Isolation and characterization of multifunctional Streptomyces species with antimicrobial, nematicidal and phytohormone activities from marine environments in Egypt

Biodegradation and antimicrobial capability-induced heavy metal resistance of the marine-derived actinomycetes Nocardia harenae JJB5 and Amycolatopsis marina JJB11

Currently, heavy metal-resistant (HMR) marine actinomycetes have attracted much attention worldwide due to their unique capabilities. In this study, 27 marine-derived actinomycetes were isolated from coastal beaches in the Arabian Gulf of Al-Jubail in Saudi Arabia and screened for resistance to 100 mg/L of the heavy metals Cd2+, Cr6+, Cu2+, Fe2+, Pb2+, and Ni2+ using different assay techniques. Six isolates were selected as HMRs, of which two isolates, JJB5 and JJB11, exhibited the highest maximum tolerance concentrations (200- > 300 mg/L). Both isolates were the highest among six-HMR screened for their biodegradation potential of plastics low-density polyethylene, polystyrene, and polyvinyl chloride, recording the highest weight loss (15 ± 1.22 - 65 ± 1.2%) in their thin films. They also showed the highest biodegradability of the pesticides acetamiprid, chlordane, hexachlorocyclohexane, indoxacarb and lindane, indicating promising removal capacities (95.70-100%) for acetamiprid and indoxacarb using HPLC analysis. Additionally, the cell-free filtrate (CFF) of both isolates displayed the highest antimicrobial activity among the six-HMR screened against a variety of microbial test strains, recording the highest inhibition zone diameters (13.76 ± 0.66 - 26.0 ± 1.13 mm). GC‒MS analyses of the ethyl acetate extract of their CFFs revealed the presence of diverse chemical compounds with a multitude of remarkable biological activities. Based on their spore morphology and wall-chemotype, they were assigned to the nocardioform-actinomycetes. Furthermore, their phenotypic characteristics, together with 16S rRNA gene sequencing (OR121525-OR121526), revealed them as Nocardia harenae JJB5 and Amycolatopsis marina JJB11. Our results suggest that marine HMR actinomycetes are promising candidates for various biotechnological applications.

[Identification and antifungal activity of halophilic bacteria isolated from saline soils in Campeche, México]

Phytopathogenic fungi Alternaria alternata and Colletotrichum gloeosporioides cause diseases in plant tissues as well as significant postharvest losses. The use of chemical fungicides for their control has negative effects on health and the environment. Secondary metabolites from halophilic bacteria are a promising alternative for new antifungal compounds. In the present study, halophilic bacteria were isolated and characterized from two sites with saline soils called branquizales in Campeche, Mexico. A total of 64 bacteria were isolated. Agrobacterium, Bacillus, Inquilinus, Gracilibacillus, Metabacillus, Neobacillus, Paenibacillus, Priestia, Staphylococcus, Streptomyces and Virgibacillus were among the identified genera. The antifungal potential of the culture supernatant (CS) of 39 halophilic bacteria was investigated against C. gloeosporioides and A. alternata. The bacteria showing the greatest inhibition of mycelial growth corresponded to Bacillus subtilis CPO 4292, Metabacillus sp. CPO 4266, Bacillus sp. CPO 4295 and Bacillus sp. CPO 4279. The CS of Bacillus sp. CPO 4279 exhibited the highest activity and its ethyl acetate extract (AcOEt) inhibited the germination of C. gloeosporioides, with IC50 values of 8,630μg/ml and IC90 of 10,720μg/ml. The organic partition of the AcOEt extract led to three fractions, with acetonitrile (FAcB9) showing the highest antifungal activity, with values exceeding 66%. Halophilic bacteria from 'blanquizales' soils of the genus Bacillus sp. produce metabolites with antifungal properties that inhibit the phytopathogenic fungus C. gloeosporioides.

Isolation, characterization and screening of actinomycetes associated with fijian ant-plant symbioses

In the search for novel therapeutics to combat the ongoing antimicrobial resistance crisis, scientists are turning to underexplored environments. Defensive mutualisms between hymenopteran insects and actinomycetes represent important reservoirs for bioactive compounds. In this study, we examined the association between actinomycetes and Squamellaria ant-plants spanning three different ant and plant species combinations (Squamellaria imberbis-Philidris nagasau, Squamellaria tenuiflora- Technomyrmex vitiensis, and Squamellaria tenuiflora-Tetramorium insolens). Eight Squamellaria plants were sampled including four containing T. vitiensis, three containing P. nagasau, and a single plant containing T. insolens. A total of 47 actinomycetes were obtained from the sampled material, with 5, 16, and 26 isolates originating from cuticle, tissue, and nest samples, respectively. Cross-streaking tests showed that 12 out of 47 isolates inhibited bacterial pathogens. The most frequently inhibited pathogens in the cross-streaking tests were S. aureus and E. coli while S. enterica was the least inhibited. Among the three primary screening media used, ISP2 agar was the most suitable for secondary metabolism as more isolates exhibited antibacterial activity when grown on the medium. TFS2010 and TFS2003, which matched to Streptomyces gramineus (>99% similarity), were the most bioactive isolates in cross-streaking tests. TFS2010 displayed the strong antibacterial on Nutrient agar, Mueller Hinton agar, and ISP2 agar while TFS2003 only exhibited strong antibacterial activity on Nutrient agar. Furthermore, a difference in potency of extracts based on batch culture medium was noted in TFS2010. DNA was extracted from 19 isolates and followed by 16SrRNA gene sequencing. Analysis of sequence data revealed the presence of six genera, including Amycolatopsis, Asanoa, Jiangella, Nocardia, Nocardiopsis, and Streptomyces, with the latter being the most abundant taxon. Among these, three isolates (PNS3002, PNS3005, and TFS3001) are likely to represent new species while one (TFS2015) is likely to be a member of a novel genus. Our work represents the first attempt to study actinomycetes from Squamellaria-ant mutualisms.

Unveiling the Pharmacological Significance of Marine Streptomyces violaceusniger KS20: Isolation, Characterization, and Assessment of Its Biomedical Applications

Marine actinomycetes represent a highly favorable source of bioactive compounds and have been the mainstay of much research in recent years. Recent reports have shown that marine Streptomyces sp. can produce compounds with diverse and potent biological activities. Therefore, the key objective of the study was to isolate and screen a potential actinomycete from marine ecosystems of Devbagh and Tilmati beaches, Karwar. Streptomyces sp. KS20 was characterized and the ethyl acetate extract (EtOAc-Ex) was screened for biomedical applications. Streptomyces sp. KS20 produced grayish-white aerial and pale-yellow substrate mycelia and revealed an ancestral relationship with Streptomyces violaceusniger. Optimum growth of the organism was recorded at 30 °C and pH 7.0. The metabolite profiling of EtOAc-Ex expressed the existence of several bioactive metabolites, whereas the functional groups were indicated by Fourier transform infrared (FTIR) spectroscopy. A considerable antioxidant activity was shown for EtOAc-Ex with IC50 of 92.56 μg/mL. In addition to this, Streptomyces sp. KS20 exhibited significant antimicrobial properties, particularly against Escherichia coli, where a zone of inhibition measuring 36 ± 0.83 mm and a minimum inhibitory concentration (MIC) of 3.12 µg/mL were observed. The EtOAc-Ex even revealed significant antimycobacterial potency with IC50 of 6.25 μg/mL. Finally, the antiproliferative potentiality of EtOAc-Ex against A549 and PC-3 cell lines revealed a constant decline in cell viability while raising the concentration of EtOAc-Ex from 12.5 to 200 μg/mL. The IC50 values were determined as 94.73 μg/mL and 121.12 μg/mL for A549 and PC-3 cell lines, respectively. Overall, the exploration of secondary metabolites from marine Streptomyces sp. KS20 represents an exciting area of further research with the potential to discover novel bioactive compounds that could be developed into therapeutics for various medical applications.

