Fig. 7

The proposed model of metabolic changes in T. vaginalis under iron-limited environments. Once trichomonad cells encountered iron-deficient conditions, most of the cells transformed into pseudocysts. The carbon source of the more active glycolysis was derived from glycogen hydrolysis because of the accumulation of ɑ-1,4-linked, glucose-composed oligosaccharides. The accumulation of cellobiose was a possible hint for cellulose biosynthesis, which is the crucial conformational component of pseudocysts. C18 fatty acids reduction implied incorporation into phospholipids for pseudocyst formation. Capric acid accumulation might be involved in the regulation of glycolysis or as a signaling molecule in response to iron-limited environments. Amino acid reduction likely resulted from dipeptide accumulation or incomplete proteolysis. In addition, the significant reductions in alanine, glutamate, and serine were all involved in the release of ammonia, which was likely a key resource for nitric oxide synthesis in T. vaginalis. Compounds labeled in red and green colors represent accumulation and reduction in ID cells, respectively. Gray-colored metabolites were the speculated metabolites associated with the detected compounds. The putative molecular function or pathways were labeled in blue color