Chiang Mai Journal of Science

Salt-tolerant heterotrophic nitrifying bacteria including strains SKNB1, SKNB2, SKNB4, and SKNB7 were collected and isolated from Pacific white shrimp farm. Strain SKNB1 was rod shape, gram positive, and endospore formation. SKNB2 and SKNB4 were rod shape. SKNB7 was coccus shape. Strains SKNB2, SKNB4, and SKNB7 were gram negative and did not form endospore. The partial 16S rRNA gene sequencing analysis with similarity range of 92-97% indicated that four strains were identified as Bacillus sp. (SKNB1), Halomonas sp. (SKNB2 and SKNB4) and Psychrobacter sp. (SKNB7). These isolates were halophilic heterotrophic bacteria and showed nitrification characteristic. They could eliminated high strength of initial ammonia concentration (815.86 mg-N/L) under saline condition. Ammonium removal efficiency of Halomonas sp. SKNB2, Psychrobacter sp. SKNB7, Bacillus sp. SKNB1 and Halomonas sp. SKNB4 were 56.18%, 42.35%, 42.28%, and 23.32%, respectively. Also, nitrite producing ability of SKNB2, SKNB1, SKNB7, and SKNB4 were 0.0751, 0.0172, 0.0169, and 0.0106 mg-N/L, respectively. While very low nitrate presentation by SKNB4 and SKNB1 (0.0086 and 0.0035 mg-N/L, respectively) and no nitrate observation was done for SKNB2 and SKNB7. Based on most ammonium removal ability, these nitrifying bacteria could be suggest as ammonium oxidizing bacteria (AOB) and they might proficient for high ammonium saline wastewater treatment.