Antioxidant and chemoprotective potential of Streptomyces levis strain isolated from human gut

In the current study, Streptomyces levis strain HFM-2 has been isolated from healthy human gut. Streptomyces sp. HFM-2 was identified based on the polyphasic approach that included cultural, morphological, chemotaxonomical, phylogenetic, physiological, and biochemical characteristics. 16S rRNA gene sequence of strain HFM-2 exhibited 100% similarity with Streptomyces levis strain 15423 (T). The EtOAc extract of Streptomyces levis strain HFM-2 showed potential antioxidant activity, along with 69.53 ± 0.19%, 64.76 ± 0.13%, and 84.82 ± 0.21% of scavenging activity for ABTS, DPPH, and superoxide radicals, respectively at 600 µg/mL. The IC50 values i.e. 50% scavenging activity for DPPH, ABTS, and superoxide radicals were achieved at 497.19, 388.13, and 268.79 (µg/mL), respectively. The extract's reducing power and total antioxidant capacity were determined to be 856.83 ± 0.76 and 860.06 ± 0.01 µg AAE/mg of dry extract, respectively. In addition, the EtOAc extract showed protection against DNA damage from oxidative stress caused by Fenton's reagent, and cytotoxic activity against HeLa cervical cancer, Skin (431) cancer, Ehrlich-Lettre Ascites-E (EAC) carcinoma, and L929 normal cell lines. The IC50 values against HeLa, 431 skin, and EAC carcinoma cell lines were found to be 50.69, 84.07, and 164.91 µg/mL, respectively. The EtOAc extract showed no toxicity  towards L929 normal cells. In addition, flow cytometric analysis exhibited reduced mitochondrial membrane potential (MMP), and enhanced levels of reactive oxygen species (ROS). The EtOAc extract was chemically analyzed using GCMS to determine the components executing its bioactivities.

Streptomyces and their specialised metabolites for phytopathogen control - comparative in vitro and in planta metabolic approaches

In the search for new crop protection microbial biocontrol agents, isolates from the genus Streptomyces are commonly found with promising attributes. Streptomyces are natural soil dwellers and have evolved as plant symbionts producing specialised metabolites with antibiotic and antifungal activities. Streptomyces biocontrol strains can effectively suppress plant pathogens via direct antimicrobial activity, but also induce plant resistance through indirect biosynthetic pathways. The investigation of factors stimulating the production and release of Streptomyces bioactive compounds is commonly conducted in vitro, between Streptomyces sp. and a plant pathogen. However, recent research is starting to shed light on the behaviour of these biocontrol agents in planta, where the biotic and abiotic conditions share little similarity to those of controlled laboratory conditions. With a focus on specialised metabolites, this review details (i) the various methods by which Streptomyces biocontrol agents employ specialised metabolites as an additional line of defence against plant pathogens, (ii) the signals shared in the tripartite system of plant, pathogen and biocontrol agent, and (iii) an outlook on new approaches to expedite the identification and ecological understanding of these metabolites under a crop protection lens.

Isolation, antibacterial screening, and identification of bioactive cave dwelling bacteria in Fiji

Bacteria are well known producers of bioactive secondary metabolites, including some of the most effective antibiotics in use today. While the caves of Oceania are still largely under-explored, they form oligotrophic and extreme environments that are a promising source for identifying novel species of bacteria with biologically active compounds. By using selective media that mimicked a cave environment, and pretreatments that suppressed the growth of fast-growing bacteria, we have cultured genetically diverse bacteria from a limestone cave in Fiji. Partial 16S rRNA gene sequences from isolates were determined and compared with 16S rRNA gene sequences in EzBioCloud and SILVA data bases. Fifty-five isolates purified from culture had Actinomycete-like morphologies and these were investigated for antibacterial activity. Initial screening using a cross streak test with pathogenic bacteria indicated that 34 of the isolates had antibacterial properties. The best matches for the isolates are bacteria with potential uses in the manufacture of antibiotics and pesticides, in bioremediation of toxic waste, in biomining, in producing bioplastics, and in plant growth promotion. Nineteen bacteria were confirmed as Actinomycetes. Thirteen were from the genus Streptomyces and six from genera considered to be rare Actinomycetes from Pseudonocardia, Kocuria, Micromonospora, Nonomuraea. Ten isolates were Firmicutes from the genera Bacillus, Lysinbacillus, Psychrobacillus and Fontibacillus. Two were Proteobacteria from the genera Mesorhizobium and Cupriavidus. Our findings identify a potentially rich source of microbes for applications in biotechnologies.

Diversity, mechanisms and beneficial features of phosphate-solubilizing Streptomyces in sustainable agriculture: A review

Currently, the use of phosphate (P) biofertilizers among many bioformulations has attracted a large amount of interest for sustainable agriculture. By acting as growth promoters, members of the Streptomyces genus can positively interact with plants. Several studies have shown the great potential of this bacterial group in supplementing P in a soluble, plant-available form by several mechanisms. Furthermore, some P-solubilizing Streptomyces (PSS) species are known as plant growth-promoting rhizobacteria that are able to promote plant growth through other means, such as increasing the availability of soil nutrients and producing a wide range of antibiotics, phytohormones, bioactive compounds, and secondary metabolites other than antimicrobial compounds. Therefore, the use of PSS with multiple plant growth-promoting activities as an alternative strategy appears to limit the negative impacts of chemical fertilizers in agricultural practices on environmental and human health, and the potential effects of these PSS on enhancing plant fitness and crop yields have been explored. However, compared with studies on the use of other gram-positive bacteria, studies on the use of Streptomyces as P solubilizers are still lacking, and their results are unclear. Although PSS have been reported as potential bioinoculants in both greenhouse and field experiments, no PSS-based biofertilizers have been commercialized to date. In this regard, this review provides an overview mainly of the P solubilization activity of Streptomyces species, including their use as P biofertilizers in competitive agronomic practices and the mechanisms through which they release P by solubilization/mineralization, for both increasing P use efficiency in the soil and plant growth. This review further highlights and discusses the beneficial association of PSS with plants in detail with the latest developments and research to expand the knowledge concerning the use of PSS as P biofertilizers for field applications by exploiting their numerous advantages in improving crop production to meet global food demands.

Marine fungi showing multifunctional activity against human pathogenic microbes and cancer

Multifunctional drugs have shown great promise in biomedicine. Organisms with antimicrobial and anticancer activity in combination with antioxidant activity need further research. The Red Sea and the Arabian Gulf coasts were randomly sampled to find fungi with multifunctional activity. One hundred strains (98 fungi and 2 lichenized forms) were isolated from 15 locations. One-third of the isolates inhibited clinical bacterial (Staphylococcus aureus, Bacillus subtilis, Vibrio cholerae, Salmonella typhi, S. paratyphi) and fungal pathogens (Talaromycets marneffei, Malassezia globose, Cryptococcus neoformans, Candida albicans, Aspergillus fumigatus) and four cancer cell lines (Hep G2 liver, A-549 lung, A-431skin, MCF 7 breast cancer). Bacterial and cancer inhibition was often accompanied by a high antioxidant activity, as indicated by the principal component analysis (PCA). PCA also indicated that fungal and bacterial pathogens appeared to be inhibited mostly by different marine fungal isolates. Strains with multifunctional activity were found more from the Rea Sea than from the Arabian Gulf coasts. The highest potential for multifunctional drugs were observed for Acremonium sp., Acrocalymma sp., Acrocalymma africana, Acrocalymma medicaginis (activity reported for the first time), Aspergillus sp. Cladosporium oxysporum, Emericellopsis alkaline, Microdochium sp., and Phomopsis glabrae. Lung, skin, and breast cancers were inhibited 85%-97% by Acremonium sp, while most of the isolates showed low inhibition (ca 20%). The highest antifungal activity was observed for Acremonium sp., Diaporthe hubeiensis, Lasiodiplodia theobromae, and Nannizia gypsea. One Acremonium sp. is of particular interest to offer a multifunctional drug; it displayed both antifungal and antibacterial activity combined with high antioxidant activity (DPPH scavenging 97%). A. medicaginis displayed combined antibacterial, anticancer, and antioxidant activity being of high interest. Several genera and some species included strains with both high and low biological activities pointing out the need to study several isolates to find the most efficient strains for biomedical applications.

