Wallace R J
Rowett Research Institute, Bucksburn, Aberdeen, U.K.
J Anim Sci. 1994 Nov;72(11):2992-3003. doi: 10.2527/1994.72112992x.
Present methods for manipulating ruminal fermentation that involve microbial biotechnology include dietary ionophores, antibiotics, and microbial feed additives. Developments in recombinant DNA technology mean that future methods will have a much wider scope. It has been suggested that genetically engineered ruminal microorganisms will be used in future to improve ruminal fermentation. Several technical objectives must be achieved before that will be possible. First, methods for inserting foreign or modified genes into ruminal microorganisms and ensuring their efficient expression must be developed. Broad host range plasmids and transposons have been used successfully to introduce new DNA into ruminal bacteria, as have shuttle vectors constructed as chimeras of plasmids from ruminal species and Escherichia coli. Although so far only antibiotic resistance markers have been transferred, the prospects for introducing other genes into selected ruminal bacteria are excellent. Second, the expression of the gene product(s) should be known to be nutritionally useful in vivo. A few examples of this type of benefit have been demonstrated, and many more proposed, including polysaccharidases for improving fiber digestion, methods for improving the amino acid composition of ruminal bacteria, and breakdown of plant toxins. Third, the difficulty that has been examined least, yet may prove most difficult to overcome, is that mechanisms have to be found for introducing and maintaining the new strain in the mixed ruminal population. Factors governing the survival of new strains in vivo are ill-understood, and attempts to select in favor of added new organisms have so far been unsuccessful. Because of the last obstacle, it may be advantageous, at least in the short term, to use nonruminal organisms, such as Saccharomyces cerevisiae, rather than indigenous ruminal species as a vehicle for implementing the benefits of recombinant DNA technology to ruminal fermentation. Yeast is already in widespread use as a feed additive, so no enrichment is necessary; and its genetics are already well known. Alternatively, adding particular enzymes to the diet may achieve some of the objectives described above, with the advantage that the manipulation could be achieved without the release of a recombinant microorganism.
目前涉及微生物生物技术的瘤胃发酵调控方法包括日粮离子载体、抗生素和微生物饲料添加剂。重组DNA技术的发展意味着未来的方法将具有更广泛的范围。有人提出，未来将使用基因工程瘤胃微生物来改善瘤胃发酵。在这成为可能之前，必须实现几个技术目标。首先，必须开发将外源或修饰基因插入瘤胃微生物并确保其有效表达的方法。广泛宿主范围的质粒和转座子已成功用于将新DNA引入瘤胃细菌，来自瘤胃物种和大肠杆菌的质粒嵌合体构建的穿梭载体也已成功应用。尽管到目前为止仅转移了抗生素抗性标记，但将其他基因引入选定瘤胃细菌的前景非常广阔。其次，应该知道基因产物的表达在体内具有营养益处。已经证明了这种益处的一些例子，并且提出了更多例子，包括用于改善纤维消化的多糖酶、改善瘤胃细菌氨基酸组成的方法以及植物毒素的分解。第三，研究最少但可能最难克服的困难是，必须找到将新菌株引入并维持在瘤胃混合菌群中的机制。体内新菌株存活的控制因素了解甚少，迄今为止选择有利于添加新生物体的尝试均未成功。由于最后一个障碍，至少在短期内，使用非瘤胃生物体，如酿酒酵母，而不是本地瘤胃物种作为实现重组DNA技术对瘤胃发酵益处的载体可能是有利的。酵母已广泛用作饲料添加剂，因此无需富集；而且其遗传学已经为人熟知。或者，在日粮中添加特定酶可能实现上述一些目标，其优点是可以在不释放重组微生物的情况下实现调控。
