Xylose fermentation by yeasts

Summary Utilization and fermentation of xylose by the yeasts Pachysolen tannophilus I fGB 0101 and Pichia stipitis 5773 to 5776 under aerobic and anaerobic conditions are investigated. Pa. tannophilus requires biotin and thiamine for growth, whereas Pi. stipitis does not, and growth of both yeasts is stimulated by yeast extract. Pi. stipitis converts xylose (30 g/l) to ethanol under anaerobic conditions with high yields of 0,40 and it produces only low amounts of xylitol. The yield coefficient is further increased at lower xylose concentrations.Publication Nr. 2 of this series: Eur. J. Appl. Microbiol. Biotechnol. (1983) 17, 287–291.     

Isolation and characterization of a symbiotic cellulolytic mixed bacterial culture

Summary By using batch-culture enrichment techniques a mixed culture of two bacterial spe cies identified as Cellulomonas flavigena and Xanthomonas sp was isolated. The capacity of both bacteria to grow as pure cultures in a min eral medium with alkaline pretreated sugar cane bagasse or cellobiose was tested. C. flavigena as pure culture was able to grow on both substrates only when yeast extract or biotin and thiamine were added to the culture medium, while Xanthomonas sp. could not grow on sugar cane ba gasse, but assimilated cellobiose if yeast extract was supplied. However, both bacteria in mixed culture grew very well on both substrates and did not require any growth factor. It was concluded that the interaction was favourable to both species. The mixed culture had the capacity to degrade a number of different agricul tural wastes and to use them as the sole carbon and energy source for the production mainly of biomass. More than 80% of pineapple bagasse, without chemical pretreatment, was used up by the microbial system.     

An investigation of ethanol inhibition and other limitations occurring during the fermentation of concentrated whey permeate byKluyveromyces fragilis

Based on the well-known fact thatKluyveromyces fragilis strains show sub-optimal performance when grown in concentrated whey permeate, previously optimized medium was investigated for possible limitations appearing at high concentrations. Shaken flask cultures showed that no additional vitamin or mineral sources were required when the optimized amount of yeast extract was added to the concentrated permeate. Several aspects of the ethanol inhibition of the growth ofK. fragilis NRRL 665 were investigated in continuous culture. The maximum ethanol concentration tolerated by this yeast, i.e. 45 g/l, was much lower than commonly reported for other strains. Ethanol and biomass production were also influenced by the increased ethanol concentration of the medium. At 31 g/l of alcohol product yield was reduced to 0.23 g/g whereas biomass yield was 0.05 g/g. Some evidence suggested that residence time and residual lactose concentration played a significant role in modulating the toxic effect of ethanol.     

Electron flow shift inClostridium acetobutylicum fermentation by electrochemically introduced reducing equivalent

Electrochemical energy as a source of reducing equivalent was applied to the cultures ofClostridum acetobutylicum to understand the effects of the pressure by reducing equivalent on anaerobic bacteria. The fermentation byC. acetobutylicum with methyl viologen and electrochemical energy produced more butanol (up to 26%) than the control culture, whilst less acetone (up to 25%) was produced. But no effect was observed on the growth of the culture. These results were indirectly supported byin vitro electrochemical reduction of NAD⁺ and artificial electron carriers.     

The effect of aeration on D-xylose fermentation byPachysolen tannophilus,Pichia stipitis,Kluyveromyces marxianus andCandida shehatae

Summary The fermentation of D-xylose byPachysolen tannophilus Y2460,Pichia stipitis Y7124,Kluyveromyces marxianus Y2415 andCandida shehatae Y12878 was investigated in aerobic, anaerobic and microaerophilic batch cultures. The aeration rate greatly influenced the fermentations; growth, rate of ethanol production and oxidation of ethanol are affected. Of the strains tested,Pichia stipitis appears superior; under anaerobic conditions it converts D-xylose (20 g/l) to ethanol with a yield of 0.40 g/l and it exhibits the highest ethanol specific productivity (3.5 g of ethanol per g dry cell per day) under microaerophilic conditions.     

Production of dextranase byLipomyces starkeyi

Summary The optimal growth rate ofLipomyces starkeyi, with dextran as sole carbon source, was found within the pH range 2.5–4.0, and temperature between 25–30°C. This yeast was unable to grow above 33°C. Dextranase production optima paralleled growth optima, except at pH 2.5. Decrease in enzyme yield at this pH could not be attributed to poor yeast growth or enzyme stability.     

