Soil Streptomycetes Research Articles

Streptomyces castrisilvae sp. nov. and Streptomyces glycanivorans sp. nov., novel soil streptomycetes metabolizing mutan and alternan.

Six bacterial strains, Mut1T, Mut2, Alt1, Alt2, Alt3T, and Alt4, were isolated from soil samples collected in parks in Gothenburg, Sweden, based on their ability to utilize the insoluble polysaccharides α-1,3-glucan (mutan; Mut strains) or the mixed-linkage α-1,3/α-1,6-glucan (alternan; Alt strains). Analysis of 16S rRNA gene sequences identified all strains as members of the genus Streptomyces. The genomes of the strains were sequenced and subsequent phylogenetic analyses identified Mut2 as a strain of Streptomyces laculatispora and Alt1, Alt2 and Alt4 as strains of Streptomyces poriferorum, while Mut1T and Alt3T were most closely related to the type strains Streptomyces drozdowiczii NBRC 101007T and Streptomyces atroolivaceus NRRL ISP-5137T, respectively. Comprehensive genomic and biochemical characterizations were conducted, highlighting typical features of Streptomyces, such as large genomes (8.0-9.6 Mb) with high G+C content (70.5-72.0%). All six strains also encode a wide repertoire of putative carbohydrate-active enzymes, indicating a capability to utilize various complex polysaccharides as carbon sources such as starch, mutan, and cellulose, which was confirmed experimentally. Based on phylogenetic and phenotypic characterization, our study suggests that strains Mut1T and Alt3T represent novel species in the genus Streptomyces for which the names Streptomyces castrisilvae sp. nov. and Streptomyces glycanivorans sp. nov. are proposed, with strains Mut1T (=DSM 117248T=CCUG 77596T) and Alt3T (=DSM 117252T=CCUG 77600T) representing the respective type strains.

Metagenomic exploration of the rhizosphere soil microbial community and their significance in facilitating the development of wild-simulated ginseng.

Panax ginseng, a prized medicinal herb, has faced increasingly challenging field production due to soil degradation and fungal diseases in Northeast China. Wild-simulated cultivation has prevailed because of its sustainable soil management and low disease incidence. Despite the recognized benefits of rhizosphere microorganisms in ginseng cultivation, their genomic and functional diversity remain largely unexplored. In this work, we utilized shotgun metagenomic analysis to reveal that Pseudomonadota, Actinomycetota, and Acidobacteriota were dominant in the ginseng rhizobiome and recovered 14 reliable metagenome-assembled genomes. Functional analysis indicated an enrichment of denitrification-associated genes, potentially contributing to the observed decline in soil fertility, while genes associated with aromatic carbon degradation may be linked to allelochemical degradation. Further analysis demonstrated enrichment of Actinomycetota in 9-year-old wild-simulated ginseng (WSG), suggesting the need for targeted isolation of Actinomycetota bacteria. Among these, at least three different actinomycete strains were found to play a crucial role in fungal disease resistance, with Streptomyces spp. WY144 standing out for its production of actinomycin natural products active against the pathogenic fungus Ilyonectria robusta. These findings not only enhance our understanding of the rhizobiome of WSG but also present promising avenues for combating detrimental fungal pathogens, underscoring the importance of ginseng in both medicinal and agricultural contexts.IMPORTANCEWild-simulated ginseng, growing naturally without human interference, is influenced by its soil microbiome. Using shotgun metagenomics, we analyzed the rhizospheric soil microbiome of 7- and 9-year-old wild-simulated ginseng. The study aimed to reveal its composition and functions, exploring the microbiome's key roles in ginseng growth. Enrichment analysis identified Streptomycetes in ginseng soil, with three strains inhibiting plant pathogenic fungi. Notably, one strain produced actinomycins, suppressing the ginseng pathogenic fungus Ilyonectria robusta. This research accelerates microbiome application in wild-simulated ginseng cultivation, offering insights into pathogen protection and supporting microbiome utilization in agriculture.

