Recombinant rumen bacteria: problems and opportunities.
2003
Kobayashi, Y.
Gene manipulation of rumen bacteria was initiated in the early 1980s with most of the effort primarily focused on developing plasmid vectors. From the 1990s, more functional (fibrolytic, essential amino acid-producing or detoxifying) rumen bacteria were produced using stable and efficient host vector systems, all of which were based on the sophisticated DNA and protein engineering techniques that had been developed in the preceding decade. However, the recombinants often suffered from poor settlement in the rumen when inoculated, showing rapid decreases in abundance within hours or a few days. However, a mixture of four recombinants, each exhibiting detoxifying enzyme activity, was settled in the rumen of sheep at a level up to 10<sup>7</sup>/ml. This level was high enough to degrade the toxic monofluoroacetate offered in the diet, making the sheep tolerant to the toxin. This success demonstrated the potential of using recombinants and suggested strategies for successfully settling recombinants in the rumen. In addition to promoting animal health and production, the gene cloning system for rumen bacteria may be used to clone genes and produce proteins that, to date, can not be cloned and expressed in an <i>Escherichia coli</i> system. This review describes (i) the methodology of gene manipulation; (ii) recombinant rumen bacteria obtained so far; (iii) fate of recombinants inoculated in the rumen; and (iv) perspectives and problems in current and future applications.
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