The effect of various atmospheric conditions on the 2,3-butanediol fermentation from glucose byBacillus polymyxa

The examination of the effect of N₂, air and O₂ on the glucose to 2,3-butanediol fermentation byBacillus polymyxa showed that N₂ sparging resulted in best 2,3-butanediol production at low yeast extract concentration (0.5%, w/v) whereas aeration produced best results with high yeast extract levels (1.2%, w/v). However, under all atmospheric conditions, improvements in rates and yields of 2,3-butanediol production and rates of glucose utilization were observed with high yeast extract. Regardless of the yeast extract levels, highest concentrations of ethanol and acetoin were obtained with N₂ sparging and aeration respectively. No acetoin accumulated under anaerobic (N₂) conditions and no ethanol accumulated with aeration. The rate of glucose utilization, in all fermentations, was highest under N₂ and lowest with O₂ sparging. In addition to the biochemical results, morphological observations with O₂, N₂ and air sparging are also reported.NRCC No. 23868     

Production of extracellular 5-aminolevulinic acid byClostridium thermoaceticum grown in minimal medium

Summary A growth associated formation of extracellular 5-aminolevulinic acid (ALA) was found in the homoacetogenesis of glucose byClostridium thermoaceticum grown in minimal defined medium. The growth and ALA production was enhanced by L-cysteine HCl both in complex medium (UM) and minimal defined medium (MDM). The amount of ALA produced extracellularly in MDM wasca. 15 mg/L after 90-h anaerobic cultivation (cell-mass: 1.5 g/l; glucose consumed: 20 g/l).     

Kinetics of biphasic growth of yeast in continuous and fed-batch cultures

The influence of dilution rate on the production of biomass, ethanol, and invertase in an aerobic culture of Saccharomyces carlsbergensis was studied in a glucose-limited chemostat culture. A kinetic model was developed to analyze the biphasic growth of yeast on both the glucose remaining and the ethanol produced in the culture. The model assumes a double effect where glucose regulates the flux of glucose catabolism (respiration and aerobic fermentation) and the ethanol utilization in yeast cells. The model could successfully demonstrate the experimental results of a chemostat culture featuring the monotonic decrease of biomass concentration with an increase of dilution rate higher than 0.2 hr^?1 as well as the maximum ethanol concentration at a particular dilution rate around 0.5 hr^?1. Some supplementary data were collected from an ethanol-limited aerobic chemostat culture and a glucose-limited anaerobic chemostat culture to use in the model calculation. Some parametric constants of cell growth, ethanol production, and invertase formation were determined in batch cultures under aerobic and anaerobic states as summarized in a table in comparison with the chemostat data. Using the constants, a prediction of the optimal control of a glucose fed-batch yeast culture was conducted in connection with an experiment for harvesting a high yield of yeast cells with high invertase activity.     

Symbiotic growth of a yeast and a bacteria in batch fermentors

Summary Single cell protein was produced from cassava starch by symbiotic growth of the -amylase producing bacteria Bacillus subtilis and the yeast Candida utilis, which is accepted as fodder. By batch fermentations it was shown, that the pH fluctuation during the fermentation and the inoculum were extremely important parameters.     

Production of HBsAg by growth rate control with recombinantSaccharomyces cerevisiae in fed-batch

Summary To maintain a constant specific growth rate for a recombinantS.cerevisiae in fed-batch, the medium feeding rate has been controlled with respect to the hourly calculated glucose uptake rate. The recombinant yeast producing HBsAg showed the exponential production trend in proportion to the exponential cell growth. Total cell yield in fed-batch was about 0.402 g cells/g glucose, and HBsAg was produced about ten times more than in batch. Decrease of growth rate by HBsAg produced was not shown.     

The kinetics of glucose fermentation bySelenomonas ruminantium HD4 grown in continuous culture

Summary The production of organic acids (acetate, lactate, and propionate) by the anaerobic, ruminal bacteriumSelenomonas ruminantium HD4 was investigated in both glucose-limited and glucose-sufficient (phosphate-limited) continuous cultures. The fermentation pattern of products exhibited a shift upon release of glucose limitation from acetate and propionate to lactate at a dilution rate of 0.2 h^–1. Glucose sufficiency brought about two-to fourfold increase in specific glucose utilization rate, lactate productivity, and lactate yield relative to glucose-limited growth conditions. The increased lactate production under glucose-sufficient growth conditions was attributed to the overutilization of excess glucose.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.     

Fermentation of cellobiose and wood sugars to ethanol byCandida shehatae andPichia stipitis

Summary Three pentose fermenting yeast strains ofCandida shehatae and three ofPichia stipitis were examined for their ability to produce ethanol from cellobiose and from sugars liberated by hydrolysis of lignocellulosic biomass. All of thePichia strains tested produced some ethanol;P. stipitis CBS 5776 gave the highest yield: 10.3 g/L on complete fermentation of 25 g/L cellobiose within 48 hours. This yeast also produced considerably more ethanol from the wood sugar mixture.     

