Isolation and Molecular Identification of Streptomyces spp. with Antibacterial Activity from Northwest of Iran

Exploring Bioactive Potential of Streptomyces thinghirensis WAE1 from Wadi El-Natron, Egypt

This study aimed to investigate the bioactive metabolites produced by Streptomyces thinghirensis WAE1, an actinomycete isolated from El-Hamara Lake in Egypt. The discovery of new bioactive compounds from natural sources is crucial for the advancement of therapeutic treatments, and this study aimed to contribute to this field by exploring the potential of Streptomyces thinghirensis WAE1 as a source of such compounds. Streptomyces thinghirensis WAE1 was screened for its ability to produce antimicrobial, antioxidant, and anti-inflammatory metabolites. The results revealed that S. thinghirensis WAE1 exhibited strong antimicrobial activity against Streptococcus pneumoniae and moderate activity against Listeria monocytogenes, Staphylococcus aureus, and Candida albicans. Streptomyces thinghirensis WAE1 also displayed antioxidant activity through scavenging free radicals and chelating iron, and moderate anti-inflammatory activity as determined by its IC50 value. The isolate's demonstration of L-asparaginase activity suggests that S. thinghirensis WAE1 is a promising source of bioactive compounds with potential therapeutic uses. The high salinity and alkalinity of El-Hamara Lake, which create favorable conditions for the production of bioactive metabolites, further add to its potential as a source of actinomycetes strains with bioactive properties. These findings make both S. thinghirensis WAE1 and El-Hamara Lake valuable subjects for further exploration in the field of bioactive compounds.

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

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

Identification and Characterization of a Multifunctional Biocontrol Agent, Streptomyces griseorubiginosus LJS06, Against Cucumber Anthracnose

Twenty-eight bacterial strains isolated from Chinese herb extracts, beer fermentation waste, and raw oyster shells were evaluated for their efficacy in controlling cucumber anthracnose. Four bacterial strains, namely TG01, TG02, LJS06, and LJS08, were found to effectively reduce the mycelial growth of Colletotrichum orbiculare COC3 on PDA media. Spraying or drenching LJS06 spore suspension before inoculation significantly p < 0.05 reduced disease severity; thus, LJS06 was subject to further characterization. On the basis of the morphological, physiological, and biochemical characteristics and a multilocus sequence analysis of partial 16S rRNA, atpD, rpoB, and trpB genes, LJS06 was identified to be Streptomyces griseorubiginosus (Ryabova and Preobrazhenskaya) Pridham et al. Physiological and biochemical tests revealed that S. griseorubiginosus LJS06 can produce amylase, cellulase, chitinase, protease, siderophore, polyamines, and indole-3-acetic acid. Thus, a culture filtrate of LJS06 (specifically SL06) was formulated and evaluated for its efficacy against conidial germination, appressorium formation, and anthracnose management. Diluted SL06 was found to significantly (p < 0.05) inhibit conidial germination and appressorium formation, which can be attributed to impaired membrane integrity, accumulated reactive oxygen species (ROS), and impaired energy metabolism in the conidia. In addition, the spraying and drenching of diluted SL06 before inoculation consistently and significantly (p < 0.05) reduced anthracnose severity. These results jointly suggest that S. griseorubiginosus LJS06 can aid in the management of cucumber anthracnose by directly inhibiting conidial function and priming the plant defense system.

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.

In vitro antibacterial activities and molecular characterization of bacterial species isolated from farmlands against selected pathogens

This study aims to screen bacterial isolates from Olabisi Onabanjo University Farmland for antibacterial activity against pathogenic microorganisms. Agar well diffusion method was used. Isolates were identified molecularly. Chi-square test revealed significant association between isolates, antibacterial activity with likelihood p-value = 0.000 and 5% significant level. Six among thirty-five isolates exhibited antibacterial activity against the test pathogenic species. A greater antibacterial activity (50 % inhibition) was observed in Lysinibacillus sphearicus strain PRE16. It inhibited the growth of Bacillus subtilis, Staphylococcus aureus and Escherichia coli by 23.00 ± 2.00, 18.00 ± 2.00 and 20.00 ± 4.00 respectively. DNA sequencing revealed antagonist isolates as Bacillus sp. BCN2, Brochothrix thermosphacta strain P30C4, Bacillus aryabhattai strain KNUC205, Alcaligenes faecalis strain KEM24, Bacillus arsenicus strain CSD05 and Lysinibacillus sphaericus strain PRE16. Phylogenetic analysis revealed close relatedness of most isolates with Bacillus species strains. These strains are suggested to be effective for the discovery of new antibacterial agents.

