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'Simple' bacterium shows surprising complexity
An in-depth "blueprint" of an apparently minimalist species has revealed details that challenge preconceptions about how genes operate.
Mycoplasma pneumoniae, which causes a form of pneumonia in people, has just 689 genes, compared with 25,000 in humans and 4000 or more in most other bacteria. Now a study of its inner workings has revealed that the bacterium has uncanny flexibility and sophistication, allowing it to react fast to changes in its diet and environment.
To retrieve protein complexes and interacting proteins and get a detailed view of the functional and spatial organisation of the proteome, the study, just published in Science, combined several technics: genomic analysis, tandem affinity purification–mass spectrometry (TAP-MS), protein modeling, single-particle electron microscopy and electron tomography.
It shows in particular that the organism gets by with just eight gene "switches", or transcription factors, compared with more than 50 in other bacteria such as Escherichia coli.
The protein analysis also revealed that the bacterium compensates for having so few proteins by employing each one in a multitude of functions.
Maps were generated for the ribosome, the chaperone GroEL, the structural core of the pyruvate dehydrogenase (PdhC, Mpn391, homomultimer), and RNA polymerase. These large complexes are excluded from the tip, an organelle required for the attachment to epithelial cells, illustrating that even in a simple, minimal bacteria the proteome is spatially organized.
In
contrast to E. coli that contains a compact nucleoid forming an
exclusion area in the cell center, circular DNA in M. pneumoniae is
apparently uniformly distributed. It is estimated that the average
number of complexes per cell to be 140 for the ribosome, 100 for
GroEL, 100 for pyruvate dehydrogenase, and 300 for RNA polymerase.
See the complete article by Andy Coghlan at
http://www.newscientist.com/article/dn18206-simple-bacterium-shows-surprising-complexity.html
and the research article published 27 November 2009 in Science:
Proteome Organization in a Genome-Reduced Bacterium
Sebastian Kühner, et al. Science 326, 1235 (2009)
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