Genome Information:

When Mycoplasma species were first cultured, they were thought to have been virus because of their size. However, after discovered the presence of DNA and RNA, they are said to be types of bacteria. They are very tiny and able to fit through 450nm pore diameter membrane filters. One of the members of Mycoplasma is M. pneumomiae. The complete sequence of M. pneumoniae genome indicates that it is a circular duplex DNA of 816,394 bp. The presumptive origin of replication is in an A+T rich region between dnaA and dnaN. A total of 677 open reading frames (ORFs) and 39 genes coding for various RNAs were identified. M. pneumoniae has a degenerate genome because it uses some unique genetic code to make its code more similar to mitochondria than to other bacteria. It lacks the cellular machinery for making new purines and pyrimidines. However, it has tri-carboxylic acid cycle and an incomplete electron transport chain.

The coding regions in M. pneumoniae comprise a total length of 724,174 bp, or 88.7% of the genome. The average size of a gene is 1011 bp, giving an average of one gene every 1140 bp. This is similar to the gene size and density seen with both the smaller M. genitalium genome as well as the H. influenza genome, which is more than twice as large.

Below is the comparison of genome information between M. pneumoniae and M. genitalium:

We compare them with emphasis on genome organization and coding capacity. All the 470 proposed open reading frames (ORFs) of the smaller M.genitalium genome (580 kb) were contained in the larger genome (816 kb) of M.pneumoniae. There were some discrepancies in annotation, but inspection of the DNA sequences showed that the corresponding DNA was always present in M.pneumoniae. The two genomes could be subdivided into six segments. The order of orthologous genes was well conserved within individual segments but the order of these segments in both bacteria was different. We explain the different organization of the segments by translocation via homologous recombination. The translocations did not disturb the continuous bidirectional course of transcription in both genomes, starting at the proposed origin of replication. The additional 236 kb in M.pneumoniae, compared to the M.genitalium genome, were coding for 209 proposed ORFs not identified in M.genitalium. Of this ORFs 110 were specific to M.pneumoniae exhibiting no significant similarity to M.genitalium ORFs, while 76 ORFs were amplifications of ORFs existing mainly as single copies in M.genitalium. In addition, 23 ORFs containing a copy of either one of the three repetitive DNA sequences RepMP2/3, RepMP4 and RepMP5 were annotated in M.pneumoniae but not in M.genitalium, although similar DNA sequences were present. The M.pneumoniae-specific genes included a restriction-modification system, two transport systems for carbohydrates, the complete set of three genes coding for the arginine dihydrolase pathway and 14 copies of the repetitive DNA sequence RepMP1 which were part of several different translated genes with unknown function.