外文翻譯---木質纖維素生物預處理的現(xiàn)狀潛力、進展與挑戰(zhàn)的初步研究

1、<p><b>　　畢業(yè)設計/論文</b></p><p>　　外 文 文 獻 翻 譯</p><p>　　院 系 XXXXXXXX </p><p>　　專 業(yè) 班 級 生物工程0901班 </p><p>　　姓　 名

2、 XXXXX </p><p>　　原 文 出 處School of Life Science&Technology,</p><p>　　Huazhong University of Science & Technology </p><p>　　評 分

3、</p><p>　　指 導 教 師 XXXX </p><p>　　XXXXXXXXXXXX</p><p>　　2013 年 3月 7日</p><p>　　畢業(yè)設計/論文外文文獻翻譯要求：</p><p>　　1．外文文獻翻譯的內容應與畢業(yè)設計/論文課題相關。</p

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5、原文均需單獨編制頁碼（底端居中）并注明出處。本附件為封面，封面上不得出現(xiàn)頁碼。</p><p>　　4．外文文獻翻譯原文由指導教師指定，同一指導教師指導的學生不得選用相同的外文原文。</p><p><b>　　譯文：</b></p><p>　　木質纖維素生物預處理的現(xiàn)狀：潛力、進展與挑戰(zhàn)</p><p><b&

6、gt;　　摘 要</b></p><p>　　通過生化平臺從木質纖維素中生產生物燃料和生化制劑的可行性在很大程度上取決于從植物細胞壁上的纖維素和半纖維素獲得糖類的推進技術。本文概述了發(fā)展中的植物細胞壁結構生物預處理技術在從纖維素聚合物中進行糖的后續(xù)酶提取方面的成果和挑戰(zhàn)。該技術已經成為了一個打破瓶頸的新選擇。盡管由于許多固有的局限性沒有引起多少注意，生物預處理還是由于其自身的許多優(yōu)勢而存在很大潛力，包

7、括更環(huán)保、耗能更少、反應產生抑制劑更少、副產物更少等。在白蟻和白腐菌方面不斷取得的科技成果為實現(xiàn)這些利益，發(fā)展新一代生物預處理技術提供了理論依據(jù)。本文綜述了以木質素降解酶為主的酶系統(tǒng)，描述了當前對微生物降解植物細胞壁的理解，對比了生物與化學的預處理過程。還對生物制漿的成果進行了總結，提供了一個未來生物預處理過程的發(fā)展方向。</p><p><b>　　簡介</b></p>&l

8、t;p>　　獲得可再生燃料和化學制劑的唯一方式是通過利用綠色植物吸收太陽能，再以有機碳源的形式存儲起來。大自然還開發(fā)了各種途徑以額外的最小輸入能量來利用和回收這些植物材料。這樣做，大自然能夠一直保持一個可持續(xù)發(fā)展的平衡的生態(tài)系統(tǒng)數(shù)百萬年。如何利用木質纖維素的生物分解來進行生物燃料和生化生產是這些天然生物過程需要解決的主要障礙，他們往往最節(jié)能并且對環(huán)境產生的影響不大。隨著化石燃料資源的衰退和對氣候變化的擔憂，發(fā)展生物質燃料和化學制劑

9、顯得愈發(fā)緊迫。例如， 到2022年，每年生產的360億加侖可再生燃料中，生物燃料必須占到210億加侖。未來生化和生物燃料發(fā)展的基礎是生物質原料的供應。所有的類型中，木質纖維素、木質生物、作物殘留物、草和藻類的生物質能含量是最豐富的。木質生物質是地球上最豐富的可再生生物資源，在地球上,每年可生產109~ 200噸，其中只有3%用于諸如造紙工業(yè)的非食品領域。目前纖維素的消費量與谷物消費持平，是鋼鐵消費的3倍。為了既能將這些材料用于生產生物燃

