Characterizations of sulfur oxidizing bacteria from extensive shrimp ponds

Abstract

The aim of this study is to characterize the sulfur oxidizing bacteria (SOB) isolates from the sediments of extensive shrimp ponds for recommending the use of this group for water quality management in aquaculture. Sediment samples were collected from 12 extensive shrimp ponds located in Tra Vinh, Soc Trang, Bac Lieu, and Ca Mau provinces. To screen the potential sulfur oxidizing bacteria, medium was amended with sodium thiosulfate, and the sulfate ion production ability and sulfur oxidase enzyme activity of the isolates were measured spectrophotometrically. Results showed that 30 isolates grew on the thiosulfate agar medium. Among these, only five isolates reduced the pH of the growth medium and showed high sulfur oxidase activity and production of sulfate ion when isolates were inoculated with thiosulfate as a substrate. Physiological and biochemical tests indicated that five selected isolates were Gram negative, short rod, non-motile, non-spore forming, negative for oxidase reaction, and positive for catalase reaction. The isolates SOBTB1.1 and SOBTB6.2 showed the significantly higher sulfur oxidase activity and production of sulfate ion compared to other isolates. SOBTB6.2 isolate produced sulfate ion and exhibited higher sulfur oxidase activity at pH4-5, followed by pH6-7. It is, therefore, suggested that the SOBTB 1.1 and SOBTB6.2 could be promising sulfur oxidizers for further research and uses in aquaculture.