A novel mesophilic sulfate-reducing bacterium, EMSSDQ(4)(T), was isolated from olive mill wastewater in the semi-arid region of Morocco (Marrakech). Cells were Gram-negative, catalase-positive, straight rods that were non-motile and non-spore-forming and contained cytochrome c(3) and desulfoviridin. The DNA G+C content was 65.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the isolate was a member of the genus Desulfovibrio with Desulfovibrio carbinoliphilus D41(T), Desulfovibrio alcoholivorans SPSN(T), Desulfovibrio fructosivorans JJ(T) and Desulfovibrio carbinolicus EDK82(T) as the most closely related strains with validly published names. In addition to the classical substrates used by Desulfovibrio species, the isolate oxidized 1,4-tyrosol, one of the most abundant phenolic compounds occurring in olive mill wastewater, to 4-hydroxyphenylacetate without ring cleavage. D. alcoholivorans SPSN(T) was also found to carry out this reaction. Under air, strain EMSSDQ(4)(T) exhibited limited growth on lactate and yeast extract in the absence of sulfate. On the basis of genotypic and phenotypic characteristics, it is proposed that the isolate represents a novel species, Desulfovibrio marrakechensis sp. nov. The type strain is EMSSDQ(4)(T) (=DSM 19337(T) =ATCC BAA-1562(T)).