10、料又不與人類的糧食供應構成沖突，未來的生物煉制將以木質生物質原料為主。</p><p>　　植物細胞壁(PCW)是存儲能源和有機碳的主要材料。PCW的組成和結構決定了以它為原料來設計下游加工流程生產各種目標分子。植物由有序排列的有壁細胞組成。細胞壁中含有不同比例的混合纖維素(Ca.40%)、半纖維素(Ca.20 - 30%)和(Ca.20 - 30%)。纖維素是一種葡萄糖單元由β-1,4-糖苷鍵聯(lián)系在一起的線性聚

11、合物。半纖維素是許多糖(木糖、甘露糖、半乳糖、阿拉伯糖、鼠李糖)單體的雜聚合物形成的隨機非晶態(tài)結構。另一方面，木質素是由一個包含三種DPH（對香豆醇、松柏醇、芥子醇）的大分子單體交叉鏈接組成。木質纖維素是一個緊湊的復雜結構。其中一部分含有復雜晶體，和多糖緊密連接成的層狀超細纖維形成的穩(wěn)定劑來防止它們被水解酶和其他外部因素分解 。以木材為例來解釋其結構：通常，支持細胞死亡后的管腔可以作為水分運輸?shù)耐ǖ?，其內層是一個成分未知的異構混合部分，

12、內層外面的次生壁可以進一步分為S3, S2 ,S1三個子層，三個子層都是由纖維素超細纖維嵌入在不同的半纖維素和木質素的一個非晶體混合物中組成的。纖維素的濃度最高的是S2子層,并且向中間層依次減少。富含半纖維素的S3層是最靠近導管的。中層</p><p>　　初生壁中高度支鏈化的木質素比次生壁中的線性木質素更能抑制細胞壁的降解。大多數(shù)生物過程集中于用糖作為能源和碳源通過發(fā)酵獲得不同的產品。主要的糖單元是葡萄糖，在植

13、物細胞壁結構中呈有界的共價纖維素聚合物。從物理化學加工中獲得糖是一個重大的生物精煉的瓶頸。鎖在纖維素和半纖維素聚合物中的糖單位是用于發(fā)酵生產生物燃料和生物化學制劑的唯一能源和碳源。纖維素聚合物的生化分解一般是由稱為木纖維質酵素的纖維素酶完成的。由極其復雜而且種類繁多的纖維素復合而成的木質纖維素，有專門用來抵御攻擊的結構。木質素和半纖維素的復雜的結構和疏水性的細胞壁可以防止酶與纖維素聚合物接觸。因此，木質素和半纖維素的結構需要被消減或修改

14、為可以允許纖維素酶隨意移動的自由空間。這通常是通過一個預處理的過程來解決的。</p><p>　　我們越來越多的需要新的預處理方法。我們正在進入一個工業(yè)生物技術、合成生物學、代謝工程和系統(tǒng)生物學的新時代，這些新興技術和學科提供新的工具微生物用以生產諸如碳氫化合物的先進生物燃料。在使用這些工具進行生物燃料生產方面的真正進步將是有限的，如果給這些微生物供應的糖仍然是一個主要障礙?？紤]到自然已經通過進化創(chuàng)造了復合酶作為

15、生物催化劑，它有能力通過選擇性地斷裂化學鍵之間的基本單位解開木質素分子的復雜結構，我們應該尋求利用類似的物理化學加工過程，利用木質素和半纖維素降解酶實現(xiàn)在預處理中整合和糖化的終極目標。這些酶在傳統(tǒng)的預處理之前或之后使用以實現(xiàn)減少，并最終取代熱化學處理，從而減少整個預處理在大分子水平和簡化工藝的嚴重影響。</p><p>　　在可持續(xù)發(fā)展和能源效率的前提下，生物工藝由于其可以在自然環(huán)境下發(fā)生且環(huán)保的特點優(yōu)于理化過程

16、。基于此的生物預處理未來將吸引更多的關注。本文將在這個話題上提供一個全面的調查。本文將在目前生物預處理工藝的理論基礎上，概述先進的知識，指出信息和技術的差距。最后,本文還提供了一些猜測，提出一些未來研究和發(fā)展方向。需要指出的是,理想的預處理過程需要木質素和半纖維素的解構。本文將，主要側重于木質素降解。本文首先從木質素分解酶系統(tǒng)入手，其次是不同的微生物如何分解木質素。對生物預處理和熱化學預處理作出比較，然后提供生物制漿的應用實例，得出結論

