Abstract
Poly-β-hydroxybutyrates producing Azotobacter strains were isolated from zones with heterogenous environmental conditions from Romanian Carpathians and Transylvanian Plateau: alpine, karstic and xeric meadows and flood plain. These strains were grown on Azotobacter specific media with different carbon sources (mannitol and sucrose). In order to assess the cell viability the following parameters were determined: optical density – by spectrophotometry; viability – by measuring ATP quantity based on bioluminescence luciferase reaction but also using plate culture method of numbering the viable cells, proteins concentration – by Lowry method. The viability assessed by ATP measuring was checked by numbering the viable cells from Petri dishes stained with methylene blue.