Intact yeast cells are present in the distended (A) proximal and (B) distal gastrointestinal tract of C. elegans after feeding for 36 h on C. neoformans strain KN99α. Black arrows point to the intestinal lumen. The white arrowheads note the pharyngeal grinder organ, which functions to disrupt ingested organisms.

Filamentation is instrumental for Candida virulence in mammals and is also involved in the killing of C. elegans [20]. The four panels show consequences of infecting C. elegans glp-4;sek-1 animals with C. albicans and then moving them into pathogen-free liquid medium. The top panels show that C. albicans cells persist within the C. elegans intestine and form hyphae (green) that break through the C. elegans cuticle, leaving a C. elegans “ghost” (dark structure) that outlines where the cuticle used to be. The bottom panels show that Candida cells develop filaments (green) that differentiate into hyphae, long continuous germ tubes separated by true septin rings, or pseudohyphae, chains of distinct cells that fail to separate. Pictures were taken with a confocal laser microscope (TCS NT; Leica Microsystems, http://www.leica-microsystems.com/). Concanavalin A-Alexafluor (fluorescence emission at 519 nm) is a fluorescent green dye that binds to polysaccharides. FUN-1, which was also used in the bottom right panel, is a fluorescent yellow dye that is absorbed by metabolically active fungal cells and fluoresces red when illuminated with a fluorescence emission 480 nm [20].