Endophytic Actinobacteria Research Articles

Plant growth-promoting of olive and walnut actinobacteria: isolation, screening PGP traits, antifungal activities, identification, and hydroponic production of wheat

ABSTRACT Bacteria are among the most frequently studied microorganisms in plant growth-promoting traits and fighting against different pathogens. Actinobacteria are prokaryotic organisms that produce mycelium, spores, and can form various secondary metabolites, especially antibiotics. In our study, free-living and endophytic Actinobacteria were isolated from rhizosphere soils and plant parts of olive (Olea europaea L.) and walnut (Juglans regia L.) trees, which are commercially essential agricultural products for Turkey. The study aimed to explore the plant growth-promoting activities of these Actinobacteria as biological fertilizers. Some of the properties of purified Actinobacteria that regulate the plant growth-promoting (PGP) traits; phosphate solubilization, indole-3-acetic acid, siderophore, ammonia, protease, beta-galactosidase, chitinase production, and antagonistic activities against various plant-pathogen fungi were investigated. As a result, 422 Actinobacteria were isolated, and 88 Actinobacteria determined to be possible plant bio-fertilizers were identified as Streptomyces spp. (70), Amycolatopsis spp. (12), Micromonospora spp. (four) and Nocardiopsis spp. (two) after the sequencing of their 16S rRNA genes. Moreover, four Streptomyces spp. and two Amycolatopsis spp. were used in hydroponic germination of wheat seeds (Triticum aestivum L.), and plant growth in terms of root and stem parts increased.

Streptomyces spinosus sp. nov. and Streptomyces shenzhenensis subsp. oryzicola subsp. nov. endophytic actinobacteria isolated from Jasmine rice and their genome mining for potential as antibiotic producers and plant growth promoters.

Two endophytic actinobacteria, strains SBTS01T and W18L9T, were isolated from leaf sheath and leaf tissue, respectively, of Jasmine rice (Oryza sativa KDML 105) grown in a rice paddy field in Roi EtProvince, Thailand. A polyphasic taxonomic study showed that both strains belong to the genus Streptomyces; they are aerobic, forming well-developed substrate mycelia and aerial mycelia with long chains of spores. Strain SBTS01T shares high 16S rRNA gene sequence similarity with Streptomyces rochei NRRL B-2410T (99.0%) and Streptomyces naganishii NRRL ISP-5282T (99.0%). Strain W18L9T shares high 16S rRNA gene sequence similarity with Streptomyces shenzhenensis DSM 42034T (99.7%). The genotypic and phenotypic properties of strains SBTS01T and W18L9T distinguish these two strains from the closely related species with validly published names. The genome analysis showed the dDDH, ANIb and ANIm values of the draft genome between strain SBTS01T and its close neighbour in the phylogenomic tree, Streptomyces corchorusii DSM 40340T to be 54.1, 92.6, and 94.3%, respectively; similarly for strain W18L9T and the closely related species S. shenzhenensis DSM 42034T values were 72.5, 95.1 and 97.0%. The name proposed for the new species represented by the type strain SBTS01T is Streptomyces spinosus (= NRRL B-65636T = TBRC 15052T). The name proposed for the novel subspecies of strain W18L9T is Streptomyces shenzhenensis subsp. oryzicola (= NRRL B-65635T = TBRC 15051T). Recognition of this subspecies also permits the description of Streptomyces shenzhenensis subsp. shenzhenensis. Strains SBTS01T and W18L9T can produce antibiotic against rice and human pathogens and showed plant growth promoting properties such as production of indole acetic acid, cytokinin, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, siderophores and cellulase. Genomic data mining of these two strains confirmed their potential as antibiotic producers and plant growth promoters. Their genomes contain multiple biosynthetic gene clusters including those for terpene, type 1, 2 and 3 polyketide synthase, Non-ribosomal peptide synthetase and lanthipeptides. Genes encoding plant growth promoting traits such; nitrogen fixation, ACC deaminase, siderophore production and stress-related adaption may have ecological significance.

Synergistic Plant-Microbe Interactions between Endophytic Actinobacteria and Their Role in Plant Growth Promotion and Biological Control of Cotton under Salt Stress.

