Purification and Characterization of Bioactive Metabolite from Streptomyces monomycini RVE129 Derived from the Rift Valley Soil of Hawassa, Ethiopia.

Streptomyces species have produced a variety of bioactive secondary metabolites with intriguing antimicrobial and anticancer properties. In this study, the bioactive compound obtained from the potent strain RVE129 was purified and characterized. Its bioactivity against various pathogens and its cytotoxicity toward the human cervical cancer (HeLa) cell were also examined. The strain was previously isolated from unexplored areas of the rift valley soil of Hawassa (Ethiopia) and identified by phenotypic characteristics and complete sequencing of the 16S rRNA gene and found to be closely related to Streptomyces monomycini strain NRRL B-24309 (99.65%); accession no. (ON786620). The active fraction undergoes bioassay-guided purification using the TLC method after being extracted by ethyl acetate. Then, it was subjected to physicochemical and structural characteristics using UV-Vis, FTIR, and NMR spectroscopic methods. A minimum inhibitory concentration of the purified antibiotic was achieved by the broth microdilution method. The cytotoxicity of HeLa cells was determined using the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The acquired data from spectroscopic studies was compared with that of the reported natural compounds in data bases and found to be the known antibiotic, setamycin. The antibiotic (RVE-02) showed a broad spectrum of bioactivity against both Gram-positive and Gram-negative bacteria, with MIC values that ranged from 1.97 to 125 µg/ml. The bioactivity results also demonstrated antiproliferation and morphological change in HeLa cells with an IC50 value of 24.30µg/ml of antibiotic. The antibiotic, obtained from S. monomycini RVE129, could be a potential candidate to combat pathogens including drug-resistant S. aureus. Further, the effect on HeLa cells suggests that it could be a prominent cancer chemotherapeutic agent.

Antimicrobial Potential of Streptomyces spp. Isolated from the Rift Valley Regions of Ethiopia.

The study was undertaken to isolate, screen, and identify actinomycetes with antimicrobial metabolites. Twenty-one composite soil samples were randomly collected from various unique agroecological niches in the Rift Valley of Ethiopia. The soil samples were serially diluted and spread on starch casein agar medium supplemented with 50 µg/ml cycloheximide and 25 µg/ml nalidixic acid. Two hundred and forty-nine (249) actinomycetes cultures were isolated and screened by cross streaking against various human pathogens. Twenty-four isolates with pronounced antimicrobial activity were selected for identification and further screening. Among the isolates, 172 (69.1%) showed antimicrobial activities against tested pathogens. The inhibition zone of the isolates ranged from 5 ± 0.31 to >40 mm during primary screening. The antimicrobial activity of the crude extracts of promising isolates showed a statistically significant difference (P < 0.05) between them and the control. The isolates RVE129 and RVE217 showed the maximum zone of inhibition at 27 ± 0.6 mm and 26 ± 0.6 mm, respectively, against S. aureus, and the results were higher than the standard drug streptomycin (25 ± 0.58 mm). The inhibition zone of crude extracts from RVE129 was at the maximum of 22 ± 0.0 mm against P. aeruginosa, almost comparable to the standard drug streptomycin (24 ± 0.58 mm). Crude extract from the isolates RVE129 and RVE187 showed higher inhibition zones of 22 ± 0.6 mm and 16 ± 0.33 mm against A. niger ATCC10535, which, however, were smaller than those obtained with the standard drug amphotericin B (29 ± 0.6 mm). Twenty-four actinomycete strains with remarkable bioactivity were characterized using various cultural, morphological, physiological, and biochemical characteristics and assigned under the genus Streptomycetes. The finding of the current study indicates that Streptomyces sp. isolated from the Rift Valley of Ethiopia was found to possess a broad spectrum of bioactivity against a range of human pathogens.

Phosphate Solubilization Potential of Rhizosphere Fungi Isolated from Plants in Jimma Zone, Southwest Ethiopia.

Phosphorus (P) is one of the major bioelements limiting agricultural production. Phosphate solubilizing fungi play a noteworthy role in increasing the bioavailability of soil phosphates for plants. The present study was aimed at isolating and characterizing phosphate solubilizing fungi from different rhizospheres using both solid and liquid Pikovskaya (PVK) medium. A total of 359 fungal isolates were obtained from 150 rhizosphere soil samples of haricot bean, faba bean, cabbage, tomato, and sugarcane. Among the isolates, 167 (46.52%) solubilized inorganic phosphate. The isolated phosphate solubilizing fungi belonged to genera of Aspergillus (55.69%), Penicillium spp. (23.35%), and Fusarium (9.58%). Solubilization index (SI) ranged from 1.10 to 3.05. Isolates designated as JUHbF95 (Aspergillus sp.) and JUFbF59 (Penicillium sp.) solubilized maximum amount of P 728.77 µg·mL(-1) and 514.44 µg mL(-1), respectively, from TCP (tricalcium phosphate) after 15 days of incubation. The highest (363 µg mL(-1)) soluble-P was released from RP with the inoculation of JUHbF95 in the PVK broth after 10 days of incubation. The present study indicated the presence of diverse plant associated P-solubilizing fungi that may serve as potential biofertilizers.