Systems-Based Analysis of the Sarcocystis neurona Genome Identifies Pathways That Contribute to a Heteroxenous Life Cycle

Blazejewski, Tomasz; Nursimulu, Nirvana; Pszenny, Viviana; Dangoudoubiyam, Sriveny; Namasivayam, Sivaranjani; Chiasson, Melissa A.; Chessman, Kyle; Tonkin, Michelle; Swapna, Lakshmipuram S.; Hung, Stacy S.; Bridgers, Joshua; Ricklefs, Stacy M.; Boulanger, Martin J.; Dubey, Jitender P.; Porcella, Stephen F.; Kissinger, Jessica C.; Howe, Daniel K.; Grigg, Michael E.; Parkinson, John

Reconstruction and analysis of S. neurona metabolism reveal the potential to exploit alternative sources of energy. S. neurona has 372 metabolic enzymes (unique enzyme classification [EC] numbers, excluding those involved in nonmetabolic reactions) in common with T. gondii but is missing 42 enzymes and has an additional 13 enzymes that are expressed by RNA-Seq in the merozoite stage ( Fig. 6A ; see Text S1 in the supplemental material). Our analyses predict putative T. gondii orthologs for 12 of these enzymes, including the fatty acid elongation genes verylong-chain 3-oxoacyl coenzyme A synthase ( We incorporated these differences into our previously published metabolic reconstruction of T. gondii named iCS382 (8) and performed flux balance analyses of both iCS382 and the modified S. neurona reconstruction. Scaling the iCS382 model to produce a doubling time of 11.8 h with glucose as the sole energy source (see Text S1 in the supplemental material), we show that S. neurona has a slightly longer doubling time of 13.8 h. Singlereaction knockouts identified 22 reactions whose deletion resulted in a significantly greater impact on S. neurona than on T. gondii (Ͼ20% maximal growth rate difference) ( Fig. 6B ; see Table S2 in the supplemental material). Critical reactions include members of the pentose phosphate and glycolysis pathways, the tricarboxylic acid (TCA) cycle, and two members of the pyrimidine biosynthetic pathway, nucleoside-diphosphate kinase (EC 2.7.4.6) and cytidylate kinase (EC 2.7.4.14). Conversely, we identified only a single reaction, catalyzed by pyruvate dehydrogenase, whose deletion had a significantly greater impact on T. gondii than on S. neurona (Ͼ20% maximal growth rate difference).