Bacterial endophytes are well-acknowledged inoculants to promote plant growth and enhance their resistance toward various pathogens and environmental stresses. In the present study, 71 endophytic strains associated with the medicinal plant Thymus roseus were screened for their plant growth promotion (PGP), and the applicability of potent strains as bioinoculant has been evaluated. Regarding PGP traits, the percentage of strains were positive for the siderophore production (84%), auxin synthesis (69%), diazotrophs (76%), phosphate solubilization (79%), and production of lytic enzymes (i.e., cellulase (64%), lipase (62%), protease (61%), chitinase (34%), and displayed antagonistic activity against Verticillium dahliae (74%) in vitro. The inoculation of strain XIEG05 and XIEG12 enhanced plant tolerance to salt stress significantly (p < 0.05) through the promotion of shoot, root development, and reduced the activities of antioxidant enzymes (SOD, POD, and CAT), compared with uninoculated controls in vivo. Furthermore, inoculation of strain XIEG57 was capable of reducing cotton disease incidence (DI) symptoms caused by V. dahliae at all tested salt concentrations. The GC-MS analysis showed that many compounds are known to have antimicrobial and antifungal activity. Our findings provide valuable information for applying strains XIEG05 and XIEG12 as bioinoculant fertilizers and biological control agent of cotton under saline soil conditions.

Bioinformatic comparison of three Embleya species and description of steffimycins production by Embleya sp. NF3.

The Embleya genus is a new member of the Streptomycetaceae family formed by only two species isolated from soil (Embleya scabrispora and Embleya hyalina). Strain NF3 is an endophytic actinobacterium obtained from the medicinal tree Amphipterygium adstringens. By 16S rRNA gene analysis, NF3 strain was identified as Embleya sp., closely related to E. hyalina. In our interest to deep into the NF3 strain features, a bioinformatic study was performed on the Embleya genus based on their genome information to produce secondary metabolites. A comparative analysis of the biosynthetic gene clusters (BGCs) of NF3 with the two released Embleya genomes revealed that NF3 has 49 BGCs, E. scabrispora DSM41855 has 50 BGCs, and E. hyalina NBRC13850 has 46 BGCs. Although bearing similar cluster numbers, the three strains shared only 25% of the BGCs information. NF3 encoded the nybomycin cluster detected in E. hyalina NBRC13850 and lacked the hitachimycin cluster present in E. scabrispora DSM41855. On the contrary, strain NF3 contained a cluster for the anthracycline steffimycin, neither encoded by E. hyalina NBRC13850 nor by E. scabrispora DSM41855. Our results and previous characterization studies supported strain NF3 as a new member of the genus Embleya. The chemical analysis of the steffimycins produced by strain NF3 showed the production of eight compounds of the steffimycins and steffimycinone families. Four of these molecules have already been described: steffimycin B, steffimycin C, 8-demethoxy-10-deoxysteffimycinone, and 7-deoxiesteffimycinone, and four are new natural products: 8-demethoxysteffimycin B, 8-demethoxy-10-deoxysteffimycin B, 7-deoxy-8-demethoxysteffimycinone, and 7-deoxy-10-deoxysteffimycinone. With this information, we proposed an alternative pathway to produce StefB. Among steffimycins, StefB was the main compound produced by this strain (29.8%) and showed the best cytotoxic activity. KEY POINTS: • The Embleya genus and its biosynthetic potential • An alternative biosynthetic pathway for steffimycins biosynthesis • Four new natural products of the steffimycin family.

Morphological Characterization and Antioxidant Activity of Actinobacteria from Xylocarpus granatum Growing in Mangrove Habitat

Xylocarpus granatum produces various bioactive compounds with diverse biological activities, one of them as an antioxidant. Endophytic actinobacteria can also produce bioactive compounds. This study aimed to explore the existence of the endophytic actinobacteria of X. granatum fruit and determine its antioxidant activity. The research method was carried out by isolating the endophytic actinobacteria from the fruit using selective media Humic Acid (HV). Furthermore, characterizing the obtained isolates using four different media, namely YSA, ISP2, ISP3, and ISP4, measured antioxidant activity for actinobacterial supernatants and actinobacterial ethyl acetate extracts using the DPPH method. The results showed that from X. granatum, 15 isolates of endophytic actinobacteria were obtained from fruit, seeds, and leaves. Endophytic actinobacteria isolates from X. granatum showed different colors of aerial mycelium, substrate mycelium, and spore chain type. XGF11, XGF12, and XGF4 isolates produced high antioxidant activity of the supernatant; 57.30%, 49.77%, and 41.90% inhibition, respectively. The antioxidant capacity of XGF12 ethyl acetate extract was 501.60 μg AEAC/mg extract and 465.47 μg AEAC/mg extract for XGF11 ethyl acetate extract. Based on 16S rRNA gene analysis, isolates XGF12 and XGF11 showed similarities with Streptomyces xylanilyticus, and isolated XGF4 showed similarities with Brevibacterium sediminis.

