Abstract
BackgroundIn 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.ResultsThis 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.ConclusionsThese 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.
Highlights
In prior work, adding a gene to phage T7 that degraded the host K1 capsule facilitated growth when plated on capsulated hosts
The only strict requirements for the control phage are that its intrinsic growth be superior to that of T7E1 and that it benefit from the presence of exogenous endosialidase
The short term evolutionary fate of a gene cloned into a phage genome and expressed as a free protein obeyed principles underlying the evolution of cooperation
Summary
In prior work, adding a gene to phage T7 that degraded the host K1 capsule facilitated growth when plated on capsulated hosts. Among many exciting prospects for synthetic biology, one is to engineer microbes that degrade environmental compounds – pollutants, bacterial biofilms, or foodstuff for fuel. For many applications, it would be ideal if the engineered microbial population persisted and purveyed its beneficial role indefinitely, generation after generation. The successful engineering of a genome that performs our desired function is not sufficient to confer transgenic immortality. For some purposes, engineered microbes must not be inferior to wild competitors, competitive inferiority may be desired as a way of limiting the environmental impact of the strain. The competition factor is ecological, and is not relevant if the engineered microbes are released into a closed environment from which outside competitors are excluded
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