THIOBACILLUS SP W5, THE DOMINANT AUTOTROPH OXIDIZING SULFIDE TO SULFUR IN A REACTOR FOR AEROBIC TREATMENT OF SULFIDIC WASTES

The floating filter technique was successfully adapted for the isolati on of the dominant, chemolithoautotrophic, sulfide-oxidizing bacterium from a sulfur-producing reactor after conventional isolation techniqu es had failed. The inoculated polycarbonate filters, floating on miner al medium, were incubated under gaseous hydrogen sulfide at non-toxic levels. This technique gave 200-fold higher recoveries than convention al isolation techniques. Viable counts on the filters, making up 15% o f the total count, appeared to be all of the same species. Chemostat c ultures of the new isolate had a very high sulfur-forming capacity, co nverting almost all hydrogen sulfide in the medium to elemental sulfur under high sulfide loads (27.5 mmol l(-1) h(-1)) and fully aerobic co nditions. This behaviour closely resembled that of the microbial commu nity in the sulfur-producing reactor. Moreover, similar protein patter ns were obtained by electrophoresis of cell-free ex-tracts from the is olate and the mixed culture. It has therefore been concluded that this isolate represents the dominant sulfide-oxidizing population in the r eactor. The isolate has been shown to be a new Thiobacillus species, r elated to Thiobacillus neapolitanus. In view of the general confusion currently surrounding the taxonomy of the thiobacilli, a new species h as not been formally created. Instead, the isolate has been given the working name Thiobacillus sp. W5.