摘要
Abstract (Summary)Rising energy prices, depletion of petroleum reserves and global warming have made the development of renewable fuels a national priority. Molecular hydrogen as a transportation fuel looms as an ethanol alternative, since it produces only water as a by-product. A promising route to hydrogen is microbial because it is less environmentally intensive than traditional chemical or electrochemical processes. Caldicellosiruptor saccharolyticus (Csac) , an extremely thermophilic bacterium, produces hydrogen from cellulose-, hemicellulose and pectin-containing plant biomass. To understand the growth physiology of this microorganism with an eye towards optimizing bioenergy yields, the Csac genome was sequenced and a whole genome oligonucleotide microarray was developed and implemented. Csac was studied with focus on plant biomass deconstruction. Previous studies indicated that this bacterium co-fermented glucose and xylose without carbon catabolite repression (CCR), an attractive physiological characteristic since these two sugars are the major components of lignocellulose hydrolysates. Here, growth on glucose, xylose, galactose, fructose, mannose and arabinose, and a mixture of all six monosaccharides indicated that Csac preferred fructose (a hexose) and xylose and arabinose (both pentoses). No microbiological or transcriptomic evidence for CCR was found during growth on monosaccharide mixtures. Transcriptomes from growth on monosaccharides and hemicelluloses were used to predict sugar substrates for most of the 24 putative carbohydrate ATP-binding cassette (ABC) transporters and one phosphotransferase system (PTS) identified in the Csac genome. Broad growth substrate preferences, diversity of ABC sugar transporters, and concomitant lack of CCR support Csac 's capacity to deconstruct plant biomass.Another distinct feature of Csac and other similar organisms is the presence of novel multi-domain glycoside hydrolases. This can also be attributed to two glycoside hydrolase (GH)-laden loci in the Csac genome ( Csac _1076- Csac _1080 and Csac _2404-2411). Csac _2404- Csac _2411 encodes intracellular and extracellular GH10 glycoside hydrolases that were found to not only breakdown xylan and xylan side-chains, but also hydrolyze carboxymethyl cellulose (CMC). Csac _1076- Csac _1080 encodes several multi-domain, extracellular glycoside hydrolases (GH). Within this locus is CelB (Csac_1078), a 118 kDa enzyme so far unique to C. saccharolyticus , constructed of both a GH10 and GH5 domain separated by a family 3 carbohydrate-binding module (CBM). CelB hydrolyzed xylan and CMC, as well as barley β-glucan, glucomannan and arabinoxylan. CelB transcripts were among the most highly transcribed (top 10%) in C. saccharolyticus during growth on switchgrass and poplar.Given the physiological and biochemical characteristics of Csac , this bacterium has the potential for consolidated bioprocessing (biomass deconstruction and conversion to H 2 by a single microorganism) and merits additional study in expanding efforts to replace petroleum with biofuels produced from renewable feedstocks.
摘要译文
摘要（摘要）能源价格上涨，石油储量和全球变暖的枯竭已经取得的可再生燃料的发展是国家优先事项。分子氢作为运输燃料织机作为乙醇的替代，因为它仅产生水作为副产物。一个有前途的途径是氢微生物，因为它比传统的化学或电化学方法不太密集的环境。Caldicellosiruptor saccharolyticus（CSAC），一个极端嗜热菌，产生氢的纤维素，半纤维素和果胶含植物生物量。为了理解该微生物与针对优化生物能源产量的眼睛的生长生理学的CSAC基因组测序和全基因组寡核苷酸微阵列的开发和实施。CSAC进行了研究，重点对植物生物质解构。以前的研究表明，这种细菌共发酵葡萄糖和木糖无碳分解代谢物阻抑（CCR），因为这两个糖具有吸引力生理特性是木质纤维素水解产物的主要成分。在这里，葡萄糖，木糖，半乳糖，果糖，甘露糖和阿拉伯糖，以及所有六个单糖的混合物中生长表明CSAC优选果糖（己糖），和木糖和阿拉伯糖（戊糖两者）。没有微生物或转录证据CCR是对单糖混合物的增长过程中发现的。从单糖和半纤维素生长转录被用来预测糖底物的大部分24推定的糖ATP结合盒（ABC）转运和在CSAC基因组标识的一个磷酸转移酶系统（PTS）。广阔的成长基板的爱好，ABC转运糖的多样性，以及随之而来的缺乏CCR的支持中钢铝业的产能解构CSAC和其他类似生物的植物biomass.Another显着特点是新颖的多域糖苷水解酶的存在。这也可以归因于2糖苷水解酶（GH）中的CSAC基因组（CSAC _1076- CSAC _1080和CSAC _2404-2411）-laden位点。CSAC _2404- CSAC _2411编码细胞内，并发现不仅击穿木聚糖和木聚糖侧链胞外GH10糖苷水解酶，而且水解羧甲基纤维素（CMC）。CSAC _1076- CSAC _1080编码数多域，细胞外糖苷水解酶（GH）。在该基因座是CelB（Csac_1078），一个118 kDa的酶迄今唯一给C. saccharolyticus，两者一GH10和GH5结构域由一个家族3糖结合模块（CBM）的分离构造。CelB水解木聚糖和CMC，以及大麦β葡聚糖，甘露聚糖和阿拉伯木聚糖。CelB转录物中的C. saccharolyticus对柳枝稷和poplar.Given CSAC的生理生化特性生长过程中最高度转录（前10％的25），这种细菌具有综合生物加工（生物质解构和转换为H 2的潜力由单一的微生物）和案情的进一步研究扩大努力，从可再生原料生产的生物燃料替代石油。
VanFossen, Amy Lynne. Functional Genomic, Microbiological and Biochemical Characterization of Plant Biomass Deconstruction by the Extrememly Thermophilic Bacterium Caldicellulosiruptor saccharolyticus[D]. US: North Carolina State University, 2010