Propionigenium and Vibrio species identified as possible component causes of shrimp white feces syndrome (WFS) associated with the microsporidian Enterocytozoon hepatopenaei

White feces syndrome (WFS) in cultivated shrimp is characterized by white shrimp midguts (intestines) and white fecal strings that float as mats on pond surfaces. The etiology of WFS is complex, but one type called EHP-WFS is associated with the microsporidian Enterocytozoon hepatopenaei (EHP). The hepatopancreas (HP), midgut and fecal strings of EHP-WFS shrimp exhibit massive quantities of EHP spores together with mixed, unidentified bacteria. In EHP-WFS ponds, some EHP-infected shrimp show white midguts (WG) and produce white feces while other EHP-infected shrimp in the same pond show grossly normal midguts (NG) and produce no white feces. We hypothesized that comparison of the microbial flora between WG and NG shrimp would reveal probable combinations of microbes significantly associated with EHP-WFS. To test this, we selected a Penaeus vannamei cultivation pond exhibiting severe WFS and used microscopic and microbial profiling analyses to compare WG and NG samples. Histologically, EHP was confirmed in the HP and midgut of both WG and NG shrimp, but EHP burdens were higher and EHP tissue damage was more severe in WG shrimp. Further, intestinal microbiomes in WG shrimp were less diverse and had higher abundance of bacteria from the genera Vibrio and Propionigenium. Propionigenium burden in the HP of WG shrimp (9364 copies/100ng DNA) was significantly higher (P = 1.1 x 10^-5) than in NG shrimp (12 copies/100ng DNA). These findings supported our hypothesis by revealing two candidate bacterial genera that should be tested in combination with EHP as potential component causes of EHP-WFS in P. vannamei.