Antifungal potential of bacterial rhizosphere isolates associated with three ethno-medicinal plants (poppy, chamomile, and nettle)

The objective of the present study was to isolate Actinobacteria, preferably Streptomyces spp. from the rhizosphere soils of three ethno-medicinal plants collected in Serbia (Papaver rhoeas, Matricaria chamomilla, and Urtica dioica) and to screen their antifungal activity against Candida spp. Overall, 103 sporulating isolates were collected from rhizosphere soil samples and determined as Streptomyces spp. Two different media and two extraction procedures were used to facilitate identification of antifungals. Overall, 412 crude cell extracts were tested against Candida albicans using disk diffusion assays, with 42% (43/103) of the strains showing the ability to produce antifungal agents. Also, extracts inhibited growth of important human pathogens: Candida krusei, Candida parapsilosis, and Candida glabrata. Based on the established degree and range of antifungal activity, nine isolates, confirmed as streptomycetes by 16S rRNA sequencing, were selected for further testing. Their ability to inhibit Candida growth in liquid culture, to inhibit biofilm formation, and to disperse pre-formed biofilms was assessed with active concentrations from 8 to 250 μg/mL. High-performance liquid chromatographic profiles of extracts derived from selected strains were recorded, revealing moderate metabolic diversity. Our results proved that rhizosphere soil of ethno-medicinal plants is a prolific source of streptomycetes, producers of potentially new antifungal compounds.

Isolation, Identification and Evaluation of Antimicrobial Activity of Streptomyces flavogriseus, strain ACTK2 from Soil Sample of Kodagu, Karnataka State (India)

Background:

The search for novel antibiotics continues to be of immense importance in research programs around the world for pharmaceutical, industrial and agricultural applications. Filamentous soil bacteria, belonging to the Streptomyces genus, are widely used as an important biological tool for their ability to produce a wide range of novel secondary metabolites, such as “antibiotics”.

Objectives:

The aim of the present study was to isolate and identify a strain of Streptomyces with high antibiotic production capability.

Materials and Methods:

The soil sample was collected randomly from the agricultural land of Kushalnagar Taluk of Kodagu district, Karnataka, India. The ACTK2 strain was isolated by serial dilution method and identified based on cultural, morphological, microscopic, biochemical and sequence analysis of 16S rRNA gene parameters. The isolated ACTK2 was analyzed for antimicrobial activities by perpendicular streak and disc diffusion methods, against the Gram-positive bacteria Staphylococcus aureus (MTCC 96), Bacillus subtilis (MTCC 121), Gram-negative Escherichia. coli (MTCC 729), Enterococcus aerogenes (MTCC 2829) and filamentous fungi (Trichoderma harizianum (MTCC6046), Fusarium proliferatum (MTCC 9375). Further, an antimicrobial metabolite from the ACTK2 strain was extracted by solvent extraction method, using n-butanol. The production of the antimicrobial compound by the ACTK2 strain was optimized by using different nutritional media and cultural conditions.

Results:

The strain Streptomycesflavogriseus designated as ACTK2 (Accession number KC990785) isolated from the soil sample of Kushalnagar Taluk, Kodagu, Karnataka, India, exhibited a broad spectrum of antimicrobial activity against test microorganisms. The optimum growth and antimicrobial compound production by strain ACTK2 was found to be a maximal pH 8, in the shaker incubator at 28ºC, for a period of 10 days.

Conclusions:

The crude n-butanol extract of the ACTK2 strain of S. flavogriseus showed a broad spectrum of antimicrobial activities against the test organisms and this opened further research investigations on purification and structural characterization of the active compounds from the crude extract.