Kinetic studies on alac-containing strain ofZymomonas mobilis

Summary Batch and continuous culture studies have been carried out on a strain ofZ.mobilis (ZM6306) which can convert lactose directly to ethanol. Previous strain development has established that thelac operon encoded on the transposon Tn951 can be expressed inZ.mobilis. Using a medium containing 80 g/l glucose and 40 g/l lactose, it was found that strain ZM6306 could convert about 13 g/l lactose to 4 g/l ethanol and 6 g/l galactose in continuous culture. Further lactose conversion is likely with increased cell concentration using a cell recycle system.     

Ethanol production by Zymomonas mobilis CP4 from sugar cane chips

Summary The fermentation of large sugar cane chips (1.0–1.5 in) to ethanol by Zymomonas mobilis CP4 (Z. mobilis) was studied in two glass fermentors operating with culture circulation for agitation (the EX-FERM type): a. A laboratory scale(2.5 liter) cylindrical vessel; b. A bench scale (8 liter) wide vessel. Z. mobilis cultures consumed 89–96% of the cane sucrose, converting it to ethanol by 90–97% of the theoretical yield in the laboratory scale fermentor and by 83–90% in the bench scale fermentor culture. Comparative Saccharomyces spp. cultures in laboratory fermentor consumed 96–98% of the cane sucrose, with ethanol conversion of only 75–79% of the theoretical yield.These preliminary results indicated that sucrose in agricultural size sugar cane chips was ethanol fermentable as compared to small size sugar cane chips or to sugar cane juice. Z. mobilis CP4 cultures converted sucrose more efficiently to ethanol than Saccharomyces spp. as shown in the laboratory scale fermentor studies.The ethanol yields in a wide bench scale fermentor cultures were slightly lower than in a laboratory fermentor.     

The macromolecular composition and essential amino acid profiles of strains of Zymomonas mobilis

Summary From continuous culture studies it has been shown that the protein concentrations of strains of Z. mobilis (62–68%) were appreciably higher than for the yeast S.uvarum (45–50%). The DNA and RNA contents were similar for the two species. Comparison of the essential amino acids indicated that Z.mobilis did not exhibit the deficiency in methionine which was apparent in the yeast. Such a study of the macromolecular composition of cells of Z.mobilis is important in assessing its by-product nutritional value for animal feed supplementation.     

A high molecular weight plasmid ofZymomonas mobilis harbours genes for HgCl2 resistance

Summary Plasmids fromZ. mobilis could be stably maintained inE. coli HB101 in which the expression of various drug resistance markers could be monitored. A large molecular weight plasmid (5.2 kbp) ofZ. mobilis was found to harbour the genes for mercuric chloride degradation and to confer uponE. coli, resistance to a higher mercuric chloride concentration as compared toZ. mobilis. The introduction of this plamsid madeE. coli sensitive to concentrations of cadmium acetate which were originally non-inhibitory to it.     

Ethanol production byZymomonas mobilis in continuous culture at high glucose concentrations

Summary Ethanol production byZ.mobilis has been studied in continuous culture with 10, 15 and 20% glucose media. At 10% glucose, steady state conditions were achieved under glucose-limited conditions. At 15 and 20% glucose, the glucose was not fully metabolized even at low dilution rates and oscillatory behavior was evident. It is proposed that ethanol inhibition of growth is responsible for these phenomena. Comparison of kinetic parameters with those from previously published batch data revealed similar values. The maintenance energy coefficient (m) forZ.mobilis was relatively high and was calculated as 1.6 g/g/h for 10% glucose and 3.1 g/g/h for 15% glucose.     

Continuous ethanol production by immobilized cells of Zymomonas mobilis

Summary Studies have been carried out with a highly productive strain of Zymomonas mobilis in an immobilized cell reactor using both Ca alginate and -carrageenan as supporting matrices. Productivities above 50 g/l/h have been found at ethanol concentrations in excess of 60 g/l. With immobilized cells of Z. mobilis, there was a decline of approximately 30s% in activity after 800 h operation.     

Kinetics of alcohol production by zymomonas mobilis at high sugar concentrations

Summary Studies on the growth ofZ.mobilis revealed that high concentrations of glucose (10-25%) can be efficiently and rapidly converted to ethanol in batch culture. By comparison withS. carlsbergensis,Z.mobilis had specific glucose uptake rates and specific ethanol productivies several times greater than the yeast.Z.mobilis also had ethanol yields of up to 97% of a theoretical value.     

