【正文】 由于第一代基因工程產(chǎn)品都以大腸桿菌作宿主，無生物傳送系統(tǒng)，故產(chǎn)品處于胞內(nèi)。另一種方法是先把種子液在安全柜內(nèi)移至供接種用的小罐內(nèi)，再將其與培養(yǎng)罐連接，用蒸汽對連接部分滅菌后，把種子罐中的種子液接入培養(yǎng)罐內(nèi)。用高壓滅菌器使其滅菌或是連接后用蒸汽滅菌，滅菌結(jié)束后將樣品從罐中取出送入樣品管中。還有，機(jī)械密封受使用壽命所限，在溢漏發(fā)生前就應(yīng)定期更換。在罐排氣口外安裝冷卻冷凝器，其后才是加熱器，排氣氣體經(jīng)此加熱至 60~80176。為此，在通用通氣攪拌型培養(yǎng)罐上安裝排氣鼓泡器，以防止激烈起泡時(shí)泡沫直接外溢 和外部微生物侵入污染，同時(shí)還能肉眼觀察通氣狀態(tài)等 (圖 118)。一是在高壓滅菌器中進(jìn)行培養(yǎng)基及培養(yǎng)罐的滅菌，罐本身通常是玻璃制的，容量在 10L以下的居多；另一類是 20L以上的 培養(yǎng)罐，一般為不銹鋼制品，多采用通新鮮蒸氣進(jìn)行滅菌。在質(zhì)粒穩(wěn)定基礎(chǔ)上，應(yīng)盡可能提高細(xì)胞內(nèi)質(zhì)?？截悢?shù) 。在此情況下，可采取培養(yǎng)過程中，在調(diào)節(jié) pH 值同時(shí)補(bǔ)加氨基酸混合物和葡萄糖的方法，以便培養(yǎng)過程葡萄糖及氨基酸濃度的基本恒定，從而實(shí)現(xiàn)高密度培養(yǎng) ，如 E． coli C600 株培養(yǎng)時(shí)可獲得 6％干菌體。其原因主要與基因工程細(xì)胞特點(diǎn)有關(guān)，首先基因工程細(xì)胞的生長速率及表達(dá)率與其所載外源 DNA 的穩(wěn)定性及產(chǎn)物分泌過程有關(guān)，其中重組 DNA 的穩(wěn)定性尤為重要，重組 DNA 在宿主內(nèi)表達(dá)方式有兩種，其一是游離表達(dá)方式、其二是結(jié)合表達(dá)方式。后 來，美、日等國都制定了有關(guān) DNA 重組實(shí)驗(yàn)的準(zhǔn)則，即在試管內(nèi)用酶等構(gòu)建異種 DNA 的重組分子，并用它轉(zhuǎn)入活細(xì)胞中的實(shí)驗(yàn)，以及使用重組體的實(shí)驗(yàn)應(yīng)遵循的規(guī)程。 6，將重組后 DNA 分子引入到受體細(xì)胞內(nèi)，然后選擇合適的培養(yǎng)條 件使細(xì)胞繁殖。 1976 年，科學(xué)們在 5個(gè)實(shí)驗(yàn)室里幾乎同時(shí)發(fā)現(xiàn)并提取出一種酶，這種酶可以將兩個(gè) DNA 片段連接起來，修復(fù)好 DNA 鏈的斷裂口。 第一節(jié) 工程菌的來源和應(yīng)用 一、何謂基因工程 基因工程 （ geic engineering）是指在基因水平上，采用與工程設(shè)計(jì)十分類似的方法，根據(jù)人們的意愿，主要是在體外進(jìn)行基因切割、拼接和重新組合，再轉(zhuǎn)入生物體內(nèi)，產(chǎn)生出人們所期望的產(chǎn)物，或創(chuàng)造出具有新的遺傳特征的生物類型，并能使之穩(wěn)定地遺傳給后代。 3，含芳香烴廢水 利用固定化混合菌群可降解芳香烴廢 水。 thus minimising cell removal from the fermenter Cell recycle system Cell recycle is used in activated sludge systems. A portion of the cells are separated in a settling tank and returned to the activated sludge fermenter. Biomass recycling for product or biomass production is more difficult due to the need for maintaining sterility during cell separation. Centrifugation w hich is a faster process than settling would be used to separate the cells. Biomass recycle systems can be easily modelled. 固定床反應(yīng)器（ Fixed bed reactors ） In fixed bed fermenters, the cells are immobilized by absorption on or entrapment in solid, nonmoving solid surfaces. In one type of fixed bed fermenter, the cells are immobilized on the surfaces of immobile solid particles such as plastic blocks, concrete blocks, wood shavings or fibrous material such as plastic or glass wool. Fixed bed reactors The liquid feed is either pumped through or allowed to trickle over the surface of the solids where the immobilized cells convert the substrates into products. Once steady state has been reached there will be a continuous cell loss from the solid surfaces. These types of fermenters are widely used in waste treatment In other types of fixedbed fermenters, the cells are immobilized in solidified gels such as agar or carrageenin In these fermenters, the cells are physically trapped inside the pores of the gels and thus giving better cell retention and a large effective surface area for cell entrapment. In order to increase the surface area for cell immobilization, some researchers have investigated the use of hollow fibres and pleated membranes as immobilization surfaces. Industrial applications of fixed bed reactors include waste water treatment, production of enzymes and amino acids, and steroid transformations One advantage fixed bed reactors is that nongrowing cells can be used. In such systems, the cells enzymatically act on substrates in the feed. The cells can be either inactivated or not fed nutrients required for growth. 流化床反應(yīng)器（ Fluidized bed reactors） The fluidisation of the particles in the reactor leads to the surface of the particles being continuously turned over. This also increases the mass transfer rate. Fluidised beds are typically categorized as either being a 2 phase system which are not aerated and 3 phase system which is aerated by sparging Fluidized bed reactors Fluidized bed bioreactors are used widely in wastewater treatment. Fluidized bed bioreactors are also used for animal cell culture. Animal cells are trapped in gels or on the surface of special particles known as microcarriers. Fluidized bed reactors are one example of perfusion culture technology used for animal cell culture. Comparing fluidised bed and fixed reactors Fluidised bed reactors are considerably more efficient than fixed b