以玉米浆和木薯为原料机械搅拌发酵制备细菌纤维素的研究

本文以玉米浆和木薯为原料,用机械搅拌式发酵罐制备细菌纤维素（BC）,对发酵过程的纤维素产量、还原糖消耗、溶氧变化和茵浓变化进行了监测,并以葡萄糖一蛋白胨-酵母粉培养基为对照进行了比较。实验得出玉米浆作氮源时不溶BC的产量为9．2g／L,而氮源成本只是对照组的15％;木薯水解液作碳源时的不溶BC产量达到11．7g／L,比对照组（10．8g／L）高8％;而用玉米浆搭配木薯水解液发酵生产BC,产量也达到10．1g／L,验证了这两种天然原料的廉价高效性,用于工业生产细菌纤维素具有良好的前景。     

哺乳动物的消化策略（英文）

理解动物的营养生态位是充分理解其整个生态学的基础,对于害兽控制和物种保护也很重要,食肉动物的小肠很发达,这可能与对食物的高消化能力有关;杂食性动物有更复杂的胃肠器官,其后端有可进行发酵的盲肠,消化物的平均滞留时间（mean retention times,MRTs)更长;最长的平均滞留时间见于食草动物,其消化道内高密度的微生物种群对不同滞留区内的消化物进行发酵,但是,并不是所有的食草动物都能够最大程度地消化植物纤维,只有反刍动物、骆驼和个体较大的后肠发酵动物（hindgut fermenter)能够具有这种能力,对比而言,许多其它的食草动物,如前肠发酵的有袋类和小型的后肠发酵动物如兔子、田鼠和负鼠等,它们具备可以使植物纤维消化效率最大的消化系统,可以在食物中的纤维素含量非常高的情况下仍能处理大量的食物。这些不同的消化策略使哺乳动物具有广幅的营养生态位。     

Production of poly(3-hydroxybutyrate) from whey by fed-batch culture of recombinant Escherichia coli in a pilot-scale fermenter

Production of poly(3-hydroxybutyrate) [P(3HB)] from wheyby fed-batch culture of recombinant Escherichia coli CGSC 4401 harboring a plasmid containing the Alcaligenes latus polyhydroxyalkanoate (PHA) biosynthesis genes was examined in a 30 l fermenter supplying air only. With lactose below 2 g l^–1, cells grew to 12 g dry cell l^–1 with 9% (w/w) P(3HB) content. Accumulation of P(3HB) could be triggered by increasing lactose to 20 g l^–1. By employing this strategy, 51 g dry cell l^–1 was obtained with a 70% (w/w) P(3HB) content after 26 h. The productivity was 1.35 g P(3HB) l^–1 h^–1. The same fermentation strategy was used in a 300 l fermenter, and 30 g dry cell l^–1 with 67% (w/w) P(3HB) content was obtained in 20 h.     

Continuous production of ethanol in a two-stage fermentation process using a protein — Phospholipid complex as a protective agent

A two-stage continuous fermentation process, using a continuous stirred tank fermenter (CSTF) and a tower fermenter (TF) connected in series, has been studied for ethanol production from d-glucose. The addition of a protein-phospholipid complex as a protective agent (PA) in the TF led to a three-fold increase in ethanol productivity and a 23.63% increase in final ethanol concentration in the tower effluent. The results are consistent with our previous findings on a cascade operation of CSTFs, namely, that the addition of PA to the tower increases cell tolerance towards ethanol at ethanol concentrations up to 70 gl^?1. Both studies indicate that beyond this experimentally determined critical ethanol concentration, ethanol production is significantly inhibited. Mathematical modelling of the behaviour of a single flocculated yeast floc suggested that, for yeast flocs up to 1 mm diameter, neither internal nor external diffusion of substrate is limiting. Therefore, a simplified mathematical method was developed for the analysis of the TF system. By plotting the calculated values from the derived performance equation and the experimental values of substrate conversion vs. residence time, good agreement was obtained between these two for the addition of PA. However, a small deviation was observed for the PA-free system.     