Study of agronomically valuable synergistic effects in binary cultures of soil streptomycetes

Co-culturing of microorganisms can be an effective way to control their enzymatic activity and synthesis of secondary metabolites based on the phenomenon of synergism. The effect of co-culturing in different combinations of four local Streptomyces isolates on their cellulase activity, antiphytopathogenic and phytoregulatory effects was evaluated. Strains S. antimycoticus 8Al3 and Streptomyces sp. H 27-25 exhibited an antagonistic effect against fungi of the genus Fusarium and Alternaria. Binary cultures were composed so that the cellulolytic and antagonist strains were present. Significantly higher cellulase activity in comparison with monoculture (3800 units/10 min/g) was demonstrated by the binary association of strains S. griseoaurantiacus Mb 4-2 + S. antimycoticus 8Al3 (13215 units/10 min/g). When these isolates were co-cultured, an increase in the antifungal activity of the binary culture (18.76±6.1 mm) compared to that of its constituent S. antimycoticus 8Al3 (11.09±6.39 mm) was also noted. The mean value of the growth inhibition zones of phytopathogenic fungi (18.76±6.1 mm) was comparable with that of the reference preparation, the commercial antimycotic terbinafine (19.8±6.2 mm). Binary artificial associations in tests for phytoregulatory action, as well as monocultures of their constituent streptomycete isolates, had no significant effect on germination and morphometry of wheat seedlings. The absence of phytoinhibitory effect of the binary culture S. griseoaurantiacus Mb 4-2 + S. antimycoticus 8Al3, combined with agronomically valuable properties such as cellulase activity and antagonism to phytopathogenic fungi give grounds for its use for the development of a soil-improving biopreparation. Further study of the properties of the binary association, in particular, the possibility of its combination with PGPR-bacteria (Plant Growth-Promoting Rhizobacteria), will constitute the subject of further research.

Pals and enemies: Streptomycetes as promoters of plant illness and symbiosis

The ecological functions of soil streptomycetes within the plant root surroundings are currently gaining multiplied interest. This assessment describes our recent advances in elucidating the complex interactions between streptomycetes, plant lifes, and pathogenic and symbiotic microorganisms. Streptomycetes play diverse roles in plant-related microbial groups. Some act as biocontrol tools, inhibiting plant interactions with pathogenic organisms. As a result of the adversarial properties of streptomycetes, they exert a selective strain on soil microbes, which won’t constantly be for plant benefit. Others modulate the formation of symbioses among plant roots and microbes, and that is made possible due to their direct superb influence at the symbiotic association, expressed as, for example, enabling of hyphal elongation of symbiotic fungi. At present, streptomycetes have been diagnosed as modulators of plant defense using repressing plant responses to pathogens that they facilitate root colonization with pathogenic fungi. In contrast, other strains induce local and systemic resistance against pathogens or promote plant growth. In conclusion, while streptomycetes have an obvious ability of appearing as biocontrol agents, care has to be taken to avoid strains that become virulent pathogens or promote disease development. We argue toward using an included screening approach in the look for efficient biocontrol agents, consisting of assays on in vitro antagonism, plant growth, and disorder suppression.

Streptomyces sp. BV410: Interspecies cross-talk for staurosporine production.

Sequencing and genome analysis of two co-isolated streptomycetes, named BV410-1 and BV410-10, and the effect of their co-cultivation on the staurosporine production. Identification of two strains through genome sequencing and their separation using different growth media was conducted. Sequence analysis revealed that the genome of BV410-1 was 9.5Mb, whilst that of BV410-10 was 7.1Mb. AntiSMASH analysis identified 28 biosynthetic gene clusters (BGCs) from BV410-1, including that responsible for staurosporine biosynthesis, whilst 20 BGCs were identified from BV410-10. The addition of cell-free supernatant from BV410-10 monoculture to BV410-1 fermentations improved the staurosporine yield from 8.35 mg L-1 up to 15.85 mg L-1 , whilst BV410-10 monoculture ethyl acetate extract did not have the same effect. Also, there was no improvement in staurosporine production when artificial mixed cultures were created using three different BV410-1 and BV410-10 spore ratios. The growth of BV410-10 was inhibited when the two strains were grown together on agar plates. Culture supernatants of BV410-10 showed potential to stimulate staurosporine production in BV410-1, but overall co-cultivation attempts did not restore the previously reported yield of staurosporine produced by the original mixed isolate. This work confirmed complex relations between streptomycetes in soil that are difficult to recreate under the laboratory conditions. Also, mining of streptomycetes genomes that mainly produce known bioactive compounds could still be the fruitful approach in search for novel bioactive molecules.

