Constructing a minimal genome

Abstract

To determine how far the genome of Mycoplasma genitalium could be reduced without hampering its survival, Hutchison et al.1 Hutchison C.A. et al. Global transposon mutagenesis and a minimal mycoplasma genome. Science. 1999; 286: 2165-2169 Crossref PubMed Scopus (727) Google Scholar used large-scale transposon mutagenesis to establish a minimum genome size for an independently replicating cell living under laboratory conditions. They found that at least 129 genes in M. genitalium can be disrupted without lethal consequences. However, what constitutes such a minimal genome is, of course, relative to the environment it requires. Assuming a Poisson distribution of transposon insertions, the minimal gene set of M. genitalium consists of 265–350 protein-coding genes, with 180–215 non-essential genes, implying that at least 75% of the undisrupted genes are essential. One might expect that a large fraction of essential genes would be shared with many species – a core set of genes required for bacterial life. However, the disrupted gene set contains, for example, only one ribosomal protein. Nevertheless, 42 of the genes that were not disrupted are unique to the Mycoplasmas. Such genes could encode, for example, the Mycoplasma cytoskeleton that is unique to these bacteria. Thus, which genes constitute a minimal genome becomes a taxon-specific question, implying that there might be many, quite different, minimal genomes possible.