Horizontal Gene Transfers in Mycoplasmas (Mollicutes)

Area of Science:

• Microbiology
• Bacterial Genetics
• Evolutionary Biology

Background:

• Mollicutes (mycoplasmas) are wall-less bacteria with reduced genomes.
• Their evolution was traditionally attributed solely to gene loss.
• Recent findings highlight the significant role of horizontal gene transfer (HGT).

Purpose of the Study:

• To investigate the role of mobile genetic elements, particularly integrative and conjugative elements (ICEs), in mycoplasma evolution.
• To understand the mechanisms driving adaptation and genomic diversity in Mollicutes.
• To re-evaluate the evolutionary dynamics of minimal bacterial cells.

Main Methods:

• Identification and characterization of mobile genetic elements in various mycoplasma species.
• Analysis of the unique features of mycoplasma integrative and conjugative elements (MICEs).
• Investigation of the genetic basis for chromosomal integration and horizontal dissemination.

Main Results:

• Integrative and conjugative elements (ICEs) are pivotal in mediating massive HGT in mycoplasmas.
• Mycoplasma ICEs exhibit unique random chromosomal integration via a DDE recombinase.
• Conjugation facilitates transfer of large chromosomal fragments, leading to mosaic genomes and high genomic mobility.

Conclusions:

• Mycoplasmas actively acquire genetic resources through extensive HGT, challenging the 'gene loss only' evolutionary model.
• The plasticity of mycoplasma genomes, driven by MICEs, is key to their adaptation to diverse hosts.
• This expands the concept of minimal cells to include dynamic information flow and acquisition.