ANTAGONIST ACTIVITY OF Streptomyces sp. Y20 AGAINST FUNGI CAUSING DISEASES IN PLANTS AND FRUITS

<p><strong>Background</strong>: Crop microbial pathogens reduce the production and quality of agricultural products. They cause substantial increase costs for producers of fruits, vegetables, and ornamental plants with negative consequences on economy and food security at household, national and global levels. Annually, the losses represent around 40% to 50% for root crops, vegetables, and fruits. Chemical control with fungicides can prevent, kill, mitigate, or inhibit the growth of plant pathogenic fungi. Nevertheless, biological control with microorganisms and natural molecules is an increasingly popular alternative to protect crops. <strong>Objective:</strong> Here, the antagonist activity of soil <em>Streptomyces</em> sp. Y20 against the pathogenic fungi causing diseases in plants and fruits was evaluated. <strong>Methodology</strong>: Streptomycetes bacteria was isolated from soils collected at open field cultures of local farms with tomato. The antagonism was evaluated <em>in vitro</em> via a dual confrontation experiment against fungal species of <em>Fusarium</em>, <em>Lasiodiplodia</em>, <em>Colletotrichum</em>, <em>Aspergillus</em>, <em>Botrytis, </em>and <em>Sclerotium</em>. <em>Streptomyces </em>sp. Y20 was characterized phenotypically and molecularly identified by the 16S rDNA gene. The biosynthetic gene clusters for polyketide synthases (PKS Type I) and non-ribosomal peptide synthase (NSPS) were detected. <strong>Results</strong>: Preliminary, the isolate Y20 was selected by the higher antagonism against <em>F. oxysporum</em> f sp. <em>lycopersici</em>. Taxonomic characterization of the isolate Y20 by the analysis of the 16S rDNA sequence led to its identification as member of <em>Streptomyces</em> genus. Spore surface morphology by Scanning Electronic Microscopy (SEM) showed barrel-like spores. Antagonistic activity of <em>Streptomyces</em> sp Y20 was comparable to the commercial strain <em>S. lydicus</em> WYEC108 (P > 0.5). However, there was a superior antagonism of Y20 strain versus the commercial strain WYEC108 against <em>F. oxysporum</em> f sp. <em>lycopersici</em>, <em>Fusarium</em> sp. CDBB1172, <em>F. oxysporum</em>, <em>Lasiodiplodia</em> sp., and <em>Aspergillus</em> sp. (P < 0.05). <strong>Implications: </strong>Soil streptomycetes with <em>in vitro</em> antagonistic activity on plant pathogenic fungi could be a natural alternative to the use of chemical fungicides to control plant diseases. <strong>Conclusion</strong>: This study presented a novel soil <em>Streptomyces</em> specie which showed <em>in vitro</em> antagonism against a diversity of plant pathogenic fungal species. <em>Streptomyces</em> strain Y20 could be used as a biocontrol agent.</p>

Synthesis and biological evaluation of platensic alcohol as an adamantane surrogate in antitumor drug lead adaphostin

