天然纤维素的微生物降解机理研究进展

天然纤维素的微生物降解机理研究进展李宪臻，黄云战，徐德贵，金凤燮（大连轻工业学院食品工程系，大连，１１６００１）高培基（山东大学微生物研究所，济南，２５０１００）由于纤维素是一种潜在的可再生资源，因此微生物降解纤维素的研究一直受到人们的重视。有关纤维...     

纤维素的微生物降解研究进展

纤维素是自然界储量最丰富的可再生生物质原料,具有解决能源危机的巨大潜力,但结构复杂,难以降解,导致综合利用率较低.利用微生物处理技术降解纤维素,是实现其循环利用的一项重要策略.本文从单一菌株、天然复合菌群、优化组合纯培养菌株三个方面对纤维素的微生物降解进行了综述,总结归纳了每种筛选策略的优势特点和应用价值,并阐述了纤维...     

氧化纤维素的体外及酶促体外降解行为研究

用TEMPO碱性氧化体系制备氧化纤维素,在模拟体液环境下,通过对氧化纤维素质量损失(Mms)和聚合度(DP)的变化,研究羧基含量和降解时间对氧化纤维素体外降解行为的影响;并采用在体液中添加纤维素酶的方式,对氧化纤维素的酶促体外降解进行研究。结果表明:在模拟体液环境下,随着羧基含量和降解时间的增加,氧化纤维素的体外降解和酶促体外降解的Mms均呈增长趋势,DP呈下降趋势;当羧基含量为1.56mmol/g,降解时间为3周时,氧化纤维素体外降解的质量损失为11.11%,聚合度下降50.42%;酶促体外降解质量损失提高至15.35%,聚合度下降64.44%。因此提高羧基含量,结合酶促降解,可提高纤维素的降解程度。该研究为氧化纤维素在生物医学领域的应用提供了理论依据。     

木质素的微生物降解

本文概述了木质素生物降解的化学反应机制 ,介绍了几种降解木质素的微生物 ,并列举了一些木质素降解的实例     

瘤胃微生物在生物质废物资源化领域应用研究进展

瘤胃微生物作为古老的微生物体系,其多样的生物酶系及卓越的木质纤维素降解能力使其在多种领域被研究和利用。本文主要介绍了瘤胃微生物的组成,瘤胃细菌及真菌对纤维类物质的降解能力及作用,并从瘤胃微生物对不同种类富纤维素固体废弃物的水解能力及降解性能、产甲烷效率及厌氧反应器研究现状角度出发,归纳和总结了瘤胃微生物在生物质废物资源化领域应用的研究现状,并指出了其今后的研究方向。     

利用木素纤维素生产燃料乙醇的微生物代谢工程

用木素纤维素生产乙醇，与谷物生产乙醇相比，因其低廉的原料价格，显得更有竞争力。这种方法的关键是要有一种有效的微生物，它不仅要能够利用各种糖(戊糖和己糖)来发酵乙醇，而且能够耐受各种环境胁迫。     

颗粒化处理对牧草瘤胃降解率的影响研究

利用尼龙袋法，采用本地山羊，分别测得羊草，苜蓿草颗粒及粉料经0，12，24，48，72h后在瘤胃内的降解率。研究结果表明：（1）＿羊草粉料和颗粒料在24，48h干物质，酸性洗涤纤维的降解率差异不显著（P＞0．05），而在0，12h内的干质、酸性洗涤纤维的降解率差异不显著（P＜0．05），在24，48，72h内粗蛋白质，中性洗涤纤维的降解率差异不显著（P＜0．05）；（2）苜蓿粉料和颗粒料在各时间段内的粗蛋白质，酸性洗涤纤维的降解率差异不显著（P＞0．05）。而干物质解率有所提高但差异不显著（P＞0．05）。中性洗涤纤维的降解率显著提高。（3）经72h发后，苜蓿草的干物质，粗蛋白质降解率均显著高于羊草。     

纤维素降解菌群的研究进展

对纤维素降解菌的种类及纤维素降解菌群的研究近况进行综述,对目前存在的问题进行探讨。     

可降解蛋白及非蛋白氮对模拟瘤胃体外营养物质降解率的影响

试验以11.85%和8.38%两个水平的可降解蛋白(RDP)及非蛋白氮(尿素)作为试验因子,进行2×2试验设计.应用体外短期发酵技术,研究了RDP、RDP与非蛋白氮组合对模拟瘤胃中营养物质降解率的影响.结果表明,8.38%RDP日粮的干物质(DM)、中性洗涤纤维(NDF)降解率分别为51.32%和31.17%,11.85%RDP日粮的分别为60.01%和46.11%,两者差异显著(P＜0.05);说明RDP水平的提高对模拟瘤胃内营养物质降解率具有明显的促进作用.日粮中RDP水平与适量添加的非蛋白氮使模拟瘤胃中营养物质降解率提高,添加尿素日粮与不添加尿素日粮营养物质的消化率相比,差异显著(P＜0.05);说明RDP与非蛋白氮的添加对瘤胃营养物质降解率有明显的互作作用.     

