The chitin attenuator: the Ca2+/calcineurin pathway maintains the viability of Candida albicans cells with supra-normal chitin levels

Chitin is an essential structural polysaccharide component of the cell walls and septa of fungi. Recent reports have suggested that Candida cells can resist killing by echinocandins by up-regulation of chitin synthesis thereby sustaining cell wall integrity both in vitro and in vivo (Lee et al. 2012). This increase in chitin content seen in C. albicans cells that are less susceptible to caspofungin is coordinated simultaneously by the PKC, Ca2+/calcineurin and HOG pathways (Munro et al. 2007, Walker et al. 2008). However, when echinocandins are removed, the chitin content quickly returns to basal levels, suggesting that elevated chitin cell wall content represents a fitness cost. We show here that those cells that die in the presence of caspofungin often have supra-normal chitin levels rather than low chitin levels, and therefore that having too much chitin in the cell wall may be detrimental for viability. Chitin content may therefore need to be clamped at levels that enable cells to survive cell wall stresses but are not so high that they negatively affect cell viability.