Abstract: An assay is provided for determining the presence of contaminating microbial host cells in a culturing vessel containing a microbial host cell strain that utilizes more than one carbohydrate source as a substrate comprising:(a) culturing the microbial host cell strain in the vessel, wherein the strain comprises nucleic acid encoding a polypeptide of interest and is genetically marked so as not to utilize a carbohydrate source as a substrate;(b) plating an isolated sample of culture from step (a) onto culture media supplemented with a carbohydrate source not utilized by the host cell strain as a substrate;(c) incubating the plated cells at a temperature and for a time sufficient for any positive colony to grow to a detectable level; and(d) detecting whether any colonies are growing on the supplemented culture media.

Abstract: An assay is provided for determining the presence of contaminating microbial host cells in a culturing vessel containing a microbial host cell strain that utilizes more than one carbohydrate source as a substrate comprising:(a) culturing the microbial host cell strain in the vessel, wherein the strain comprises nucleic acid encoding a polypeptide of interest and is genetically marked so as not to utilize a carbohydrate source as a substrate;(b) plating an isolated sample of culture from step (a) onto culture media supplemented with a carbohydrate source not utilized by the host cell strain as a substrate;(c) incubating the plated cells at a temperature and for a time sufficient for any positive colony to grow to a detectable level; and(d) detecting whether any colonies are growing on the supplemented culture media.

Abstract: A method for refolding insoluble, improperly folded IGF-I is provided, wherein the IGF-I, precipitated from prokaryotic host cells, is concurrently solubilized, unfolded, and refolded into a biologically active conformation in a single buffer. The buffer contains reducing agent and chaotropic agent to solubilize the IGF-I at concentrations sufficiently low to allow solubilization and refolding to occur. Also provided is a triple-protease deficient E. coli host suitable for use in the process.

Abstract: A method for refolding insoluble, improperly folded IGF-I is provided, wherein the IGF-I, precipitated from prokaryotic host cells, it concurrently solubilized, unfolded, and refolded into a biologically active conformation in a single buffer. The buffer contains reducing agent and chaotropic agent to solubilize the IGF-I at concentrations sufficiently low to allow solubilization and folding to occur. Also provided is a triple-protease deficient E. coli host suitable for use in the process.