Screening and identification of organics-degrading bacteria from the sediment of sea cucumber Apostichopus japonicus ponds

The organics-degrading bacteria were isolated from sea cucumber (Apostichopus japonicus) outdoor rearing ponds sediment. The bacterial strains were selected according to the isolation growth, pathogenicity, organic degradation rate, and effects on A. japonicus growth and water quality. The screened strains were identified on physiological, biochemical, and genetic characteristics. Among 68 strains isolated, two strains (L15 and E4) were identified as potential organics-degrading probiotics. The degradation rates on sediment chemical oxygen demand (COD) were 46.95 ± 1.58 % for the L15 strain and 44.31 ± 1.44 % for the E4 strain. The L15 strain enhanced the specific growth rate (SGR) of A. japonicus by 1.97 ± 0.49 %, and the E4 strain enhanced SGR by 2.24 ± 0.44 % compared with the SGR of 0.55 ± 0.41 % in the control group without probiotics. The COD level increased by −0.9 ± 1.42 % of L15 and 47.9 ± 0.06 % of E4 inoculations after 7 days, while the COD increased by 140.6 ± 4.22 % in the control. Based on the analyses of biochemical characteristics and 16S rRNA gene sequences, the L15 and E4 strains were identified as Bacillus spp. and Pseudomonas spp., respectively.