Pure strains as well as mixed cultures are studied and recommended. Most studied strains belong to genera: Pseudomonas, Bacillus, Sphingomonas, Aeromonas, Citrobacter, Escherichia and Desulphovibrio. In the present study, two Pseudomonas strains were tested. They are Gram-negative bacteria. As it is well known, Gram-negative bacteria have thin cell wall containing up to 10 % of peptidoglycan and outer membrane composed of proteins, phospholipids and lipopolysaccharides (Salyers and Whitt 2000; Schlegel 1993).