Objective: To isolate, evaluate and characterize potential antibiotic producing actinomycetes
from water and sediments of Lake Tana, Ethiopia. Methods: A total of 31 strains of actinomycetes
were isolated and tested against Gram positive and Gram negative bacterial strains by primary
screening. In the primary screening, 11 promising isolates were identified and subjected to
solid state and submerged state fermentation methods to produce crude extracts. The fermented
biomass was extracted by organic solvent extraction method and tested against bacterial strains
by disc and agar well diffusion methods. The isolates were characterized by using morphological,
physiological and biochemical methods. Results: The result obtained from agar well diffusion
method was better than disc diffusion method. The crude extract showed higher inhibition zone
against Gram positive bacteria than Gram negative bacteria. One-way analysis of variance
confirmed most of the crude extracts were statistically significant at 95% confidence interval. The
minimum inhibitory concentration and minimum bactericidal concentration of crude extracts
were 1.65 mg/mL and 3.30 mg/mL against Staphylococcus aureus, and 1.84 mg/mL and 3.80 mg/
mL against Escherichia coli respectively. The growth of aerial and substrate mycelium varied in
different culture media used. Most of the isolates were able to hydrolysis starch and urea; able to
survive at 5% concentration of sodium chloride; optimum temperature for their growth was 30 °C.
Conclusions: The results of the present study revealed that freshwater actinomycetes of Lake
Tana appear to have immense potential as a source of antibacterial compounds