Minimal Cells-Real and Imagined

Abstract

A minimal cell is one whose genome only encodes the minimal set of genes necessary for the cell to survive. Scientific reductionism postulates the best way to learn the first principles of cellular biology would be to use a minimal cell in which the functions of all genes and components are understood. The genes in a minimal cell are, by definition, essential. In 2016, synthesis of a genome comprised of only the set of essential and quasi-essential genes encoded by the bacterium Mycoplasma mycoides created a near-minimal bacterial cell. This organism performs the cellular functions common to all organisms. It replicates DNA, transcribes RNA, translates proteins, undergoes cell division, and little else. In this review, we examine this organism and contrast it with other bacteria that have been used as surrogates for a minimal cell.

Figure 1.

Plots of nonessential (NE) gene number versus genome size and total genes in Mycoplasma species and reduced strains. NE genes were determined by transposon mutagenesis in Mycoplasma genitalium (580 kb), Mycoplasma pneumoniae (816 kb), Mycoplasma pulmonis (963 kb), Mycoplasma mycoides JCVI-syn1.0 (1080 kb), M. mycoides JCVI-syn2.0 (576 kb), and M. mycoides JCVI-Syn3.0 (531 kb). (A) Plotting NE genes versus genome size yields an extrapolated value of 423 kb for the minimal genome size when NE = 0. (B) Plotting NE genes versus total genes yields an extrapolated value of 413 genes when NE = 0.