ScienceDaily (Nov. 27, 2009) — What are the bare essentials of life, the indispensable ingredients required to produce a cell that can survive on its own? Can we describe the molecular anatomy of a cell, and understand how an entire organism functions as a system? These are just some of the questions that scientists in a partnership between the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, and the Centre de Regulacion Genòmica (CRG) in Barcelona, Spain, set out to address.
In three papers published back-to-back in Science, they provide the first comprehensive picture of a minimal cell, based on an extensive quantitative study of the biology of the bacterium that causes atypical pneumonia, Mycoplasma pneumoniae. The study uncovers fascinating novelties relevant to bacterial biology and shows that even the simplest of cells is more complex than expected.
This image represents the integration of genomic, metabolic, proteomic, structural and cellular information about Mycoplasma pnemoniae in this project: one layer of an Electron Tomography scan of a bottle-shaped M. pneumoniae cell (grey) is overlaid with a schematic representation of this bacterium's metabolism, comprising 189 enzymatic reactions, where blue indicates interactions between proteins encoded in genes from the same functional unit. Apart from these expected interactions, the scientists found that, surprisingly, many proteins are multifunctional. For instance, there were various unexpected physical interactions (yellow lines) between proteins and the subunits that form the ribosome, which is depicted as an Electron microscopy image (yellow). (Credit: Takuji Yamada /EMBL)
Mycoplasma pneumoniae is a small, single-cell bacterium that causes atypical pneumonia in humans. It is also one of the smallest prokaryotes -- organisms whose cells have no nucleus -- that don't depend on a host's cellular machinery to reproduce. This is why the six research groups which set out to characterize a minimal cell in a project headed by scientists Peer Bork, Anne-Claude Gavin and Luis Serrano chose M. pneumoniae as a model: it is complex enough to survive on its own, but small and, theoretically, simple enough to represent a minimal cell -- and to enable a global analysis.
A network of research groups at EMBL's Structural and Computational Biology Unit and CRG's EMBL-CRG Systems Biology Partnership Unit approached the bacterium at three different levels. One team of scientists described M. pneumoniae's transcriptome, identifying all the RNA molecules, or transcripts, produced from its DNA, under various environmental conditions. Another defined all the metabolic reactions that occurred in it, collectively known as its metabolome, under the same conditions. A third team identified every multi-protein complex the bacterium produced, thus characterising its proteome organisation.
"At all three levels, we found M. pneumoniae was more complex than we expected," says Luis Serrano, co-initiator of the project at EMBL and now head of the Systems Biology Department at CRG.
When studying both its proteome and its metabolome, the scientists found many molecules were multifunctional, with metabolic enzymes catalyzing multiple reactions, and other proteins each taking part in more than one protein complex. They also found that M. pneumoniae couples biological processes in space and time, with the pieces of cellular machinery involved in two consecutive steps in a biological process often being assembled together.
Remarkably, the regulation of this bacterium's transcriptome is much more similar to that of eukaryotes -- organisms whose cells have a nucleus -- than previously thought. As in eukaryotes, a large proportion of the transcripts produced from M. pneumoniae's DNA are not translated into proteins. And although its genes are arranged in groups as is typical of bacteria, M. pneumoniae doesn't always transcribe all the genes in a group together, but can selectively express or repress individual genes within each group.
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Journal References:
Kühner et al. Proteome Organization in a Genome-Reduced Bacterium. Science, 2009; DOI: 10.1126/science.1176343
Yus et al. Impact of Genome Reduction on Bacterial Metabolism and Its Regulation. Science, 2009; DOI: 10.1126/science.1177263
Güell et al. Transcriptome Complexity in a Genome-Reduced Bacterium. Science, 2009; DOI: 10.1126/science.1176951
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NOTA IMPERTINENTE DESTE BLOGGER:
O darwinismo 'arrota' ser uma ciência estritamente baconiana. Ora, o espírito baconiano de se fazer ciência é 'ir à natureza, fazer perguntas a ela, e seguir as evidências aonde eles forem dar'. No tocante ao design real encontrado na natureza, nós temos uma 'montanha de evidências' [dêem licença agora, mas o pessoal do Design Inteligente é que pode usar este termo] que apontam para a presença e detecção de design. Se os darwinistas são realmente baconianos como dizem ser, basta seguir as evidências aonde elas forem dar: Design Inteligente!
