Although the study of sulfur cycle bacteria wasalready started around the 1890's by the famousmicrobiologists Winogradsky and Beijerinck,there are nowadays still many new discoveriesto be made about the metabolic properties,phylogenetic position and ecological behaviourof bacteria that play a role in the biologicalsulfur cycle. The current interest of thescientific community in the biological sulfurcycle is very high, especially because of themany special organisms that have recently beendiscovered in deep sea and other environmentscharacterised by extreme conditions (such ashigh salt, low/high pH or temperature) and alsoin bioreactor environments. This paperhighlights the many unique opportunities thesulfur cycle bacteria offer for sulfurpollution abatement and sulfur recovery.Special attention is given to bioreactorsystems where dissimilatory sulfate reductionis an important bioconversion.