Abstract
BackgroundDNA repair is essential for the maintenance of genome stability in all living beings. Genome size as well as the repertoire and abundance of DNA repair components may vary among prokaryotic species. The bacteria of the Mollicutes class feature a small genome size, absence of a cell wall, and a parasitic lifestyle. A small number of genes make Mollicutes a good model for a “minimal cell” concept.ResultsIn this work we studied the DNA repair system of Mycoplasma gallisepticum on genomic, transcriptional, and proteomic levels. We detected 18 out of 22 members of the DNA repair system on a protein level. We found that abundance of the respective mRNAs is less than one per cell. We studied transcriptional response of DNA repair genes of M. gallisepticum at stress conditions including heat, osmotic, peroxide stresses, tetracycline and ciprofloxacin treatment, stationary phase and heat stress in stationary phase.ConclusionsBased on comparative genomic study, we determined that the DNA repair system M. gallisepticum includes a sufficient set of proteins to provide a cell with functional nucleotide and base excision repair and mismatch repair. We identified SOS-response in M. gallisepticum on ciprofloxacin, which is a known SOS-inducer, tetracycline and heat stress in the absence of established regulators. Heat stress was found to be the strongest SOS-inducer. We found that upon transition to stationary phase of culture growth transcription of DNA repair genes decreases dramatically. Heat stress does not induce SOS-response in a stationary phase.
Highlights
DNA repair is essential for the maintenance of genome stability in all living beings
The interesting question here is which polymerase is recruited for DNA repair because DNA-polymerase I is absent in M. gallisepticum as well as in most of Mollicutes
In M. gallisepticum and most of Mollicutes, this mechanism is likely substituted with DNA-polymerase III and Exo protein, which is an exonuclease, homologous to the 5′-3′ exonuclease domain of PolA
Summary
DNA repair is essential for the maintenance of genome stability in all living beings. Genome size as well as the repertoire and abundance of DNA repair components may vary among prokaryotic species. The bacteria of the Mollicutes class feature a small genome size, absence of a cell wall, and a parasitic lifestyle. Genomic DNA is constantly subject to damage. This includes the misincorporation of nucleotides by DNApolymerases and chemical modification either by endogenous metabolites or external compounds. Bacteria of the class Mollicutes features a small though sufficient genome to grow on a cell-free medium and a low GC content (31% for Mycoplasma gallisepticum). Their genome size typically ranges from 580 thousand to
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