高温厌氧条件下纤维素的直接乙醇发酵

本文介绍了出分解纤维素的嗜热厌氧菌Clostridium celluloflavus sp.nov.直接发酵纤维素产乙醇的初步研究、发酵于60℃下进仃,其主要产物为乙醇、乙酸、氢气和二氧化碳。文中介绍了间歇发酵的若干特征与影响发酵的因素,1％纤维素发酵至120小时,大约有70％纤维素被分解;乙醇的转化率约为0.36g/g降解纤维素;发酵液中乙醇浓度达到56至61mM。发酵中乙醇与乙酸浓度的比值因发酵时间与其它发酵条件的不同而不同。     

Glycerol accumulation while recycling thin stillage in corn fermentations to ethanol

Summary By succesive recycling of the thin stillage in mashing and fermenting fresh corn, the glycerol content in each fermentation increased by about 0.4% and accumulated to a high of 2.1% in the beer of the fifth recycle. Glycerol concentration declined after the fifth recycle. The original fermentation contained 0.8% glycerol.Presented in part at the Society for Industrial Microbiology Annual Meeting, August 7–12, 1988, Chicago, IL.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Transformation of the extremely thermoacidophilic archaeon Sulfolobus solfataricus via a self-spreading vector

Abstract The comparative chromosomal locations of polymeric β-fructosidase SUC genes have been determined by Southern blot hybridization with the SUC2 probe in 91 different strains of Saccharomyces cerevisiae . Most of the strains exhibited a single SUC2 gene, but in some strains two or three SUC genes were found. All Suc⁻ strains carried a silent suc2⁰ sequence. The accumulation of SUC genes was observed in populations derived from sources containing sucrose and seems to be absent in strains from sources promoting the MEL gene.     

自养黄杆菌合成羟基丁酸和羟基戊酸共聚体的发酵研究

采用本实验室从土壤中分离到的一株自养黄杆菌进行了羟基丁酸和羟基戊酸共聚体〔P(HB-co-HV)〕的发酵试验。实验结果表明,该菌株是自养黄杆菌葡萄糖运输突变株,可以葡萄糖、果糖、蔗糖、麦芽糖、乙酸盐、乳酸盐和苹果酸盐作为唯一碳源,尤以葡萄糖和果糖效果最佳。硫酸铵、氯化铵和蛋白胨等不同氮源不影响其生长,却影响细胞中P(HB-co-HV)的含量和P(HB-co-HV)中HV/HB的比例。应用两阶段控制方式,经42h的补料分批发酵,细胞浓度达34.9g·L~(-1),P(HB-co-HV)浓度达25.28g·L~(-1)。细胞和P(HB-co-HV)生产速率系数分别为0.83g·L~(-1)”·h~(-1)和0.61g·L~(-1)·h~(-1)。以基质为基准的细胞得率系数(Yx/s)、产物得率系数(Yp/s)和以干细胞为基准的产物得率系数(Yp/x)分别为0.283(g/g)、0.174(g/g)和0.73(g/g)。改变培养基中碳氮源组分可将P(HB-co-HV)中HB的含量调节在24％～78％之间。     

Production of fuel alcohol from oats by fermentation

Very high gravity (>30 g dissolved solids per 100 ml) mashes were prepared from hulled and hulless oats and fermented at 20° C with active dry yeast to produce ethanol. Excessive viscosity development during mashing was prevented by hydrolyzing -glucan with crude preparations of -glucanase or Biocellulase. Both these preparations possessed endo--glucanase activity. By using these enzymes and by decreasing the water to grain ratio, very high gravity mashes with low viscosity were prepared. Unlike wheat and barley mashes, oat mashes contained sufficient amounts of assimilable nitrogen to promote a fast rate of fermentation. The free amino nitrogen (FAN) content of oat mash could be predicted by the equation, mg FAN L^–1=8.9n wheren is the number of grams of dissolved solids in 100 ml of mash supernatant fluid. Ethanol yields of 353.2±3.7 L and 317.6±1.3 L were obtained per tonne (dry weight basis) of hulless (59.8% starch) and hulled (50.8% starch) oats respectively. The efficiency of conversion of starch to ethanol was the same in normal and very high gravity mashes.     