Adamantane has been widely used as a “lipophilic bullet” in drug discovery and development, due to its unique diamond-like architecture with benign pharmacological/ pharmaceutical properties. Platensimycin is a natural product isolated from a soil streptomycete, which contains an adamantane-like moiety extensively modified from a diterpenoid precursor. In the current study, platensic alcohol was semisynthesized from platensimycin and used as an adamantane surrogate in anticancer drug lead adaphostin. The resulting hybrid platensic alcohol/adaphostin compounds, eg. 4a and 4b, exhibited similar cytotoxic activity with adaphostin against the tested cancer cell lines. In particular, 4b generates significantly more reactive oxygen species (ROS) and shows stronger synergy with the clinically used histone deacetylase inhibitor vorinostat than adaphostin, probably due to the presence of two hydroquinone groups. Density functional theory calculation supports that there could be certain π-π stacking interaction in 4b in aqueous solution, which might explain that 4b has similar serum stability with adaphostin. Our study not only leads to the identification of 4b as a potent ROS generating agent, but showcases a simple scaffold hopping strategy to harvest lipophilic scaffolds from natural products.

Biosynthesis of Polyene Antibiotics and Phytohormones by Streptomyces netropsis IMV Ac-5025 under the Action of Exogenous Isopentenyladenosine

Streptomyces are active producers of a wide range of metabolites with multidirectional biological activity. Streptomyces netropsis IMV Ac-5025 synthesizes a polyene antibiotic complex in which two fractions were identified: heptaene candidine and a new tetraene fraction of unknown structure. The influence of secondary metabolites on the polyene antibiotics biosynthesis by soil streptomycetes is insufficiently explored. The aim of this work was to research the effect of exogenous isopentenyladenosine on the biosynthesis of polyene antibiotics and cytokinins by S. netropsis IMV Ac-5025. Methods. The strain was cultured in submerged cultivation condition in organic (soy) and synthetic (starch-ammonia) liquid nutrient media. The studies of biomass accumulation (gravimetric method), glucose consumption (glucose oxidase method), pH changes of culture media (ionometric method), biosynthesis of polyene antibiotics, and phytohormones (quantitative and qualitative thin layer chromatography spectrodensitometric method) were conducted. The results were analyzed in Statisticav.6.0 program. Results. It was found that polyene antibiotics are synthesized after the first day of cultivation, which indicates their role in the metabolism of streptomycetes. The biggest amount of the polyene antibiotics was accumulated in the stationary phase of producer growth (on the 7th day). It was found the decrease of polyene antibiotics and cytokinins accumulation in the producer’s biomass with the increase of exogenous cytokinin concentration from 25 ng/mL to 500 ng/mL. The bioproduction of the tetraene fraction was suppressed to a greater extent – up to 92% in the synthetic and up to 23% – in organic nutrient media. However, the amount of producer biomass increased under the action of the exogenous substance that confirming the positive effect of exogenous cytokinin on cell division of S. netropsis IMV Ac-5025. Exogenous isopentenyladenosine reduced the accumulation of endogenous cytokinins in streptomycetes biomass. Conclusions. The obtained results indicate an indirect metabolic relationship between the biosynthesis of polyene antibiotics and cytokinins in soil streptomycetes and provide a basis for the regulation of the biotechnological process for bioproduct formation with the appropriate quantitative composition of its components.

Isolation and Characterization of Antagonistic Activity of Some Streptomycetes and their Specific Actinophages from Soil.

