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Mechanism of Isolated Hemicellulose and Xylan Degradation by Cellulolytic Rumen Bacteria

机译：纤维素瘤胃细菌分离半纤维素和木聚糖降解的机理

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Although certain strains of cellulolytic rumen bacteria cannot utilize isolated hemicelluloses or xylan as a source of energy, all strains examined can degrade or solubilize these materials from an 80% ethyl alcohol insoluble to a soluble form. Centrifugation and washing of the cellobiose-grown bacterial cells did not affect the rate or extent of utilization or degradation or both. When the level of a nonutilizing culture inoculum (either normal or washed) was doubled, a corresponding increase in the initial rate of degradation was observed. With a nitrogen-free medium, utilization of xylan was almost completely inhibited for a utilizing strain, whereas degradation by either type of organism was not markedly affected. Cellobiose medium cell-free culture filtrates from a nonutilizing strain were able to degrade or solubilize xylan. The percentage of degradation increased with the volume of cell-free filtrate, and all activity was lost when the filtrate was boiled. No utilization (loss in total pentose) was observed with cell-free filtrates from utilizing or nonutilizing strains. The release of free hexose from insoluble cellulose by culture filtrates from a nonutilizing strain was very limited. On the other hand, carboxymethylcellulose (CMC-70L) and cellulodextrins were degraded to an 80% ethyl alcohol soluble form by filtrates from both types of organisms. Similar enzyme activity was obtained in cell-free culture filtrates from four additional strains of cellulolytic rumen bacteria (one xylan utilizer and three nonutilizers). When the assays were carried out aerobically, CMC-70L solubilization was reduced to a much greater extent than xylan or cellulodextrin solubilization. The enzyme or enzymes responsible for the degradation of hemicellulose by cellololytic rumen bacteria unable to utilize the hemicellulose as an energy source appear to be constitutive in nature, and this activity may be a nonspecific action of a β-1, 4-glucosidase or -cellulase.
机译：尽管某些纤维素分解瘤胃细菌菌株不能利用分离的半纤维素或木聚糖作为能源，但所有检测到的菌株都可以将这些物质降解或溶解，从80％的乙醇不溶性变为可溶形式。纤维二糖生长的细菌细胞的离心和洗涤不影响利用或降解或两者的速率或程度。当未利用的培养接种物（正常或洗涤）的水平加倍时，观察到初始降解速率相应增加。在无氮培养基中，利用菌株几乎完全抑制了木聚糖的利用，而两种生物体的降解均未受到明显影响。来自未利用菌株的纤维二糖培养基无细胞培养滤液能够降解或溶解木聚糖。降解百分数随无细胞滤液的体积而增加，当滤液沸腾时，所有活性均丧失。利用或未利用菌株的无细胞滤液未观察到利用（总戊糖损失）。通过不利用菌株的培养滤液从不溶性纤维素中释放游离己糖非常有限。另一方面，羧甲基纤维素（CMC-70L）和纤维素糊精被两种生物的滤液降解为可溶于80％乙醇的形式。在来自另外四个纤维素分解瘤胃细菌菌株（一个木聚糖利用者和三个非利用者）的无细胞培养滤液中获得了相似的酶活性。当需氧测定时，CMC-70L的溶解度比木聚糖或纤维素糊精的溶解度降低得多。不能由半纤维素瘤胃作为能源的纤维素分解瘤胃细菌负责降解半纤维素的酶本质上是组成性的，该活性可能是β-1、4-葡萄糖苷酶或-纤维素酶的非特异性作用。

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