NOVELTY - Expression system for producing a multi-enzyme complex, comprises a nucleic acid molecule containing a promoter operatively linked to a nucleotide sequence including 1 to 150 genes encoding 1 to 150 enzymes that are components of the multi-enzyme complex, where the genes of the nucleotide sequence are regulated artificially to allow expression of the enzymes in a desired level ratio such that the multi-enzyme complex exhibits a desired enzymatic specificity and enzymatic activity.    USE - The expression system is useful for producing multi-enzyme complex. The system, host cell and methods are useful for expressing cellulosome; producing cellusome; and for degrading biomass (all claimed).    ADVANTAGE - The invention provides high order multi-enzyme complexes for use in efficient degradation of biomass and other purposes.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) a host cell for expressing a cellulosome, comprising a nucleic acid molecule containing a promoter operatively linked to a nucleotide sequence including 1 to 150 genes encoding 1 to 150 enzymes that are components of the cellulosome and a gene that encodes a scaffolding protein that is capable of binding to the 1 to 150 enzymes, where the genes of the nucleotide sequence are regulated artificially to allow expression of the enzymes in a desired level ratio such that the multi-enzyme complex exhibits a desired enzymatic specificity and enzymatic activity;    (2) a method for producing a cellusome, comprising growing the host cell in a liquid culture under conditions that allow expression of the scaffolding protein, the 1 to 150 enzymes, and the microbial cell surface protein, where the 1 to 150 enzymes, the scaffolding protein and the microbial cell surface protein assemble to form the cellulosome; and    (3) a method of degrading a biomass comprising providing the host cell; growing the host cell in a liquid culture under conditions allowing expression of the cellusome; collecting: (i) the cell; or (ii) a supernatant of the culture and isolating the cellulosome from the supernatant; and contacting the collected cell or the isolated cellusome with a biomass, where the cellusome on the collected cell or the isolated cellusome degrades the biomass.