Growth requirements and the establishment of a chemically defined minimal medium inZymomonas mobilis

Summary A chemically defined minimal medium which fulfils the growth requirements of differentZymomonas mobilis strains has been established. The kinetics of ethanol production of the strains ATCC 10988, CU1, CP4 and 11163 grown on the minimal medium at different glucose concentrations were measured. All strains produced ethanol at rates similar to those on complete medium. The minimal medium described is suitable to study spontaneous metabolic deficiciencies and regulation of enzyme activities inZ.mobilis.     

Kinetic studies on a highly productive strain of Zymomonas mobilis

Summary Previous studies have demonstrated that Zymomonas mobilis is a very promising organism for ethanol production. In the present study comparative kinetic data from batch and continuous cultures on glucose media are presented which show that a new strain of Z. mobilis has higher specific rates of growth and ethanol production as well as a higher tolerance to ethanol.     

The kinetics of ethanol production by Zymomonas mobilis on fructose and sucrose media

Summary Z.mobilis is strain ZM4 was grown on 250 g/l fructose and sucrose media in batch culture and on 100 and 150 g/l sucrose media in continuous culture. With fructose, a significant reduction in the growth rate and the cell yield was apparent although the other kinetic parameters were similar to those previously reported for fermentation of glucose. With sucrose the major differences were a reduction in ethanol yield, (due to levan formation) and a lower final ethanol concentration. Ethanol inhibition of sucrose metabolism occurred at relatively low ethanol concentrations compared to those inhibiting glucose metabolism.     

Evaluation of semiconductor gas sensor system for on-line ethanol estimation

Summary On-line estimation of ethanol concentration during a fermentation was carried out with a semiconductor gas sensor system using a semipermeable membrane to separate a gas stream from the fermentor broth. The system has the advantages of low-cost, in-situ steam sterilization and a relatively fast response time (1 min.). Good agreement was found between on-line and off-line measurements with fermentation of 25% glucose media using S.uvarum and Z.mobilis. However, significant deviations occurred with the fermentation of sugar-cane juice, grape-juice and molasses.     

Ethanol fermentation of hexose and pentose wood sugars produced by hydrogen-fluoride solvolysis of aspen chips

Summary Hexose and pentose sugars, produced by hydrogen-fluoride solvolysis of aspen wood chips, were totally consumed in a coculture fermentation by Zymomonas mobilis and a mutant of Clostridium saccharolyticum. Z. mobilis converted the glucose to ethanol, while the mutant, which was improved in both ethanol production and tolerance, converted the xylose component to ethanol. A high conversion efficiency of wood sugars to ethanol was obtained, and the cells after the fermentation were successfully used for cell recycle.NRCC no. 23211     

Expression of a Lactose Transposon (Tn951) in Zymomonas mobilis

The potential utility of Zymomonas mobilis as an organism for the commercial production of ethanol would be greatly enhanced by the addition of foreign genes which expand its range of fermentable substrates. We tested various plasmids and mobilizing factors for their ability to act as vectors and introduce foreign genes into Z. mobilis CP4. Plasmid pGC91.14, a derivative of RP1, was found to be transferred from Escherichia coli to Z. mobilis at a higher frequency than previously reported for any other plasmids. Both tetracycline resistance and the lactose operon from this plasmid were expressed in Z. mobilis CP4. Plasmid pGC91.14 was stably maintained in Z. mobilis at 30°C but rapidly lost at 37°C.     

pH influence on ethanol production and retained biomass in a passively immobilizedZymomonas mobilis system

Summary A broad pH range of 4.5–7.5 for maximum ethanol productivity and ethanol yield was observed with a passively immobilizedZ. mobilis system. Total retained biomass (as suspended flocs and entrapped cells) was >50 g/l for medium pH values between 4.0–8.0. The entrapped cells to suspended flocs ratio was highest at pH 4.0, whereas at pH above 5.2 it was close to 1.0. The observed enhancement of cell immobilization on the packing support at low pH seemed to be related to formation of bacterial filaments.     

Ethanol production from fructose in continuous culture by free and flocculent cells of Zymomonas mobilis

Summary Zymomonas mobilis strain ZM4 was used for ethanol production from fructose (100 g/l) in continuous culture with a mineral (containing Ca pantothenate) or a rich (containing yeast extract) mediium. With both media high conversion yields were observed but the ethanol productivity was limited by the low biomass content of the fermentor. A new flocculent strain of Z.mobilis (ZM4F) was cultivated in a CSTR with an internal settler and showed a maximal productivity of 93 g/l.h (fructose conversion of 80%). When the fructose conversion was 96% an ethanol productivity of 85.6 g/l.h with an ethanol yield of 0.49 g/g (96% of theoretical) was observed.     