<b>Background and Objective:</b> Phages specific to actinomycetes are common, active in the soil and gladly detected. Soil streptomycetes are having antibiosis activities against numerous bacteria, fungi and plant viruses. Thus, this study was designed to isolate, purify and characterize some streptomycetes active against some microorganisms from soil followed by isolation of their specific phages. <b>Materials and Methods:</b> Antagonistic activities of these streptomycetes isolates were tested against <i>Bacillus subtilis</i>,<i> Pseudomonas</i> sp., <i>Serratia</i> sp. and <i>Aspergillus niger</i>. To confirm their biological characterization of the streptomycetes isolates under investigation, the 16SrRNA gene was also used. The presence of specific lysate actinophages in the soil samples were tested by spot test technique and then propagated and purified for further characterization. The morphology of the purified actinophages was determined by electron microscopy. <b>Results:</b> The five selected <i>Streptomyces</i> isolates having effective antagonistic activity were biologically and molecularly identified as <i>Streptomyces sclerogranulatus </i>(QQ06), <i>Streptomyces mutabilis </i>(QQ07), <i>Streptomyces heilongjiangensis </i>(QQ08), <i>Streptomyces sparsus </i>(QQ09) and <i>Streptomyces purpurascens </i>(QQ10) strains. Electron micrographs showed the presence of filamentous virus-like particles with lengths of 21.4×928.57, 25×750, 21.4×857.14, 21.4×885.7 and 21.4×857.14 nm specific to <i>Streptomyces</i> strains QQ06, QQ07, QQ08, QQ09 and QQ10, respectively and belong to the family Inoviridae. <b>Conclusion:</b> Phage of Inoviridae was considered as the first time against streptomycetes isolates, therefore, additional and advanced studies should be carried out at the level of molecular characterization.

Biological activity of edaphotopes of anthropogenic transformed ecosystems

As a result of the carried out studies of biological activity of edaphotopes of anthropogenic transformed ecosystems, it was found that the largest number of microorganisms and streptomycetes it was characteristic for common chernozem. For the soil horizons of primitive undeveloped fragmented soils, was recorded the lowest percentage of the microorganisms number (on average 4-5% relative to the control). The number of streptomycetes in both intrazonal and soils of anthropogenic transformed soils and zonal soils varies in horizons. However, we have noted that in intrazonal and anthropogenic transformed soils streptomycetes are in most cases concentrated in underlying soil horizons. Our studies on micromycetes have found that this group of microscopic fungi accounts for up to 50% of the total number of microbiocenosis, with the smallest number recorded in the genetic horizons of primitive undeveloped soils on sandstone. Cellulose-destroying microorganisms in the soil microbocenosis of monitoring sites are least represented.

Screening of Soil Streptomycetes – Producers of Antibiotics against Phytopathogenic Bacteria

Soil is an inexhaustible source of bacteria of the genus Streptomyces – the producers of the vast majority of known antibiotics that are successfully used in medicine, veterinary and agriculture. The emergence and spread of pathogenic bacteria resistance to antibiotics requires the search for new antibiotic compounds capable of overcoming this problem. Aim. The purpose of this work was to isolate streptomycetes from soil samples of Kyiv and the Kyiv region and study their antibiotic activity against four strains of the different species of phytopathogenic bacteria. Methods. A suspension of soil in distilled water was sown on solid Chapek or corn-soybean medium in Petri dishes, in which trimethoprim and nystatin were introduced to inhibit bacterial and fungal growth. The antibiotic activity of the streptomycetes was tested by setting their agar discs on lawns of phytopathogenic bacteria in Petri dishes. Antibiotics were extracted from the streptomycetes agar cultures with a mixture of chloroform and acetone (2:1), dried in a rotary vacuum evaporator, dissolved in ethanol, separated and purified by thin layer chromatography on aluminum plates (Silica gel 60 F254 from Merck KGaA). The UV/Vis absorption spectra of the antibiotics were measured with a Beckman DU 8 spectrophotometer. Results. 10 strains of streptomycetes were isolated from the soil samples of Kyiv and the Kyiv region, whose antibiotic activity was tested against four phytopathogenic bacteria using the agar block method. Three of the streptomycetes – B8, SK and KZ, formed growth inhibition zones of different phytopathogens on complete medium in Petri dishes, among which the strain SK was the most active. This strain showed antibiotic activity against all four phytopathogenic bacteria – P. syringae 8511, P. carotovorum 8982, C. michiganensis 10 and X. campestris 8003. Conclusions. The results obtained are of interest for the protection of sensitive plants by isolated antibiotics against phytopathogenic bacteria in hothouse conditions.

Evaluation of BOX-PCR and REP-PCR as Molecular Typing Tools for Antarctic Streptomyces.

