Translocation of proteins across the cell envelope of Gram-positive bacteria

In contrast to Gram-negative bacteria, secretory proteins of Gram-positive bacteria only need to traverse a single membrane to enter the extracellular environment. For this reason, Gram-positive bacteria (e.g. various Bacillu s species) are often used in industry for the commercial production of extr acellular proteins that can be produced in yields of several grams per lite r culture medium. The central components of the main protein translocation system (See system) of Gram-negative and Gram-positive bacteria show a high degree of conservation, suggesting similar functions and working mechanism s. Despite this fact, several differences can be identified such as the abs ence of a clear homolog of the secretion-specific chaperone SecB in Gram-po sitive bacteria. The now available detailed insight into the organization o f the Gram-positive protein secretion system and how it differs from the we ll-characterized system of Escherichia coli may in the future facilitate th e exploitation of these organisms in the high level production of heterolog ous proteins which, so far, is sometimes very inefficient due to one or mor e bottlenecks in the secretion pathway. In this review, we summarize the cu rrent knowledge on the various steps of the protein secretion pathway of Gr am-positive bacteria with emphasis on Bacillus subtilis, which during the l ast decade, has arisen as a model system for the study of protein secretion in this industrially important class of microorganisms. (C) 2001 Federatio n of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.