The study of microbial life has contributed significantly to our understanding of biological systems and underpins much of our knowledge of more highly evolved organisms. One theme in this month's issue is an appreciation of the impact and contribution the study of microorganisms has made to different areas of biology and medicine.
The association between microorganisms and chronic human diseases has been hotly debated. Although infectious agents have been linked with autoimmunity, it has proven difficult to implicate a single microorganism as a cause. On page 151, von Herrath and colleagues propose an intriguing hypothesis to explain how microorganisms might induce and exacerbate autoimmunity. A less controversial issue that we can all agree on is the pioneering contributions microbiologists have made to genomics, and the many sequenced microbial genomes now provide a wonderful opportunity to explore the power of comparative genomics. The review on page 127 by Eugene Koonin illustrates how this approach, in combination with experimental techniques, is being used to identify the repertoire of genes that is necessary and sufficient for supporting cellular life and the connection of such a gene-set with the last universal common ancestor. Given that its complete genome sequence has been available for 6 years, Bacillus subtilis is probably better defined in terms of its biochemistry, physiology and genetics than any other organism (with the exception of Escherichia coli). Sporulation in this prokaryote is probably the best-understood example of cellular differentiation and development — Jeff Errington reviews recent progress on page 117.