17、并展望未來。</p><p><b>　　外文文獻原文：</b></p><p>　　Status of Biological Pretreatment of Lignocellulosics: Potential, Progress and Challenges</p><p>　　Shulin Chen, Xiaoyu Zhang, Dee

18、pak Singh, Hongbo Yu, Xuewei Yang </p><p>　　Department of Biological Systems Engineering, Washington State University, </p><p>　　Pullman, WA 99164.</p><p>　　School of Life Science

19、 & Technology, Huazhong University of Science & Technology,</p><p>　　Wuhan, Hubei, P.R.China, 430074.</p><p><b>　　Abstract</b></p><p>　　The feasibility of produc

20、ing biofuels and biochemicals from lignocellulosic biomass via the biochemical platform depends largely on advancing technologies obtaining sugars from the cellulose and hemicelluloses of the plant cell walls. This paper

21、 provides an overview on the merit and challenges related to developing biological pretreatment processes as a new alternative to break the barriers of the plant cell wall structure for subsequent enzymatic extraction of

22、 sugars from cellulose polymer. Alt</p><p>　　Introduction </p><p>　　The only way to obtain renewable transportation fuels and chemicals is through the use of plant biomass that stores the interc

23、epted solar energy via photosynthesis in the forms of organic carbon. Nature has also developed various pathways for utilizing and recycling these plant materials with minimum input of additional energy. In doing so, nat

24、ure has been able to maintain a sustainable, yet balanced ecosystem for millions of years. These naturally occurring biological processes should be adopte</p><p>　　The plant cell walls (PCW) are the primary

25、materials where energy and organic carbon are stored. The composition and structure of PCW determines the design of the down stream processes using PCW as raw materials to produce various target molecules. Plant consists

26、 of an orderly arrangement of cells with walls composed of varying amounts of a mixture of cellulose (ca. 40%), hemicellulose (ca. 20-30%) and lignin (ca. 20-30%) [8]. Cellulose is a linear polymer of D-glucose units lin

27、ked by β-1, 4-gly</p><p>　　The essence of converting lignocellulosics to fuels and chemicals is to obtain the desirable form of organic carbon molecules from the PCW to be used either as precursor molecules

28、or energy sources for the targeted fuel products. There are typically two major platforms for biomass conversion. The first one is biochemical platform in which various sugar molecules are first obtained from the biomass

29、. The sugars are then used by microorganisms to be converted subsequently to target fuel molecules s</p><p>　　The current pretreatment technologies for making an easy access for the cellulase enzyme to catal

30、yze cellulose degradation to sugars are physiochemical in nature. The purpose of these processes is to degrade the hemicelluloses or lignin structure. Hydrothermal processes include steam explosion [15], carbon dioxide e

31、xplosion [16], or hot water treatment [17]. Likewise, chemical processes include dilute-acid treatment [18], alkali treatment [19], organosolv process using organic solvents [20], amm</p><p>　　There is incre

32、asing needs for new pretreatment approaches. As we are entering a new era of industrial biotechnology, synthetic biology, metabolic engineering, and system biology provide new tools to engineer microbes to produced advan

33、ced biofuels such as hydrocarbons. The real advancement in biofuel production using these tools will be limited if the supply of sugars to these microorganisms remains a major barrier. Considering the fact that nature

34、has been created through evolution biological </p><p>　　In the interests of sustainability and energy efficiency, biological process is superior to the physiochemical ones as they occurs under natural enviro

35、nment and do not produce disruptions that are not tolerable by the environment. Based on the belief that such a biological pretreatment will attract more attention in the future, this review aims at providing a comprehen

36、sive survey on this topic. It is xpected that this paper will present the rationale of biological pretreatment process, overview </p><p>　　1. Ligninolytic enzyme system</p><p>　　Lignin can be de

37、gradated by enzymes produced by various organisms among which white rot fungus has been found the most effective. Lignin biodegradation by white rot fungi involves various enzymes, and the most significant three are lacc

