Aims: To verify the taxonomic affiliation of bacterium Butyrivibrio fibrisolvens strain A from our collection and to characterize its enzyme(s) responsible for digestion of sucrose. Methods and Results: Comparison of the 16S rRNA gene of the bacterium with GenBank showed over 99% sequence identity to the species Pseudobutyrivibrio ruminis. Molecular filtration, native electrophoresis on polyacrylamide gel, zymography and thin layer chromatography were used to identify and characterize the relevant enzyme. An intracellular sucrose phosphorylase with an approximate molecular mass of 52 kDa exhibiting maximum activity at pH 6 center dot 0 and temperature 45 degrees C was identified. The enzyme was of inducible character and catalysed the reversible conversion of sucrose to fructose and glucose-1-P. The reaction required inorganic phosphate. The K-m for glucose-1-P formation and fructose release were 3 center dot 88 x 10(-3) and 5 center dot 56 x 10(-3) mol l(-1) sucrose, respectively - while the V-max of the reactions were -0 center dot 579 and 0 center dot 9 mu mol mg protein(-1) min(-1). The enzyme also released free glucose from glucose phosphate. Conclusion: Pseudobutyrivibrio ruminis strain A utilized sucrose by phosphorolytic cleavage. Significance and Impact of the Study: Bacterium P. ruminis strain A probably participates in the transfer of energy from dietetary sucrose to the host animal.