Isolation and Characterization of a Novel Actinomycete Isolated from Marine Sediments and Its Antibacterial Activity against Fish Pathogens

Marine habitats are especially complex, with a varied diversity of living organisms. Marine organisms, while living in such intense conditions, have developed great physiological and metabolic potential to survive. This has led them to produce several potent metabolites, which their terrestrial counterparts are unable to produce. Over the past few years, marine Actinomycetes have been considered one of the most abundant sources of diverse and novel metabolites. In this work, an attempt was made to isolate Actinomycetes from marine sediments in terms of their ability to produce several novel bioactive compounds. A total of 16 different Actinomycete colonies were obtained from marine sediment samples. Among the 16 Actinomycete isolates, 2 isolates demonstrated in vitro antibacterial activity against Aeromonas hydrophila and Vibrio parahemolyticus. However, among them, only one isolate was found to have potent antibacterial activity, and hence, was taken for further analysis. This isolate was designated as Beijerinickia fluminensis VIT01. The bioactive components obtained were extracted and later subjected to Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy (GC-MS) analyses for identification. Several novel bioactive compounds were reported from the data obtained and were found to have potent antibacterial activity. Hence, they could be used as an alternative to antibiotics for treating several fish pathogens in the aquaculture industry.

Enhanced Isolation of Streptomyces from Different Soil Habitats in Calamba City, Laguna, Philippines using a Modified Integrated Approach

Streptomyces species are considered to be the most prolific sources of various bioactive secondary metabolites that are important for antibiotic production. Here, we describe a modified integrated approach to isolate Streptomyces species from diverse soil habitats, such as dumpsite, garden, forest, grassland, and riverside in Calamba City, Laguna, Philippines. A total of 25 soil samples were collected from a depth of 0–20 cm using systematic random soil sampling. All soil samples were air-dried, crushed, pretreated with calcium carbonate, and incubated on a rotary shaker. Isolation of Streptomyces in soil samples was then performed using the standard serial dilution plate technique on starch casein agar supplemented with nystatin (50 μg/ml) and ampicillin (5 μg/ml). Identification of the Streptomyces isolates was done using a polyphasic method that includes morphological and biochemical characterization. A total of 103 morphologically and biochemically distinct Streptomyces were isolated from diverse soil habitats. The number of Streptomyces isolates varied in each collection site, with the highest number collected from dumpsite soil and the least from forest soil. Most of the hydrogen sulfide producers were noted to be isolated from dumpsite samples. Moreover, more Streptomyces were isolated in soil habitats at higher altitudes with a slightly acidic to alkaline pH and a temperature ranging from 29 to 33°C. Employing the modified integrated approach, we have isolated up to 10 times more Streptomyces compared to early studies. These Streptomyces isolates can be valuable for future drug discovery and development research.

Rhizosphere soil microbial community and its response to different utilization patterns in the semi-arid alpine grassland of northern Tibet

As the link between plants and soils, rhizosphere soil microorganisms play an important role in the element cycle. This study aimed to understand the response of the rhizosphere soil microbial community structure and interaction network to grassland utilization in the alpine steppe of the northern Tibet Plateau. High-throughput sequencing was employed to study the composition, diversity, and species interaction network of rhizosphere soil microbial communities under grazing, mowing, and enclosing treatments. Proteobacteria (47.19%) and Actinobacteria (42.20%) were the dominant bacteria in the rhizosphere soil. There was no significant difference in relative abundance among rhizosphere soil microorganisms at phylum and genus levels, but differences were found in Chlorobi, Ignavibacteriae, and Micromonospora. The alpha diversity index based on Shannon, Chao1, and Simpson indices revealed that except for a significant difference in the Shannon index of the Artemisia nanschanica group, the richness and evenness of rhizosphere soil microbial communities among all groups were similar. Non-metric multidimensional scaling (NMDS) and multi-response permutation procedure (MRPP) analyses showed that the inter-group differences of three plants (Stipa purpurea, Carex moorcroftii, and Artemisia nanschanica) were greater than the differences within the groups; however, only the inter-group difference with the Stipa purpurea group was significant. The microbial interaction network showed that the network complexity of the Artemisia nanschanica group and the enclosing treatment, which were not easily influenced by external factors, were higher than those of the other groups and treatments; this again demonstrated that Proteobacteria and Actinobacteria were the network core microbial species in alpine steppe of the northern Tibet Plateau and were crucial for maintaining stability of the microbial communities. Findings from this study provide a theoretical basis for the restoration of degraded alpine grassland and the development of microbial functions.

Evaluation and comparison of antibiotic susceptibility profiles of Streptomyces spp. from clinical specimens revealed common and region-dependent resistance patterns

Notwithstanding the fact that streptomycetes are overlooked in clinical laboratories, studies describing their occurrence in disease and potential pathogenicity are emerging. Information on their species diversity in clinical specimens, aetiology and appropriate therapeutic treatment is scarce. We identified and evaluated the antibiotic susceptibility profile of 84 Streptomyces clinical isolates from the Czech Republic. In the absence of appropriate disk diffusion (DD) breakpoints for antibiotic susceptibility testing (AST) of Streptomyces spp., we determined DD breakpoints by correlation with the broth microdilution method and by the distribution of zone diameters among isolates. Correlation accuracy was high for 9 antibiotics, leading to the establishment of the most valid DD breakpoints for Streptomyces antibiotic susceptibility evaluation so far. Clinical strains belonged to 17 different phylotypes dominated by a cluster of strains sharing the same percentage of 16S rRNA gene sequence identity with more than one species (S. albidoflavus group, S. hydrogenans, S. resistomycificus, S. griseochromogenes; 70% of isolates). AST results showed that Streptomyces exhibited intrinsic resistance to penicillin, general susceptibility to amikacin, gentamycin, vancomycin and linezolid, and high percentage of susceptibility to tetracyclines and clarithromycin. For the remaining antibiotics, AST showed inter- and intra-species variations when compared to available literature (erythromycin, trimethoprim-sulfamethoxazole), indicating a region-dependent rather than species-specific patterns.

Streptomyces spp. Isolated from Marine and Caatinga Biomes in Brazil for the Biological Control of Duponchelia fovealis

Actinobacteria have been drawing attention due to their potential for the development of new pest control products. We hereby assess the effects of Streptomyces isolated from marine and caatinga biomes against Duponchelia fovealis Zeller (Lepidoptera: Crambidae), a pest associated with the strawberry culture at a global scale. To this end, eggs deposited by adults were immersed for 5 s in a bacterial suspension, and the larvae were fed on leaflets placed in glass tubes containing bacterial suspensions. In both treatments, the control was a saline solution. The bioassays demonstrated that the Streptomyces strains were able to cause the death of D. fovealis eggs (≈ 40%) and larvae (≈ 65%) compared to untreated eggs (1.4%) and larvae (2.0%). The crude extract of strain T49 and the chitinase extract of strain T26 affected larval growth when applied directly to the thorax of first-instar larvae (larval-adult lifespan of 65.3 ± 0.5 days and 67.5 ± 0.7 days, respectively; survival of 61.2 ± 1.2%) in relation to the control treatment (larval-adult lifespan of 41.75 ± 0.2 days and survival of 83.7 ± 2.6%). The Streptomyces spp. strains T41, T49, and T50 caused antifeeding activity. Apart from larval mortality, the adults that emerged from the larvae exposed to the extracts presented morphological abnormalities, and the moths' chitin spectra showed clear alterations to the pupa and wings. Our studies show, for the very first time, that Streptomyces isolated from the marine environment and the Caatinga biome are effective at provoking the mortality of D. fovealis and are promising agents for developing new products with biological control properties.

