FROM GENOME TO INDUSTRIAL APPLICATION

From genome to industrial application. The possibility to use modified microorganisms constructed by genetic engineering for food production in the next future will radically change our approach to optimize pro cesses and improve the quality of the corresponding products. The rese arch holding on this domain should allow the construction of strains m ore resistant to phage attack, producing new molecules (e.g. beneficia l for health) or modified for their metabolism (growth, production of metabolites, resistance to stress, etc). The construction of such stra ins can be achieved by genetic engineering, either by modifying a path way, or by expressing new genes. The engineering of known pathways all owed the development of new process and some of them are technically r eady to be applied in the industry. For example, the expression of the anabolic acetolactate synthase, the inactivation of the LDH or of the acetolactate decarboxylase lead to the redirection of pyruvate to dia cetyl instead of lactate. This might lead to a 10-fold increase in dia cetyl production, and there are still some possibilities of improvemen t. Another project of metabolic engineering that is quite advanced, is the modification of proteolysis in Lactococcus lactis, including the degradation of casein, peptides and amino acids. Most genes involved i n the assimilation of proteins have been characterized (cell-wall prot ease, peptides transporters, and peptidases). Isogenic strains with di fferent level of peptidase activities are built in order to improve pe ptidolysis or change the pattern of its product. In addition to the mo dification of already existing pathways, the introduction of new pathw ays in a cell could brighten the metabolic possibilities of bacteria a nd lead to the construction of new strains, producing new aroma for ex ample. Building a new pathway generally requires the expression of het erologous genes. However, the certitude that a gene is absent supposes that there is an exhaustive knowledge of the bacterial genome, as som e genes may be cryptic or uninduced under the conditions tested in the laboratory. Although the important progresses in the research related to lactic acid bacteria in the last years, only few pathways have bee n well characterized, covering, in terms of genetic information, a sma ll percentage of the real metabolic possibilities. The size of the chr omosome of most lactic acid bacteria is usually 1.8-3.3 Mb, about the half of the one of Escherichia coli, Bacillus subtilis and of some soi l bacteria which have broad metabolic possibilities. On the other side , it is 4-5 fold the size of the smallest known genome, suggesting tha t the metabolic potentialities of lactic acid bacteria an underestimat ed. An investigation of data present in databases shows that only 6% o f the genome of L. lactis an available. These data cover genes involve d in amino acids and base biosynthesis (33%), degradation of peptides (17%), carbon catabolism (16%), stress responses (13%) and the remaini ng genes are related to the cell machinery (ribosome, replication, sec retion, etc). The real potentialities of these bacteria remain to be e stimated and exploited. (C) Inra/Elsevier, Paris.