Actinobacterial Strain Research Articles

Streptomyces coriariae sp. nov., a novel streptomycete isolated from actinorhizal nodules of Coriaria intermedia.

An actinobacterial strain, CMB-FB, was isolated from surface-sterilized root nodules of a Coriaria intermedia plant growing along Halsema Highway in the province of Benguet (Luzon, Philippines). The 16S rRNA gene sequence of CMB-FB showed high sequence similarity to those of the type strains of Streptomyces rishiriensis (99.4 %), Streptomyces humidus (99.1 %), Streptomyces cacaoi subsp. asoensis (99.0 %), and Streptomyces phaeofaciens (98.6 %). The major menaquinones of CMB-FB were composed of MK-9(H4), MK-9(H6) and MK-9(H8), and there was a minor contribution of MK-9(H10). The polar lipid profile consisted of phosphatidylethanolamine, unidentified aminolipids and phospholipids, a glycophospholipid and four unidentified lipids. The diagnostic diamino acid of the peptidoglycan was meso-diaminopimelic acid. The major fatty acids were iso-C16 : 0, anteiso-C15 : 0 and anteiso-C17 : 0. The results of physiological analysis indicated that CMB-FB was mesophilic. The results of phylogenetic, genome-genome distance calculation and average nucleotide identity analysis indicated that the isolated strain represents the type strain of a novel species. On the basis of these results, strain CMB-FB (=DSM 112754T=LMG 32457T) is proposed as the type strain of the novel species Streptomyces coriariae sp. nov.

Antibacterial and Anti-HIV Metabolites from Marine Streptomyces albus MAB56 Isolated from Andaman and Nicobar Islands, India.

Marine-derived actinobacteria have tremendous potential to produce novel metabolites with diverse biological activities. The Andaman coast of India has a lot of microbial diversity, but it is still a relatively unknown ecology for isolating novel actinobacteria with beneficial bioactive compounds. We have isolated 568 actinobacterial strains from mangrove rhizosphere sediments and sponge samples. Crude extracts from 75 distinct strains were produced by agar surface fermentation and extracted using ethyl acetate. In the disc diffusion method, 25 actinobacterial strains showed antimicrobial activity; notably, the strain MAB56 demonstrated promising broad-spectrum activity. Strain MAB56 was identified as Streptomyces albus by cultural, microscopic, and molecular methods. Conditions for bioactive metabolites from MAB56 were optimized and produced in a lab-scale fermenter. Three active metabolites (C1, C2, and C3) that showed promising broad-spectrum antimicrobial activity were isolated through HPLC-based purification. Based on the UV, FT-IR, NMR, and LC-MS analysis, the chemical nature of the active compounds was confirmed as 12-methyltetradecanoic acid (C1), palmitic acid (C2), and tridecanoic acid (C3) with molecular formulae C14H28O2, C16H32O2, and C13H26O2, respectively. Interestingly, palmitic acid (C2) also exhibited anti-HIV activity with an IC50 value of < 1µg/ml. Our findings reveal that the actinobacteria from the Andaman marine ecosystems are promising for isolating anti-infective metabolites.

Statistical Medium Optimization for the Production of Anti-Methicillin-Resistant Staphylococcus aureus Metabolites from a Coal-Mining-Soil-Derived Streptomyces rochei CMB47

The development of novel antibacterial drugs needs urgent action due to the global emergence of antibiotic resistance. In this challenge, actinobacterial strains from arid ecosystems are proving to be promising sources of new bioactive metabolites. The identified Streptomyces rochei strain CMB47, isolated from coal mine Saharan soil, provided an ethyl acetate extract which tested against a series of pathogens. It displayed a minimum inhibitory concentration of &lt;0.439 µg/mL against MRSA. A statistical experimental design using a response surface methodology (RSM) based on the second-order rotatable central composite design (RCCD) was planned to develop an efficient fermentation process able to improve the bioactive metabolite production. The optimal conditions were determined for starch and NaNO3 concentrations, incubation time and the initial pH value, reaching the inhibition zone diameter of 20 mm, close to the experimental value, after validation of the model. A bioassay-guided fractionation of the crude extract provided the most active fractions, which were analyzed by HPLC equipped with a photodiode array detector and coupled online with an electrospray mass spectrometer (HPLC-DAD/ESI-MS), obtaining preliminary indications on the molecular structures of the metabolites. These results support the potential interest in further investigations into the purification and full characterization of the metabolites responsible for the biological activity observed so far.

