Ribosomal RNA genes in Mycoplasma

Area of Science:

• Microbiology
• Molecular Biology
• Genomics

Background:

• Ribosomal RNA (rRNA) cistrons are crucial genetic elements in bacteria.
• Understanding rRNA gene organization provides insights into bacterial phylogeny and evolution.
• Mycoplasma species, known for their minimal genomes, offer a unique model for studying rRNA cistron structure.

Purpose of the Study:

• To characterize the rRNA cistron structure in Mycoplasma capricolum.
• To compare the rRNA gene organization of M. capricolum with other related bacteria, including E. coli.
• To investigate the evolutionary relationships among Mycoplasma and Acholeplasma species based on rRNA cistron homology.

Main Methods:

• Southern blotting analysis using labelled mycoplasmal ribosomal RNA as a probe.
• EcoR I digestion of Mycoplasma capricolum DNA to identify rRNA-encoding fragments.
• Cloning of a 5 Kb EcoR I fragment containing rRNA sequences for further characterization.
• Comparative analysis of rRNA cistron structures across different Mycoplasma and Acholeplasma strains.

Main Results:

• Two EcoR I DNA fragments (1 Kb and 5 Kb) were detected in Mycoplasma capricolum.
• The 5 Kb fragment contains both 16S rRNA sequences and the complete 23S rRNA gene.
• The 1 Kb fragment exclusively contains 16S rRNA sequences.
• Significant homology was observed between M. capricolum rRNA sequences and those of E. coli, Mycoplasma mycoides subsp. capri, and Acholeplasma laidlawii.
• Mycoplasma capricolum possesses one rRNA cistron, while M. mycoides subsp. capri and A. laidlawii have two.

Conclusions:

• Mycoplasma capricolum has a single, compact rRNA cistron structure.
• The rRNA gene organization in M. capricolum shows evolutionary links to both Gram-negative bacteria (E. coli) and other mollicutes.
• Variations in rRNA cistron copy number (one vs. two) among related species highlight genomic plasticity within the Mycoplasma genus.