Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Patent
1991-08-05
1993-01-26
Robinson, Douglas W.
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
435161, 435163, 435165, 4352525, 435813, C12P 714, C12P 706, C12P 708
Patent
active
051821990
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to alcohol, that is to say ethanol, production by fermentation.
GENERAL DISCUSSION
Alcohol production from waste or by-product sugars whether arising as such or derived from conversion of other carbohydrates has long been known but is currently of growing importance. Cheap oil at present, and severe food shortages in particular regions, cannot detract from the basic unsoundness of relying on non-renewable energy sources when, properly managed, agriculture could provide food and energy world wide.
We have studied known alcohol production processes, largely by yeasts, and concluded that a key improvement in economic operation, if achievable in practice, is use of temperatures at which the alcohol can conveniently be removed directly as vapour from the fermentation medium. Yeasts of course are incapable of growth at such temperatures, and we have turned to thermophilic bacteria.
Yeasts ferment only glucose, maltose or sucrose whereas some bacteria can also utilise cellobiose from enzymic hydrolysis of cellulose or xylose and arabinose from hydrolysis of hemicellulose. The latter (pentose) sugars are the major components of waste streams from paper-making or from pretreatments of straw such as steam-explosion or dilute acid hydrolysis. The economics of ethanol production from sugar cane would for example be greatly improved if the bagasse could be so utilised as well as the juice.
Some thermophiles have been described which can utilise all these sugars to produce high yields of ethanol e.g. Clostridium thermosaccharolyticum, Cl. thermohydrosulfuricum or Thermoanaerobacter ethanolicus. However they are strict anaerobes and their reported properties compare unfavourably with the Bacillus stearothermophilus strains described below. Moreover we have seen that facultative anaerobes have additional advantages by allowing a novel mixed aerobic-anaerobic process which allows by-products of the anaerobic phase to be utilised aerobically to regenerate catalytic biomass.
Most facultative anaerobes do not produce high yields of ethanol. In previous disclosures we described a `metabolic steering` strategy whereby mutants believed to be of Bacillus stearothermophilus NCA 1503 may be manipulated to make high yields of ethanol .sup.1, 2. That strategy involved eliminating L-lactate production by selecting mutations in L-lactate dehydrogenase. The resulting mutant was expected to make acetate, ethanol and formate anaerobically in yields of 2:2:4 per mole of sucrose. Surprisingly however yields of ethanol were higher than this theoretical maximum under certain conditions, notably low pH and higher temperatures, and this was ascribed to a catalytic conversion of sucrose to ethanol+CO.sub.2 during a final non-growth stage in batch cultures.
We have now discovered that the results previously reported are to an extent in error in that the organism described is not a derivative of B. stearothermophilus NCA 1503 (NCIB 8924) as we assumed (Payton and Hartley 3) nor indeed of any specific known thermophilic bacillus. Instead it appears to be derived from a novel strain of the species Bacillus stearothermophilus that has properties that make it much superior to known strains for the purposes described above. In particular, it has a much higher growth rate than strain NCA 1503 both aerobically and anaerobically at temperatures above 60.degree. C. and grows anaerobically above 70.degree. C., at which temperature growth ceases with strain NCA 1503. Moreover, it utilises both cellobiose and the pentose sugars found in a crude dilute acid hydrolysis of wheat straw produced by the ICI process described by Ragg and Fields .sup.4.
Hence though this invention is not restricted to particular bacteria, it concerns facultative anaerobes such as B. stearothermophilus strain LLD-R (NCIB deposit details below) that rapidly ferment a wide range of sugars including cellobiose and pentoses both aerobically and anaerobically above 70.degree. C. Such strains would normally produce lactate anaerobically, but this
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Knode Marian C.
Robinson Douglas W.
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