Isolation and characterization of sulphur oxidizing bacteria (Halothiobacillus sp.) from aquaculture farm soil

Abstract

Isolation and characterization of Halothiobacillus sp. from the shrimp aquaculture farm soil and their sulphur oxidation ability and utilization of H S in in-vitro model. 2 Starkeys mineral salt medium was used to screen autotrophic sulphur oxidizing bacteria. For the qualitative screening, bacterial isolates were inoculated in mineral salt medium containing bromo phenol blue indicator to monitor change in pH. The isolates were studied further for their sulphate ion production, sulphur oxidase enzyme production and utilization of Na S. Identification was carried out by 2 conventional biochemical and molecular methods. Fifty isolates showed distinct sulphur oxidizing ability on the mineral salt medium. The pH reduction test revealed that out of fifty isolates six could efficiently reduce the pH of the medium to 3.0 from an o-1 initial pH of 7 within 96 hr of incubation at 30 C. Maximum sulphate ion (12.65 mg ml) and sulphur oxidase-1-1 enzyme (16.64 mM sulphate hr ml) was produced by a bacterial isolate, Halothiobacillus sp. strain rk3. All the six isolates efficiently utilized Na S in in-vitro conditions. Conventional and molecular identification (16S 2 rRNA sequence analysis) revealed that the sulphur oxidizing bacterial isolates belonged to Halothiobacillus spp. Furthermore, sequencing similarity calculation showed an average nucleotide identity (ANI) values higher than 99% which suggests that the isolates were not genetically different. The present investigation revealed the presence of Halothiobacillus sp. as natural microflora of farm soils in shrimp aquaculture.

Characterizations of sulfur oxidizing bacteria from extensive shrimp ponds

“…Most recently, some SOB strains as Thiobacillus aquaesulis, Halothiobacillus sp. have been identified in fresh water fish and brackish water shrimp ponds using molecular studies (Kumar et al, 2018;Nadella et al, 2019). However, the role of these bacteria in sulfur dynamics in aquaculture farms is still needed in further studies.…”

“…Sulfate production resulting from bacterial growth was observed by measuring the initial and the final sulfate concentration of the culture broth. Bacterial broth culture was centrifuged at 10,000 rpm and 4 o C for 5 min to remove the bacterial cells (Nadella et al, 2019). The cell free supernatant (CFS) was used for determination of sulfate ion according to the turbidimetric method 4500-SO 4 2-E (American Public Health Association [APHA] et al, 2017).…”

“…The method for sulfur oxidase activity was based on Hirano et al (1996) and Nadella et al (2019) with slight modifications. The sulfide-oxidizing activity of SOB isolates cells were determined by measuring the increase in sulfate concentration in a reaction mixture.…”

“…H 2 S is a source of electrons for these bacteria under aerobic and anaerobic (Forte & Giuffre, 2016). Sulfur oxidizing bacteria are able to metabolize sulfide to sulfate which is nontoxic (as cited in Nadella et al, 2019) to aquatic animals. Sulfur oxidizing bacteria have been isolated for removal of H 2 S in the activated sludge bioreactor (Barbosa et al, 2006), biotrickling filters (Aroca et al, 2007), or removal of heavy metals from activated sludge (Li et al, 2012).…”

“…Sulfur oxidizing bacteria have been isolated for removal of H 2 S in the activated sludge bioreactor (Barbosa et al, 2006), biotrickling filters (Aroca et al, 2007), or removal of heavy metals from activated sludge (Li et al, 2012). In aquaculture, few studies were carried out to enumerate or to isolate these bacteria from various aquaculture systems (Abraham et al, 2004;2015;Krishnani et al, 2010;Jaffer et al, 2019;Nadella et al, 2019). However, characteristics of SOB in shrimp ponds in the Mekong Delta have received less attention.…”