Preparation of seaweed detritus for the sea cucumber Apostichopus japonicus feed

Abstract

Twenty-three various bacterial sources were collected from different sources in Busan, Korea to isolate seaweed degrading strains. Accordingly, the bacteria degraded brown seaweeds: Laminaria japonica and Undaria pinnatifida were identified as strain GR2, strain 52 and strain 53. Based on 16S rDNA gene amplification and sequence strain GR2 with 99% similarly was matched with Bacillus thermolactis R-6488. Also strain 52& 53 were match with Marinobacter salicampi ISL-40, and M. sp with similarly 99.66% and 96.33% respectively. The optimum conditions for the growth of GR2 were liquid medium with temperature of 52.5oC, pH of 7.5-8.0, salinity of 2%, incubation time of 48 h. Similarly growth conditions were observed for the other two bacterial strains 52 and 53, which were found effective in digesting the other brown seaweed U. pinnatifida. Also the optimum substrate concentration of the brown seaweeds was 60 gm in a 1 liter jar. Fermentation of two brown-seaweeds tissue with above optimum conditions, to degraded U. pinnatifida by strains 52, 53 and L. japonica by strain GR2 gave detritus particle size of 40 - 50µm after 72 h and 120 h respectively. The number of bacteria cell increased up to 36 h for all the bacteria strains and then dropped rapidly at 60 h with strain GR2. Similar trend was observed for strain 52, 53 after 84 h. Fermentation by strain 52, 53 increased the reducing sugar amount up to 36 h from 0.077 to 0.105 mg/mL and then dropped 0.038 mg/mL at 108 h, similarly, digestion by strain GR2 rose the reducing sugar amount from 0.08 to 0.109 mg/mL at 36 h of fermentation, decreased 0.036 mg/mL at 108 h. Viscosity increased until 36 h and it reached 3.6 c. P and 2.5 c. P by strain 52, 53 and GR2 digestion respectively. The alginate content was decreased by strains 52, 53 and strain GR2 from 0.134 to 0.034 g alginate dry wt/ tissue wet wt, and 0.137 to 0.032 g alginate dry wt/ tissue wet wt, respective. The results of the present study suggest that inoculation of brown-seaweeds with tissue degrading bacteria not only shortened the time of degradation but also protected marine environment and utilized its for animal feed purposes.