Compost-derived indole-3-acetic-acid-producing bacteria and their effects on enhancing the secondary fermentation of a swine manure-corn stalk composting

Composting, as an effectively bio-oxidative process, has been widely used for converting organic waste to organic fertilizer. However, the low fertilizer efficiency of composting product limited its application in agriculture. To improve the growth-promoting effect of composting product, the present study investigated the bioaugmentation strategy of inoculating indole-3-acetic-acid (IAA)-producing bacteria. Firstly, two IAA-producing bacteria (Bacillus safensis 33C and Rhodococcus rhodochrous YZ) were isolated from composting products with high IAA yields of 39.18 and 16.32 μg mL^-1, respectively. Secondly, the microbial inoculants were prepared with 33C, YZ and a previously isolated IAA-producing strain Corynebacterium stationis 29B. To increase the accumulation of microbial secondary metabolites, microbial inoculants were amended at the secondary fermentation stage of composting. Physicochemical characterization showed that the maturity of composting product was significantly promoted by inoculating microbial inoculants prepared with 33C and 29B (single and combined inoculants). Finally, bioaugmentation with 33C and 29B increased the IAA contents of composting products by 2.9-5.2 times, which benefited the germination and early vegetative growth of plants. In summary, inoculating proper IAA-producing bacteria during secondary fermentation of composting could improve the quality of composting product and expand its application.

Bioprospection and secondary metabolites profiling of marine Streptomyces levis strain KS46

The quest for novel broad spectrum bioactive compounds is needed continuously because of the rapid advent of pathogenic multi drug resistant organisms. Actinomycetes, isolated from unexplored habitats can be a solution of this problem. The motive of this research work was isolation of actinomycetes having potential antimicrobial activities from unexplored regions of Devbag and Tilmati beach. The isolated actinomycetes were screened against pathogenic microbes for antimicrobial activities through cross streak method. Enzyme production activity was checked for these actinomycetes for amylase, protease, cellulase and lipase enzymes. Further antimicrobial activity of ethyl acetate extract of the potent strain KS46 was performed. The strain KS46 was identified with 16S rRNA gene sequencing and secondary structure was analysed. Gas chromatography–Mass spectrometry (GC–MS) profiling was conducted to ascertain the presence of bioactive metabolites in the ethyl acetate extract. The collected samples were pre-treated and 70 actinomycetes were isolated. The Streptomyces sp. strain KS46 showed the best antimicrobial activity in primary screening. Ethyl acetate extract of the strain KS46 revealed antimicrobial activity against S. aureus, B. subtilis, B. cereus, E. faecalis, K. pneumoniae, E. coli, S. flexneri, C. albicans and C. glabrata. The 16S rRNA gene sequencing identified the strain KS46 as Streptomyces levis strain KS46. The GC–MS metabolite profiling of the ethyl acetate extract revealed the availability of 42 compounds including fatty acid esters, fatty acid anhydrides, alkanes, steroids, esters, alcohols, carboxylic ester, etc. having antibacterial, antifungal, antiproliferative, antioxidant activities. This study indicated that Devbag and Tilmati beaches being untapped habitats have enormous diversity of promising antimicrobial metabolite producing actinomycetes. Therefore, further exploration should be carried out to characterize the potential actinomycetes, which can be optimistic candidates for generation of novel antimicrobial drugs.

Evolutionary genomics and biosynthetic potential of novel environmental Actinobacteria

Actinobacteria embroil Gram-positive microbes with high guanine and cytosine contents in their DNA. They are the source of most antimicrobials of bacterial origin utilized in medicine today. Their genomes are among the richest in novel secondary metabolites with high biotechnological potential. Actinobacteria reveal complex patterns of evolution, responses, and adaptations to their environment, which are not yet well understood. We analyzed three novel plant isolates and explored their habitat adaptation, evolutionary patterns, and potential secondary metabolite production. The phylogenomically characterized isolates belonged to Actinoplanes sp. TFC3, Streptomyces sp. L06, and Embleya sp. NF3. Positively selected genes, relevant in strain evolution, encoded enzymes for stress resistance in all strains, including porphyrin, chlorophyll, and ubiquinone biosynthesis in Embleya sp. NF3. Streptomyces sp. L06 encoded for pantothenate and proteins for CoA biosynthesis with evidence of positive selection; furthermore, Actinoplanes sp. TFC3 encoded for a c-di-GMP synthetase, with adaptive mutations. Notably, the genomes harbored many genes involved in the biosynthesis of at least ten novel secondary metabolites, with many avenues for future new bioactive compound characterization-specifically, Streptomyces sp. L06 could make new ribosomally synthesized and post-translationally modified peptides, while Embleya sp. NF3 could produce new non-ribosomal peptide synthetases and ribosomally synthesized and post-translationally modified peptides. At the same time, TFC3 has particularly enriched in terpene and polyketide synthases. All the strains harbored conserved genes in response to diverse environmental stresses, plant growth promotion factors, and degradation of various carbohydrates, which supported their endophytic lifestyle and showed their capacity to colonize other niches. This study aims to provide a comprehensive estimation of the genomic features of novel Actinobacteria. It sets the groundwork for future research into experimental tests with new bioactive metabolites with potential application in medicine, biofertilizers, and plant biomass residue utilization, with potential application in medicine, as biofertilizers and in plant biomass residues utilization. KEY POINTS: • Potential of novel environmental bacteria for secondary metabolites production • Exploring the genomes of three novel endophytes isolated from a medicinal tree • Pan-genome analysis of Actinobacteria genera.

Antagonistic Potential of Soil Streptomyces Isolates from Southern Thailand to Inhibit Foodborne Bacterial Pathogens

Streptomyces are well known for their competence to produce thousands of bioactive secondary metabolites and enzymes. This study aimed to assess the inhibitory activities of crude extracts from diverse Streptomyces collected from rice soils in Narathiwat, Thailand, against foodborne bacterial pathogens. In total, 136 Actinomycete isolates were screened using a cross-streak method for the ability to produce effective metabolites against 5 pathogenic bacteria. Out of these, 19 (13.97%) isolates had antibacterial activity against at least one tested bacterium. Most of the isolates could strongly suppress the growth of S. aureus ATCC25923 and B. cereus MTCC430 except P. aeruginosa ATCC27853. On the basis of morphological, cultural, and biochemical characteristics, all potent isolates exhibited typical features that fitted the genus Streptomyces. Two of the 7 selected ethyl acetate crude extracts had good antagonistic activity against S. aureus ATCC25923 and B. cereus MTCC430 when tested using the agar well diffusion assay. Furthermore, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of the 2 extracts evaluated using the colorimetric broth microdilution method ranged from 256 to >1,024 μg/ml against the tested bacteria. The partial nucleotide sequences of the 16S rRNA gene led to identifying both active isolates as Streptomyces species. These active Streptomyces isolates could provide an interesting source for generating innumerable natural compounds with antibacterial activity that can presumably be developed to fight bacterial pathogens in the near future.

Apis andreniformis associated Actinomycetes show antimicrobial activity against black rot pathogen (Xanthomonas campestris pv. campestris)

This study aimed to investigate cultivable actinomycetes associated with rare honey bee species in Thailand and their antagonistic activity against plant pathogenic bacteria. Actinomycetes were selectively isolated from the black dwarf honey bee (Apis andreniformis). A total of 64 actinomycete isolates were obtained with Streptomyces as the predominant genus (84.4%) followed by Micromonospora (7.8%), Nonomuraea (4.7%) and Actinomadura (3.1%). All isolates were screened for antimicrobial activity against Xanthomonas campestris pv. campestris, Pectobacterium carotovorum and Pseudomonas syringae pv. sesame. Three isolates inhibited the growth of X. campestris pv. campestris during in vitro screening. The crude extracts of two isolates (ASC3-2 and ASC5-7P) had a minimum inhibitory concentration (MIC) of 128 mg L-1against X. campestris pv. campestris. For isolate ACZ2-27, its crude extract showed stronger inhibitory effect with a lower MIC value of 64 mg L-1 against X. campestris pv. campestris. These three active isolates were identified as members of the genus Streptomyces based on their 16S rRNA gene sequences. Phylogenetic analysis based on the maximum likelihood algorithm showed that isolate ACZ2-27, ASC3-2 and ASC5-7P were closely related to Streptomyces misionensis NBRC 13063T (99.71%), Streptomyces cacaoi subsp. cacaoi NBRC 12748T (100%) and Streptomyces puniceus NBRC 12811T (100%), respectively. In addition, representative isolates from non-Streptomyces groups were identified by 16S rRNA gene sequence analysis. High similarities were found with members of the genera Actinomadura, Micromonospora and Nonomuraea. Our study provides evidence of actinomycetes associated with the black dwarf honey bee including members of rare genera. Antimicrobial potential of these insect associated Streptomyces was also demonstrated especially the antibacterial activity against phytopathogenic bacteria.