Nocardioides mangrovi sp. nov., a novel endophytic actinobacterium isolated from root of Kandelia candel.

A novel species of endophytic actinobacterium, designated strain GBK3QG-3T, was isolated from surface-sterilized root of Kandelia candel collected from Beilun Estuary, Guangxi Zhuang Autonomous Region, PR China. Cells of strain GBK3QG-3T were Gram-stain-positive, aerobic, non-spore-forming and rod-shaped. Growth of GBK3QG-3T was observed at 10-40 °C (optimum, 30 °C), pH 5.0-9.0 (optimum, pH 7.0) and in the presence of 0-3 % (w/v) NaCl (optimum, 0 %). The G+C content of genomic DNA was determined to be 72.2 mol%. On the basis of 16S rRNA gene sequence analysis, strain GBK3QG-3T was most related to the type strain of Nocardioides agrisoli CCTCC AB 2017058T (97.7 % 16S rRNA gene sequence similarity), followed by Nocardioides ginkgobilobae SYP-A7303T (97.0 %) and Nocardioides aquiterrae GW-9T (96.9 %). Average nucleotide identity and digital DNA-DNA hybridization values between strain GBK3QG-3T and some strains of the genus Nocardioides with publicly available genomes were below 84.3 and 30.0 %, respectively. The cell-wall peptidoglycan contained ll-diaminopimelic acid. The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, an unknown phospholipid and an unknown lipid. The major menaquinone was identified as MK-8(H4), and the major fatty acids were identified as iso-C16 : 0, iso-C17 : 0 and anteiso-C17 : 0. Based on evidence collected from the phenotypic, genotypic and phylogenetic analyses, we propose a novel species named Nocardioides mangrovi sp. nov. The type strain is GBK3QG-3T (=CGMCC 4.7708T=JCM 34553T).

Dynamics of Bacterial Root Endophytes of Malus domestica Plants Grown in Field Soils Affected by Apple Replant Disease.

Apple replant disease (ARD) is a worldwide problem for tree nurseries and orchards leading to reduced plant growth and fruit quality. The etiology of this complex phenomenon is poorly understood, but shifts of the bulk soil and rhizosphere microbiome seem to play an important role. Since roots are colonized by microbes from the rhizosphere, studies of the endophytic microbiome in relation to ARD are meaningful. In this study, culture-independent and culture-dependent approaches were used in order to unravel the endophytic root microbiome of apple plants 3, 7, and 12 months after planting in ARD-affected soil and ARD-unaffected control soil at two different field sites. Next to a high diversity of Pseudomonas in roots from all soils, molecular barcoding approaches revealed an increase in relative abundance of endophytic Actinobacteria over time in plants grown in ARD and control plots. Furthermore, several amplicon sequence variants (ASVs) linked to Streptomyces, which had been shown in a previous greenhouse ARD biotest to be negatively correlated to shoot length and fresh mass, were also detected in roots from both field sites. Especially in roots of apple plants from control soil, these Streptomyces ASVs increased in their relative abundance over time. The isolation of 150 bacterial strains in the culture-dependent approach revealed a high diversity of members of the genus Pseudomonas, confirming the data of the molecular barcoding approach. However, only partial overlaps were found between the two approaches, underlining the importance of combining these methods in order to better understand this complex disease and develop possible countermeasures. Overall, this study suggests a key role of Streptomyces in the etiology of ARD in the field.

