Section of Integrative Biology, The University of Texas, Austin, USA.
J Biol Eng. 2012 Sep 4;6(1):13. doi: 10.1186/1754-1611-6-13.
In prior work, adding a gene to phage T7 that degraded the host K1 capsule facilitated growth when plated on capsulated hosts. However, the transgenic protein (an endosialidase) is expressed as an exoenzyme, released from the cell at lysis but unattached to the phage particle. There is thus the possibility that the gene will be subject to a tragedy of the commons and be selected against, if the enzyme benefits other genomes.
This evolutionary perspective was supported in short term experiments. The genome carrying the endosialidase gene was favored on a capsulated host if grown in physical isolation of control genomes (lacking the gene) but was selected against otherwise.
These results challenge efforts to engineer phages with exoenzymes that degrade biofilm polymers. If biofilms do not facilitate spatially structured phage growth, the transgenic enzymes may be rapidly eliminated from the phage population after release in the environment, even if the transgene benefits overall phage growth on the biofilm.
在之前的工作中，向噬菌体 T7 添加一种可降解宿主 K1 荚膜的基因，有利于在有荚膜的宿主上生长。然而，转基因蛋白（一种内切唾液酸酶）作为胞外酶表达，在细胞裂解时释放出来，但不附着在噬菌体颗粒上。因此，如果这种酶对其他基因组有益，就有可能出现公地悲剧，从而被选择淘汰。
这一进化观点在短期实验中得到了支持。如果在与对照基因组（缺乏该基因）物理隔离的情况下在有荚膜的宿主上生长，携带内切唾液酸酶基因的基因组会受到青睐，但如果不是这样，它就会被淘汰。
这些结果对用降解生物膜聚合物的胞外酶工程改造噬菌体的努力提出了挑战。如果生物膜不能促进噬菌体的空间结构生长，那么转基因酶在环境中释放后，可能会很快从噬菌体群体中被淘汰，即使该转基因基因对生物膜上噬菌体的整体生长有益。
