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Extreme microbial life: the origin

Researchers track evolutionary history of bacterial spores

Oeiras, 04.06.2013
Bacterial spores are arguably the most resistant cellular structure known to us. Spores are able to survive simulated and actual extraterrestrial conditions, and above all, spores can resist the passage of time, remaining viable for periods of time in excess of millions of years. These properties have stimulated scenarios, mostly in popular science accounts, in which spores, travelling through space, have brought life to earth, a concept called panspermia. A collaborative study published by the Microbial Development group of the ITQB, and the Computational Genomics Laboratory of the IGC (J. Bacteriol. 195:2101-15), placed bacterial sporulation some 0.7 billions of years after the appearance of life on earth, demonstrating that it is indeed an old process, but not sufficiently old as to support the panspermia hypothesis.

Just like other developmental processes in more complex organisms, the metamorphosis of a bacterial cell into a highly resistant spore requires the coordinated expression of a large number of genes in space and time. By comparing gene sequences from many different bacteria, researchers defined a minimal evolutionary machinery for spore formation, a group of genes conserved among all bacterial species known to form spores. A subset of these genes represents the genomic signature for sporulation and allowed the identification of new sporulating organisms from their genome sequence, even though sporulation may not have yet been verified under laboratory conditions.

Among the identified new sporulating bacteria is a very ancient group of organisms able to live in a range of extreme environmental conditions. Researchers believe sporulation may have been the evolutionary response to the unstable and extreme environmental conditions of primitive Earth: organisms may have used the faculty to produce highly resistant spores to survive new environmental challenges and to explore with success new ecological niches. Significantly, many of the bacterial predicted to be spore-formers have been isolated from the inhospitable environment of the gastrointestinal tract of various healthy animals, including humans.

Several spore-forming bacteria are able to cause severe animal or human disease. How some spore-forming bacteria cause disease while others establish beneficial interactions with their hosts remains an important research goal.

 Original Article

J. Bacteriol. (2013) 195(9): 2101-2115

A Genomic Signature and the Identification of New Sporulation Genes

Ana B. Abecasis, Mónica Serrano, Renato Alves, Leonor Quintais, José B. Pereira-Leal and Adriano O. Henriques

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