Discovery of new indolosesquiterpenoids bearing a N-O linkage by overexpression of LuxR regulator in a marine bacterium Streptomyces sp.

The xiamycins are bioactive indolosesquiterpenoids that have been isolated from actinobacterial strains belonging to the Streptomyces genus. The overexpression of orf2011, which encodes the LuxR family regulator in a marine Streptomyces strain (HK18) isolated from a hypersaline saltern, significantly increased the production of xiamycin dimers, namely the previously reported dixiamycins A and C (3 and 4), compared to the wild-type strain. In addition, the engineered strain produced new members of the xiamycin family (lipoxiamycins A and B), which possessed a lipophilic chain linked to the indolosesquiterpenoid core structure by a N–O bond. The transcription analysis of the N-hydroxylase-encoding xiaH by semiquantitative reverse transcription polymerase chain reaction (RT-PCR) revealed that the transcription level of xiaH responsible for the formation of a nitroxyl radical was increased by the overexpression of orf2011, which is located outside the xiamycin biosynthetic gene cluster. The structures of these compounds were determined by full spectroscopic analysis, and the connectivity between the lipophilic chain and the indolosesquiterpenoid moiety was confirmed in both lipoxiamycins A and B (1 and 2) by MS/MS analysis. Moreover, the absolute configurations of these compounds were established using quantum mechanics-based electronic circular dichroism and DP4 calculations. Finally, it was demonstrated that lipoxiamycin A (1) displayed inhibitory activity against lipopolysaccharide-induced NO production at an IC50 of 9.89 ± 0.92 µM in RAW 264.7 cells.

Collinsella urealyticum sp. nov., a urease-positive bacterial strain isolated from swine faeces

A novel actinobacterial strain, designated AGMB00827T, was isolated from swine faeces. Strain AGMB00827T was obligately anaerobic, Gram-stain-positive, non-motile, non-spore-forming and rod-shaped bacterium. Comparative analyses based on the 16S rRNA gene and whole genome sequence revealed that strain AGMB00827T was affiliated to the genus Collinsella, and was most closely related to Collinsella vaginalis Marseille-P2666T (= KCTC 25056T). Biochemical analysis showed strain AGMB00827T was negative for catalase and oxidase. Interestingly, strain AGMB00827T possessed urease activity, which was determined by traditional methods (API test and Christensen's urea medium), unlike related strains. Furthermore, the major cellular fatty acids (> 10%) of the isolate were C18:1 ω9c, C16:0, C16:0 DMA and C18:2 ω9,12c DMA. Based on the whole genome sequence analysis, the DNA G + C content of strain AGMB00827T was 52.3%, and the genome size and numbers of rRNA and tRNA genes were 1,945,251bp, 3 and 46, respectively. The average nucleotide identity and digital DNA-DNA hybridization values between strain AGMB00827T and C. vaginalis KCTC 25056T were 71.0 and 23.2%, respectively. Additionally, the genome analysis revealed that strain AGMB00827T possesses urease gene cluster including ureABC and ureDEFG while the related strains do not have those genes, which is consistent with the urease activity. On the basis of polyphasic taxonomic approach, strain AGMB00827T represents a novel species within the genus Collinsella, for which the name Collinsella urealyticum sp. nov. is proposed. The type strain is AGMB00827T (= KCTC 25287T = GDMCC 1.2724T).

Nocardioides okcheonensis sp. nov., isolated from riverside soil.

