Microorganism strain for producing recombinant proteins

New microbial strain comprises a gene coding for a recombinant protein that is secreted during fermentation and a mutated gene that codes for a host protein and has a mutation such that expression of the host protein is reduced. Independent claims are also included for: (1) producing a microbial strain as above by transforming a host cells with the gene for the recombinant protein, culturing the cell in a fermentation medium so that the recombinant protein and host proteins are secreted into the medium, characterizing the host proteins, and reducing or preventing expression of a gene coding for one of the host proteins; (2) producing a recombinant protein by culturing a microbial strain as above in a fermentation medium and then separating the medium from the cells of the microbial strain.