A novel obligately anaerobic, non-spore-forming, rod-shaped mesophilic bacterium, which stained Gram-positive but showed the typical cell wall structure of Gram-negative bacteria, was isolated from an upflow anaerobic filter treating abattoir wastewaters in Tunisia. The strain, designated LIND7H(T), grew at 20-45 °C (optimum 35-40 °C) and at pH 5.0-8.5 (optimum pH 6.5-7.5). It did not require NaCl for growth, but was able to grow in the presence of up to 2 % NaCl. Sulfate, thiosulfate, elemental sulfur, sulfite, nitrate and nitrite were not used as terminal electron acceptors. Strain LIND7H(T) used cellobiose, glucose, lactose, mannose, maltose, peptone, rhamnose, raffinose, sucrose and xylose as electron donors. The main fermentation products from glucose metabolism were lactate, acetate, butyrate and isobutyrate. The predominant cellular fatty acids were anteiso-C(15 : 0), C(15 : 0), C(17 : 0) 2-OH and a summed feature consisting of C(18 : 2)ω6,9c and/or anteiso-C(18 : 0), and the major menaquinones were MK-9, MK-9(H(2)) and MK-10. The G+C content of the genomic DNA was 41.4 mol%. Although the closest phylogenetic relatives of strain LIND7H(T) were Parabacteroides merdae, Parabacteroides goldsteinii and Parabacteroides gordonii, analysis of the hsp60 gene sequence showed that strain LIND7H(T) was not a member of the genus Parabacteroides. On the basis of phylogenetic inference and phenotypic properties, strain LIND7H(T) ( = CCUG 60892(T) = DSM 23697(T) = JCM 16313(T)) is proposed as the type strain of a novel species in a new genus within the family Porphyromonadaceae, Macellibacteroides fermentans gen. nov., sp. nov.