The synthesis of metal oxide nanocomposite by using the green method has gotten special consideration due to a cheaper and eco-friendly approach. Decreasing antibiotic effectiveness calls for the fast advancement of other alternative antimicrobials. CuO, ZnO, and CuO/ZnO nanocomposites were successfully synthesized using Zingiber officinale rhizome extract as a mild, renewable, and nontoxic reducing agent and proficient stabilizer with the nonappearance of hazardous and toxic chemicals. UV-Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) were used to characterize CuO, ZnO, and CuO/ZnO nanocomposites. The UV-Visible result showed the absorbance peak at 270nm, 355nm, 365nm, and 370nm corresponding to the characteristic band of CuO NPs, ZnO NPs, 10 CuO/ZnO, and 20 CuO/ZnO nanocomposites, respectively. FT-IR confirmed the nature of bonds and the presence of different functional groups in the Zingiber officinale rhizome extract, CuO, ZnO, and CuO/ZnO nanocomposites. The XRD analysis revealed that all the synthesized particles have a crystalline nature with a particle size of 4.35nm, 14.54nm, 18.41nm, and 20.50nm of CuO NPs, ZnO NPs, 10 CuO/ZnO, and 20 CuO/ZnO NCs, respectively. The synthesized nanoparticles and nanocomposites showed inhibition against Gram-positive and Gram-negative bacteria up to a concentration of 12.5mg/mL. The highest inhibition against Staphylococcus aureus ATCC 25926 and Escherichia coli ATCC was 20±0.7mm and 16±0.5mm in diameter, respectively, by 50mg/mL of 20 CuO/ZnO NCs. In general, the biosynthesized nanoparticles and nanocomposites showed effective antibacterial activity.

Phenotypic and genotypic characteristics of cowpea rhizobia indigenous to soils of Ethiopia are unknown. Forty indigenous cowpea rhizobial isolates were collected from cowpea-growing areas of the country and were characterized for their growth and genetic properties. Based on their cultural characteristics, the isolates were categorized into fast (FG), slow (SG), and extraslow-growings (ESG). The FG, SG, and ESG isolates had mean generation time (h)/colony diameter (mm)/date of turbidity formation (d) in the range of 2.5-7.5/2-4/2-3, 7.5-30/0.5-3.5/3-5, and 30-50/0.5-1/5-7, respectively. Thirty two and sixteen percentages of the isolates were FG and ESG, respectively. Most of the isolates (87%) could grow on culture medium of pH 4.5, but were intolerant of pH 8. The intrinsic antibiotics resistance (IAR) pattern was FG>SG>ESG for ampicillin, ciprofloxacin, chloramphenicol, erythromycin, neomycin sulfate and penicillin, whereas the pattern was FGESG for dextrin, dextrose, glucose, starch and sucrose whereas it was FG<SG7.5 h were grouped together at 70% of similarity. Partial sequence analysis of 16S rRNA gene showed the existence of isolates most similar to rhizobial species of Bradyrhizobium species, Bradyrhizobium japonicum, Bradyrhizobium elkanii, Rhizobium rubi, and Mesorhizobium species. In general, cowpea rhizobial isolates from soils of Ethiopia in this study were mainly SG and sensitive to stress in vitro conditions, but versatile in utilization of varieties of C and N substrates. Such studies are important in Ethiopia to identify rhizobial isolates that could be amendable for use as inoculants to improve cowpea production. Key words: Phylogeny, diversity, isolates, growth categories, cluster analysis.

