Figure 1. Transfer of symbiont-produced sterols reflects control by both host and symbiont.

(A) Gas chromatography/mass spectrometry (GC/MS)-generated sterol profiles of the given organisms, with relative composition (%) of each sterol in key. Values, Figure 1—source data 1. Symbiont-free animals (‘aposymbiotic’) were fed Artemia brine shrimp comprising nearly only cholesterol (Tolosa et al., 2011). ‘Intermediate’ were symbiotic Aiptasia more recently starved of brine shrimp diet than ‘symbiotic’ animals. Aiptasia strain F003 hosts Symbiodiniaceae strains SSA01 and SSB01 (Grawunder et al., 2015). Acropora digitifera endogenous Symbiodiniaceae are uncultured but closely related to the cultured strain CCMP2466 (see Materials and methods). (B) GC/MS-generated sterol profiles of Symbiodiniaceae strains in culture (upper row) and in symbiosis with adults of different Aiptasia host lines (Grawunder et al., 2015) (lower row). (C) Sterol profiles of Aiptasia CC7 homogenate separated by centrifugation into symbiont-enriched (Pellet) and symbiont-depleted (Supernatant) fractions with the corresponding Symbiodiniaceae strain SSA01 in culture.

Figure 1—figure supplement 1. Some of the symbiont-produced sterols.

Symbiodiniaceae, like their dinoflagellate relatives, produce many sterols, including the unique gorgosterol with its unusual cyclopropyl group. Colors correspond to those in Figure 1.

Figure 1—figure supplement 2. GC/MS-generated sterol profiling of symbionts in culture vs. in symbiosis.

(A) compositions of the centrifugally separated homogenates of the indicated Aiptasia clonal line (CC7, F003) and Symbiodiniaceae strain (SSA01, SSB01) pairings. Shown are total number of particles (left) and sample composition (right) per size gate. Average values ± SEM (error bars) of technical duplicates. (B) GC/MS-generated sterol profiles, as in Figure 1, of the samples shown in A and Symbiodiniaceae strains in culture. Values, Figure 1—source data 1.