Example of results of the semi-quantitative SLM drop assay showing various categories of mutator phenotype.

<p>Cell suspensions were serially diluted and spotted onto selection plate (with canavanine or 5′-FOA) and onto dilution control plate as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0021124#s4" target="_blank">Materials and Methods</a>. <i>WT</i> – SLM level in parental strain, M - increased SLM phenotype, HM - high SLM phenotype, ρ<sup>−</sup> - increased SLM due to respiratory incompetence in <i>WT</i> ρ<sup>−</sup> strain, Rρ<sup>−</sup> – resistance to selection conditions acquired along with the loss of respiratory competence, M/GD - high SLM phenotype accompanied by decreased survival rate, seen also without selection, R - full resistance to selection conditions.</p>