A systematic survey for thermophilic fermentative bacteria and archaea in high temperature petroleum reservoirs

Abstract: Production waters from 36 high temperature petroleum reservoirs were examined for the presence of thermophilic, fermentative microorganisms. The direct supplementation of production waters with glucose and either yeast extract, peptone, tryptone or casamino acid resulted in the isolation of thermophilic, fermentative microorganisms from 47% of the petroleum reservoirs examined. Three distinctive morphological groups were isolated from the production waters of petroleum reservoirs with depths ranging from 396–3048 metres, temperatures ranging from 21–130°C, salinities ranging from 2.8–128 gl⁻¹ and pHs ranging from 6.0–8.5. Group 1 were pleomorphic rod-shaped bacteria, Group 2 were sheathed rod-shaped bacteria, and Group 3 were coccoid archaea. Partial characterisation of strains from one seawater-flooded petroleum reservoir and three non-waterflooded petroleum reservoirs tentatively identified some strains in Group 1 as members of the genera Thermoanaerobacter and Thermoanaerobacterium , Group 2 as members of the Thermotogales order, and Group 3 as members of the genus Thermococcus . Production water salinity determined the type of microorganisms that were isolated. Group 1 organisms were found primarily in petroleum reservoirs with salinities less than 30 g/l, while Group 2 and 3 organisms were found to dominate in more saline reservoirs. The successful isolation of thermophilic, fermentative microorganisms from petroleum reservoirs decreased significantly with increasing salinity and temperature. These findings support the existence of a deep biosphere where fermentative microorganisms are widespread.     

Production of microbial rennin from Mucor miehei in a continuously fed fermenter

In this study, microbial production of rennin, a milk-clotting enzyme, from a commercial strain of Mucor miehei NRRL 3420 has been investigated in a continuously fed fermenter for prolonged times. The spherical film-type growth of the culture has been accomplished in the fermenter and the effects of medium pH, mixing and dilution rates, and feed -glucose concentration on milk-clotting activity have been elaborated. In the fermenter, optimum operational parameters have been determined as 400 rpm, 0.125 day⁻¹, and 7.5 g l⁻¹ for mixing rate, dilution rate, and feed -glucose concentration, respectively. Under these conditions, the fermenter operated 575 h continuously producing 1.24 IU ml⁻¹ maximum milk-clotting activity without concentration. In the fermenter sample at maximum milk clotting activity, the R factor and specific milk-clotting activity were determined as 1.55 × 10⁻³ IU PU⁻¹ and 5.28 IU mg⁻¹ medium protein, respectively, denoting competitive characteristics of a commercial rennet after concentration.     

High density cell culture of a marine photosynthetic bacterium Rhodovulum sp. with self-flocculated cells

High density cell cultivation of a marine photosynthetic bacterium, Rhodovulum sp. PS88 with self-flocculated cells was established by using a single-tower fermenter. High density cell culture with continuous cultivation was yielded 43 g dry matter l–1 with acetate as a substrate consumed at 22.5 g/l day. © Rapid Science Ltd. 1998     

Improvement of foam breaking and oxygen-transfer performance in a stirred-tank fermenter

This study examined a stirred-tank fermenter (STF) containing low-viscosity foaming liquids with an agitation impeller and foam-breaking impeller mounted on the same shaft. Results showed that the performance of the foam-breaking impeller can be improved by changing a conventional six-blade turbine impeller into a rod impeller as the agitation impeller. The volumetric oxygen-transfer coefficient, k _L a, in the mechanical foam-control method (MFM) using a six-blade vaned disk as the foam-breaking impeller in the STF with the rod impeller was approximately five times greater than that of the chemical foam-control method (CFM) adding an anti-foaming agent in the STF with the six-blade turbine impeller. Application of the present method to the cultivation of Saccharomyces cerevisiae K-7 demonstrated that the cultivation time up to the maximum cell concentration was remarkably shorter than that achieved using a conventional CFM.