NOVELTY - A recombinant modified Gram-positive bacterium that displays on its surface one or more cellulolytic enzymes, the bacterium comprising (i) a protein comprising one or more cellulolytic enzymes covalently linked to the surface of the bacterium; and/or (ii) a protein comprising one or more cohesin domains covalently linked to the surface of the bacterium, is new.    USE - The bacterium is useful for degrading cellulosic biomass into fermentable sugars, and for identifying cellulolytic enzyme combinations or variants that enhance degradation of a particular substrate (all claimed).    DETAILED DESCRIPTION - A recombinant modified Gram-positive bacterium that displays on its surface one or more cellulolytic enzymes, the bacterium comprises (i) a protein comprising one or more cellulolytic enzymes covalently linked to the surface of the bacterium, and a nucleic acid construct that encodes the protein and comprising one or more cellulolytic enzymes attached to a secretory signal sequence at the N-terminus of the protein and a cell wall sorting signal at the carboxyl terminus of the protein; and/or (ii) a protein comprising one or more cohesin domains covalently linked to the surface of the bacterium, where the bacterium, comprises a nucleic acid construct that encodes the protein comprising the one or more cohesin domains attached to a secretory signal sequence at the N-terminus of the protein and a cell wall sorting signal at the carboxyl terminus of the protein. INDEPENDENT CLAIMS are:    (1) a method of degrading cellulosic biomass into fermentable sugars, by contacting the cellulosic biomass with a bacterium above under conditions in which the bacteria partially or fully degrade cellulose in the cellulosic biomass to form one or more fermentable sugars;    (2) a consolidated bioreactor for the conversion of a lignocellulosic biomass into bioethanol, comprising a culture system that cultures bacteria above under conditions in which the bacteria partially or fully degrade cellulose in the lignocellulosic biomass to form one or more fermentable sugars; and a culture system that ferments the sugars to form a biofuel;    (3) an isolated nucleic acid that encodes: a protein comprising one or more cellulolytic enzymes attached to a secretory signal sequence at the N-terminus of the protein and a cell wall sorting signal at the carboxyl terminus of the protein; and/or a protein comprising one or more cohesin domains attached to a secretory signal sequence at the N-terminus of the protein and a cell wall sorting signal at the carboxyl terminus of the protein;    (4) a vector comprising a nucleic acid of (3) operably linked to a promoter;    (5) a method of identifying cellulolytic enzyme combinations that enhance degradation of a particular substrate by providing recombinant bacteria above, where the bacteria each display at least two cellulolytic enzymes and different bacteria display different enzymes; contacting the substrate with the bacteria; and selecting bacteria that show enhanced degradation of the substrate and/or improved growth on the substrate; and    (6) a method of identifying cellulolytic enzyme variants that enhance degradation of a particular substrate by providing recombinant bacteria above, where the bacteria each display at least one cellulolytic enzyme variant and different bacteria display different cellulolytic enzyme variants; contacting the substrate with the bacteria; and selecting bacteria that show enhanced degradation of the substrate and/or improved growth on the substrate.