The identification of the Dictyostelium discodeum axeB gene

To identify variants correlated with the ability to grow axenically (ie in the absence of prey organisms) we resequenced mutant Dictyostelium discoideum strains and compared them to their wild-type parent. We identified a single locus that is compromised in every mutant strain: most mutants carry short deletions that result in frameshifts, but we also found nonsense and missense SNPs and an in-frame inversion that leads to an 8 amino-acid substitution. Deletion of the gene enables slow axenic growth, confirming that a single mutation in this gene, axeB, is sufficient to confer the phenotype, but that further mutations are necessary for the fast growth phenotype of standard laboratory strains.