Ethanol production from sugar cane syrup using Zymomonas mobilis

Since Zymomonas mobilis cannot be made available to industry in dried or lyophilized form, cell biomass was compared with liquid culture for rapid initiation of ethanol formation. The latter gave a more constant production rate at 0.5 g l-1 dry weight equivalent. Of twelve different carbon source combinations in the pre-culture, only those containing sucrose at > 10% (w/v) secured and maintained rapid and complete overall sucrose hydrolysis (97-100%). Of all the nutrient combinations tested, the presence of 1-2 g l-1 MgSO4 and 0.5 g l-1 diammonium phosphate gave close to 20% improvement in conversion efficiency. The addition of 0.06-0.125 g l-1 invertase overcomes sucrose hydrolysis problems owing to pre-culture conditions. Sorbitol formation was reduced to 0.1-0.3% (w/v) using a continuous feeding train cultivation technique at 110 ml h-1 [D = 0.18 h-1]. Batch and continuous processes exhibit ethanol production rates of 3 g l-1 h-1 and final sucrose to ethanol conversion efficiencies in excess of 90%

Sugar-cane molasses fermentation by Zymomonas mobilis

Two different quality types of sugar-cane molasses containing a total sugar content of 48%-50% (w/v) and 35%-42% (w/v) were investigated for Zymomonas biothanol production. Molasses concentrations of up to 250 g/l (1:3 dilution) were successfully fermented within 24 h despite a higher salt concentration in the lower grade molasses. Higher molasses concentrations (300 g/l) led to fructose accumulation. The addition of sucrose to a final sugar concentration of 15% (w/v) led to 10% (v/v) ethanol with conversion efficiencies up to 96%. Sorbitol levels were negligible, but increased up to tenfold upon addition of invertase

Microbial cultures in the utilization of cellulosic materials

This review elaborates on the most recent microbial development in saccharification of cellulose and cellulase formation. A particular highlight is a new genetic-immunochemical approach investigating the mechanism of adhesion of bacterial cellulase to cellulose during cellulose conversion. New developments and recent reviews in hemicellulose and lignin degradation are also covered

ATP sensitive and ATP insensitive phosphofructokinase in Escherichia coli K 12

The purification and kinetic characteristics of two phosphofructokinases are described. Aerobic cultures of Escherichia coli exhibit two types of phosphofructokinase. Both types are dimers of mol. wt 150000 (subunit mol. wt 73000), whereas the anaerobic culture of E. coli revealed only one type, which is a tetramer of mol. wt 350000 (subunit mol. wt 90000). Type 1 of the aerobic enzyme, representing approximately 70% of the total enzyme activity, is ATP‐insensitive, whereas type II and the anaerobic enzyme are ATP‐sensitive. The addition of AMP stimulates the tetramer, relieving ATP inhibition, and also the type II dimer, which is, however, inhibited at concentrations higher than 0.5 mM AMP. No effect was observed on the type I dimer of the aerobic preparation. ADP stimulates the tetramer and inhibits type I more strongly than type II of the aerobic dimer. The kinetic characteristics together with the effect of metabolites on these phosphofructokinase types are described and discussed in the light of their importance for the regulatory mechanism of the Pasteur effect. Copyrigh

Kinetic characteristics and regulatory mechanisms of glucokinase and fructokinase from Zymomonas mobilis

Glucokinase (EC 2.7.1.2) exhibits two pH optima (pH 7.0 and 8.2), gives hyperbolic saturation curves and reacts equally with ATP, UTP, GTP, ITP and CTP. Inhibition occurs with high concentrations of these nucleotides and in addition with ADP, AMP and glucose 6-phosphate. No inhibition was observed with sucrose, glucose, fructose (11 mM), ethanol (542 mM), mannose, ribose, galactose, deoxy-glucose, lactose and gluconate and no reaction except with glucose. Fructokinase (EC 2.7.1.4) exhibits one pH optimum (7.4), gives hyperbolic saturation curves and is highly specific towards ATP and fructose. Mannose, glucose, GTP and CTP do not react. Inhibition occurs with glucose, glucose 6-phosphate and mildly fructose 6-phosphate. ATP at high concentrations gives slight inhibition, ADP and AMP show differential effects, whereas all other above mentioned compounds do not inhibit. Regulatory mechanisms for sucrose, glucose and fructose metabolism are discussed

Kinetic characteristics of phosphofructokinase from Lactobacillus casei var. Rhamnosus ATCC 7469 and Lactobacillus plantarum ATCC 14917

The enzyme phosphofructokinase (ATP:d-fructose 6-phosphate 1-phosphotransferase, EC 2.7.1.11) from Lactobacillus casei and Lactobacillus plantarum did not exhibit sigmoidal kinetics. The Km values for ATP were 0.37 mM and 0.67 mM and for Fru-6-P 1.43 mM and 0.15 mM, respectively. The addition of ADP, AMP or adenosine 3′,5′-monophosphate (cyclic AMP) resulted in a general inhibition of the phosphofructokinase from L. plantarum, but not from L. casei. NH4+ stimulated the activity of the enzyme from both sources, but P1 did so only in the case of L. casei. Citrate inhibited the enzyme at physiological concentrations (2-10 mM), but lactate only to a minor extent. The results are discussed in the light of the role of phosphofructokinase as regulatory enzyme in glucose metabolism

Gas chromatographic separation and determination of micro quantitative of C1-C7 Branched and straight-chain saturated fatty acids

A survey of thirteen different columns was carried out to find a suitable combination for the separation and determination of micro quantities of formic, acetic, propionic, isobutyric, n-butyric, isovaleric, n-valeric, isocaproic, n-caproic and heptanoic acid. A 4 ft. x 1 4 in. O.D. stainless steel column with 3.125% PEGA on acid-washed Chromosorb W ( 60 80 mesh) gave the best results in separation and sensitivity under isothermal and temperature-programming conditions. Using the dual hydrogen flame ionization detector on a Beckman GC-M, a helium flow rate of 100 ml/min and temperature programming between 100-150° at a rate of 5°/min, all acids could be separated and 0.5 μg of acid could be estimated. Isothermally with the thermoconductivity cell, 10 μg was the lowest amount detectable, for all investigated acids

Socio-ecological biotechnology concepts for developing countries

The two socio-ecological concepts described will work, of course, also with other microorganisms. Zymomonas mobilis can be replaced by yeast, Rhizopus could be replaced by Aspergillus. However, both microorganisms which are presently used can produce by-products that are unsafe for human or animal consumption. It is therefore a microbiological challenge to find further microorganisms to expand the product formation. It should also be realized that the largest renewable resource, cellulose, has not been mentioned in the context of either concept. It is well known that cellulose must eventually be included if research and development can find ways and means to separate lignin from cellulose and convert cellulose to glucose in a similar and as easy a manner as starch (Doelle 1984). In order to be successful, fermentation processes have to be fast and efficient with a low energy input (Doelle 1986a, b; Doelle & Jones 1986). This excludes the traditional microbiological sterilization of substrates, excessive substrate or product inhibitions in any of these processes. A further omission of socio-ecological concepts lies in the fermented food production. It is encouraging to see the realization that fermented foods are mixedculture processes and that it is time to start detailed and extensive investigations into the functioning of such cultures (Doelle 1985; Steinkraus 1987; Okagbu 1988; Odunfa 1988). It is the suggestion of the author to encourage a review on mixed culture with particular emphasis on fermented food production and its waste disposal