Isolation and Identification of Efficient Strains of Native Sulfur Oxidizing Bacteria rom Warm-water Fish Farms in the Central Regions Mazandaran

This study was aimed to isolate and identify the most efficient native bacteria from warm-water fish farms of Mazandaran that can potentially oxidize hydrogen sulfide. After sampling the sediments and sediment pore water of fish farms in Fereydunkenar, Babol, Babolsar and Sari counties, enrichment and isolation carried out in three liquid culture media of Starkey, Postgate, and H-3 to increase the number of the desired microorganisms. After isolation based on morphological difference (in the above solid culture media), 27 isolates (14 autotrophic and 13 heterotrophic isolates) were purified. Then preliminary screening was performed based on pH decrease in Starkey liquid culture media, among which only 6 isolates were selected. In the next stage, the amount of thiosulfate consumption, sulfate production, and the density of bacteria in Starkey liquid culture media were measured to a more detailed evaluation of the ability of sulfur oxidation. Among the 6 isolates, isolates FH-13, FH-21, and FH-14 had the highest oxidation ability of thiosulfate ions (4053.79, 3104.5, and 2878.97 mg / l for 14 days) and sulfate ion production (2240, 965 and 490 mg / l) in the liquid culture medium. Molecular identification of these isolates was performed using the 16S rRNA gene sequencing method. The results showed that three isolates FH-14, FH-13, and FH-21 had 99.70, 100, and 99.80% of identity with the Thiobacillus thioparus HM173634, respectively. Based on the results of this study, these strains can be used as effective sulfur-oxidizing strains in the bioremediation process to remove hydrogen sulfide in warm-water fish farms.