Optimizing Transformation Frequency of Cryptococcus neoformans and Cryptococcus gattii Using Agrobacterium tumefaciens

Genetic Transformation of Cryptococcus Species with Agrobacterium Transfer DNA

Transformation of foreign DNA into Cryptococcus species is a powerful tool for exploring gene functions in these human pathogens. Agrobacterium tumefaciens-mediated transformation (AtMT) has been used for the stable introduction of exogenous DNA into Cryptococcus for over two decades, being particularly impactful for insertional mutagenesis screens to discover new genes involved in fungal biology. A detailed protocol to conduct this transformation method is provided in the chapter. Scope for modifications and the benefits and disadvantages of using AtMT in Cryptococcus species are also presented.

Agrobacterium tumefaciens-Mediated Transformation of Candida glabrata

The use of broad-spectrum antimycotic therapy, immunosuppressive therapy, and indwelling medical devices has contributed to the increased frequency of mucosal and systemic infections caused by Candida glabrata. A major concern for C. glabrata and other Candida spp. infections is the increase in drug resistance. To address these issues, additional molecular tools for the study of C. glabrata are needed. In this investigation, we developed an Agrobacterium tumefaciens transformation system for C. glabrata. A number of parameters were investigated to determine their effect on transformation frequency, and then an optimized protocol was developed. The optimal conditions for the transformation of C. glabrata were found to be an infection incubation temperature of 26 °C, 0.2 mM acetosyringone in both induction media and co-culture media, 0.7% agar concentration, and a multiplicity of infection of 50:1 A. tumefaciens to C. glabrata. Importantly, the frequency of multiple integrations was low (5%), demonstrating that A. tumefaciens generally integrates at single sites in C. glabrata, which is consistent with other fungal A. tumefaciens transformation systems. The development of this system in C. glabrata adds another tool for the molecular manipulation of this increasingly important fungal pathogen.