About a year ago Crowlspace discussed the smallest free-living organisms yet discovered: Smallest Life as We Know It
Since then Craig Venter’s lab has produced an organism with an even smaller genome:
…with just 473 genes (531,000 base-pairs) yet capable of self-replication in 3 hours, it’s truly something new.
From the paper:
The minimal cell concept appears simple at first glance but becomes more complex upon close inspection. In addition to essential and nonessential genes, there are many quasi-essential genes, which are not absolutely critical for viability but are nevertheless required for robust growth. Consequently, during the process of genome minimization, there is a trade-off between genome size and growth rate. JCVI-syn3.0 is a working approximation of a minimal cellular genome, a compromise between small genome size and a workable growth rate for an experimental organism. It retains almost all the genes that are involved in the synthesis and processing of macromolecules. Unexpectedly, it also contains 149 genes with unknown biological functions, suggesting the presence of undiscovered functions that are essential for life. JCVI-syn3.0 is a versatile platform for investigating the core functions of life and for exploring whole-genome design.
Just how much information does such a minimal genome represent? In raw terms each base-pair has 4 options, thus 2 bits, implying a total information of 1.062 million bits. Of course the gene code is highly redundant – each codon of three base-pairs (4 x 4 x 4 = 64 possible states) encodes just 21 different amino acids and the ‘STOP’ message. Thus this tiny genome encodes ~130 thousand “geno-bytes” (kgbs). As we only have a vague idea of just how many possible viable genomes can be made from 130 kgbs, there’s no meaningful way of assigning probability to a random search of genomes producing viable lifeforms.