Both host trypanosomatids have glycerol kinase and 3-glycerophosphate acyltransferase, enzymes for the synthesis of 1,2-diacyl-sn-glycerol and triacylglycerol from D-glycerate. In endosymbionts, glycerolipid metabolism seems to be reduced to two enzymes: 3glycerophosphate acyltransferase and 1-acylglycerol-3-phosphate O-acyltransferase, suggesting metabolic complementation between partners. Furthermore, as well as the pathway of sterol biosynthesis that produces lanosterol from farnesyl-PP. These pathways are only complete in A. deanei. The symbionts do not have enzymes for sterol biosynthesis, in accordance with our previous biochemical analysis. Symbiosis in trypanosomatids is characterized by intensive metabolic exchanges, reducing the nutritional requirements of these trypanosomatids when compared to species without the Z-VAD-FMK Symbiotic bacterium, or to aposymbiotic strains. Several biochemical studies have been carried out analyzing the biosynthetic pathways involved in this intricate relationship as recently reviewed, and our genomic data corroborate these findings. A schematic description of the potential metabolic interactions concerning the metabolism of amino acids, vitamins, cofactors, and hemin is provided in Figure 7. Both symbiotic bacteria have genes potentially encoding for all necessary enzymes for lysine, phenylalanine, tryptophan and tyrosine synthesis, in agreement with previous experimental data. Tyrosine is required in the growth medium of A. deanei, but it is not essential for S. oncolpelti or S. culicis. Here, in the symbiotic bacteria, we found enzymes involved in tyrosine synthesis, as well as indications that phenylalanine and tyrosine can be interconverted. In fact, protozoan growth is very slow in absence of phenylalanine and tryptophan, which may indicate that larger amounts of these amino acids are required for rapid cell proliferation. Our data indicate that branched-chain amino acid synthesis mainly occurs in the symbionts except for the last step, with the branched-chain amino acid aminotransferase found in the host protozoan. Among the pathways that involve contributions from both partners, two have previously been characterized in detail, the urea cycle and heme synthesis. The urea cycle is complete in both symbiont-harboring trypanosomatids. Symbiotic bacteria SAR131675 msds contribute with ornithine carbamoyltransferase, which converts ornithine to citrulline, and with ornithine acetyltransferase, which transforms acetylornithine in ornithine. Conversely, aposymbiotic strains and symbiont-free Crithidia species need exogenous arginine or citrulline for cell proliferation. Our genomic data corroborate these studies. Contrary to symbiont-free trypanosomatids, A. deanei and S. culicis do not require any source of heme for growth because the bacterium contains the required enzymes to produce heme precursors that complete the heme synthesis pathway in the host cell. Our results support the idea that heme biosynthesis is mainly accomplished by the endosymbiont, with the last three steps of this pathway performed by the host trypanosomatid, and in most cases also by the bacterium as described in. Furthermore, this metabolic route may represent 
the result of extensive gene loss and multiple lateral gene transfer events in trypanosomatids.