The gene (1272-bp) encoding a beta-1,4-mannanase from a gut bacterium of Eisenia fetida, Cellulosimicrobium sp. strain HY-13 was cloned and expressed in Escherichia coli. The recombinant beta-1,4-mannanase (rManH) was approximately 44.0 kDa and has a catalytic GH5 domain that is 65% identical to that of the Micromonospora sp. beta-1,4-mannosidase. The enzyme exhibited the highest catalytic activity toward mannans at 50 degrees C and pH 6.0. rManH displayed a high specific activity of 14,711 and 8498 IU mg(-1) towards ivory nut mannan and locust bean gum, respectively: however it could not degrade the structurally unrelated polysaccharides, mannobiose, or p-nitrophenyl sugar derivatives. rManH was strongly bound to ivory nut mannan, Avicel, chitosan, and chitin but did not attach to curdlan, insoluble oat spelt xylan, lignin, or poly(3-hydroxybutyrate). The superior biocatalytic properties of rManH suggest that the enzyme can be exploited as an effective additive in the animal feed industry. (C) 2011 Elsevier Ltd. All rights reserved.