Differential Gene Expression in Five Isolates of the Clam Pathogen, Quahog Parasite Unknown (QPX)

Quahog parasite unknown (QPX) is a thraustochytrid protist that infects the hard clam, Mercenaria mercenaria, causing significant economic losses along the northeastern coast of North America. Previous investigations noted differences in growth dynamics and virulence in QPX cells from different geographic locations. In order to probe the molecular determinants for these variations, we investigated the transcriptomic profiles of five geographically distinct QPX isolates using custom 15k 60-mer oligonucleotide arrays. A total of 1,263 transcripts were differentially expressed (DE) among the five QPX isolates. The hierarchical clustering of gene expression profiles showed that the QPX isolates from Raritan Bay (RB, NY) and from Provincetown Harbor (MA) were more similar to each other and diverged from QPX isolates from Peconic Bay (PB, NY) and Old Plantation Creek (VA), which had more similar gene expression profiles. The most prominent difference was based on 78 transcripts coding for heat shock proteins DE between the five QPX isolates. The study generated contrasting transcriptomic profiles for QPX isolated from northern (MA) and deeper (RB, NY) locations as compared to southern (VA) and shallower (PB, NY) areas, suggesting the adaptation of the parasite to local environmental, in particular temperature, conditions.