Soybean [ Glycine max (L.)] is a leguminous crop that harbors root nodule bacteria that fix atmospheric nitrogen. However, the dinitrogen‐fixing potential of the isolates varies due to different factors that necessitate the selection of the most efficient ones from local soils. In this study, 70 soybean root nodule bacteria isolates were extracted from the acidic soil of East Wollega Zone, Ethiopia. Colony characteristics and physiological and agronomic properties of the isolates were determined. Sixty‐six isolates were confirmed as slow‐growing soybean rhizobia based on renodulation, cultural characteristics, and cluster analysis with reference strains. About 5.5%, 35%, and 45% of the isolates were tolerant of 8% salt and 45°C temperature and pH 3 of incubation conditions, respectively. The highest nodule number, nodule wet weight, nodule dry weight, shoot height, shoot dry weight, shoot wet weight, and shoot length recorded were 38 ± 1 (SRU66), 1.71 ± 0.1 g/plant (SRU66), 0.63 ± 0.49 g/plant (SRU19), 36.7 ± 1 cm/plant (SRU36), 1.41 g/plant (SRU25), 10.8 ± 1 g/plant (SRU1), and 72.0 ± 1 cm/plant (SRU1), respectively. In general, soybean rhizobial isolates in this study were diverse in their morphology, ecophysiology, substrate utilization, and symbiotic effectiveness. Seven isolates, SRU11 (82.2%), SRU25 (141.7%), SRU26 (96.5%), SRU27 (187.4%), SRU31 (1013%), SRU36 (116.1%), and SRU70 (96.5%), were strong in their relative symbiotic effectiveness and are recommended as bioinoculants to boost the productivity of the soybean after a test under field environment.

Background: Phosphorus is one of the limiting plant nutrients in most soil due to its fixation with metal ions both in acidic and alkaline soil. However, some soil bacteria have potential to solubilize the cation-fixed phosphorus and make it available to plants.Methods: Sixty-six cowpea root nodule bacterial species were tested for inorganic phosphate solubilization (PS). PS potential of the isolates from Ca3 (PO4)2, AlPO4 and FePO4 were tested on four different kinds of agar media. Solublization efficiency was determined as Solubilization Index (SI) on agar media and quantity of bioavailable phosphorous on broth media. Result: About 30% of the bacterial isolates, out of which 60% endophytes were Ca3 (PO4)2 solubilizers on Pikovskaya medium but did not grow on media containing AlPO4 and FePO4 as sole P sources. Isolates showed significant variation (p less than 0.05) in Ca3 (PO4)2 solubilization efficiency on the different culture media and ECE-21 (Pseudomonas putida) was versatile in solubilizing Ca3(PO4)2 from the four test media. However, ECE-26A (Bacillus subtilis) showed the highest PS in broth media (140.8 µg ml-1) indicating the moderate correlation (r=0.5578; p less than 0.05) of PS between solid and liquid media. Amounts of P solubilized and pH change of the culture filtrate was inversely correlated (r=-0.731; p less than 0.01). In general, ECE-21 was the most efficient P solubilizer (SI=2.67±0.1; P=87.74±7.4µg ml-1) solublizers and hence can be an ideal candidate as inoculants for the crop production in Ethiopia after field evaluation.

Okra (Abelmoschus esculentus) sauce is a cultural ready-to-eat (RTE) food in Benishangul-Gumuz region, Ethiopia, but its microbiological safety is yet to be determined. The study aimed to evaluate the microbial safety of RTE Okra sauce by enumerating common bacterial biota. Seventy-two Okra sauce samples were collected from each of the three restaurants and street-vending sites of Assosa and Oda towns during dry and wet seasons. Bacterial groups and species in the food samples were enumerated using selective and differential media. Nine percent and 55% of the samples contain 10⁷ cfu g⁻¹ of aerobic mesophilic bacteria and Enterobacteriaceae, respectively. Twenty-five percent of the food samples contain > 300 colonies of aerobic endospore-forming bacteria from 10^–2 sample dilutions. Similarly, the total coliform, fecal coliform, and S. aureus in 10^–2 sample dilution with colonies of 30–300 were 42%, 29%, and 43%, respectively. The study showed that samples collected during the dry season had significantly abundant (α = 0.05) bacterial groups compared to wet season samples. Similarly, samples from the streets were considerably contaminated compared to samples from restaurants. RTE Okra sauce food didn’t show significant variation based on the sampling site; the status of the contamination can be presented as “Oda Street Dry Season" > “Oda Street Wet Season" > “Assosa Street Dry Season” > “Oda Restaurant Dry Season". According to FAO/WHO, the RTE Okra sauce samples are unsafe for consumption and require strict supervision by relevant public agencies.