title: Isolation and characterization of potential antibiotic producing actinomycetes from water and sediments of Lake Tana, Ethiopia.
abstract: 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.
authors.affiliation: Department of Biology, Faculty of Natural and Computational Sciences, Post Box 196, University of Gondar, Ethiopia.
authors.forename: Gebreselema
authors.initials: G
authors.lastname: Gebreyohannes
authors.forename: Feleke
authors.initials: F
authors.lastname: Moges
authors.forename: Samuel
authors.initials: S
authors.lastname: Sahile
authors.forename: Nagappan
authors.initials: N
authors.lastname: Raja
mesh_terms: D039903:Actinobacteria / Q000302:isolation & purification / Q000502:physiology*; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D005002:Ethiopia; D019015:Geologic Sediments / Q000382:microbiology*; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D060106:Lakes / Q000382:microbiology*; D008826:Microbial Sensitivity Tests
chemical_list: D000900:Anti-Bacterial Agents
keywords: Actinomycetes; Agar well diffusion method; Antibacterial activity; Antibiotics; Crude extracts; Disc diffusion method; Solid state fermentation; Submerged state fermentation