Molecular studies led to the resurgence of natural products research from genus Streptomyces, already known for their long history and importance for the pharmaceutical industry. However, species belonging to this genus are difficult to identify and the most commonly used techniques, which are based on 16S rRNA sequencing, do not discriminate between related species. In this work, amplification profiles generated from BOX-PCR and REP-PCR of 49 Antarctic soil streptomycetes were compared to evaluate the diversity present in the group and to characterize the bacterial isolates, along with some 16S rRNA amplifications. The BOX-A1R primer exhibit clearer amplification fragments, different from the amplification patterns obtained using the REP 1R and 2R primers. A higher diversity was observed with REP-PCR amplifications, even though a larger number of fragments was obtained with BOX-A1R primer amplifications. There are at least four isolates that showed great similarity (about 90%) in both techniques. In other hand, there are two others that are 90% similar in BOX-PCR, but distant in REP-PCR, showing only 40% of similarity. Results of the combination of BOX-PCR and REP-PCR represent a simple and low-cost method to discriminate between Streptomyces strains. There is no species identification with only the 16S rRNA, most isolates seem to be related to S. globisporus. Further studies added to the obtained results may provide better data to help the characterization of these microorganisms.

Diversity and geographic distribution of soil streptomycetes with antagonistic potential against actinomycetoma-causing Streptomyces sudanensis in Sudan and South Sudan

BackgroundProduction of antibiotics to inhibit competitors affects soil microbial community composition and contributes to disease suppression. In this work, we characterized whether Streptomyces bacteria, prolific antibiotics producers, inhibit a soil borne human pathogenic microorganism, Streptomyces sudanensis. S. sudanensis represents the major causal agent of actinomycetoma – a largely under-studied and dreadful subcutaneous disease of humans in the tropics and subtropics. The objective of this study was to evaluate the in vitro S. sudanensis inhibitory potential of soil streptomycetes isolated from different sites in Sudan, including areas with frequent (mycetoma belt) and rare actinomycetoma cases of illness.ResultsUsing selective media, 173 Streptomyces isolates were recovered from 17 sites representing three ecoregions and different vegetation and ecological subdivisions in Sudan. In total, 115 strains of the 173 (66.5%) displayed antagonism against S. sudanensis with different levels of inhibition. Strains isolated from the South Saharan steppe and woodlands ecoregion (Northern Sudan) exhibited higher inhibitory potential than those strains isolated from the East Sudanian savanna ecoregion located in the south and southeastern Sudan, or the strains isolated from the Sahelian Acacia savanna ecoregion located in central and western Sudan. According to 16S rRNA gene sequence analysis, isolates were predominantly related to Streptomyces werraensis, S. enissocaesilis, S. griseostramineus and S. prasinosporus. Three clusters of isolates were related to strains that have previously been isolated from human and animal actinomycetoma cases: SD524 (Streptomyces sp. subclade 6), SD528 (Streptomyces griseostramineus) and SD552 (Streptomyces werraensis).ConclusionThe in vitro inhibitory potential against S. sudanensis was proven for more than half of the soil streptomycetes isolates in this study and this potential may contribute to suppressing the abundance and virulence of S. sudanensis. The streptomycetes isolated from the mycetoma free South Saharan steppe ecoregion show the highest average inhibitory potential. Further analyses suggest that mainly soil properties and rainfall modulate the structure and function of Streptomyces species, including their antagonistic activity against S. sudanensis.