Synergistic Plant-microbe Interactions between Endophytic Actinobacteria and Their Role in Plant Growth Promotion and Biological Control of Cotton under salt stress

Synergistic Plant-microbe Interactions between Endophytic Actinobacteria and Their Role in Plant Growth Promotion and Biological Control of Cotton under salt stress

Endophytic Streptomyces isolated from Ocimum tenuiflorum and Catharanthus roseus and its efficacy test to develop antibacterial fabric for wound caring

In this research work, endophytic Streptomyces sp. was isolated from Ocimum tenuiflorum (OT), Catharanthus roseus (CR), and Plectranthus barbatus (PB). Eighty percentage of medicines discovered from natural sources are from Streptomyces sp. diabetic mellitus is considered as the seventh cause for mortality and among diabetic patients, of which diabetic foot ulcer (DFU) is a major concern. Endophytic actinobacteria isolated from medicinal plants are screened for its antibacterial agent production. Desized good quality cotton fiber was finished with isolated endophytic actinobacteria metabolite using the dip-dry method and in succeeding stages AATCC90 and AATCC 147 (American Association of Textile Chemist and Colorist) methods were used for screening against Sathaphylococcus aureus and Escherichia coli. Three different isolates namely OT, CR, and PB were selected based on its efficacy and identified as Streptomyces sp. using the biochemical, morphological and molecular technique. Wash durability test confirmed that the active agent was retained on the fabric surface up to ten cycles without binder and scanning electron microscope images showed that there was no pilling or damage on the finished fabric. Solvent extraction, thin layer and column chromatography, EDAX, UV–Visible spectroscopy were performed for purification and compound identification. Streptomyces cellulosae deposited in the Genbank and obtained the number.

Revealing the underlying mechanisms mediated by endophytic actinobacteria to enhance the rhizobia - chickpea (Cicer arietinum L.) symbiosis

PurposeThe effects of endophytic actinobacterial strains, Microbispora sp. CP56, Actinomadura sp. CP84B, Streptomyces spp. CP200B and CP21A, on the chickpea-Mesorhizobium symbiosis, were investigated in planta, with the aim of revealing the underlying mechanisms of action.MethodsThe actinobacterial endophytes were co-inoculated with Mesorhizobium ciceri onto chickpea seedlings to study the effect on plant growth parameters, nodulation development and grain yield. The role of actinobacterial exudates on rhizobial growth was investigated, as was the role of root exudates of actinobacteria-colonized plants on the expression of rhizobial nod factors and biofilm formation. Changes in expression of plant flavonoids and bacterial N-fixation genes resulting from actinobacterial co-inoculation were assessed using qPCR.ResultsApplication of actinobacterial endophytes, together with M. ciceri, showed growth promotion of chickpea with an increase in root nodule number and weight. Enhanced nodulation was accompanied by increases in total plant nitrogen, larger total plant weight and a 2–3-fold increase in grain yield. Factors associated with this tripartite symbiosis are promotion of rhizobial growth, earlier nodule formation, increased secondary root formation, up-regulated expression of genes related to flavonoid synthesis and nif genes. In addition, exudates of chickpea roots colonised with actinobacteria increased nodulation-related biological processes - rhizobial chemotaxis, biofilm formation and nod gene expression.ConclusionThese endophytic actinobacteria positively affect many aspects of the chickpea-Mesorhizobium symbiosis resulting in increases in grain yield. Similar improvements recorded in chickpea growing in potted field soils, shows the potential to enhance chickpea production in the field.

English

Given that synthetic antioxidants are currently in use and have been demonstrated to have known negative side effects, it is important to look for natural antioxidant sources. Endophytic actinobacteria, especially those associated with medicinal plants, are one understudied source. The goal of this study was to investigate whether the secondary metabolites of endophytic actinobacteria isolated from Harpagophytum procumbens, commonly known as the Devil&#39;s claw, have antioxidant and DNA damage protective properties. H. procumbens secondary tubers were collected from the Khomas and Hardap regions of Namibia, yielding a total of 23 isolated actinobacteria. The identities of the actinobacterial isolates were determined by sequencing the 16S rRNA gene. This revealed 6 families affiliated to 7 genera that included the dominant Streptomyces genus (57%) whereas rare genera (Agromyces, Nocardiopsis, Rubrobacter, Patulibacter, Rhodococcus, Curtobacterium) and 2 unidentified strains accounted for 43%. The antioxidant results revealed that the ethyl acetate extracts of Streptomyces species strain A36, had the highest phenolic content of 1.993 &plusmn; 0.004 and total antioxidant activity of 0.258 &plusmn; 0.001. Meanwhile, extracts from Streptomyces spp. strain B12, had the highest radical scavenging activity of 95% at 0.1 mg&bull;mL-1 while B43, an unidentified actinobacterium, had the highest total reducing power of 0.849 &plusmn; 0.003. In addition, 61% of extracts showed the ability to protect DNA from damage when exposed to hydrogen peroxide. None of the samples contained terpenoids, while 13 (72%) contain alkaloids, 17 (94%) contain phenols and 8 (44%) contained flavonoids. The present study concludes that endophytic actinobacteria associated with H. procumbens are a potential source of bioactive compounds with pharmacological properties. Key words: Harpagophytum procumbens, actinobacteria, antioxidants, DNA damage protection, endophytes, bioactive compounds