38、ases (benzenediol: oxygen oxidoreductase, EC 1.10.3.2), lignin peroxidases (LiPs, EC 1.11.1.14), and manganese peroxidases (MnPs, EC 1.11.1.13) [26, 27]. LiPs, MnPs, and laccase are phenol oxidases which catalyze simila

39、r reactions [10]. They oxidize phenolic comp</p><p>　　2. Processes of biological deconstruction of plant cell walls </p><p>　　There are many ways of plant decay in nature by different organisms

40、in addition to fungi. Although many of the mechanisms of PCW degradation by these systems are still unknown, there is no doubt that further understanding of these processes will provide critical insight into developing n

41、ew generation of pretreatment processes. </p><p>　　3. Comparison of biological pretreatment with typical thermochemical processes </p><p>　　3.1. Effectiveness </p><p>　　Main purpose

42、 of the pretreatment for lignocelluloses is to dismantle the matrix structure of lignin and hemicelluloses to modify the pores in the material to allow cellulolytic enzymes to penetrate the barrier in the PCW to degrade

43、cellulose polymer [15]. Thus, the pretreatment should be effective to avoid degradation or loss of carbohydrate, and avoid formation of inhibitory by-products for the subsequent hydrolysis and fermentation and it must b

44、e cost-effective [11]. </p><p>　　3.2. Energy consumption</p><p>　　Comparing to the biological pretreatment, thermochemical methods to convert the lignocellulosic biomass utilizes large amount of

45、 energy in the form of heat and chemicals. For example, alkaline processes suffer from silica scaling in chemical recovery because many agricultural feedstocks, such as rice and wheat straw, have very high silica content

46、. The scaling problem prohibits the recovery of alkaline chemicals from pretreatment liquor [10]. Similarly, the use of dilute acid pretreatment is not </p><p>　　3.3. Inhibitors as by-products </p>&l

47、t;p>　　A major disadvantage of thermochemical pretreatment processes is the production of by-products that often inhibit downstream processes. During thermochemical and hydrothermal processes, some of the glucose relea

48、sed from cellulose is degraded to 5-hydroxymethylfurfural (HMF), levulinic acid, and formic acid. Likewise, the pentose from hemicellulose is converted to furfural and formic acid. During steam explosion, lignin is prim

49、arily degraded through the homolytic cleavage of β-O-4 ether and othe</p><p>　　3.4 Reaction rate</p><p>　　Although, the biological pretreatment process is a safe, low energy requiring process fo

50、r lignocellulosic material disintegration, the typical degradation process using fungi occurs in a longer incubation time. Some of the biological pretreatment time of incubation and released sugar percentage has been tab

51、ulated below. Hatakka et al. [19] studied the biological pretreatment of wheat straw by 19 fungal strains. Incubated at the 37 ℃ in the solid state fermentation, Pleurotus ostreatus was able t</p><p>　　Table

52、 1 : Biological degradation of various substrates by different fungal strains and contribution in the sugar release as well as lignin loss.</p><p>　　a : cellulose; b : hemicellulose; ab : total sugar increas

53、ed than untreated control; c : total reducing sugars; d : degradation improvement; e : total weight loss; f : Klason lignin loss; g : total lignin loss; h: pitch content reduction; NM : Not mentioned.</p><p>

54、;　　4. Near-term examples and future perspective</p><p>　　An example of near-term application of biological pretreatment is biopulping. By using fungi to alter the lignin in the cell walls of the wood, it &qu

55、ot;softens" the wood chips. Therefore, through the biopulping process, energy consumption to convert the wood into paper could be less due to the preferential removal of lignin by the fungus [15]. Therefore, biopul

56、ping is focused on lignolytic enzymes to substitute the chlorinated agents in the paper pulp bleaching [16]. In addition to this, biopulping</p><p>　　5.Concluding remarks </p><p>　　Cementing hem

57、icellulose and cellulose together in the lignocellulosic cell walls, lignin provides plant strength and makes plants hard for microbes to attack. Nonetheless, nature has developed ecologically sustainable processes for e

58、xtracting sugars from plant cell walls and for recycling the lignocellulosic biomass. The current technologies developed artificially are not as sustainable as the natural process as technologies require energy and chemi

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