TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In (M1), the Proteobacteria are gamma Proteobacteria, preferably are microorganisms belonging to Pseudomonas genus. The microorganisms belonging to gram positive low GC content bacteria are the microorganisms of Bacillus genus. The microorganisms belonging to gram positive high GC content bacteria are the microorganisms belonging to Actinobacteria genus. EXAMPLE - Sea bottom soil (1 g) was obtained and statically cultured at room temperature. Then, 0.05 ml of supernatant liquid was smeared to an antibiotic containing agar medium, cultured and the colony of decomposition bacteria was analyzed. Six to ten sorts of decomposition bacteria were isolated by visual observation. DNA was extracted from the isolated bacteria, and the 16S rDNA was amplified by PCR. The base sequence of the 16S rDNA was determined. New strains RT1, RT6, RA3, RA4, and RO1 were identify based on the base sequence analysis. The decomposition ability of the identified strains was analyzed. Sea bottom soil (1 g) was collected from Uranouchi bay and was sterilized with autoclave (121 degreesC, 20 minutes), and antibiotics were added so that it might become 10-4 M/g. Then, 0.1 ml of culture solutions of each identified strain of decomposition bacteria was added and mixed. The bacteria was statically cultured for one week in 30 degreesC incubator under conditions that promote the proliferation of decomposition bacteria. After one or two week, the antibiotics concentration was measured and decomposition ratio was obtained. The strains RT1 and RT6 were identified as thiamphenicol decomposition bacteria having decomposition ratio of 20% and 60%, respectively, the strains RA3 and RA4 were identified as ampicillin decomposition bacteria having decomposition ratio of 70% and 80%, respectively, and the RO1 strain was identified as oxytetracycline hydrochloride decomposition bacteria having decomposition ratio of 40%. The results showed that the identified bacteria enabled effective decomposition of antibiotics.