Study the stability of chickpea endophytic actinobacteria species on broth and agar culture media

The actinobacteria acts by colonising plant roots and increases the nitrogen fixation capacity of the rhizobial partner. In this study, endophytic actinobacterial strains CP21A2, CP56, CP84B, and CP200B isolated from chickpea were evaluated for the sporulation rate in solid and liquid media. These resultant spores were evaluated for their stability at different pH and temperature. Calcium carbonate in the liquid broth and MS medium in solid agar media can be used to increase the sporulation rate of the actinobacteria. Additionally, we found out that almost all spore-producing strains were stable at 70°C 4 minutes but temperatures greater than that were lethal to the spores obtained from both types of media. In addition, the tested spore strains were more sensitive and prone to lysis at alkaline pH rather than acidic. Furthermore, our study suggested that CP56 spores obtained from liquid media and CP84B from solid media can be the best performers in promoting the overall growth of plants and nodules. However, further detailed investigations need to be carried out in order to determine their influence on the growth and development of legume plants which can be useful to increase the yield in the agricultural industry.

Characterization of root-endophytic actinobacteria from cactus (Opuntia ficus-indica) for plant growth promoting traits.

The present study is the first report of isolation and characterization of endophytic actinobacteria from cactus (Opuntia ficus-indica). A total of 179 morphologically distinct endophytic actinobacterial isolates were purified from the roots of two different genetic accessions of cactus. All these isolates were screened for their plant growth promotion traits, namely, growth on N-free medium, P-solubilization, siderophore production, ACC deaminase activity and auxin production. A majority of the endophytic actinobacterial isolates (85%) exhibited their potential for plant growth promotion under in vitro conditions. Ten among the isolates were selected based on their multi-PGP traits and were identified as Streptomyces sp. following the 16S rRNA gene sequencing and phylogenetic analysis. Plant growth promotion potential of these selected endophytic Streptomyces was studied in wheat seedlings. All these selected isolates significantly enhanced the growth parameters such as seedling length and rootlets number compared to the uninoculated control. The wheat seeds inoculated with Streptomyces tuirus VL-70-IX exhibited maximum number of rootlets (6.33) compared to uninoculated control (3.67). The inoculation of endophytic actinobacteria Streptomyces levis VL-70-XII caused maximum seedling length (20.53cm) and root length (8.26cm), while the inoculation of S. radiopugnans HV-VIII resulted in highest shoot length (12.33cm). These endophytic actinobacteria isolated from the roots of cactus accessions showed potential PGP traits. This work lays foundation for characterization and selection of endophytic actinobacteria from the under-exploited, drought tolerant species such as cactus with potential cross-compatibility for the improvement of plant growth of field crops especially under abiotic stress conditions.

Nocardia coffeae sp. nov., an endophytic actinobacterium isolated from the root of Coffea arabica (L.).

The polyphasic taxonomic study of a novel endophytic actinobacterium strain (CA2R105T) was carried out. The strain formed fragmented substrate mycelium and showed chemotaxonomic properties typical of members of the genus Nocardia, i.e. the presence of mycolic acid and MK-8 (H4ω-cycl) in its cells. Strain CA2R105T exhibited the highest 16S rRNA gene sequence similarity to Nocardia jiangxiensis NBRC 101359T (99.2%). The genome-based taxonomic analysis revealed low average nucleotide identity-blast and digital DNA-DNA hybridization values (<93.7, and <65.2%, respectively) to its closest relative. Moreover, many different phenotypic characteristics were observed between strain CA2R105T and all related Nocardia-type strains. This taxonomic evidence suggested that strain CA2R105T should be judged as representing a novel species of the genus Nocardia and the name, Nocardia coffeae sp. nov. is proposed. The type strain is CA2R105T (=TBRC 11247T=NBRC 114292T).