An actinobacterial strain designated MMS20-HV4-12T, displaying a high hydrolytic potential for various substrates, was isolated from a riverside soil sample and characterized by polyphasic taxonomic analysis. Growth occurred at 10-37 °C (optimum, 30°C), with NaCl concentrations of 0-4 % (optimum, 0 %) and at pH 7-9 (optimum, pH 8). MMS20-HV4-12T was catalase-positive, oxidase-negative, rod-shaped and formed creamy white-coloured colonies. Based on the results of 16S rRNA gene sequence analysis, MMS20-HV4-12T was found to be mostly related to the type strains of Nocardioides alpinus (98.3 % sequence similarity), Nocardioides furvisabuli (98.1 %) and Nocardioides zeicaulis (98.0 %). MMS20-HV4-12T showed optimal growth on Reaoner's 2A agar, forming white-coloured colonies. The diagnostic polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol and phosphatidylinositol, the major fatty acids were iso-C16 : 0, C17 : 1 ω8c and 10-methyl-C17 : 0, the major isoprenoid quinone was MK-8(H4), the diagnostic cell-wall sugar was galactose, and the cell-wall diamino acid was ll-diaminopimelic acid. The genome of MMS20-HV4-12T was 4.47 Mbp in size with a G+C content of 72.9 mol%. The genome based analysis indicated low relatedness between MMS20-HV4-12T and all compared species of Nocardioides, as the highest digital DNA-DNA hybridization and the orthologous average nucleotide identity values were 26.8 and 83.8% respectively. Based on genotypic, phenotypic and phylogenomic characterization, MMS20-HV4-12T evidently represents a novel species of genus Nocardioides, for which the name Nocardioides okcheonensis sp. nov. (type strain=MMS20-HV4-12T=KCTC 49651T=LMG 32360T) is proposed.

Bioactive Metabolite Survey of Actinobacteria Showing Plant Growth Promoting Traits to Develop Novel Biofertilizers

The use of chemical fertilizers and pesticides has caused harmful impacts on the environment with the increase in economic burden. Biofertilizers are biological products containing living microorganisms capable of improving plant growth through eco-friendly mechanisms. In this work, three actinobacterial strains Streptomyces violaceoruber, Streptomyces coelicolor, and Kocuria rhizophila were characterized for multiple plant growth promoting (PGP) traits such as indole acetic acid production, phosphate solubilization, N2-fixation, and drought and salt tolerance. Then, these strains were investigated for their secreted and cellular metabolome, revealing a rich arsenal of bioactive molecules, including antibiotics and siderophores, with S. violaceoruber being the most prolific strain. Furthermore, the in vivo assays, performed on tomato (Solanum lycopersicum L.), resulted in an improved germination index and the growth of seedlings from seeds treated with PGP actinobacteria, with a particular focus on S. violaceoruber cultures. In particular, this last strain, producing volatile organic compounds having antimicrobial activity, was able to modulate volatilome and exert control on the global DNA methylation of tomato seedlings. Thus, these results, confirming the efficacy of the selected actinobacteria strains in promoting plant growth and development by producing volatile and non-volatile bioactive molecules, can promote eco-friendly alternatives in sustainable agriculture.

Pangenome analysis of the genus Herbiconiux and proposal of four new species associated with Chinese medicinal plants.

Five Gram-stain-positive, aerobic, non-motile actinobacterial strains designated as CPCC 205763T, CPCC 203386T, CPCC 205716T, CPCC 203406T, and CPCC 203407 were obtained from different ecosystems associated with four kinds of Chinese traditional medicinal plants. The 16S rRNA gene sequences of these five strains showed closely related to members of the genus Herbiconiux of the family Microbacteriaceae, with the highest similarities of 97.4-99.7% to the four validly named species of Herbiconiux. In the phylogenetic trees based on 16S rRNA gene sequences and the core genome, these isolates clustered into the clade of the genus Herbiconiux within the lineage of the family Microbacteriaceae. The overall genome relatedness indexes (values of ANI and dDDH) and the phenotypic properties (morphological, physiological and chemotaxonomic characteristics) of these isolates, readily supported to affiliate them to the genus Herbiconiux, representing four novel species, with the isolates CPCC 203406T and CPCC 203407 being classified in the same species. For which the names Herbiconiux aconitum sp. nov. (type strain CPCC 205763T = I19A-01430T = CGMCC 1.60067T), Herbiconiux daphne sp. nov. (type strain CPCC 203386T = I10A-01569T = DSM 24546T = KCTC 19839T), Herbiconiux gentiana sp. nov. (type strain CPCC 205716T = I21A-01427T = CGMCC 1.60064T), and Herbiconiux oxytropis sp. nov. (type strain CPCC 203406T = I10A-02268T = DSM 24549T = KCTC 19840T) were proposed, respectively. In the genomes of these five strains, the putative encoding genes for amidase, endoglucanase, phosphatase, and superoxidative dismutase were retrieved, which were classified as biosynthetic genes/gene-clusters regarding plant growth-promotion (PGP) functions. The positive results from IAA-producing, cellulose-degrading and anti-oxidation experiments further approved their potential PGP bio-functions. Pangenome analysis of the genus Herbiconiux supported the polyphasic taxonomy results and confirmed their bio-function potential.

