Figure 6: Analysis of chitin in Pneumocystis and related fungi.

(a) Enzymes and accessory proteins involved in chitin metabolism in fungi. Pneumocystis genomes do not encode any chitin synthase or chitinase, which are present in other fungi, but retain genes encoding four accessory proteins (Supplementary Data 17). (b) Gas chromatograms of partially methylated alditol acetates of P. carinii and S. cerevisiae (control) cell walls. Terminal and 4-linked N-acetylglucosamine signals (T-GlcNAc and 4-GlcNAc in red font) were detected in S. cerevisiae but not in P. carinii. Glucose (Glc) and mannose (Man) signals were detected in both species. (c–e) Detection of chitin with recombinant chitin-binding ___domain (Alexafluor 488) using P. murina-infected lung tissue (c) and C. albicans-infected kidneys (e) as a positive control. Pneumocystis organisms are demonstrated in d by dual staining with anti-Msg (red), which labels both trophic forms and cysts, and a dectin-Fc construct (green), which labels β-1,3-glucan in cysts. Chitin staining is absent in P. murina but readily detected in C. albicans, while β-1,3-glucan is easily seen in P. murina. Original magnification, × 400; scale bar, 10 μm.