Attempts to improve Bacilus subtilis protein secretion using genomics information
Sierd Bron1, Siger Holsappel1, Harold Tjalsma1, Jan Jongbloed1, and Jan Maarten van Dijl1,2
1 Department of Molecular Genetics, University of Groningen, P.O. Box 14,9750 AA Haren, the Netherlands;
2 Department of Pharmaceutical Biology, University of Groningen, A. Deusinglaan 1,9713 AV Groningen, the Netherlands
Bacillus subtilis has become the paradigm for Gram-positive bacteria. The available genome sequence has made this bacterium highly transparent at the DNA level, and genomic research projects are already on their way. Moreover, B. subtilis and related bacilli are industrially important cell factories, in particular for the production of secreted proteins. In this presentation, the emphasis will be on protein secretion by B. subtilis, in particular on the importance of genomic information in this field.
The Commission of the EU has financed both the B. subtilis genome sequencing and gene function analysis projects. In these projects, a very successful cooperation with our Japanese colleagues was established. In addition, three successive projects on B. subtilis protein secretion, and one on global gene regulation, were sponsored by the EU. These projects provide a wealth of new information, which is also important for future developments. In Europe, the major Bacillus protein secretion pathway ("Sec pathway") has mainly been studied by the European Bacillus Secretion Group (EBSG). Most components of this pathway are now known and these will be discussed globally. Several potential bottlenecks, in particular for the production of heterologous secretory proteins, have been identified.
One of the striking outcomes of the B. subtilis genome projects was the presence of a great number of paralogous genes, that is: related genes on the same genome. We will illustrate this with the signal peptidase gene family as an example. The presence of paralogous genes can seriously hamper the analyses of gene function, since the effects of mutations in one gene of the family are likely to be masked by other members of the family.
In addition to the major Sec pathway for protein secretion, alternative pathways have recently been identified. The Twin-Arginine-Transport (TAT) pathway is one of these. Genome information indicates that this pathway does exist in B. subtilis. Evidence for this idea will be presented.
We are currently setting up the DNA-micro-array system for transcription profile analyses. These, and other, analyses will help to define the secretome of this bacterium involving all components which directly or indirectly affect protein secretion. In addition to the primary components of the secretion apparatus, the secretome also includes the secretory proteins, and those functions affecting the quality and quantity of secreted proteins.
