Background: C. trachomatis relies on its own biosynthetic pathways to produce membrane phospholipids. Results: C. trachomatis expresses an acyl-acyl carrier protein synthetase to activate fatty acids. Conclusion: C. trachomatis utilizes fatty acids obtained from the host to construct phospholipids. Significance: C. trachomatis selectively scavenges host saturated fatty acids, the most energy-expensive component needed for phospholipid synthesis.

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Chromera velia is a recently discovered, photosynthetic, free-living alveolate that is the closest free-living relative to nonphotosynthetic apicomplexan parasites. Most plastids, regardless of their origin, have membranes composed chiefly of two galactolipids, mono-and digalactosyldiacylglycerol (MGDG and DGDG, respectively). Because of the hypothesized shared red algal origin between the plastids of C. velia and dinoflagellates, our primary objectives were to examine how growth temperature affects MGDG and DGDG composition via positive-ion electrospray/mass spectrometry (ESI/MS) and positive ion/electrospray/ mass spectrometry/mass spectrometry (ESI/MS/MS), and to examine galactolipid biosynthetic genes to determine if shared ancestry translates into shared MGDG and DGDG composition. When growing at 20°C, C. velia produces eicosapentaenoic acidrich 20:5(n-3)/20:5(n-3) (sn-1/sn-2) MGDG and 20:5(n-3)/20:5(n-3) DGDG as its primary galactolipids, with relative percentage compositions of approximately 35 and 60%, respectively. At 30°C these are lessened by approximately 5 and 8%, respectively, by the corresponding production of 20:5/20:4 forms of these lipids. The presence of 20:5 at the sn-1 position is similar to what has been observed previously in a cluster of peridinin-containing dinoflagellates, but the presence of 20:5(n-3) at the sn-2 position is extremely rare. Thus, the forms of MGDG and DGDG in C. velia displayed similarities and differences to what has been observed in peridinin-containing dinoflagellates, such as Lingulodinium polyedrum, which produces 20:5/18:5 and 20:5/18:4 as the major forms of MGDG and DGDG. We develop conceptual models from the galactolipids observed and galactolipid-relevant gene annotations to explain the presence of polyunsaturated fatty acid-containing MGDG and DGDG in both L. polyedrum and C. velia.

Summary Diatoms are one of the largest groups of primary producers in the oceans, yet despite their environmental importance little is known about their plastidial lipid biochemistry. It has been previously reported that Skeletonema species contain primarily C16/C16 and C20/C16 forms of mono‐ and digalactosyldiacylglycerol (MGDG and DGDG, respectively). Likewise, it was also reported that Phaeodactylum tricornutum contains primarily C16/C16 and C20/C20 forms of MGDG and DGDG. We seek to relate their studies to other diatoms, both in the centrics and pennates, with particular focus on the marennine‐producing pennate diatom, Haslea ostrearia. To this end, the composition and positional distribution of fatty acids of MGDG and DGDG were examined using positive‐ion electrospray ionization/mass spectrometry (ESI/MS). Two centric diatoms, Skeletonema marinoi and Thalassiosira weissflogii, and the pennate diatom, P. tricornutum, contained primarily C20/C16 (sn‐1/sn‐2) and C18/C16 forms of MGDG and DGDG. The other pennate diatoms, H. ostrearia and Navicula perminuta, contained primarily C18/C16 or C18/C18 forms of MGDG and DGDG, indicating a previously unrecognized fatty acid diversity in diatom MGDG and DGDG.

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