol agent against the leaf anthracnose of rubber trees caused by C. siamense and C. australisinense. The results suggest that B. velezensis could be a potential candidate agent for the leaf anthracnose of rubber trees.

High-quality complete genome sequence of Xanthomonas oryzae pv. oryzicola (Xoc) strain HB8

Here, we report a high-quality genome of Xanthomonas oryzae pv. oryzicola (Xoc) strain HB8, which causes bacterial leaf streaks in rice. The genome size of HB8 is 4,800,100 bp, with a GC content of 64.03%, which serves as an important resource for the study of the Xanthomonas-rice pathosystem.

Antagonistic transcriptome profile reveals potential mechanisms of action on Xanthomonas oryzae pv. oryzicola by the cell-free supernatants of Bacillus velezensis 504, a versatile plant probiotic bacterium

Bacterial leaf streak (BLS) of rice is a severe disease caused by the bacterial pathogen Xanthomonas oryzae pv. oryzicola (Xoc) that has gradually become the fourth major disease on rice in some rice-growing regions in southern China. Previously, we isolated a Bacillus velezensis strain 504 that exhibited apparent antagonistic activity against the Xoc wild-type strain RS105, and found that B. velezensis 504 was a potential biocontrol agent for BLS. However, the underlying mechanisms of antagonism and biocontrol are not completely understood. Here we mine the genomic data of B. velezensis 504, and the comparative transcriptomic data of Xoc RS105 treated by the cell-free supernatants (CFSs) of B. velezensis 504 to define differentially expressed genes (DEGs). We show that B. velezensis 504 shares over 89% conserved genes with FZB42 and SQR9, two representative model strains of B. velezensis, but 504 is more closely related to FZB42 than SQR9, as well as B. velezensis 504 possesses the secondary metabolite gene clusters encoding the essential anti-Xoc agents difficidin and bacilysin. We conclude that approximately 77% of Xoc RS105 coding sequences are differentially expressed by the CFSs of B. velezensis 504, which significantly downregulates genes involved in signal transduction, oxidative phosphorylation, transmembrane transport, cell motility, cell division, DNA translation, and five physiological metabolisms, as well as depresses an additional set of virulence-associated genes encoding the type III secretion, type II secretion system, type VI secretion system, type IV pilus, lipopolysaccharides and exopolysaccharides. We also show that B. velezensis 504 is a potential biocontrol agent for bacterial blight of rice exhibiting relative control efficiencies over 70% on two susceptible cultivars, and can efficiently antagonize against some important plant pathogenic fungi including Colletotrichum siamense and C. australisinense that are thought to be the two dominant pathogenic species causing leaf anthracnose of rubber tree in Hainan province of China. B. velezensis 504 also harbors some characteristics of plant growth-promoting rhizobacterium such as secreting protease and siderophore, and stimulating plant growth. This study reveals the potential biocontrol mechanisms of B. velezensis against BLS, and also suggests that B. velezensis 504 is a versatile plant probiotic bacterium.

The natural pyrazolotriazine pseudoiodinine from Pseudomonas mosselii 923 inhibits plant bacterial and fungal pathogens

Natural products largely produced by Pseudomonads-like soil-dwelling microorganisms are a consistent source of antimicrobial metabolites and pesticides. Herein we report the isolation of Pseudomonas mosselii strain 923 from rice rhizosphere soils of paddy fields, which specifically inhibit the growth of plant bacterial pathogens Xanthomonas species and the fungal pathogen Magnaporthe oryzae. The antimicrobial compound is purified and identified as pseudoiodinine using high-resolution mass spectra, nuclear magnetic resonance and single-crystal X-ray diffraction. Genome-wide random mutagenesis, transcriptome analysis and biochemical assays define the pseudoiodinine biosynthetic cluster as psdABCDEFG. Pseudoiodinine biosynthesis is proposed to initiate from guanosine triphosphate and 1,6-didesmethyltoxoflavin is a biosynthetic intermediate. Transposon mutagenesis indicate that GacA is the global regulator. Furthermore, two noncoding small RNAs, rsmY and rsmZ, positively regulate pseudoiodinine transcription, and the carbon storage regulators CsrA2 and CsrA3, which negatively regulate the expression of psdA. A 22.4-fold increase in pseudoiodinine production is achieved by optimizing the media used for fermentation, overexpressing the biosynthetic operon, and removing the CsrA binding sites. Both of the strain 923 and purified pseudoiodinine in planta inhibit the pathogens without affecting the rice host, suggesting that pseudoiodinine can be used to control plant diseases.

