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 isolation of the dominant, chemolithoautotrophic, sulfide-oxidizing bacterium from a sulfur-producing reactor after conventional isolation techniques had failed. The inoculated polycarbonate filters, floating on mineral medium, were incubated under gaseous hydrogen sulfide at non-toxic levels. This technique gave 200-fold higher recoveries than conventional isolation techniques. Viable counts on the filters, making up 15% of the total count, appeared to be all of the same species. Chemostat cultures of the new isolate had a very high sulfur-forming capacity, converting almost all hydrogen sulfide in the medium to elemental sulfur under high sulfide loads (27.5 mmol l^-1 h^-1) and fully aerobic conditions. This behaviour closely resembled that of the microbial community in the sulfur-producing reactor. Moreover, similar protein patterns were obtained by electrophoresis of cell-free extracts from the isolate and the mixed culture. It has therefore been concluded that this isolate represents the dominant sulfide-oxidizing population in the reactor. The isolate has been shown to be a new Thiobacillus species, related to Thiobacillus neapolitanus. In view of the general confusion currently surrounding the taxonomy of the thiobacilli, a new species has not been formally created. Instead, the isolate has been given the working name Thiobacillus sp. W5.