Deep-Sea Actinobacteria Mitigate Salinity Stress in Tomato Seedlings and Their Biosafety Testing

Soil salinity is an enormous problem affecting global agricultural productivity. Deep-sea actinobacteria are interesting due to their salt tolerance mechanisms. In the present study, we aim to determine the ability of deep-sea Dermacoccus (D. barathri MT2.1^T and D. profundi MT2.2^T) to promote tomato seedlings under 150 mM NaCl compared with the terrestrial strain D. nishinomiyaensis DSM20448^T. All strains exhibit in vitro plant growth-promoting traits of indole-3-acetic acid production, phosphate solubilization, and siderophore production. Tomato seedlings inoculated with D. barathri MT2.1^T showed higher growth parameters (shoot and root length, dry weight, and chlorophyll content) than non-inoculated tomato and the terrestrial strain under 150 mM NaCl. In addition, hydrogen peroxide (H₂O₂) in leaves of tomatoes inoculated with deep-sea Dermacoccus was lower than the control seedlings. This observation suggested that deep-sea Dermacoccus mitigated salt stress by reducing oxidative stress caused by hydrogen peroxide. D. barathri MT2.1^T showed no harmful effects on Caenorhabditis elegans, Daphnia magna, Eisenia foetida, and Escherichia coli MC4100 in biosafety tests. This evidence suggests that D. barathri MT2.1^T would be safe for use in the environment. Our results highlight the potential of deep-sea Dermacoccus as a plant growth promoter for tomatoes under salinity stress.

Antibacterial, Antifungal and Antibiofilm Activities of Silver Nanoparticles Supported by Crude Bioactive Metabolites of Bionanofactories Isolated from Lake Mariout

Lake Mariout is one of the polluted coastal marine ecosystems in Egypt which is considered to be a reservoir of serious effluents from different anthropogenic activities. Such selective pressure enforces indigenous microbial populations to acquire new advantageous themes. Thus, in this study, two Streptomyces strains were screened, from Lake Mariout's sediment for bioreduction of 5 mM AgNO3. Both strains were identified molecularly; their biochemical and physiological characterization revealed their ability to secrete bioactive metabolites with antagonistic activity. The cultural and incubation conditions influencing AgNPs productivity were evaluated. Subsequently, the physicochemical properties of the biofabricated AgNPs were pursued. UV-Vis spectroscopy detected surface plasmon resonance at range 458-422 nm. XRD indicated crystalline, pure, face-centered cubic AgNPs; EDX demonstrated strong silver signal at 3.5 keV. Besides, FT-IR and TGA analysis unveiled self-stabilization and functionalization of AgNPs by bioorganic molecules. However, electron microscopy micrographs depicted numerous uniform spherical AgNPs (1.17-13.3 nm). Potent bactericidal and fungicide activity were recorded by zone of inhibition assay at 50 μg/mL. Further, the antibiofilm activity was exerted in a dose-dependent manner. Moreover, the conjugation of AgNPs with the crude bioactive metabolites of both bionanofactories ameliorated the antimicrobial potency, reflecting a synergistic efficiency versus examined pathogens (free-living and biofilm).

Biological control: a novel strategy for the control of the plant parasitic nematodes

Plant parasitic nematodes (Root-knot nematodes, Meloidogyne spp.) are rounded worms, microscopic, and cause many agricultural economic losses. Their attacks have a direct impact on the productivity of cultivated crops by reducing their fruit quantity. Chemical control is widespread all over the world, but biological control is the most effective way to reduce the number of pests that infect crops, particularly by the use of microorganisms like fungi and bacteria. Biological control is rapidly evolving, and more products are being sold worldwide over time. They can be produced by fungi, bacteria, or actinomycetes that can destruct plant parasite nematodes and feed on them. Nematophagous microorganisms as the natural enemies of nematodes have a promising way of controlling nematodes. Some of them create net-like substances and traps to take the worms from outside and finally kill them. Other parasites serve as internal parasites in order to produce toxins and to produce virulence to kill nematodes. Comprehension of the molecular basis for microbial nematode interactions gives important insights into how successful biological nematode control agents can be created. We discuss recent advances in our understanding of nematodes and nematophagous microorganisms, with an emphasis on molecular mechanisms that infect nematodes with nematophagous microorganisms and on nematode safety from pathogenic attacks. Finally, we addressed numerous key areas for future research and development, including possible approaches to the application of our recent expertise in the development of successful biocontrol strategies.

Plants-nematodes-microbes crosstalk within soil: A trade-off among friends or foes

Plants interact with enormous biotic and abiotic components within ecosystem. For instance, microbes, insects, herbivores, animals, nematodes etc. In general, these interactions are studied independently with plants, that condenses only specific information about the interaction. However, the limitation to study the cross-interactions masks the collaborative role of organisms within ecosystem. Beneficial microbes are most prominent organisms that are needed to be studied due to their bidirectional nature towards plants. Fascinatingly, Plant-Parasitic Nematodes (PPNs) have been profoundly observed to cause mass destruction of agricultural crops worldwide. The huge demand for agriculture for present-day population requires optimization of production potential by curbing the damage caused by PPNs. Chemical nematicides combats their proliferation, but their extended usage has abruptly affected flora, fauna and human populations. Because of consistent pressing issues in regard to environment, the use of biocontrol agents are most favourable alternatives for managing agriculture. However, this association is somehow, tug of war, and understanding of plant-nematode-microbial relation would enable the agriculturists to monitor the overall development of plants along with limiting the use of agrochemicals. Soil microbes are contemporary bio-nematicides emerging in the market, that stimulates the plant growth and impedes PPNs populations. They form natural enemies and trap nematodes, henceforth, it is crucial to understand these interactions for ecological and biotechnological perspectives for commercial use. Moreover, acquiring the diversity of their relationship and molecular-based mechanisms, outlines their cascade of signaling events to serve as biotechnological ecosystem engineers. The omics based mechanisms encompassing hormone gene regulatory pathways and elicitors released by microbes are able to modulate pathogenesis-related (PR) genes within plants. This is achieved via Induced Systemic Resistance (ISR) or acquired systemic channels. Taking into account all these validations, the present review mainly advocates the relationship among microbes and nematodes in plants. It is believed that this review will boost zest and zeal within researchers to effectively understand the plant-nematodes-microbes relations and their ecological perspectives.

Antimicrobial Activities of Marine Sponge-Associated Bacteria

The misuse and overuse of antibiotics have led to the emergence of multidrug-resistant microorganisms, which decreases the chance of treating those infected with existing antibiotics. This resistance calls for the search of new antimicrobials from prolific producers of novel natural products including marine sponges. Many of the novel active compounds reported from sponges have originated from their microbial symbionts. Therefore, this study aims to screen for bioactive metabolites from bacteria isolated from sponges. Twelve sponge samples were collected from South Australian marine environments and grown on seven isolation media under four incubation conditions; a total of 1234 bacterial isolates were obtained. Of these, 169 bacteria were tested in media optimized for production of antimicrobial metabolites and screened against eleven human pathogens. Seventy bacteria were found to be active against at least one test bacterial or fungal pathogen, while 37% of the tested bacteria showed activity against Staphylococcus aureus including methicillin-resistant strains and antifungal activity was produced by 21% the isolates. A potential novel active compound was purified possessing inhibitory activity against S. aureus. Using 16S rRNA, the strain was identified as Streptomyces sp. Our study highlights that the marine sponges of South Australia are a rich source of abundant and diverse bacteria producing metabolites with antimicrobial activities against human pathogenic bacteria and fungi.