Actinomadura terrae sp. nov. and Actinomadura litoris OS3-89, isolated from rhizosphere soil of cactus.

Two mycelium-forming actinobacterial strains, designated OS3-83 T and OS3-89, were isolated from rhizosphere soil of a cactus (Opuntia ficus-indica) sampled on Mara Island, Jeju, Republic of Korea. Both of the isolates were found to grow at 20-37 °C, pH 6.0-10.0 and with 0-2 % (w/v) NaCl. Their taxonomic positions were investigated by a polyphasic approach. Strains OS3-83T and OS3-89 were most closely related to the type strain of Actinomadura litoris (99.5 % and 98.9 % 16S rRNA gene sequence similarity, respectively). Both of the isolates shared 99.2 % sequence similarity to each other. Morphological and chemotaxonomic characteristics supported the affiliation of the two isolates to the genus Actinomadura. 16S rRNA gene phylogeny exhibited that strain OS3-83T formed a tight cluster with A. litoris, while strain OS3-89 occupied a position located remotely from A. litoris. Nevertheless, phylogenomic analysis based on 92 core gene sequences showed that both of the isolates formed a tight clade with A. litoris. The values of average nucleotide identity and digital DNA-DNA hybridization between strain OS3-83T and the closest relative, A. litoris, were 92.2 and 46.2 %, respectively, whereas strain OS3-89 shared an average nucleotide identity value of 97.5 % and a digital DNA-DNA hybridization value of 76.9 % with A. litoris. These results strongly suggested that strain OS3-83T (=KACC 19752T=NBRC 114688T) represents a novel species and strain OS3-89 (=KACC 19753=NBRC 114400) is a strain of A. litoris. On the basis of the data obtained here, strain OS3-83T is considered to represent a new species of the genus Actinomadura, for which the name Actinomadura terrae sp. nov. is proposed.

Solicola gregarius gen. nov., sp. nov., a soil actinobacterium isolated after enhanced cultivation with Micrococcus luteus culture supernatant.

An actinobacterial strain, designated A5X3R13T, was isolated from a compost soil suspension supplemented with extracellular material from a Micrococcus luteus-culture supernatant. The strain was cultured on tenfold-diluted reasoner's 2A agar. The cells were ovoid-to-rod shaped, non-motile, Gram-stain-positive, oxidase-negative, catalase-positive and had a width of 0.5 µm and a length of 0.8-1.2 µm. The results of both 16S rRNA-based phylogenetic and whole-genome analyses indicate that A5X3R13T forms a distinct lineage within the family Nocardioidaceae (order Propionibacteriales). On the basis of the 16S rRNA gene sequence, A5X3R13T was closely related to Aeromicrobium terrae CC-CFT486T (96.2 %), Nocardioides iriomotensis IR27-S3T (96.2 %), Nocardioides guangzhouensis 130T (95.6 %), Marmoricola caldifontis YIM 730233T (95.5 %), Aeromicrobium alkaliterrae KSL-107T (95.4 %), Aeromicrobium choanae 9H-4T (95.4 %), Aeromicrobium panaciterrae Gsoil 161T (95.3 %), and Nocardioides jensenii NBRC 14755T (95.2 %). The genome had a length of 4 915 757 bp, and its DNA G+C content was 68.5 mol %. The main fatty acids were 10-methyl C17 : 0, C16 : 0, C15 : 0, C18 : 0, C17 : 0 and iso-C16 : 0. The main polar lipids were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol and two unidentified phospholipids. MK-9(H4) was the predominant respiratory quinone. The peptidoglycan type was A3γ (A41.1) and contained alanine, glycine, glutamic acid and ll-diaminopimelic acid in a molar ratio of 1.2 : 0.9 : 1.0 : 0.8. On the basis of the results of the phylogenetic and phenotypic analyses and comparisons with other members of the family Nocardioidaceae, strain A5X3R13T is proposed to represent a novel species within a novel genus, for which the name Solicola gregarius gen. nov., sp. nov. is proposed. The type strain is A5X3R13T (=DSM 112953T=NCCB 100840T).