Intestinal Bacterial Diversity and Functional Analysis of Three Lepidopteran Corn Ear Worm Larvae

Insects, as the most abundant animal group on earth, and their symbionts help their hosts to adapt to various environments. Conogethes punctiferalis, Ostrinia furnacalis and Helicoverpa armigera are three main pests co-occurring in the ear stage of corn, which significantly affect the yield and quality of corn. The purpose of this study was to compare the diversity and function of the intestinal bacteria of the three co-occurring lepidopteran pests, C. punctiferalis, O. furnacalis and H. armigera, and to explore the reason of their prevalence from the microbiota's view. Our results showed the difference of diversity and abundance of the gut bacteria of three co-occurring lepidopteran pests at the ear stage. Proteobacteria and Firmicutes were the dominant phyla, and the Enterobacteriaceae and Enterococcaceae were the dominant families in the three pests. Compared with the other two pests, Bacteroidetes was found much more in C. punctiferalis. In addition, C. punctiferalis showed more correlation and similarity in bacteria composition with corn endophytic bacteria, as well as had obvious advantages in metabolic, environmental information processing, cellular processes and organic systems function pathways. Our findings may provide insight into the prevalence of corn earworm larvae from the perspective of gut microbiota and function prediction.

Dendrobium officinale Endophytes May Colonize the Intestinal Tract and Regulate Gut Microbiota in Mice

Dendrobium officinale is a traditional Chinese medicine for treating gastrointestinal diseases by nourishing "Yin" and thickening the stomach lining. To study whether D. officinale endophytes can colonize the intestinal tract and regulate gut microbiota in mice, we used autoclave steam sterilizing and 60Co-γ radiation to eliminate D. officinale endophytes from its juice. Then, high-throughput ITS1-ITS2 rDNA and 16S rRNA gene amplicons were sequenced to analyze the microbial community of D. officinale endophytes and fecal samples of mice after administration of fresh D. officinale juice. Sterilization of D. officinale juice by autoclaving for 40 min (ASDO40) could more effectively eliminate the D. officinale endophytes and decrease their interference on the gut microbiota. D. officinale juice could increase beneficial gut microbiota and metabolites including short-chain fatty acids. D. officinale endophytes Pseudomonas mosselii, Trichocladium asperum, Titata maxilliformis, Clonostachys epichloe, and Rhodotorula babjevae could colonize the intestinal tract of mice and modulate gut microbiota after oral administration of the juice for 28 days. Thus, the regulatory effect of D. officinale juice on gut microbiota was observed, which provides a basis for inferring that D. officinale endophytes might colonize the intestinal tract and participate in regulating gut microbiota to treat diseases. Thus, this study further provides a new approach for the treatment of diseases by colonizing plant endophytes in the intestinal tract and regulating gut microbiota.

Antibacterial Activity of Aureonuclemycin Produced by Streptomyces aureus Strain SPRI-371

Actinomycetes play a vital role as one of the most important natural resources for both pharmaceutical and agricultural applications. The actinomycete strain SPRI-371, isolated from soil collected in Jiangsu province, China, was classified as Streptomyces aureus based on its morphological, physiological, biochemical and molecular biological characteristics. Its bacterial activity metabolites were identified as aureonuclemycin (ANM), belonging to adenosine derivatives with the molecular formula C16H19N5O9 for ANM A and C10H13N5O3 for ANM B. Simultaneously, the industrial fermentation process of a mutated S. aureus strain SPRI-371 was optimized in a 20 m3 fermentation tank, featuring a rotation speed of 170 rpm, a pressure of 0.05 MPa, an inoculum age of 36−40 h and a dissolved oxygen level maintained at 1−30% within 40−80 h and at >60% in the later period, resulting in an ANM yield of >3700 mg/L. In the industrial separation of fermentation broth, the sulfuric acid solution was selected to adjust pH and 4# resin was used for adsorption. Then, it was resolved with 20% ethanol solution and concentrated in a vacuum (60−65 °C), with excellent results. Antibacterial experiments showed that ANM was less active or inactive against Xanthomonas oryzae pv. oryzae, Xanthomonas citri subsp. citri and Xanthomonas oryzae pv. oryzicola and most bacteria, yeast and fungi in vitro. However, in vivo experiments showed that ANM exhibited extremely significant protective and therapeutic activity against diseases caused by X. oryzae pv. oryzae and X. oryzae pv. oryzicola in rice and X. citri in oranges and lemons. In field trials, ANM A 150 gai/ha + ANM B 75 gai/ha exhibited excellent therapeutic activity against rice bacterial leaf blight, citrus canker and rice bacterial leaf streak. Furthermore, as the dosage and production cost of ANM are lower than those of commercial drugs, it has good application prospects.

Beyond Soil-Dwelling Actinobacteria: Fantastic Antibiotics and Where to Find Them

Bacterial secondary metabolites represent an invaluable source of bioactive molecules for the pharmaceutical and agrochemical industries. Although screening campaigns for the discovery of new compounds have traditionally been strongly biased towards the study of soil-dwelling Actinobacteria, the current antibiotic resistance and discovery crisis has brought a considerable amount of attention to the study of previously neglected bacterial sources of secondary metabolites. The development and application of new screening, sequencing, genetic manipulation, cultivation and bioinformatic techniques have revealed several other groups of bacteria as producers of striking chemical novelty. Biosynthetic machineries evolved from independent taxonomic origins and under completely different ecological requirements and selective pressures are responsible for these structural innovations. In this review, we summarize the most important discoveries related to secondary metabolites from alternative bacterial sources, trying to provide the reader with a broad perspective on how technical novelties have facilitated the access to the bacterial metabolic dark matter.