The carboxylate type siderophore rhizoferrin and its analogs produced by directed fermentation

Summary Rhizoferrin is a novel carboxylate-type siderophore which has recently been isolated fromRhizopus microsporus and other fungi of the Mucorales (Zygomycetes). The present investigation shows that a variety of rhizoferrin analogs can be produced by directed fermentation. Thus both the diaminobutane backbone and the citric acid side chains of rhizoferrin have been substituted by diamine and citric acid analogs added to the culture medium. The new ligands as well as their iron complexes have been characterized by physicochemical methods. Conditions of precursor incorporation and implications for the biosynthesis of the new siderophores are discussed.     

Metabolic interactions between anaerobic bacteria in methanogenic environments

In methanogenic environments organic matter is degraded by associations of fermenting, acetogenic and methanogenic bacteria. Hydrogen and formate consumption, and to some extent also acetate consumption, by methanogens affects the metabolism of the other bacteria. Product formation of fermenting bacteria is shifted to more oxidized products, while acetogenic bacteria are only able to metabolize compounds when methanogens consume hydrogen and formate efficiently. These types of metabolic interaction between anaerobic bacteria is due to the fact that the oxidation of NADH and FADH₂ coupled to proton or bicarbonate reduction is thermodynamically only feasible at low hydrogen and formate concentrations. Syntrophic relationships which depend on interspecies hydrogen or formate transfer were described for the degradation of e.g. fatty acids, amino acids and aromatic compounds.     

Cultivation of Aspergillus niger in a pilot plant external-loop air-lift bioreactor

Abstract: Changes of the main hydrodynamic and oxygen transfer parameters during Aspergillus niger cultivation in an external-loop air-lift bioreactor of 200 dm³ operating capacity were investigated. The final average concentrations of biomass and citric acid obtained in batch fermentations were about 17 g 1^-1 and 90 g 1^-1, respectively. Significant influence of the increasing biomass concentration on the rheological properties of the broth and operating parameters was found. Volumetric oxygen transfer coefficient. k ^L a , was found to be dependent on the apparent viscosity of the broth with an exponent of -0.984.     

Acetaldehyde production in Saccharomyces cerevisiae wine yeasts

Abstract Eighty-six strains of Saccharomyces cerevisiae were investigated for their ability to produce acetaldehyde in synthetic medium and in grape must. Acetaldehyde production did not differ significantly between the two media, ranging from a few mg/l to about 60 mg/l, and was found to be a strain characteristic. The fermentation temperature of 30°C considerably increased the acetaldehyde produced. This study allowed us to assign the strains to different phenotypes: low, medium and high acetaldehyde producers. The low and high phenotypes differed considerably also in the production of acetic acid, acetoin and higher alcohols and can be useful for studying acetaldehyde production in S. cerevisiae , both from the technological and genetic point of view.     

Kinetics of growth and sugar consumption in yeasts

An overview is presented of the steady- and transient state kinetics of growth and formation of metabolic byproducts in yeasts.Saccharomyces cerevisiae is strongly inclined to perform alcoholic fermentation. Even under fully aerobic conditions, ethanol is produced by this yeast when sugars are present in excess. This so-called Crabtree effect probably results from a multiplicity of factors, including the mode of sugar transport and the regulation of enzyme activities involved in respiration and alcoholic fermentation. The Crabtree effect inS. cerevisiae is not caused by an intrinsic inability to adjust its respiratory activity to high glycolytic fluxes. Under certain cultivation conditions, for example during growth in the presence of weak organic acids, very high respiration rates can be achieved by this yeast.S. cerevisiae is an exceptional yeast since, in contrast to most other species that are able to perform alcoholic fermentation, it can grow under strictly anaerobic conditions.Non-Saccharomyces yeasts require a growth-limiting supply of oxygen (i.e. oxygen-limited growth conditions) to trigger alcoholic fermentation. However, complete absence of oxygen results in cessation of growth and therefore, ultimately, of alcoholic fermentation. Since it is very difficult to reproducibly achieve the right oxygen dosage in large-scale fermentations, non-Saccharomyces yeasts are therefore not suitable for large-scale alcoholic fermentation of sugar-containing waste streams. In these yeasts, alcoholic fermentation is also dependent on the type of sugar. For example, the facultatively fermentative yeastCandida utilis does not ferment maltose, not even under oxygen-limited growth conditions, although this disaccharide supports rapid oxidative growth.