Mycoplasma pneumoniae

Mycoplasma pneumoniae is a member of the Mollicute class of bacteria. Its members are characterised by the lack of a cell wall and small genomes. Indeed Mycoplasma pneumoniae has just 689 genes and to give you an idea of just how small its genome is, the average bacteria has more than 4,000 genes. The human genome consists of 25,000 to 30,000 genes. The bacterium is one of the smallest known self replication cells and as such is a model system for the study of the minimum genetic requirements for a cell to replicate autonomously.

Though lacking a cell wall Mycoplasma pneumoniaea obtains some structural support from the sterols incorporated in its cell membrane. This is similar to eukaryotic cells.

A study of the inner workings of Mycoplasma pneumoniae by scientists at the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany revealed that it is more complex than scientists had given it credit, and it is able to react swiftly to changes in its environment and diet.

One of the biggest surprises was that there are so few "master switches" that control gene expression by turning genes on or off - which enables an organism to respond to the environment. In fact there are only 8 transcription factors, compared to E.coli which has more than fifty. So this got scientists scratching their heads to try and figure out how Mycoplasma pneumoniae can make it through each day with so few "master controllers". They came up with a couple of ideas: -

1) Antisense RNA steps in and carries out the "switching" role. Antisense RNA is a single strand that is complementary to a messenger RNA strand.

2) Chemicals used as food may act as signalling messengers.

Other findings of the EMBL research include: -

It was already known that Mycoplasma pneumoniae genes clump together in groups known as operons, and it was thought that the genes in a group acted together. However, the EMBL research revealed that only one or two genes operate at any one time.

The proteins produced by the bacterial genes each have a multitude of functions - they take on a number of different jobs in the bacterial cell, and are involved in more than one protein complex. This is to compensate for the scarcity of genes coding for proteins.

At every level explored, the scientists found much more complexity than expected, with the cells sharing features with more evolved organisms.

European Molecular Biology Laboratory