Flocculation effect and activity of halophilic archaea isolated from Uyong Brac salt lake

Abstract:

[Objective] The present study screened the halophilic archaeal strains with flocculation effect and evaluated the flocculation effect of the fermentation liquid, fermentation supernatant, cell suspension, and extracellular polymeric substances of the strains, aiming to develop the microbial flocculants that can adapt to a wide range of salinity and pH for high-salt wastewater treatment. [Methods] The pure culture method was designed to isolate halophilic archaea from the sediment samples of Uyong Brac salt lake in Xinjiang. The 16S rRNA gene sequencing and phylogenetic analysis were performed to evaluate the taxonomic positions of the isolated strains. Furthermore, the flocculation effects of the fermentation liquid, fermentation supernatant, cell suspension, and extracellular polymeric substances of the strains were evaluated. The flocculation stability was evaluated under a wide range of salinity and pH conditions. [Results] A total of 28 strains of halophilic archaea were isolated by pure culture method, among which 16 strains were selected based on the primary screening results. The 16S rRNA sequences and phylogenetic tree suggested that these strains mainly belonged to Natrinema, Halopiger, and Haloterrigena. The fermentation liquid, fermentation supernatant, cell suspension, and extracellular polymeric substances of strains A279-1, A133, RP33, NGA0064, RM-152, and A389 had better flocculation effects than those of other strains. The fermentation liquid and supernatant of strain A389 showcased the flocculation rates reaching 61.06% and 67.92%, respectively. The cell suspensions of all the strains had the flocculation rates over 80%. The extracellular polymeric substances produced by strain RM-152 had the highest flocculation rate of 89.86%, followed by those of strain A389 (81.53%). Strain A389 had the yield of 12.53 g/L of extracellular polymeric substances and it adapted to a wide range of salinity and pH. [Conclusion] There were abundant halophilic archaea in the sediment of Uyong Brac salt lake. The fermentation liquid, fermentation supernatant, cell suspension, and extracellular polymeric substances of halophilic archaea had good flocculation effect. In particular, the extracellular polymeric substances demonstrated good flocculation effect and could withstand a wide range of salinity and pH, being suitable for further industrial recycling and utilization. The isolated strains may serve the subsequent development of functional materials for industrial high-salt wastewater treatment.

Key words:halophilic archaea;flocculation;high-salt wastewater;community composition;extracellular polymeric substances