The Arabidopsis <Emphasis Type="Italic">AtRaptor</Emphasis> genes are essential for post-embryonic plant growth

Background  

Flowering plant development is wholly reliant on growth from meristems, which contain totipotent cells that give rise to all post-embryonic organs in the plant. Plants are uniquely able to alter their development throughout their lifespan through the generation of new organs in response to external signals. To identify genes that regulate meristem-based growth, we considered homologues of Raptor proteins, which regulate cell growth in response to nutrients in yeast and metazoans as part of a signaling complex with the target of rapamycin (TOR) kinase.     

Enhancement in xylose utilization using <Emphasis Type="Italic">Kluyveromyces marxianus</Emphasis> NIRE-K1 through evolutionary adaptation approach

The evolutionary adaptation was carried out on the thermotolerant yeast Kluyveromyces marxianus NIRE-K1 at 45 °C up to 60 batches to enhance its xylose utilization capability. The adapted strain showed higher specific growth rate and 3-fold xylose uptake rate and short lag phase as compared to the native strain. During aerobic growth adapted yeast showed 2.81-fold higher xylose utilization than that of native. In anaerobic batch fermentation, adapted yeast utilized about 91 % of xylose in 72 h and produced 2.88 and 18.75 g l^?1 of ethanol and xylitol, respectively, which were 5.11 and 5.71-fold higher than that of native. Ethanol yield, xylitol yield and specific sugar consumption rate obtained by the adapted cells were found to be 1.57, 1.65 and 4.84-fold higher than that of native yeast, respectively. Aforesaid results suggested that the evolutionary adaptation will be a very effective strategy in the near future for economic lignocellulosic ethanol production.     

Accumulation of isoflavones and pterocarpan phytoalexins in cell suspension cultures of different cultivars of chickpea (Cicer arietinum)

Cell suspension cultures of chickpea (Cicer arietinum L.) were established from cultivars ILC 3279 and ILC 1929, resistant and susceptible towards the chickpea pathogenic fungus Ascochyta rabiei. The two cell culture lines possess identical growth properties and show high accumulation of the isoflavones biochanin A and formononetin together with their glucoside and malonylglucoside conjugates. The cultures of the two cultivars, however, significantly differ in their accumulation of the phytoalexins medicarpin and maackiain essentially as previously demonstrated for the plant genotypes. Phytoalexin formation was elicited by using yeast extract as an inducing agent.     

The Arabidopsis Mei2 homologue AML1 binds AtRaptor1B,the plant homologue of a major regulator of eukaryotic cell growth

Background  

TOR, the target of the antibiotic rapamycin in both yeast and mammalian cells, is a potent cell growth regulator in all eukaryotes. It acts through the phosphorylation of downstream effectors that are recruited to it by the binding partner Raptor. In Arabidopsis, Raptor activity is essential for postembryonic growth. Though comparative studies suggest potential downstream effectors, no Raptor binding partners have been described in plants.     

Clonal propagation of Trifolium Pratense,T. Resupinatum and T. Subterraneum by direct somatic embryogenesis on cultured immature embryos

Direct somatic embryogenesis on immature zygotic embryos in vitro has been confirmed for Trifolium pratense and extended to T. resupinatum and T. subterraneum. For all species direct embryo cloning can be achieved on an appropriate basal medium supplemented with 1gl^–1 yeast extract and 0.05 mgl^–1 BAP. Basal medium/sucrose formulation, level of yeast extract and level of BAP affected the nature of in vitro responses. In particular, for T. pratense and T. subterraneum lowering of the yeast extract level suppressed embryoid initiation, and raising of the BAP level stimulated formation of nodular morphogenic callus. For T. resupinatum alteration of the basal medium/sucrose formulation changed the tissue site of embryoid initiation from hypocotyl to cotyledons or both. Control of embryoid initiation is briefly discussed.Abbreviation BAP 6-benzylaminopurine     

Effects of organism type and growth conditions on cell disruption by impingement

Data for disruption of C. utilis, S. cerevisiae and B. subtilis cells by impingement of a high velocity jet of suspended cells against a stationary surface are compared. Differences between organisms were observed, but there were no general differences found between yeast and bacteria. In addition, growth conditions were found to have an effect on disruption with cells grown at a high specific growth rate easier to disrupt than cells grown at a low rate.Nomenclature a exponent of pressure (dimensionless) - D dilution rate (h^\s-1) - K dimensional rate constant (Pa ^\s-) - N number of passes (dimensionless) - P operating pressure (Pa) - R fraction of cells disrupted (dimensionless) - u_m maximum specific growth rate (h^\s-1)