Mathematical modelling of the alcoholic fermentation of glucose by Zymomonas mobilis mobilis

The kinetics of alcoholic fermentation of a strain of Zymomonas mobilis, isolated from sugarcane juice, has been studied with the objective of determining the constansts of a non-structured mathematical model that represents the fermentation process. Assays in batch and in continuous culture have been carried out with different initial concentrations of glucose. The final concentrations of glucose, ethanol and biomass were determined. The following kinetic parameters were obtained: μ_max, 0·5 h^?1; K_s, 4·64 g dm^?3; P_max, 106 g dm^?3; Y_x/s, 0·0265 g g^?1; m, 1·4 g g^?1 h^?1; α, 17·38 g g^?1; β, 0·69 g g^?1 h^?1.     

运动发酵单胞原生质球的形成和再生

运动发酵单胞(Zymomonas mobilis)ATCC29191菌株在含1～3g/L甘氨酸的液体培育12小时的菌体,用含20g/L的溶菌酶溶液处理12小时,可以稳定得到80％～90％的原生质球。原生质球稀释后在底层再生培养基上涂布,上面复盖一层半固体培养基,30℃培养5～7小时,再生率可达10~(-2)水平。     

运动发酵单胞菌发酵产乙醇的中试研究

从6株Zymomonas.mobilis基因工程菌中筛选出一株乙醇高产菌Z4,在500ml摇瓶小试的基础上利用5L全自动发酵罐进行了中试放大。结果表明Z4菌株的最适初糖浓度为18%;pH6.0,35℃,发酵48h乙醇最高含量达67.9g·L-1,得率达77.0%。补料分批培养实验结果表明,补料时机以发酵起始后24h为佳,发酵48h后乙醇含量达最高值93.1g·L-1,得率为77.6%。     

Respiration-deficient mutants of Zymomonas mobilis show improved growth and ethanol fermentation under aerobic and high temperature conditions

Respiration-deficient mutant (RDM) strains of Zymomonas mobilis were isolated from antibiotic-resistant mutants. These RDM strains showed various degrees of respiratory deficiency. All RDM strains exhibited much higher ethanol fermentation capacity than the wild-type strain under aerobic conditions. The strains also gained thermotolerance and exhibited greater ethanol production at high temperature (39°C), under both non-aerobic and aerobic conditions, compared with the wild-type strain. Microarray and subsequent quantitative PCR analyses suggest that enhanced gene expression involved in the metabolism of glucose to ethanol resulted in the high ethanol production of RDM strains under aerobic growth conditions. Reduction of intracellular oxidative stress may also result in improved ethanol fermentation by RDM strains at high temperatures.     

Duplex PCR Method for Rapid Detection of Zymomonas mobilis in Cider

A duplex PCR method was developed for Z. mobilis species detection. Two sets of primers were used; the first one targeted a 530 bp region of the 23S rRNA gene, the amplified fragment corresponding to an internal control, while the second targeted a 900 bp region spanning the 16S and 23S rRNA gene regions and was Z. mobilis specific. This second primer pair was designed by comparison with corresponding sequences of a Sphingomonas sp., a bacterium that is phylogenetically the closest to Z. mobilis, and Gluconobacter oxydans that is taxonomically the closest relative found in cider. Results showed that the method was able to specifically amplify the two targets in all studied strains of Z. mobilis while only one fragment, corresponding to the internal control, was amplified for G. oxydans and the tested lactic acid bacteria commonly found in cider. The method threshold was determined by contaminating cider samples containing natural yeast and lactic acid bacteria flora. Within a 24 h period, ciders containing 10² CFU/mL of Zymomonas were detected as positives. The rapidity and reliability of this duplex PCR for detection of Z. mobilis directly from cider will certainly prove to be useful in detecting, early on during the fermentation phase, the presence of this spoilage microorganism. It will also be of interest as a complementary test when using the HACCP approach in the cider and beer industries.     

Zymomonas mobilis: an alternative ethanol producer

Zymomonas mobilis is a unique bacterium in the microbial world, and offers a number of advantages over the existing ethanol‐producing microorganisms. Being a prokaryote, it is more amenable to genetic manipulations. Thus, it has attracted great attention in the ethanol production world and efforts have been made to commercialize its application for the purpose. Despite the various efforts made worldwide, none of the processes using this microbe has been commercialized owing to certain bottlenecks. To circumvent the hindrances currently associated with a Zymomonas process, researchers have made various attempts to improve the technology using different techniques. This paper reviews the different substrates and the genetic improvement techniques with special emphasis on mutagenesis and recombinant DNA technology used for ethanol production by Zymomonas strains. Copyright © 2006 Society of Chemical Industry     

Sago starch saccharification and simultaneous ethanol fermentation by amyloglucosidase and Zymomonas mobilis

Simultaneous saccharification and ethanol fermentation (SSF) of sago starch was studied using amyloglucosidase (AMG) and Zymomonas mobilis. The optimal concentration of AMG and operating temperature for the SSF process were found to be 0.5% (v/w) and 35°C, respectively. Under these conditions with 150 g dm^?3 sago starch as a substrate, the final ethanol concentration obtained was 69.2 g dm^?3 and ethanol yield, Y_P/S, 0.50 g g^?1 (97% of theoretical yield). Sago starch in the concentration range of 100–200 g dm^?3 was efficiently converted into ethanol. When compared to a two-step process involving separate saccharification and fermentation stages, the SSF reduced the total process time by half.     

DETECTION OF ZYMOMONAS

A simple, semi-defined medium has been evaluated and is recommended for detection of Zymomonas in brewery samples.     

pH值对运动发酵单胞菌葡萄糖代谢酶活性影响的研究

以运动发酵单胞菌(Zymomonas mobilis)ATCC31821为模式菌株,研究pH值条件对其葡萄糖代谢关键酶活力的影响.结果表明:发酵液pH5.5时,胞内乙醇脱氢酶、丙酮酸脱羧酶、葡萄糖激酶、葡萄糖-6-磷酸脱氢酶的活力较高,而异柠檬酸脱氢酶活性较低,能促进乙醇的生成;pH 5.0时,苹果酸脱氧酶的酶活力较低,使糖酵解反应向另一个方向发生偏移,促进乙醇的形成.pH 4.0～6.5时,丙酮酸激酶和甘油醛-3-磷酸脱氢酶的酶活力水平相差不大,说明pH值对这2种酶的活性影响甚微.因此,pH5.0～5.5,代谢途径(如糖酵解途径、ED途径等)中的胞内代谢酶活性增强,有利于乙醇的产生.