Microbial signature and biosynthetic gene cluster profiling of poly extremophilic marine actinobacteria isolated from Vhan Island, Tamil Nadu, India

Marine microbes are gaining attention among researchers for their polyextremophilic nature and ability to produce novel secondary metabolites. The coastal wetlands are widely investigated for their accessibility, leaving the islands, deep-sea, and other poly-extremophilic sites untouched. This study unveils marine actinobacteria and their biosynthetic gene clusters from the polyextremophilic island ecosystem. Thirty-eight polyextremophilic marine actinobacterial strains of 12 genera were isolated from 6 sediment samples collected around Vhan Island, India. Streptomyces sp. (39 %) was found predominantly, followed by; Micrococcus sp. (13 %), Rhodococcus sp. (10 %), Actinomyces sp. (8 %), Nesterenkonia sp. (5 %), Nocardia sp. (5 %), Brevibacterium sp. (5 %), Verrucosispora sp. (3 %), Actinoplanes sp. (3 %), Corynebacterium sp. (3 %), Jishengella sp. (3 %), and Microbispora sp. (3 %). Together twenty-two strains showed the presence of Polyketide Synthase-I (PKS-I) (13 strains), Polyketide Synthase-II (PKS-II) (18 strains), and Non-Ribosomal Peptide Synthetases (NRPSs) (10 strains). In addition, combinatorial gene clusters PKS-I + PKS-II (9 strains), PKS-II + NRPS (8 strains), and PKS-I + II + NRPS (3 strains) were also detected. Further, the Gas Chromatography and Mass Spectrometry (GC–MS) and Liquid Chromatography with Tandem Mass Spectrometry (LC-MS/MS) analysis for the selected strains demonstrated their ability to produce diverse secondary metabolites with potential therapeutic and industrial values. In correlation, the antimicrobial studies also revealed that the isolated microbes could significantly inhibit the tested marine pathogens' growth. Further, all the gene clusters were stored as gene libraries for further usage. This study is one of its kind in exploring the extreme ecological niches and unveiling the diversity of rare and polyextremophilic marine actinomycetes from the Island ecosystem with its biosynthetic gene cluster potential.

Agromyces seonyuensis sp. nov., isolated from island soil.

A Gram-positive, non-motile, pale yellow coloured actinobacterial strain designated MMS17-SY077T was isolated from island soil, and its taxonomic position was investigated using a polyphasic approach. Strain MMS17-SY077T grew optimally at 30 °C, at pH 7 and in the absence of NaCl on Reasoner's 2A agar. Based on the 16S rRNA gene sequence analysis, the strain was assigned to the genus Agromyces of the family Microbacteriaceae, and the most related species were Agromyces italicus DSM 16388T (98.8 % sequence similarity), Agromyces allii UMS-62T (98.1 %) and Agromyces terreus DS-10T (97.8 %). Strain MMS17-SY077T formed a distinct cluster within the Agromyces clade in the phylogenetic tree. Genome-based comparative analyses confirmed a clear distinction between the strain and neighbouring species, as the highest orthologous average nucleotide identity and digital DNA-DNA hybridization values with other related species were 77.2 and 21.4% respectively, which were far below the cutoffs for species distinction. The diagnostic polar lipids of MMS17-SY077T were diphosphatidylglycerol and phosphatidylglycerol, and unidentified glycolipids and an unidentified aminolipid were also present. The main isoprenoid quinones were menaquinones with 11 and 12 isoprene units (MK-11 and MK-12), and main fatty acids were anteiso-C15 : 0 (34.4 %) and iso-C16 : 0 (33.2 %). The whole-cell hydrolysates contained rhamnose, ribose and galactose as diagnostic sugars, and l-2,4-diaminobutyric acid as the major diamino acid. The DNA G+C content was 72.1 mol %. Based on phenotypic, chemotaxnomic and phylogenetic characterization, strain MMS17-SY077T should be classified as representing a new species of the genus Agromyces, for which the name Agromyces seonyunensis sp. nov. is proposed (type strain MMS17-SY077T=KCTC 49423T=LMG 31762T).