Кореляційна залежність біосинтезу антибіотичних сполук і інших біологічно активних речовин у ґрунтових стрептоміцетів

Кореляційна залежність біосинтезу антибіотичних сполук і інших біологічно активних речовин у ґрунтових стрептоміцетів

INTEGRATED POTATO PROTECTION SYSTEM FROM GOLDEN POTATO CYST NEMATODES

An integrated system for protecting potatoes from a golden potato cyst nematode has been developed, adapted for use in agricultural farms of various forms of ownership and includes a number of protective measures: the imposition of quarantine, a differentiated choice of unaffected crops (in collective and farm enterprises: lupine, winter wheat, sugar beet, Vico – oats , corn, barley with clover seed, clover, winter wheat, fodder beet; peas, winter wheat, corn. in individual farms: strawberries, green cultures, table beets, resistant varieties of potatoes, carrots, cabbage, cucumbers, peas, onions, garlic, cabbage. To reduce the level of invasion by the larvae of the initial phases of growth and development of plants to a golden potato cyst nematode, the treatment of tubers with a Kruiser 350 FS bp is recommended. – 0.3 l / t, as well as preparations based on metabolites of soil streptomycetes (Averkom, Averstim), as well as planting tubers in an early-optimal time in order to obtain seedlings of potatoes before the mass release of larvae from cysts. Local selective harvesting of susceptible varieties in the budding-flowering phase of potatoes and destruction of sprouts of unwanted vegetation by manual and mechanical means of tillage are aimed at interrupting the cycle of development of a golden potato cyst nematode and reducing the level of soil population. compliance with environmentally safe and affordable protective measures ensures effective control of the golden potato cyst nematode and the prevention of significant losses of potato yield. The developed protective measures do not require significant investments and are acceptable for implementation in farms of various forms of ownership.

RNAi-Based Biocontrol of Wheat Nematodes Using Natural Poly-Component Biostimulants.

With the growing global demands on sustainable food production, one of the biggest challenges to agriculture is associated with crop losses due to parasitic nematodes. While chemical pesticides have been quite successful in crop protection and mitigation of damage from parasites, their potential harm to humans and environment, as well as the emergence of nematode resistance, have necessitated the development of viable alternatives to chemical pesticides. One of the most promising and targeted approaches to biocontrol of parasitic nematodes in crops is that of RNA interference (RNAi). In this study we explore the possibility of using biostimulants obtained from metabolites of soil streptomycetes to protect wheat (Triticum aestivum L.) against the cereal cyst nematode Heterodera avenae by means of inducing RNAi in wheat plants. Theoretical models of uptake of organic compounds by plants, and within-plant RNAi dynamics, have provided us with useful insights regarding the choice of routes for delivery of RNAi-inducing biostimulants into plants. We then conducted in planta experiments with several streptomycete-derived biostimulants, which have demonstrated the efficiency of these biostimulants at improving plant growth and development, as well as in providing resistance against the cereal cyst nematode. Using dot blot hybridization we demonstrate that biostimulants trigger a significant increase of the production in plant cells of si/miRNA complementary with plant and nematode mRNA. Wheat germ cell-free experiments show that these si/miRNAs are indeed very effective at silencing the translation of nematode mRNA having complementary sequences, thus reducing the level of nematode infestation and improving plant resistance to nematodes. Thus, we conclude that natural biostimulants produced from metabolites of soil streptomycetes provide an effective tool for biocontrol of wheat nematode.

The Concept of an Ideal Antibiotic: Implications for Drug Design.

The emergence and spread of antibiotic-resistant pathogens is a major public health issue, which requires global action of an intersectoral nature. Multidrug-resistant (MDR) pathogens—especially “ESKAPE” bacteria—can withstand lethal doses of antibiotics with various chemical structures and mechanisms of action. Pharmaceutical companies are increasingly turning away from participating in the development of new antibiotics, due to the regulatory environment and the financial risks. There is an urgent need for innovation in antibiotic research, as classical discovery platforms (e.g., mining soil Streptomycetes) are no longer viable options. In addition to discovery platforms, a concept of an ideal antibiotic should be postulated, to act as a blueprint for future drugs, and to aid researchers, pharmaceutical companies, and relevant stakeholders in selecting lead compounds. Based on 150 references, the aim of this review is to summarize current advances regarding the challenges of antibiotic drug discovery and the specific attributes of an ideal antibacterial drug (a prodrug or generally reactive compound with no specific target, broad-spectrum antibacterial activity, adequate penetration through the Gram-negative cell wall, activity in biofilms and in hard-to-treat infections, accumulation in macrophages, availability for oral administration, and for use in sensitive patient groups).