微生物纤维素的非均相氧化研究

将微生物纤维素进行氧化改性,以开发其在生物材料领域的新用途.研究了微生物纤维素与高碘酸钠非均相氧化的过程.利用红外光谱技术验证了氧化微生物纤维素的结构.考察了一定条件下氧化温度,氧化时间,反应体系pH值对氧化产物中醛基含量的影响.实验结果表明,微生物纤维素被成功氧化产生了醛基基团,适当提高温度和酸性环境反应有利于醛基生成,氧化时间则存在一个最佳值.     

苹果酸对山羊瘤胃纤维降解率及发酵类型的影响

以4头装有永久性瘤胃瘘管的本地山羊为试验动物,采用4×4拉丁方设计,研究苹果酸(0、5、10和15 g/d)对山羊瘤胃纤维降解率及瘤胃发酵类型的影响。结果表明,日粮中添加苹果酸能够显著提高瘤胃内中性洗涤纤维(NDF)和酸性洗涤纤维(ADF)的降解率(P<0.05);瘤胃液中乙酸与丙酸比值显著降低(P<0.05),改变了瘤胃发酵类型;氨态氮浓度显著降低(P<0.05),促进了瘤胃微生物对氨、氮的利用。     

不同木素降解成分对纤维素降解的影响

用经过驯化的瘤胃菌厌氧降解加入不同木素降解成分的纤维素，结果表明，木素中的香兰素对瘤胃微生物降解纤维素降解的启动有明显影响，但不影响其最终降解程度，香兰素对乙酸、丁酸的产生有促进作用，但对丙酸的产生有抑制作用；乙酰基愈创木酚和愈创木酚对纤维素的降解影响不大，对降解启动略有影响，愈创木酚对丙酸的产生也有抑制作用，但不如香兰素的抑制作用强，而乙酰基愈创木酚对丙酸的产生无影响。混合态的酸淅木素对纤维素降解有明显的抑制作用。     

Cellulose acetate,a new candidate feed supplement for ruminant animals: In vitro evaluations

Cellulose acetate (CA), a derivative of cellulose in which some hydroxyl groups are substituted with acetyl groups, was evaluated as a new cellulosic feed source for ruminants. In the present work, a series of in vitro studies was carried out to determine how CA supplementation affects rumen fermentation and microbiota. Batch culture studies were conducted to select the type of CA suitable for feed use and to define the optimal supplementation level. Rumen fluid from 2 Holstein cows was mixed with McDougall's buffer in test tubes into which grass hay and concentrate containing a fiber source [cellulose (control), water-soluble CA (WSCA), or insoluble CA] had been placed. Each fiber source was supplemented at 10% of total substrate. Tubes were incubated for 24 h to determine fermentation and microbial parameters. Then, the dose response of these parameters to different supplementation levels of WSCA (0, 7.5, 15, 22.5, and 30%) was tested in the same manner. We also operated a continuous culture system with WSCA supplementation and evaluated the effects on digestibility, fermentation, and microbial parameters. The supplementation level of WSCA was set at 15% of total feed. In batch culture studies, WSCA, but not insoluble CA, yielded dose-dependent increases in ruminal acetate levels. In the continuous culture system study, WSCA yielded increases in ruminal acetate levels and in the abundance of bacteria of the genus Prevotella, including Prevotella ruminicola. Dry matter digestibility and total gas production were not affected. These results suggest that WSCA supplementation at 15% of total feed yielded increased acetate levels without negatively affecting feed digestion; these effects may reflect activation of Prevotella species. As ruminal acetate is involved in milk fat synthesis, WSCA can be considered as a candidate feed additive suitable for dairy cattle.     

促进微生物生产多不饱和脂肪酸的研究

多不饱和脂肪酸(PUFAs)作为功能性油脂已被广泛应用于食品工业领域。随着对纯PUFAs脂质的需求量越来越多,来自于动植物和深海洋鱼的PUFAs远远不能满足市场需求,且动植物含油量及不饱和脂肪酸类型、比例均受到一定的限制。一系列的研究表明,微生物特别是藻类、真菌能合成几乎所有的PUFAs,并能在工业规模上培育有开发价值的可替代生物资源。作者在近年来国内外有关研究的基础上,从培养条件、菌种选育、基因工程、代谢调控等方面对促进微生物产PUFAs的研究进行了综述,为相关的研究提供参考。     

Rumen volatile fatty acid molar proportions,rumen epithelial gene expression,and blood metabolite concentration responses to ruminally degradable starch and fiber supplies

