| Comments |
P.2 left column 4th paragraph: "2. Gene number, genome size and cell size: Table 1 gives the number of genes and the number of kbp for a number of genomes from free-living organisms, with an emphasis on those with a small number of genes. While the gene number is very important, the genome size is also worth considering as an indicator of resource requirement to replicate the genome, and, with gene number, the gene density. The organisms with the smallest genomes (as reported in peer-reviewed publications) found in free-living organisms occur in the Archaea and Bacteria. Those photolithotrophic organisms (oxygenic cyanobacteria) with the most reduced genomes have more genes than do the chemoorganotrophs (Proteobacteria) with the most reduced genomes, but fewer genes than the most reduced known genome of a chemolithotroph (autotrophic methanogenic Archaea) (table 1). This suggests that relatively few specific genes are needed for osmochemoorganotrophy (= saprochemoorganotrophy): these genes involve transport of solutes across the membrane and assimilation into core metabolism. Table 1 suggests that a greater number of specific genes are associated with autotrophy (chemolithotrophy and photolithotrophy): one category of such genes involves those coding for autotrophic carbon dioxide assimilation. A further group of genes relate to the energy transformation that converts the energy from reactions of inorganic compounds (in chemolithotrophy) or electromagnetic radiation (in photolithotrophy). It should be emphasized that these very small genomes are evolutionarily derived from larger genomes, e.g. in Cyanobacteria [ref 32]." |