Role of antimicrobial agents in simultaneous saccharification and fermentation of paddy malt mash to ethanol by mixed cultures of Saccharomyces cerevisiae PH03 and Zymomonas mobilis ZM4

Summary Among various antimicrobial plant extracts, chemicals and antibiotics used for simultaneous saccharification and fermentation, penicillin G prevented contamination and did not inhibit amylase activity and growth of the synergistic co-cultures Saccharomyces cerevisiae PH03 and Zymomonas mobilis ZM4 during a 7-day fermentation of paddy malt (25.0%) mash (18.0% dextrose equivalent) to ethanol at 30°C and pH 5.5. The treatment yielded 10.1% (v/v) ethanol from the mash which was significantly more than that of the boiled and fermented mash (9.3% v/v) and equal to that of the mash boiled and fermented (10 2% v/v) after added amylases treatment. Most of the other compounds (kanamycin, streptomycin, polymyxin, tetracycline) had growth inhibitory effect especially on Z.mobilis.     

Stability against stop of flow of an immobilizedZymomonas mobilis bioreactor

Summary Starvation responses of a passively immobilizedZymomonas mobilis system have been studied. The system recovered its total activity after starvation for a two month period at 4°C and no differences were observed when fresh medium was added previously to reactor storage. When the starvation temperature was 25–28°C, complete glucose conversion was achieved even after 11 days without feeding, whereas the longer the starvation time the lower steady state glucose conversion achieved.     

Complete Genome Sequence of the Ethanol-Producing Zymomonas mobilis subsp. mobilis Centrotype ATCC 29191

Zymomonas mobilis is an ethanologenic bacterium that has been studied for use in biofuel production. Of the sequenced Zymomonas strains, ATCC 29191 has been described as the phenotypic centrotype of Zymomonas mobilis subsp. mobilis, the taxon that harbors the highest ethanol-producing Z. mobilis strains. ATCC 29191 was isolated in Kinshasa, Congo, from palm wine fermentations. This strain is reported to be a robust levan producer, while in recent years it has been employed in studies addressing Z. mobilis respiration. Here we announce the finishing and annotation of the ATCC 29191 genome, which comprises one chromosome and three plasmids.     

By-products formed during direct conversion of sugar beets to ethanol byZymomonas mobilis in conventional submerged and solid-state fermentations

Summary The nature and amounts of by-products formed during conversion of sugar beets to ethanol byZ. mobilis in Conventional Submerged Fermentation (CSF) and Solid-State Fermentation (SSF) were investigated. It was found that the bacterium produced fewer by-products in SSF than CSF, and that by-products profile was different. The influence of fermentation temperature on synthesis of by-products in SSF was also studied. High fermentation temperature favoured sorbitol synthesis and low fermentation temperature the synthesis of levan. The best results were obtained at 35°C. An ethanol yield of up to 95% of the theoretical value with final ethanol concentration of 142 g/L were obtained.     

Development of sequential-co-culture system (Pichia stipitis and Zymomonas mobilis) for bioethanol production from Kans grass biomass

Sequential-co-culture technique was investigated in this study for the production of bioethanol from relatively cheaper lignocellulosic biomass of Kans grass (Saccharum spontaneum). The consortium of Pichia stipitis and Zymomonas mobilis was used to develop a suitable sequential-co-culture system. The Kans grass biomass was hydrolyzed in such a manner that the two sugar fractions, xylose rich and glucose rich were generated (a separate study). The P. stipitis cells and respective fermentation media (xylose rich) were fed to the fermentation vessel, after the set fermentation time Z. mobilis cells and respective media were fed to the same vessel. Different strategies have been followed and experiments were conducted initially at flask level. The selected strategy was then applied at bioreactor level using both synthetic fermentation media and Kans grass hydrolysate media to compare the kinetic parameters. The sequential addition of cultures with their respective media and imposed process conditions, showed better utilization of total sugars added (>95%). Microaerobic condition for P. stipitis and strictly anaerobic condition for Z. mobilis fermentation were found significant. The average ethanol yield (Y_p/s) and overall volumetric productivity (r_po) were found as 0.453 g_p/g_s and 1.580 g/l/h respectively for Kans grass hydrolysate media and 0.474 g_p/g_s and 2.901 g/l/h respectively for synthetic fermentation media.