The complete nucleotide sequence (580,070 base pairs) of the Mycoplasma genitalium genome, the smallest known genome of any free-living organism, has been determined by whole-genome random sequencing and assembly. A total of only 470 predicted coding regions were identified that include genes required for DNA replication, transcription and translation, DNA repair, cellular transport, and energy metabolism. Comparison of this genome to that of Haemophilus influenzae suggests that differences in genome content are reflected as profound differences in physiology and metabolic capacity between these two organisms.

The complete 1.66-megabase pair genome sequence of an autotrophic archaeon, Methanococcus jannaschii, and its 58- and 16-kilobase pair extrachromosomal elements have been determined by whole-genome random sequencing. A total of 1738 predicted protein-coding genes were identified; however, only a minority of these (38 percent) could be assigned a putative cellular role with high confidence. Although the majority of genes related to energy production, cell division, and metabolism in M. jannaschii are most similar to those found in Bacteria, most of the genes involved in transcription, translation, and replication in M. jannaschii are more similar to those found in Eukaryotes.

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The invasion of HEp-2 cells by Salmonella typhimurium was studied under various conditions. Anaerobiosis was shown to markedly affect the internalization of bacterial cells by HEp-2 cells. Anaerobically grown bacteria incubated with HEp-2 cells under anaerobic conditions markedly stimulated the rate of invasion. Anaerobiosis may therefore be a controlling factor in the invasion process. Cells obtained during the logarithmic phase of growth invaded at much higher rates than cells obtained during the stationary phase of growth. The presence of mannose-sensitive type 1 fimbriae on the bacterial surface also promoted invasion, and these fimbriae appear to play a role as an accessory virulence factor.