Chemistry: molecular biology and microbiology – Treatment of micro-organisms or enzymes with electrical or... – Modification of viruses
Patent
1995-03-01
1998-11-17
Degen, Nancy
Chemistry: molecular biology and microbiology
Treatment of micro-organisms or enzymes with electrical or...
Modification of viruses
435 691, 435 711, 4352523, 4353201, 435853, 536 841, C12N 1511, C12N 1574, C12N 121, C12P 2102
Patent
active
058375090
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention pertains to the field of genetically improved food grade lactic acid bacteria. In particular there are provided methods for isolating useful lactic acid bacterial promoters and construction of recombinant lactic acid bacteria in which such promoters are utilized to obtain improved lactic acid bacteria which are useful in the manufacturing of foods, animal feed and probiotically active compositions.
TECHNICAL BACKGROUND AND PRIOR ART
For centuries, lactic acid bacterial cultures have been used in food production due to their ability to convert sugars by fermentation into preserving organic acids, predominantly lactic acid, and various metabolites associated with the development in fermented food products of desirable taste and flavour. Several lactic acid bacteria produce hydrolytic enzymes including peptidases, proteases and lipolytic enzymes, the production of which may e.g. contribute to a desired flavour development in cheeses.
However, for industrial production of a wide range of fermented food products such as all the well-known traditional dairy products including yoghurt, acidophilus milk, butter and cheeses; fermented vegetables; fermented meat products and animal feed, a large range of lactic acid bacterial starter cultures, each being adapted to particular types of food products, are required. Such cultures are presently being selected from naturally occurring strains of lactic acid bacteria on the basis of characteristics such as their ability to ferment sugars present in the food product to be fermented, specific growth temperature requirements, production of desired flavouring compounds, the specific combination of which characteristics renders a specifically selected wild-type culture useful for the production of a particular food product but normally less useful for the production of others.
Obviously, this presently used procedure for developing useful lactic acid bacterial cultures by selection of naturally occurring strains is cumbersome and costly. Furthermore, it has proven difficult to provide starter culture strains which combine all of the required characteristics at an optimal level. Presently, this problem is usually solved by the use of starter cultures comprising a multiplicity of selected lactic acid bacterial strains each having one or several of the characteristics desirable for a particular food product. The necessity to use such mixed cultures will of course add to the costs in the manufacture of lactic acid bacterial starter cultures.
Based on their traditional and long term application in food manufacturing and the fact that they are considered as non-pathogenic, the lactic acid bacteria are generally recognized as safe (GRAS) food ingredients, even if they are present in a fermented food product as live bacteria at a very high number, such as 10.sup.8 to 10.sup.9 per g.
Currently, it is widely recognized that a substantial industrial need exists to find economically and technically more feasible ways of developing starter cultures. It is obvious that gene technology may provide the means to meet this need. In this context, it is crucial that lactic acid bacteria for food manufacturing which are developed by introduction of desired genes by use of gene technology can still by recognized as safe for consumption. It is therefore considered by the industry that it is essential that recombinant lactic acid bacteria contain only DNA of lactic acid bacterial origin including DNA from wild-type extrachromosomal plasmids frequently found in starter culture strains or non-lactic acid bacterial DNA which does not confer to the recombinant strains any hazardous phenotypic traits.
There have been several attempts of providing genetically improved lactic acid bacteria. Most of these attempts have been directed to the construction of recombinant expression vectors coding for desired gene products and capable of replicating in lactic acid bacteria. However, very few of these attempts have resulted in vectors comprising only lactic acid bacterial DNA.
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Hansen Egon Bech
Israelsen Hans
Johansen Eric
Madsen Soeren Michael
Nilsson Dan
Bioteknologisk Institut
CHR Hansen's Laboratorium Danmark A/S
Degen Nancy
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