An antimicrobial thiopeptide producing novel actinomycetes Streptomyces terrae sp. nov., isolated from subsurface soil of arable land.

An antimicrobial producing Gram-positive, aerobic, nonmotile, and filamentous actinobacterial strain SKN60T was isolated from soil The isolate exhibited 99.3% and 99.0% identity with Streptomyces laurentii ATCC 31255T and S. roseicoloratus TRM 44457T, respectively, in 16S rRNA gene sequence analysis. However, the genome sequence displayed maximum ANI (88.45%) and AAI (85.61%) with S. roseicoloratus TRM 44457T. Similarly, the dDDH showed 33.7% identity with S. roseicoloratus TRM 44457T. It formed a cluster with S. roseicoloratus TRM 44457T and S. laurentii ATCC 31255T in phylogenomic tree. Cell wall analysis revealed the presence of diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylcholine as major polar lipids and diaminopimelic acid as diagnostic diamino acid. Major fatty acids were iso-C15:0, anteiso-C15:0, and iso-C16:0. The G+C content was found to be 72.3 mol%. Genome sequence analysis using antiSMASH database showed occurrence of a thiopeptide biosynthesis gene cluster with 94% similarity to berninamycin from S. bernensis UC5144. The mass of 1146Da is identical with berninamycin. But subtle differences observed in leader peptide sequence of thiopeptide and berninamycin. Notably, S. bernensis is not validly reported and thus SKN60T is the only strain containing berninamycin BGC as no other phylogenetic relative had it. Additionally, strain SKN60T differed in phenotypic and genetic characteristics with all phylogenetic relatives of the genus Streptomyces. Therefore, it is proposed as a novel species with the name Streptomyces terrae sp. nov. strain SKN60T (=MTCC 13163T; = JCM 35768T).

Streptomyces guryensis sp. nov. exhibiting antimicrobial activity, isolated from riverside soil.

A novel Gram-stain-positive, aerobic actinobacterial strain designated NR30T was isolated from riverside soil. A polyphasic approach was employed for the taxonomic characterization of NR30T. The strain developed extensively branched light brown to light pink substrate mycelia and light grey aerial mycelia, and produced spiny spores in loose spiral spore chains on ISP 3 and 4 agars. NR30T grew at 10-40°C (optimum, 30°C), at pH 6.0-9.0 (optimum, pH 8.0) and in the presence of 0-3 % NaCl (optimum, 0 %). Analysis of 16S rRNA gene sequences indicated that NR30T represents a member of the genus Streptomyces. NR30T shared the highest 16S rRNA gene sequence similarity with Streptomyces cyaneus NRRL B-2296T (98.6 %). On the basis of orthologous average nucleotide identity, NR30T was most closely related to Streptomyces panaciradicis NBRC 109811T with 86.3 % identity. The results of the digital DNA-DNA hybridization analysis also indicated low levels of relatedness with other species, as the highest value was observed with Streptomyces panaciradicis NBRC 109811T (31.1 %). The major fatty acids of the strain were anteiso-C15 : 0, C16 : 0, iso-C16 : 0 and anteiso-C17 : 0. The major respiratory quinones were MK-9(H8) and MK-9(H6). The diagnostic polar lipids were diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol mannoside. The major cell wall diamino acid was ll-diaminopimelic acid, and the characteristic whole-cell sugars were rhamnose, ribose and glucose. The DNA G+C content was 70.3 mol %. NR30T exhibited antimicrobial activity against several Gram-negative bacteria and yeasts. On the basis of the results of both phenotypic and phylogenetic analyses, strain NR30T evidently represents a novel species of the genus Streptomyces, and the name Streptomyces guryensis sp. nov. (type strain=NR30T =KCTC 49653T=LMG 32476T) is proposed accordingly.

Persicamidines-Unprecedented Sesquarterpenoids with Potent Antiviral Bioactivity against Coronaviruses.

