Study of the effect of pH and dissolved heavy metals on the growth of sulfate-reducing bacteria by a fractional factorial design

Metallurgical processes and mining are the main source of heavy metal contamination of water sources, rivers and lakes. Some biological alternatives can be used to mitigate or remedy these contaminations. One of such processes, the sulfide bioprecipitation is mediated by microorganisms (called sulfate-reducing bacteria) able to catalyze, under anaerobic conditions, the reduction of sulfate to sulfide, using organic compounds as electron donors. In this paper we studied the effect of the presence of some heavy metals (zinc, chromium, cobalt, nickel, copper and cadmium) and the pH of culture medium on the growth of a mesophilic sulfate-reducing strain isolated from the effluent of a tannery. For these comparisons, a fractional factorial design 2III7−3 was used. To analyze the possible effect of other members of the bacterial community on the sulfate reduction, the same study was done using the original sulfate-reducing consortium which showed a faster sulfate reduction. Our results showed that in both cases, sulfate reduction was significantly affected by pH changes whereas the presence of heavy metals did not show a significant effect. In addition, similar metal precipitation was obtained using the isolated strain and the original community. Changes in the bacterial community due to heavy metals' presence and pH were analyzed using DGGE technique.