Assessment of the Detrimental Impact of Polyvalent Streptophages Intended to be Used as Biological Control Agents on Beneficial Soil Streptoflora.

Streptophages are currently being investigated to control potato common scab, however, since a majority of streptophages are reported to be polyvalent, their potential to infect beneficial soil streptomycetes during the application process may have unintended consequences. To test this hypothesis, two phytopathogenic fungi, namely Fusarium solani and Rhizoctonia solani, were tested for their detrimental effect on the test crop wheat (Triticum aestivum cv. Gutha). F. solani caused a significant root weight reduction (34%) in the wheat plant and therefore was tested further in the pot trials with actinomycetes present. Sixty-seven streptomycete isolates from a Tasmanian potato farm were screened for their antifungal abilities against the two phytopathogenic fungi. Four actinomycetes found to be strongly antifungal were then tested for their disease-protective abilities against F. solani in pot trials again using wheat. Addition of the streptomycetes into the container media protected the plants against F. solani, indicating that streptomycetes have a disease-suppressive effect. A further pot trial was conducted to evaluate whether these beneficial streptomycete species would be affected by streptophage treatment and subsequently result in an increased risk of fungal infections. When streptophages were added to the pots, the shoot and root growth of wheat declined by 23.6% and 8.0%, respectively, in the pots with the pathogenic fungus compared to the control pots. These differences might suggest that removal of antifungal streptomycetes by polyvalent phages from plant rhizosphere when biocontrol of plant pathogenic streptomycetes (e.g. Streptomyces scabiei)is targeted might encourage secondary fungal infections in the farm environment. The presented data provide preliminary evidence that streptophage treatment of pathogenic streptomycetes may lead to an aggravated disease risk by soil-borne fungal pathogens when naturally present antagonists are removed. As a result, extensive farm site trials are required to determine the long-term detrimental impact of polyvalent streptophage treatments on beneficial soil streptoflora.

Streptomyces AcH 505 triggers production of a salicylic acid analogue in the fungal pathogen Heterobasidion abietinum that enhances infection of Norway spruce seedlings.

The necrotrophic fungus Heterobasidion spp. is the causal agent of 'annosum root rot' of Norway spruce. In the presence of the rhizosphere bacterium Streptomyces AcH 505, enhanced colonization of Norway spruce roots with Heterobasidion abietinum 331 has previously been observed. By analyzing dual cultures of H. abietinum 331 and Streptomyces AcH 505 with HPLC, a fungal metabolite was identified that was increased in the presence of Streptomyces AcH 505. Likewise, challenge of H. abietum 331 with common antifungals produced by soil streptomycetes rendered the same effect. The structure of the compound, 5-formylsalicylic acid (5-FSA), was elucidated by HPLC-HR-ESI-Orbitrap-mass spectrometry and NMR spectroscopy. Based on in vivo measurements of maximum photosystem II efficiency of Norway spruce seedlings, 5-FSA did not influence plant vitality. However, when challenged with H. abietinum 331, ergosterol amounts in infected roots increased significantly for 5-FSA pre-treated seedlings. The severity of the infection was comparable to that observed in the presence of Streptomyces AcH 505. 5-FSA is a structural analogue of salicylic acid, an important signalling molecule active in plant defence. Thus, the expression of two defence-response related marker genes (PR1, Hel) was analysed in 5-FSA treated Arabidopsis thaliana seedlings by Northern blot analysis. The transcription of both marker genes was altered, indicating that 5-FSA is perceived by Arabidopsis in a similar manner to salicylic acid and is able to interfere with Arabidopsis defence signalling. The role of 5-FSA as a potential virulence factor of H. abietinum 331 in the presence of Streptomyces AcH 505 is discussed.

Sterols biosynthesis by soil streptomycetes

Sterols biosynthesis by soil streptomycetes