Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Recombinant dna technique included in method of making a...
Patent
1998-09-11
2000-11-21
Yucel, Remy
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Recombinant dna technique included in method of making a...
435243, 435244, 4352523, 43525233, 43525411, 43525421, C12N 1500
Patent
active
061501336
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the control of fed-batch or continuous fermentation processes. In fermentation processes where a maximum biomass yield is required or the build-up of acids such as acetic acid might become toxic or may be detrimental to the product, the presence of such acids is undesirable.
BACKGROUND AND PRIOR ART
Correct control of medium addition rate to fermentation processes where accumulation of metabolites is to be prevented is a primary objective. Some microorganisms produce undesirable metabolites when fed at too high a medium addition rate. Examples are Bakers' yeast and Escherichia coli (De Deken, 1966; Doelle, 1981). Bakers' yeast will produce fermentation products such as ethanol and acetate when too much sugar is added (Fiechter et al, 1981). During the production of Bakers' yeast this will cause a loss of cell and product yield (Fiechter et al, 1981). The bacterium E. coli will produce acids such as acetic acid at sugar excess (Doelle, 1981). Also when microorganisms are used for the production of heterologous products the formation of these metabolites is undesirable, especially when these have a toxic or inhibitory effect. Acetate, ethanol and organic acids in general can be toxic to cell metabolism (Moon, 1983; Pampulha & Loureiro-Dias, 1989). This will become particularly apparent when growing mutant strains, which are often less robust than the wild-type strain. Therefore, good control of the feed addition rate to a fed-batch or continuous fermentation process is desirable.
Many ways of on-line computer control are possible. For example CO.sub.2 evolution rates and O.sub.2 consumption rates are often analysed on-line to calculate the so-called Respiratory Quotient (RQ) (Wang et al, 1977). The RQ is the CO.sub.2 evolution rate divided by the O.sub.2 consumption rate. Under sugar-limited conditions the RQ will be approximately 1.multidot.0 to 1.multidot.1, the exact value depending on the strain. However, when a culture of Bakers' yeast is fed at too high a sugar addition rate ethanol will be produced and the RQ values in that case will then be significantly higher than 1.multidot.1 (Wang et al, 1977; Fiechter et al, 1981). This then can be used to change the feed rate such that the RQ decreases (Wang et al, 1977).
EP 283 726 (Hitachi) and Turner et al (1994) disclose the control of fermentations by monitoring acetate levels, but the control was achieved by sampling the medium and using HPLC or similar discontinuous methods. HPLC has also been used to measure glucose levels in order to control acetate accumulation (Sakamoto et al, 1994).
The problem which is solved by the present invention is to provide an alternative and improved method of controlling such fermentations.
One aspect of the present invention provides a process of culturing a microorganism in a culture medium in which process the addition of feed medium is controlled by using the production of a by-product as a measure of the culture conditions, characterised in that the by-product is an electrically charged metabolite produced by the microorganism, and in that the production of the metabolite is monitored by measuring the conductance of the culture medium.
The evolution of electrically charged metabolites has not been used previously to control the addition of feed medium. RQ, for example, is 1 (one) when acetate is produced in a sugar fermentation, so RQ measurement is not useful, as this RQ value is near that obtained during sugar-limited growth. Electrical conductivity has been used to measure the formation of relatively large amounts of desired organic acids such as lactate in yogurt cultures and other lactobacillus fermentations (Latrille et al, 1992; Belfares et al, 1993), acetic acid production (SU-A-1 495 367) and for the control of salt content of fermentation cultures (Soyez et al, 1983). In the latter case, inorganic salts were added to the medium, and the technique simply measured those artificially added salts in order to maintain a desired salt concentration. Conduc
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Mead David John
van Urk Hendrik
Biswas Naomi S.
Delta Biotechnology Limited
Yucel Remy
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