A new family of highly unusual sesquarterpenoids (persicamidines A-E) exhibiting significant antiviral activity was isolated from a newly discovered actinobacterial strain, Kibdelosporangium persicum sp. nov., collected from a hot desert in Iran. Extensive NMR analysis unraveled a hexacyclic terpenoid molecule with a modified sugar moiety on one side and a highly unusual isourea moiety fused to the terpenoid structure. The structures of the five analogues differed only in the aminoalkyl side chain attached to the isourea moiety. Persicamidines A-E showed potent activity against hCoV-229E and SARS-CoV-2 viruses in the nanomolar range together with very good selectivity indices, making persicamidines promising as starting points for drug development.

Rare Halophilic Nocardiopsis from Algerian Saharan Soils as Tools for Biotechnological Processes in Pharmaceutical Industry.

The Sahara Desert, one of the most extreme ecosystems in the planet, constitutes an unexplored source of microorganisms such as mycelial bacteria. In this study, we investigated the diversity of halophilic actinobacteria in soils collected from five regions of the Algerian Sahara. A total of 23 halophilic actinobacterial strains were isolated by using a humic-vitamin agar medium supplemented with 10% NaCl. The isolated halophilic strains were subjected to taxonomic analysis using a polyphasic approach, which included morphological, chemotaxonomic, physiological (numerical taxonomy), and phylogenetic analyses. The isolates showed abundant growth in CMA (complex medium agar) and TSA (tryptic soy agar) media containing 10% NaCl, and chemotaxonomic characteristics were consistent with their assignment to the genus Nocardiopsis. Analysis of the 16S rRNA sequence of 23 isolates showed five distinct clusters and a similarity level ranging between 98.4% and 99.8% within the Nocardiopsis species. Comparison of their physiological characteristics with the nearest species showed significant differences with the closely related species. Halophilic Nocardiopsis isolated from Algerian Sahara soil represents a distinct phyletic line suggesting a potential new species. Furthermore, the isolated strains of halophilic Nocardiopsis were screened for their antagonistic properties against a broad spectrum of microorganisms by the conventional agar method (agar cylinders method) and found to have the capacity to produce bioactive secondary metabolites. Except one isolate (AH37), all isolated Nocardiopsis showed moderate to high biological activities against Pseudomonas syringae and Salmonella enterica, and some isolates showed activities against Agrobacterium tumefaciens, Serratia marcescens, and Klebsiella pneumoniae. However, no isolates were active against Bacillus subtilis, Aspergillus flavus, or Aspergillus niger. The obtained finding implies that the unexplored extreme environments such as the Sahara contain many new bacterial species as a novel drug source for medical and industrial applications.

New Alkali-tolerant and Halo-tolerant Nocardiopsis Strain B20 from Algerian Saharan Soil: Isolation, Taxonomy, and Antifungal Activity

Abstract A newly characterized actinobacterial strain, designated B20, displayed remarkable tolerance to extreme pH and NaCl conditions, while showcasing a diversity in carbon source utilization. Phylogenetic analysis confirmed its taxonomic assignment within the genus Nocardiopsis. However, several physiological features were found to differentiate B20 from its most closely related Nocardiopsis species. Notably, Nocardiopsis sp. B20 demonstrated potent and selective antifungal activity against various micro-fungi, suggesting its potential as a valuable source for targeted antifungal compounds. Ethyl acetate extract contains a bioactive compound, B20-1, displaying antifungal properties. Chemical revelations indicated the presence of sugars and polycyclic aromatic hydrocarbons (PAHs) in B20-1 compound. The discovery of antifungal PAHs derived from natural sources presents promising opportunity for addressing fungal infections while mitigating environmental concerns and resistance risks associated with synthetic fungicides. However, further research is warranted to evaluate efficacy, assess ecological impacts, and explore potential applications across diverse industries.