Janibacter endophyticus sp. nov., an Endophytic Actinobacterium Isolated from the Root of Paris polyphylla Smith var. Yunnanensis.

A novel endophytic actinobacterium, designated as strain YIM B02568T, was isolated from the root of Paris polyphylla Smith var. Yunnanensis obtained from Yunnan Province, southwest China. Strain YIM B02568T was characterized using a polyphasic approach. Phylogenetic analysis indicated that this isolate belonged to the genus Janibacter. The 16S rRNA gene sequence similarity values of strain YIM B02568T to the type strains of members of this genus ranged from 95.8 to 98.6%. However, overall genome relatedness indices were significantly lower than the widely accepted species-defined threshold. The cell wall of strain YIM B02568T contained meso-diaminopimelic acid. The major menaquinone was MK-8(H4). The main polar lipids were phosphatidylglycerol, diphosphatidylglycerol, and phosphatidylinositol. The major cellular fatty acids were comprised of iso-C16:0 and C18:1 ω9c. The DNA G + C content was 71.6mol%. Based on the data from the polyphasic studies, we propose that strain YIM B02568T represents a novel species within the genus Janibacter, Janibacter endophyticus sp. nov. The type strain is YIM B02568T (= JCM 34639T = CGMCC 1.18658T).

Isolation, Characterization and Antimicrobial Activity of Endophytic Actinobacteria from Medicinal Plants

The current study is aimed to isolate endophytic actinobacteria from various medicinal plants for exploring its antimicrobial activity against clinical pathogens. Out of 50 actinobacterial cultures isolated from eleven medicinal plants, 58 % of the cultures showed antimicrobial activity against at least two out of nine pathogens tested. Strain KCA1 isolated from Phyllanthus niruri leaves showed maximum zone of inhibition against all of the nine pathogens tested. Strain KCA1 exhibited maximum level of antimicrobial metabolite production in solid state fermentation during 9 d of incubation. Three well separated spots were observed when the ethyl acetate extract of strain KCA1 was analyzed through thin-layer chromatography. One spot with retardation factor value 0.82 was found to inhibit Staphylococcus aureus in thin-layer chromatography bioautographic assay. The active fraction eluted from thin-layer chromatography was further characterized by gas chromatography-mass spectral analysis. The mass spectral data revealed the presence of three compounds viz., 2,4-di-tert-butylphenol (C14H22O), 1-hexadecanol (C16H34O) and 1-nonadecene (C19H38) present in major proportions which are responsible for the antimicrobial activity of the strain KCA1. In fermentation experiment, variables such as glucose, yeast extract and sodium chloride were found to influence the antimicrobial compound production. The potential strain KCA1 was identified as Streptomyces sp. on the basis of microscopic, cultural, physiological and 16S ribosomal ribonucleic acid analysis.

Biocontrol Potential of Endophytic Actinobacteria against Fusarium solani, the Causal Agent of Sudden Decline Syndrome on Date Palm in the UAE.

Thirty-one endophytic streptomycete and non-streptomycete actinobacteria were isolated from healthy date palm root tissues. In vitro screening revealed that the antifungal action of isolate #16 was associated with the production of cell-wall degrading enzymes, whereas with diffusible antifungal metabolites in isolate #28, albeit their production of volatile antifungal compounds. According to the 16S rRNA gene sequencing, isolates #16 and #28 were identified as Streptomyces polychromogenes UAE2 (Sp; GenBank Accession #: OK560620) and Streptomyces coeruleoprunus UAE1 (Sc; OK560621), respectively. The two antagonists were recovered from root tissues until 12 weeks after inoculation, efficiently colonized root cortex and xylem vessels, indicating that the date palm roots are a suitable habitat for these endophytic isolates. At the end of the greenhouse experiments, the development of sudden decline syndrome (SDS) was markedly suppressed by 53% with the application of Sp and 86% with Sc, confirming their potential in disease management. Results showed that the estimated disease severity indices in diseased seedlings were significantly (p < 0.05) reduced from 4.75 (scale of 5) to 2.25 or 0.67 by either Sp or Sc, respectively. In addition, conidial numbers of the pathogen significantly (p < 0.05) dropped by 38% and 76% with Sp and Sc, respectively, compared to infected seedlings with F. solani (control). Thus, the suppression of disease symptoms was superior in seedlings pre-inoculated with S. coeruleoprunus, indicating that the diffusible antifungal metabolites were responsible for F. solani retardation in these plants. This is the first report of actinobacteria naturally existing in date palm tissues acting as microbial antagonists against SDS on date palm.

