Coordinated and contrasting maturation of phenotypically distinct strains of Eimeria maxima

Intraspecific phenotypic variation markedly influences the damage that parasites inflict on their hosts. Such is the case for strains of Eimeria maxima, a costly enteric parasite of poultry, where strain APU-1 exhibits greater pathogenicity than APU-2. Here, we examined how these strains differ as oocysts mature to the fully-sporulated stage. We performed mi-croscopy and RNA-Sequencing on oocysts at regular intervals (6-12 hours) during sporulation. Although each strain underwent parallel development, APU-1 initially approached maturation more slowly. Each strain achieved full sporu-lation and similar transcription profiles by hour 36, after which strains appeared to diverge. These differences may in-fluence subsequent virulence. Candidate biomarkers of oocyst viability include 58 genes contributing at least 1,000 Transcripts Per Million throughout sporulation. Many genes resemble constitutively expressed genes also important to Eimeria acervulina. Mature and immature oocysts differentially express certain genes. Expression of some such bi-omarkers appears strain-specific. These data illuminate processes that may generally underlie sporulation in Eimeria and related genera, such as Cyclospora, and identify biological processes which differentiate among them. Drivers of devel-opment and senescence may provide tools to assess the viability of oocysts, which would greatly benefit the poultry industry and food safety applications. Overall design: To investigate transcriptional changes during oocyst development that may differentiate pathogenically distinct strains of E. maxima, oocysts from chickens (replicates) were collected every 6-12 hours over a 48 hour sporulation time course for RNA-Sequencing