Bacterial Protein Export

Abstract

Consideration of protein export by bacteria is of major importance to many research institutions and industrial organisations currently involved in biotechnology. Bacteria (in particular, Escherichia coli), are used as hosts for the biosynthesis of proteins. Genes encoding these products may have been introduced into the cells by the elegant and powerful techniques of genetic engineering. It would be highly desirable if the bacterial host could export such proteins into the extracellular medium, namely the fermentation broth. There are two principal reasons for this: first, downstream processing (i.e. product separation, concentration and purification) would be simplified and, consequently, less expensive, and second, export would overcome the problem of product degradation by intracellular protease enzymes. Both of these factors could well influence the financial viability of a process and are, therefore, of significant concern to the biotechnologist. What is desired and what can be achieved are, however, entirely different and this is, in part, questioning the continuing use of existing bacterial strains in recombinant DNA technology. There are other factors relating to host suitability which need to be taken into account — for example, genetic instability, glycosylation, pyrogen and toxin production; these will be discussed later.