Isolation and Identification of Streptomyces spp. from Desert and Savanna Soils in Sudan

The purpose of this study was to investigate streptomycete populations in desert and savanna ecozones in Sudan and to identify species based on 16S rRNA gene sequences. A total of 49 different Streptomyces phenotypes (22 from sites representing the desert and semi-desert ecozone; 27 representing the savanna ecozone) have been included in the study. The isolates were characterized phenotypically and confirmed using 16S rRNA gene sequence analysis. The two ecozones showed both similarities and uniqueness in the types of isolates. The shared species were in cluster 1 (Streptomyces (S.) werraensis), cluster 2 (Streptomyces sp.), cluster 3 (S. griseomycini-like), and cluster 7 (S. rochei). The desert ecozone revealed unique species in cluster 9 (Streptomyces sp.) and cluster 10 (S. griseomycini). Whereas, the savanna ecozone revealed unique species in cluster 4 (Streptomyces sp.), cluster 5 (S. albogriseolus/ S. griseoincarnatus), cluster 6 (S. djakartensis), and cluster 8 (Streptomyces sp.). Streptomycetes are widely distributed in both desert and the savanna ecozones and many of these require full descriptions. Extending knowledge on Streptomyces communities and their dynamics in different ecological zones and their potential antibiotic production is needed.

Steptomyces fagopyri sp. nov., a novel actinomycete isolated from rhizospheric soil of Fagopyrum dibotrys

A novel actinomycete, designated strain QMT-28^T, was isolated from rhizosphere soil of Fagopyrum dibotrys collected from Shuangfeng, Hunan Province, PR China. Strain QMT-28^T grew well on International Streptomyces Project series media and formed well-developed, branched substrate hyphae and aerial mycelium that differentiated into loose spiral spore chains consisting of cylindrical spores with smooth surfaces. The diagnostic diamino acid was ll-diaminopimelic acid and the whole-cell sugars were galactose and glucose. The predominant fatty acids were C_18 : 1 cis9, summed feature 6 (C_18 : 2 cis 9,12/C_18 : 0 a) and C_16 : 0. The polar lipids included diphosphatidylglycerol, hydroxy phospatidylethanolamine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannosides, phospholipids of unknown structure containing glucosamine and several unidentified phospholipids. The major menaquinones were MK-9, MK-9(H₂), MK-9(H₄), MK-9(H₆) and MK-9(H₈). The genome size of strain QMT-28^T was about 8.7 Mbp with a G+C content of 71.2 mol%. Phylogenetic analysis showed that the novel strain was closely related to Streptomyces olivochromogenes DSM 40451^T (99.5 % similarity), Streptomyces mirabilis NBRC 13450^T (98.9 %), Streptomyces kanamyceticus NBRC 13414^T (98.9 %), Streptomyces kaempferi I37^T (98.9 %) and Streptomyces arcticus ZLN234^T (98.8 %). However, the average nucleotide identity values, the digital DNA-DNA hybridization values and the multilocus sequence analysis evolutionary distances between this strain and closely related strains showed that it belonged to a distinct species. In addition, these results were also supported by differences in the phenotypic characteristics between QMT-28^T and five closely related type strains. Consequently, strain QMT-28^T should represent a novel species of the genus Streptomyces, with the suggested name Streptomyces fagopyri sp. nov. The type strain is QMT-28^T (=CICC 24808^T=JCM 33796^T).

Current Utility of Plant Growth-Promoting Rhizobacteria as Biological Control Agents towards Plant-Parasitic Nematodes

Plant-parasitic nematodes (PPN) are among the most economically and ecologically damaging pests, causing severe losses of crop production worldwide. Chemical-based nematicides have been widely used, but these may have adverse effects on human health and the environment. Hence, biological control agents (BCAs) have become an alternative option for controlling PPN, since they are environmentally friendly and cost effective. Lately, a major effort has been made to evaluate the potential of a commercial grade strain of plant growth-promoting rhizobacteria (PGPR) as BCAs, because emerging evidence has shown that PGPR can reduce PPN in infested plants through direct and/or indirect antagonistic mechanisms. Direct antagonism occurs by predation, release of antinematicidal metabolites and semiochemicals, competition for nutrients, and niche exclusion. However, the results of direct antagonism may be inconsistent due to unknown endogenous and exogenous factors that may prevent PGPR from colonizing plant's roots. On the other hand, indirect antagonism may occur from the induced systemic resistance (ISR) that primes whole plants to better fight against various biotic and abiotic constraints, actuating faster and/or stronger defense responses (adaption), enhancing their promise as BCAs. Hence, this review will briefly revisit (i) two modes of PGPR in managing PPN, and (ii) the current working models and many benefits of ISR, in the aim of reassessing current progresses and future directions for isolating more effective BCAs and/or developing better PPN management strategy.

Marine Actinomycetes-Derived Secondary Metabolites Overcome TRAIL-Resistance via the Intrinsic Pathway through Downregulation of Survivin and XIAP

Resistance of cancer cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis represents the major hurdle to the clinical use of TRAIL or its derivatives. The discovery and development of lead compounds able to sensitize tumor cells to TRAIL-induced cell death is thus likely to overcome this limitation. We recently reported that marine actinomycetes’ crude extracts could restore TRAIL sensitivity of the MDA-MB-231 resistant triple negative breast cancer cell line. We demonstrate in this study, that purified secondary metabolites originating from distinct marine actinomycetes (sharkquinone (1), resistomycin (2), undecylprodigiosin (3), butylcyclopentylprodigiosin (4), elloxizanone A (5) and B (6), carboxyexfoliazone (7), and exfoliazone (8)), alone, and in a concentration-dependent manner, induce killing in both MDA-MB-231 and HCT116 cell lines. Combined with TRAIL, these compounds displayed additive to synergistic apoptotic activity in the Jurkat, HCT116 and MDA-MB-231 cell lines. Mechanistically, these secondary metabolites induced and enhanced procaspase-10, -8, -9 and -3 activation leading to an increase in PARP and lamin A/C cleavage. Apoptosis induced by these compounds was blocked by the pan-caspase inhibitor QvD, but not by a deficiency in caspase-8, FADD or TRAIL agonist receptors. Activation of the intrinsic pathway, on the other hand, is likely to explain both their ability to trigger cell death and to restore sensitivity to TRAIL, as it was evidenced that these compounds could induce the downregulation of XIAP and survivin. Our data further highlight that compounds derived from marine sources may lead to novel anti-cancer drug discovery.

Τhe Nematicidal Potential of Bioactive Streptomyces Strains Isolated from Greek Rhizosphere Soils Tested on Arabidopsis Plants of Varying Susceptibility to Meloidogyne spp

A total of 461 indigenous Streptomycetes strains recovered from various Greek rhizosphere habitats were tested for their bioactivity. All isolates were examined for their ability to suppress the growth of 12 specific target microorganisms. Twenty-six were found to exert antimicrobial activity and were screened for potential nematicidal action. S. monomycini ATHUBA 220, S. colombiensis ATHUBA 438, S. colombiensis ATHUBA 431, and S. youssoufensis ATHUBA 546 were proved to have a nematicidal effect and thus were further sequenced. Batch culture supernatants and solvent extracts were assessed for paralysis on Meloidogyne javanica and Meloidogyne incognita second-stage juveniles (J2). The solvent extracts of S. monomycini ATHUBA 220 and S. colombiensis ATHUBA 438 had the highest paralysis rates, so these Streptomycetes strains were further on tested for nematodes' biological cycle arrest on two Arabidopsis thaliana plants; the wild type (Col-0) and the katanin mutant fra2, which is susceptible to M. incognita. Interestingly, S. monomycini ATHUBA 220 and S. colombiensis ATHUBA 438 were able to negatively affect the M. incognita biological cycle in Col-0 and fra2 respectively, and increased growth in Col-0 upon M. incognita infection. However, they were ineffective against M. javanica. Fra2 plants were also proved susceptible to M. javanica infestation, with a reduced growth upon treatments with the Streptomyces strains. The nematicidal action and the plant-growth modulating abilities of the selected Streptomycetes strains are discussed.

