Isolation and screening of sulfur-oxidizing bacteria from coast of Bhavnagar, India, and formulation of consortium for bioremediation.

Abstract

Reduced sulfur compounds are a nuisance in coastal industries causing heavy economical as well as ecological loss. One such compound, hydrogen sulfide, is proven toxic to aquatic animals as it interferes with their respiration and metabolism as well as overall development, thereby causing direct increase in mortality. Typically, 96-h LC50 values to freshwater and marine fishes are 0-25µM and 525-700µM, respectively. Management of sulfide and other reduced sulfur compounds from aquaculture water and sediment using bioremediating sulfur-oxidizing bacteria as probiotics has attracted attention in recent decades due to its efficiency and minimized environmental effects. In the present study, 201 native and indigenous probiotic candidates were isolated, from various coastal environments. The prospective candidates were screened based on pH reduction and 19 sulfur-oxidizing bacteria were selected and tested for salt tolerance. Further screening was done based on biosafety, ability to produce sulfate by oxidizing thiosulfate, and 16S rRNA-based identification to obtain nine probiotic candidates. Three strains (Enterobacter ludwigii HS1-SOB, Pseudomonas stutzeri B6-SOB, and Cytobacillus firmus C8-SOB) exerting highest sulfate-ion production were selected for formulating a probiotic consortium using mixture design matrix. The optimal composition was determined to be equal ratios of the three isolates that yielded 0.083mM of sulfate from thiosulfate broth medium at room temperature in 7days. This is a standalone report of sulfur-oxidizing probiotic consortium composed of the said bacteria. The consortium may be used as a strong tool for remediation of reduced sulfur in aquaculture and associated coastal environments.