Genetic modification of Candida maltosa, a nonpathogenic CTG species, reveals EFG1 function

Candida maltosa is closely related to important pathogenic Candida species, but it has been rarely isolated from humans. Therefore, through comparative studies, it could be a powerful model to understand the pathogenicity underpinnings of Candida species. To facilitate studying C. maltosa at a molecular level, we built a cohesive genomic sequence composed of 45 scaffolds, a substantial improvement from the thousands of contigs of the available draft. Comparison with C. albicans and C. tropicalis revealed a reduction in the total number of genes in C. maltosa. However, gene loss seems not to be associated to its avirulence given that most pathogenicity genes were also present in C. maltosa. To genetically edit C. maltosa we generated triple auxotrophic strains so that gene deletions can be performed as has been routinely done in pathogenic species. As a proof of concept, we generated gene knockouts of Efg1, a transcription regulator involved in filamentation and biofilm formation in pathogenic species. Although in C. maltosa Efg1 also played a role in these processes, it seems to rather be a repressor of filamentation. The genome assembly and auxotrophic mutants developed are a key step to start using C. maltosa for comparative studies at a molecular level.