Isolation and selection of purple non-sulfur bacteria form intensive striped catfish (Pangasianodon hypophthalmus) ponds

Abstract

The sustainable development of striped catfish cultivation are closely linked to water quality and fish health maintenance. One of the important elements in aquatic ecosystems are the microbial communities, in which purple nonsulfur bacteria (PNSB) play an important role in the overall balance and functionality of the ecosystem. This study aimed to isolate and to select indigenous PNSB from intensive striped catfish ponds in An Giang, Vinh Long and Dong Thap provinces based on their abilities to remove ammonium and hydrogen sulfide for further applications in wastewater treatments in catfish culture industry. The results showed that a total of 21 isolates was identified as members of the genus Rhodopseudomonas and Rhodobacter. All isolates exhibited gram-negative, nonspore formation, positive reaction to catalase, oxidase and motility tests, as well as reaching the exponential growth under light-anaerobic as well as dark-aerobic conditions. Interestingly, these isolates could simultaneously eliminate ammonium and sulfide with removal efficancies in a range of 56.9-97.2% and 36.3- 65.9%, respectively. Among isolates, two isolates of AG-G5 and DT-A10 had the maximum removal and regarded as safe for the catfish by non-hemolytic nature. Additionally, the pH values ranging from 6.5 to 7.5 and malate as a sole carbon were considered to be the optimum conditions for accelerating the growth performance of selected AG-G5 and DT-A10 isolates. It is suggested that two candidates, including AG G5 and DT-A10 have a promising alternative for improving water quality in aquaculture practices, especially striped catfish farming in the Mekong Delta region.