The objective of this work was to characterize rumen volatile fatty acid (VFA) concentrations, rumen epithelial gene expression, and blood metabolite responses to diets with different starch and fiber sources. Six ruminally cannulated yearling Holstein heifers (body weight = 330 ± 11.3 kg) were arranged in a partially replicated Latin square experiment with 4 treatments consisting of different starch [barley (BAR) or corn (CRN)] and fiber [timothy hay (TH) or beet pulp (BP)] sources. Treatments were arranged as a 2 × 2 factorial. Beet pulp and TH were used to create relative changes in apparent ruminal fiber disappearance, whereas CRN and BAR were used to create relative changes in apparent ruminal starch disappearance. Each period consisted of 3 d of diet adaptation and 15 d of dietary treatment. In situ disappearance of fiber and starch were estimated from bags incubated in the rumen from d 10 to 14. From d 15 to 17, rumen fluid was collected every hour from 0500 to 2300 h. Rumen fluid samples were pooled by animal/period and analyzed for pH and VFA concentrations. On d 18, 60 to 80 papillae were biopsied from the epithelium and preserved for gene expression analysis. On d 18, one blood sample per heifer was collected from the coccygeal vessel. In situ ruminal starch disappearance rate (7.30 to 8.72%/h for BAR vs. 7.61 to 10.5%/h for CRN) and the extent of fiber disappearance (22.2 to 33.4% of DM for TH vs. 34.4 to 38.7% of DM for BP) were affected by starch and fiber source, respectively. Analysis of VFA molar proportions showed a shift from propionate to acetate, and valerate to isovalerate on TH diets compared with BP. Corn diets favored propionate over butyrate in comparison to BAR diets. Corn diets also had higher molar proportions of valerate. Expression of 1 gene (SLC9A3) were increased in BP diets and 2 genes (BDH1 and SLC16A4) tended to be increased in TH diets. Plasma acetate demonstrated a tendency for a starch by fiber interaction with BAR-BP diets having the highest plasma acetate, but other metabolites measured were not significant. These results suggest that TH has the greatest effect on shifts in VFA molar proportions and epithelial transporters, but does not demonstrate shifts in blood metabolite concentrations.     

Milk odd- and branched-chain fatty acids in relation to the rumen fermentation pattern

The objectives of this study were 1) to determine whether a relationship exists between molar proportions of volatile fatty acids in the rumen and milk odd-and branched-chain fatty acid concentrations (i.e., iso C13:0, anteiso C13:0, iso C14:0, C15:0, iso C15:0, anteiso C15:0, iso C16:0, C17:0, iso C17:0, anteiso C17:0, and cis-9 C17:1); and 2) to evaluate the accuracy of prediction of the latter equations using an independent data set. For development of the regression equations, individual cow data from 10 feeding experiments with rumen-fistulated dairy cows were used, resulting in a data set of 148 observations. Milk odd- and branched-chain fatty acids were closely related to the molar proportions of acetate (SE = 15.3 mmol/mol), propionate (SE = 14.7 mmol/mol), and butyrate (SE = 9.2 mmol/mol). These regression equations were further validated using data from the literature (n = 14). Evaluation of these prediction equations using the independent data set resulted in a root mean square prediction error of 3.0, 9.0, and 8.9% of the observed mean for acetate, propionate, and butyrate, respectively. In addition, less then 5% of the mean square prediction error was due to line bias. This suggests that the currently developed prediction equations based on milk odd- and branched-chain fatty acids show potential to predict molar proportions of individual volatile fatty acids in the rumen.     

卡拉库尔羊瘤胃液对几种秸秆饲料体外降解率的研究

在厌氧环境、适宜温度、恒定pH值条件下,模拟卡拉库尔羊瘤胃环境,对3种农作物秸秆(棉花秸秆、稻草、玉米秸秆)进行离体消化试验。采用批次培养法,在培养后4、8、12、24、48h分别测定干物质(DM)、中性洗涤可溶物(NDS)、半纤维素(HC)、纤维素(CEL)体外降解率。结果表明:①“玉米秸秆 4%尿素”组比玉米秸秆组DM、NDS、HC、CEL体外降解率分别降低3.12、6.29、4.74和0.2个百分点,这说明添加尿素能引起瘤胃液对粗饲料体外降解的抑制。②棉叶、棉花秸秆上1/3细茎、棉桃壳组48h干物质降解率(DMD48)分别为65.47%、36.66%和31.32%,这说明棉叶组的体外降解率高于棉桃壳组及棉花秸秆上1/3细茎组的体外降解率。     

高效降解氧化乐果菌的初步筛选

以扬州、天津、吴江、泰州等地区施用过氧化乐果或农药厂排污口的土壤为菌源，以氧化乐果作为惟一碳源和能源，采用逐渐加量的驯化方式，分离得到10株对氧化乐果有一定降解能力的微生物。