Biocontrol of root rot complex disease of Phaseolus vulgaris by Streptomyces sp. strains in the field

Soil-borne pathogens associated with root rot complex diseases cause major yield losses in common bean (Phaseolus vulgaris L.) worldwide. The lack of active ingredients available against these pathogens makes disease control difficult. Seed treatments with Streptomyces spp. have been described as a potential ecofriendly strategy against this complex disease. Here, we evaluate the effect of Streptomyces sp. strains CBQ-EA2 and CBQ-B-8 as biological control agents (BCAs) against root rot complex disease of P. vulgaris, mainly caused by Macrophomina phaseolina and Rhizoctonia solani under natural field conditions in Cuba. To this end, seed treatments with Streptomyces sp. strains CBQ-EA2 and CBQ-B-8, using single or mixed applications, were examined. Seed treatments with the BCA Trichoderma harzianum Rifai A-34 and the chemical Celest® Top 312 FS were included for comparison. In all experimental fields, treatments with Streptomyces spp. had significantly higher efficacy in reducing disease incidence (DI) and disease severity (DS) than the chemical Celest® Top 312 FS, and a similar effect as that by the BCA T. harzianum A-34. Most of the treatments evaluated showed higher germination, quality and yield of legumes than the nontreated control. Seed treatments using the combination of the two actinobacterial strains (Streptomyces sp. CBQ-EA-2+ CBQ-B-8) showed higher effectiveness in reducing DI and DS, and enhancing germination, yield and quality of legumes compared with the nontreated control, with a similar effect as that with the BCA T. harzianum A-34 and the chemical Celest® Top 312 FS. Overall, microbial consortia deserve further research in the future to develop potential biological products for crop protection.

Six novel Micromonospora species associated with the phyllosphere and roots of leguminous plants: Micromonospora alfalfae sp. nov., Micromonospora cabrerizensis sp. nov., Micromonospora foliorum sp. nov., Micromonospora hortensis sp. nov., Micromonospora salmantinae sp. nov., and Micromonospora trifolii sp. nov.

Six actinobacterial strains isolated from diverse legume tissues collected in various locations in Spain were characterized to determine their taxonomic status. Using 16S rRNA gene sequencing, the strains were primarily identified as members of the genus Micromonospora with more than 99 % similarity. Digital DNA-DNA hybridization values and average nucleotide identities between the six strains and the nearest type strains confirmed that each strain represented a novel species. Genome sequences were analysed to infer their metabolic profiles, their potential to produce secondary metabolites and plant growth promoting features. Chemotaxonomic and physiological studies were carried out to complete the phenotypic characterization and to distinguish the new Micromonospora species. The genomic and phenotypic characterization of the Micromonospora strains strongly support their classification as representatives of new species with the following names: Micromonospora alfalfae sp. nov., Micromonospora cabrerizensis sp. nov., Micromonospora foliorum sp. nov., Micromonospora hortensis sp. nov., Micromonospora salmantinae sp. nov. and Micromonospora trifolii sp. nov., with the type strains MED01T, LAH09T, PSH25T, NIE111T, PSH03T and NIE79T, respectively.

Isolation and bioactive potentials of Streptomyces from Tripura forest soil, North-east India

Aim: The bioactive potential of Actinobacteria from Tripura forest soil, Northeast India was investigated in this study. Methodology: Sixty seven actinobacterial isolates recovered from six soil samples were screened for antimicrobial activity against a panel of pathogenic bacteria and fungi. The production of antimicrobial metabolites from the potential strain TFA59 was done by both solid state and submerged fermentation. The antimicrobial compounds were further extracted using ethyl acetate as solvent and the activity was tested against Staphylococcus aureus and Candida albicans. The actinobacterial strain TFA59 was characterized based on its phenotypic and molecular characteristics. Results: Antimicrobial activity was exhibited by 28 actinobacterial cultures against atleast one of the test pathogens. Among the solvents tested for extraction, only ethyl acetate extract exhibited activity against S. aureus (21 mm) and C. albicans (23 mm). The production of antimicrobial compounds by TFA59 was influenced by raffinose, starch, yeast extract and pH 7 when compared with other variables. Based on the phenotypic and molecular characterization, the strain TFA59 was identified as a species of the genus Streptomyces. Interpretation: This study concluded that the Streptomyces strains isolated from Tripura forest soil show potential in producing bioactive metabolites that are effective against wide range of pathogens. Key words: Actinobacteria, Antimicrobial, Bioprospecting, North-east India, Streptomyces