Diving Into Reef Ecosystems for Land-Agriculture Solutions: Coral Microbiota Can Alleviate Salt Stress During Germination and Photosynthesis in Terrestrial Plants

From their chemical nature to their ecological interactions, coral reef ecosystems have a lot in common with highly productive terrestrial ecosystems. While plants are responsible for primary production in the terrestrial sphere, the photosynthetic endosymbionts of corals are the key producers in reef communities. As in plants, coral microbiota have been suggested to stimulate the growth and physiological performance of the photosynthetic endosymbionts that provide energy sources to the coral. Among them, actinobacteria are some of the most probable candidates. To explore the potential of coral actinobacteria as plant biostimulants, we have analyzed the activity of Salinispora strains isolated from the corals Porites lobata and Porites panamensis, which were identified as Salinispora arenicola by 16S rRNA sequencing. We evaluated the effects of this microorganism on the germination, plant growth, and photosynthetic response of wild tobacco (Nicotiana attenuata) under a saline regime. We identified protective activity of this actinobacteria on seed germination and photosynthetic performance under natural light conditions. Further insights into the possible mechanism showed an endophytic-like symbiosis between N. attenuata roots and S. arenicola and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity by S. arenicola. We discuss these findings in the context of relevant ecological and physiological responses and biotechnological potential. Overall, our results will contribute to the development of novel biotechnologies to cope with plant growth under saline stress. Our study highlights the importance of understanding marine ecological interactions for the development of novel, strategic, and sustainable agricultural solutions.

Mersaquinone, A New Tetracene Derivative from the Marine-Derived Streptomyces sp. EG1 Exhibiting Activity against Methicillin-Resistant Staphylococcus aureus (MRSA)

New antibiotics are desperately needed to overcome the societal challenges being encountered with methicillin-resistant Staphylococcus aureus (MRSA). In this study, a new tetracene derivative, named Mersaquinone (1), and the known Tetracenomycin D (2), Resistoflavin (3) and Resistomycin (4) have been isolated from the organic extract of the marine Streptomyces sp. EG1. The strain was isolated from a sediment sample collected from the North Coast of the Mediterranean Sea of Egypt. The chemical structure of Mersaquinone (1) was assigned based upon data from a diversity of spectroscopic techniques including HRESIMS, IR, 1D and 2D NMR measurements. Mersaquinone (1) showed antibacterial activity against methicillin-resistant Staphylococcus aureus with a minimum inhibitory concentration of 3.36 μg/mL.

Potential of Bioremediation and PGP Traits in Streptomyces as Strategies for Bio-Reclamation of Salt-Affected Soils for Agriculture

Environmental limitations influence food production and distribution, adding up to global problems like world hunger. Conditions caused by climate change require global efforts to be improved, but others like soil degradation demand local management. For many years, saline soils were not a problem; indeed, natural salinity shaped different biomes around the world. However, overall saline soils present adverse conditions for plant growth, which then translate into limitations for agriculture. Shortage on the surface of productive land, either due to depletion of arable land or to soil degradation, represents a threat to the growing worldwide population. Hence, the need to use degraded land leads scientists to think of recovery alternatives. In the case of salt-affected soils (naturally occurring or human-made), which are traditionally washed or amended with calcium salts, bio-reclamation via microbiome presents itself as an innovative and environmentally friendly option. Due to their low pathogenicity, endurance to adverse environmental conditions, and production of a wide variety of secondary metabolic compounds, members of the genus Streptomyces are good candidates for bio-reclamation of salt-affected soils. Thus, plant growth promotion and soil bioremediation strategies combine to overcome biotic and abiotic stressors, providing green management options for agriculture in the near future.

Phyllosphere Colonization by a Soil Streptomyces sp. Promotes Plant Defense Responses Against Fungal Infection

Streptomycetes are soil-dwelling, filamentous actinobacteria and represent a prominent bacterial clade inside the plant root microbiota. The ability of streptomycetes to produce a broad spectrum of antifungal metabolites suggests that these bacteria could be used to manage plant diseases. Here, we describe the identification of a soil Streptomyces strain named AgN23 which strongly activates a large array of defense responses when applied on Arabidopsis thaliana leaves. AgN23 increased the biosynthesis of salicylic acid, leading to the development of salicylic acid induction deficient 2 (SID2)-dependent necrotic lesions. Size exclusion fractionation of plant elicitors secreted by AgN23 showed that these signals are tethered into high molecular weight complexes. AgN23 mycelium was able to colonize the leaf surface, leading to plant resistance against Alternaria brassicicola infection in wild-type Arabidopsis plants. AgN23-induced resistance was found partially compromised in salicylate, jasmonate, and ethylene mutants. Our data show that Streptomyces soil bacteria can develop at the surface of plant leaves to induce defense responses and protection against foliar fungal pathogens, extending their potential use to manage plant diseases.

Marine bacteria as source of antimicrobial compounds

The marine environment encompasses a huge biological diversity and can be considered as an underexplored location for prospecting bioactive molecules. In this review, the current state of art about antimicrobial molecules from marine bacteria has been summarized considering the main phylum and sources evolved in a marine environment. Considering the last two decades, we have found as most studied group of bacteria producers of substances with antimicrobial activity is the Firmicutes phylum, in particular strains of the Bacillus genus. The reason for that can be attributed to the difficult cultivation of typical Actinobacteria from a marine sediment, whose members are the major producers of antimicrobial substances in land environments. However, a reversed trend has been observed in recent years with an increasing number of reports settling on Actinobacteria. Great diversity of chemical structures have been identified, such as fijimicyns and lynamicyns from Actinomycetes and macrolactins produced by Bacillus.

From Isolation of Phosphate Solubilizing Microbes to Their Formulation and Use as Biofertilizers: Status and Needs

The production of biofertilizers at industrial level is a bottleneck because bacterial strains are generally developed and managed by research laboratories and not by production units. A seamless transition from laboratory to field application is, therefore necessary. This review provides an overview of the constraints that limiting the application or the implementation of Actinobacteria based biofertilizers especially in agricultural field and suggests solutions to overcome some of these limits. General processes of making and controlling the quality of the inoculum are briefly described. In addition, the paper underlines the opportunity of biofertilizers alone or in combination with chemical fertilizers. This review also, highlights the latest studies (until June 2019) and focuses on P-solubilization microorganisms mainly Actinobacteria. The biotechnology of these bacteria is a glimmer of hope for rock phosphate (RP) bioformulation. Since direct application of RP fertilizer is not always agronomically effective due to its sparse solubility.

Transcriptomes of the interaction between Fusarium verticillioides and a Streptomyces strain reveal the fungal defense strategy under the pressure of a potential biocontrol agent

The actinobacteria Streptomyces sp. AV05 appears to be a potential biocontrol agent (BCA) against mycotoxigenic fungi. It was found to significantly inhibit F. verticillioides growth and mycotoxin production during their co-cultivation. F. verticillioides growth was durably affected while the decrease of the toxin production levels was reversible, suggesting different BCA actions. The study of both transcriptomes brought useful information on the microbial interaction. RNA-seq data indicated that the dual interaction modified genetic expression of both microorganisms as 18.5 % of the genes were differentially expressed for the fungus against 3.8 % for the actinobacteria. Fungal differentially expressed genes (DEGs) were equally up and down regulated while bacterial ones were mainly upregulated. We especially focused the analysis of DEGs on fungal defense reaction to bacterial attack. For example, if this potential BCA implements a strategy of antibiosis with the over expression of 'siderophore-interacting protein' linked to the production of bacteriocins, the fungus in a state of stress is able to adapt its metabolism by up-regulation of amidase. It could correspond to the induction of resistance gene clusters and suggest a detoxification process. Moreover fumonisins-related pathway appears underexpressed in the presence of Streptomyces that explain the reduction of fumonisin accumulation observed.