Antagonistic activity of endophytic actinobacteria from native potatoes (Solanum tuberosum subsp. tuberosum L.) against Pectobacterium carotovorum subsp. carotovorum and Pectobacterium atrosepticum

BackgroundThe native potatoes (Solanum tuberosum subsp. tuberosum L.) grown in Chile (Chiloé) represent a new, unexplored source of endophytes to find potential biological control agents for the prevention of bacterial diseases, like blackleg and soft rot, in potato crops.ResultThe objective of this study was the selection of endophytic actinobacteria from native potatoes for antagonistic activity against Pectobacterium carotovorum subsp. carotovorum and Pectobacterium atrosepticum, and their potential to suppress tissue maceration symptoms in potato tubers. This potential was determined through the quorum quenching activity using a Chromobacterium violaceaum ATCC 12472 Wild type (WT) bioassay and its colonization behavior of the potato plant root system (S. tuberosum) by means of the Double labeling of oligonucleotide probes for fluorescence in situ hybridization (DOPE-FISH) targeting technique. The results showed that although Streptomyces sp. TP199 and Streptomyces sp. A2R31 were able to inhibit the growth of the pathogens, only the Streptomyces sp. TP199 isolate inhibited Pectobacterium sp. growth and diminished tissue maceration in tubers (p ≤ 0.05). Streptomyces sp. TP199 had metal-dependent acyl homoserine lactones (AHL) quorum quenching activity in vitro and was able to colonize the root endosphere 10 days after inoculation.ConclusionsWe concluded that native potatoes from southern Chile possess endophyte actinobacteria that are potential agents for the disease management of soft rot and blackleg.

Biodiversity of Culturable Endophytic Actinobacteria Isolated from High Yield Camellia oleifera and Their Plant Growth Promotion Potential

Camellia oleifera Abel. is one of the world’s four famous woody oil trees and has drawn increasing attention because of its high commercial value. Endophytes are microorganisms inhabiting inside plant tissues, and their functions vary with the change of host status and environmental parameters. To deepen our understanding of the interactions between C. oleifera and their endophytic actinobacteria, the present study investigated the four endophytic actinobacterial composition-residing high-yield C. oleifera trees. A total of 156 endophytic actinobacterial isolates were obtained distributed in 17 genera. Among them, Streptomyces was the dominant endophytic actinobacteria, followed by Nocardia, Amycolatopsis, Microbiospora, Micromonospora and other rare actinobacteria genera. Soil characteristics including soil pH and organic matter were found to play crucial roles in shaping the endophytic actinobacterial community composition. Furthermore, all isolates were studied to determine their plant growth-promotion traits, 86.54% could produce Indole 3-Acetic Acid, 16.03% showed nitrogen-fixing, 21.15% showed phosphorus solubilizing, and 35.26% produced siderophore. Under the glasshouse condition, some isolates exhibited growth promotion effects on C. oleifera seedlings with significant increase in spring shoot length and ground diameter. Altogether, this study demonstrated that C. oleifera plants harbored a high diversity and novelty of culturable endophytic actinobacteria, which represent important potential as natural biofertilizers for the high production of C. oleifera.

Bioactive compounds and molecular diversity of endophytic actinobacteria isolated from desert plants

With the aim to find endophytic actinomycetes that synthesize bioactive compounds over 800 strains were isolated from 53 desert plants of the Gobi-Sumber, Umnugobi, Dundgobi, Dornogobi, Bayankhongor, and Gobi-Altai provinces of Mongolia. The HPLC study of strains with high anti-quorum sensing and antibacterial activities revealed that they produced flavonoids and phenolic compounds. Molecular diversity evaluated with 16S rRNA gene sequences of 123 strains showed that they belonged to 12 genera: Streptomyces, Promicromonospora, Micromonospora, Streptosporangium, Kribbella, Pseudonocardia, Nocardia, Micromonospora, Saccharothrix, Friedmanniella, Actinocatenispora, and Geodermatophilus, the latter two genera were registered in Mongolia for the first time. Moreover, the genus Actinocatenispora was isolated from plants for the first time.