Ecophysiology and Application of Acidophilic Sulfur-Reducing Microorganisms

Sulfur-reducing prokaryotes play an important role in the sulfur biogeochemical cycle, especially in deep-sea vents, hot springs and other extreme environments. The reduction of elemental sulfur is not very favorable thermodynamically, but still provides enough energy for growth of microorganisms. Currently known sulfur reducers are spread over about 69 genera within 9 phyla in the Bacteria domain and 37 genera within 2 phyla in the Archaea domain. Elemental sulfur reduction can occur with polysulfide as an intermediate or via direct cell attachment to the solid substrate. At least four different enzymes are involved in those pathways, and these enzymes are also detected in several microorganisms that are potential sulfur reducers, but not reported as such in literature so far. The ecological distribution of sulfur respiration seems to be more widespread at high temperatures with neutral pH. However, some sulfur reducers can grow at pH as low as 1. The sulfide produced from sulfur reduction can selectively precipitate metals by varying the pH values from 2 to 7, depending on the target metal. Therefore, acidophilic sulfur reducers are of particular interest for application in selective precipitation and recovery of heavy metals from metalliferous waste streams. This chapter explores the ecology and physiology of elemental sulfur reducers, and discusses technologies that can be set up to exploit acidophilic sulfur reducers.