The effect of combined application of Streptomyces rubrogriseus HDZ-9-47 with soil biofumigation on soil microbial and nematode communities

Meloidogyne incognita causes significant damage to many different crops. Previous studies showed that Streptomyces rubrogriseus HDZ-9-47 is a promising biocontrol agent. Combining it with biofumigation improved its efficacy against M. incognita. In the present study, the reason for the improved efficacy of the combination was investigated by analyzing its impact on both the soil microbial and the nematode communities in the field. The results showed that the combined application reduced root galls by 41% and its control efficacy was greater than each treatment alone. Cultivation-based analyses showed that the combination treatment affected the soil microbial community. Actinomycetes and bacterial densities were negatively correlated with the root knot score. In contrast, the fungal densities were positively correlated with the root knot score. Denaturing gradient gel electrophoresis (DGGE) results showed that the combination of S. rubrogriseus HDZ-9-47 and biofumigation enriched beneficial microbes and reduced certain soil-borne fungal phytopathogens, thereby enhancing the efficacies of both S. rubrogriseus HDZ-9-47 and biofumigation against M. incognita. And HDZ-9-47 could colonize in soil. The total abundance of nematode and plant parasites, the ratio of soil fungivore nematode to fungivore plus bacterivore nematode, and the nematode diversity indices all decreased with the combination treatment. Overall, the results of this study demonstrate that combined application of HDZ-9-47 with biofumigation was a useful and effective approach to suppress M. incognita by manipulating soil microbial communities in field.

Abscisic acid deficiency caused by phytoene desaturase silencing is associated with dwarfing syndrome in citrus

In citrus, abscisic acid-deficiency was associated with a dwarfing phenotype, slow growth, small leaves, decreased fresh weight, and faster water loss. ABA supplementation reversed the dwarfing phenotype and enhanced growth. Abscisic acid (ABA) is a ubiquitously distributed phytohormone, which is almost produced by all living kingdoms. In plants, ABA plays pleiotropic physiological roles in growth, development, and stress responses. We explored the hidden relationship between ABA deficiency, and citrus dwarfing. We used targeted-HPLC, targeted-GC-MS, molecular genetics, immunoassays, and gene expression techniques to investigate the effects of the silencing of phytoene desaturase (PDS) gene on the ABA-biosynthetic pathway, endogenous ABA content, and other phytohormones. Silencing of PDS directly suppressed the carotenoids compounds involved in ABA biosynthesis, altered phytohormonal profile, and caused phytoene accumulation and ABA deficiency. The reduction of ABA presumably due to the limited availability of its precursor, zeaxanthin. The ABA-deficient citrus cuttings displayed photobleaching, a dwarf phenotype with impaired growth characteristics that included slow growth, small leaves, decreased fresh weight, and faster water loss. ABA supplementation enhanced the growth and reversed the dwarfing phenotype of the ABA-deficient cuttings. Our data demonstrate that ABA-deficiency may lead to dwarfing phenotype and impaired growth in citrus cuttings. The negative influence of ABA-deficiency on growth rate is the result of altered water relations. Addition of ABA to the CTV-tPDS roots restored shoot growth and reversed the dwarfing phenotype.

Comparative Genomics of Marine Sponge-Derived Streptomyces spp. Isolates SM17 and SM18 With Their Closest Terrestrial Relatives Provides Novel Insights Into Environmental Niche Adaptations and Secondary Metabolite Biosynthesis Potential

The emergence of antibiotic resistant microorganisms has led to an increased need for the discovery and development of novel antimicrobial compounds. Frequent rediscovery of the same natural products (NPs) continues to decrease the likelihood of the discovery of new compounds from soil bacteria. Thus, efforts have shifted toward investigating microorganisms and their secondary metabolite biosynthesis potential, from diverse niche environments, such as those isolated from marine sponges. Here we investigated at the genomic level two Streptomyces spp. strains, namely SM17 and SM18, isolated from the marine sponge Haliclona simulans, with previously reported antimicrobial activity against clinically relevant pathogens; using single molecule real-time (SMRT) sequencing. We performed a series of comparative genomic analyses on SM17 and SM18 with their closest terrestrial relatives, namely S. albus J1074 and S. pratensis ATCC 33331 respectively; in an effort to provide further insights into potential environmental niche adaptations (ENAs) of marine sponge-associated Streptomyces, and on how these adaptations might be linked to their secondary metabolite biosynthesis potential. Prediction of secondary metabolite biosynthetic gene clusters (smBGCs) indicated that, even though the marine isolates are closely related to their terrestrial counterparts at a genomic level; they potentially produce different compounds. SM17 and SM18 displayed a better ability to grow in high salinity medium when compared to their terrestrial counterparts, and further analysis of their genomes indicated that they possess a pool of 29 potential ENA genes that are absent in S. albus J1074 and S. pratensis ATCC 33331. This ENA gene pool included functional categories of genes that are likely to be related to niche adaptations and which could be grouped based on potential biological functions such as osmotic stress, defense; transcriptional regulation; symbiotic interactions; antimicrobial compound production and resistance; ABC transporters; together with horizontal gene transfer and defense-related features.

Ecological Strategies Behind the Selection of Cultivable Actinomycete Strains from the Yucatan Peninsula for the Discovery of Secondary Metabolites with Antibiotic Activity

The quest for novel natural products has recently focused on the marine environment as a source for novel microorganisms. Although isolation of marine-derived actinomycete strains is now common, understanding their distribution in the oceans and their adaptation to this environment can be helpful in the selection of isolates for further novel secondary metabolite discovery. This study explores the taxonomic diversity of marine-derived actinomycetes from distinct environments in the coastal areas of the Yucatan Peninsula and their adaptation to the marine environment as a first step towards novel natural product discovery. The use of simple ecological principles, for example, phylogenetic relatedness to previously characterized actinomycetes or seawater requirements for growth, to recognize isolates with adaptations to the ocean in an effort to select for marine-derived actinomycete to be used for further chemical studies. Marine microbial environments are an important source of novel bioactive natural products and, together with methods such as genome mining for detection of strains with biotechnological potential, ecological strategies can bring useful insights in the selection and identification of marine-derived actinomycetes for novel natural product discovery.

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.

Actinobacteria Isolated From Laminaria ochroleuca: A Source of New Bioactive Compounds

Nature is the major reservoir of biologically active molecules. The urgent need of finding novel molecules for pharmaceutical application is prompting the research of underexplored environments, such as marine ecosystems. Here, we investigated cultivable actinobacteria associated with the macroalgae Laminaria ochroleuca and assessed their potential to produce compounds with antimicrobial or anticancer activities. A specimen of L. ochroleuca was collected in a rocky shore in northern Portugal, and fragments of tissues from different parts of the macroalgae (holdfast, stipe, and blades) were surface sterilized and plated in three culture media selective for actinobacteria. A total of 90 actinobacterial strains were isolated, most of which affiliated with the genus Streptomyces. Isolates associated with the genera Isoptericola, Rhodococcus, Nonomuraeae, Nocardiopsis, Microbispora, and Microbacterium were also obtained. Organic extracts from the isolates were tested for their antimicrobial activity using the agar-based disk diffusion method, followed by determination of minimum inhibitory concentration (MIC) values. Forty-five isolates inhibited the growth of Candida albicans and/or Staphylococcus aureus, with MIC values ranging from <0.5 to 1000 μg mL⁻¹. The actinobacterial isolates were also tested for their anticancer potential on two human cancer cell lines. Twenty-eight extracts affected the viability of at least one human cancer cell line (breast carcinoma T-47D and neuroblastoma SH-SY5Y) and non-carcinogenic endothelial cell line (hCMEC/D3). Seven extracts affected the viability of cancer cells only. This study revealed that L. ochroleuca is a rich source of actinobacteria with promising antimicrobial and anticancer activities and suggests that macroalgae may be a valuable source of actinobacteria and, consequently, of new molecules with biotechnological importance.