Compound‐specific δ¹³C analyses reveal sterol metabolic constraints in an aquatic invertebrate

Abstract

RATIONALE: Dietary sterol deficiencies can have severe life history consequences for consumers. Compound-specific stable isotope analysis (CSIA) was applied to the exploration of the sterol metabolic constraints and bioconversion capacities of the amphipod Gammarus roeselii. Evaluating structural sterol requirements has great potential to improve our understanding of the ecological relevance of sterols as limiting nutrients. METHODS: Juvenile G. roeselii were reared on food mixtures consisting of different ratios of the two algae Scenedesmus obliifuus (cultivated with 13 C-labeled NaHC0 3 ) and Nannochloropsis limnetica (unlabeled), which have been shown previously to differ in food quality. We measured the sterol content and composition using a gas chromatograph equipped with a flame ionization detector and the o 13 C values of sterols using compound-specific isotope ratio mass spectrometry to examine potential sterol-mediated nutritional constraints of G. roeselii. CONCLUSIONS: We provide evidence that the the ~7-phytosterols present in S. obliifUUS cannot be metabolized to cholesterol in G. roeselii, resulting in the accumulation of lathosterol in the animals and potentially in sterol-limited growth. These findings emphasize the advantage of CSIA in revealing the physiological mechanisms associated with n utritional constraints.

Microbial Sterolomics as a Chemical Biology Tool

“…In the cross-class algal study [ 53 ], the researchers presented these profiles, along with their quantification, as references to the algal sterolome. As prey, Δ 7 and Δ 7,22 sterols are often nutritionally inadequate to invertebrate consumers [ 53 , 56 , 57 ]. Many invertebrates are auxotrophic for sterols and rely on diet to fulfill their sterol needs for cell membrane and hormonal requirements.…”

“…Prey alga N. limnetica , rich in cholesterol, and alga S. obliquus , lacking cholesterol but rich in Δ 7 sterols (See Table 1 ), were fed to G. roeselii . The sterol profile of S. obliquus -fed G. roeselii decreased in cholesterol, and increased in the Δ 7 metabolite lathosterol 69 , detectable when the diet was 50% S. obliquus ( Figure 5 ) [ 56 ].…”

“…( b ) Proposed synthesis of cholesterol in herbivorous insects via dealkylation of dietary plant sterols (sitosterol) [ 58 ]. ( c ) Amphipod Gammarus roeselii can dealkylate the side chain of Δ 7 algal sterols, such as fungisterol and chondrillasterol, but cannot produce cholesterol [ 56 ].…”

Stable isotopes of fatty acids: current and future perspectives for advancing trophic ecology

“…[26,27]), sterols (e.g. [28,29]) or fatty acids [30], offer potential solutions to some of the limitations of bulk stable isotope analyses because even without distinct bulk signals, resources can contain isotopically distinct compounds. Isotopic separation at the compound-specific level may occur as a result of differing synthesis pathways or when prey derive or 'route' individual compounds from specific dietary sources that differ from those of the bulk diet [31,32].…”

Lipid markers and compound-specific carbon isotopes as diet and biosynthesis reflectors in the northern Neptune whelk Neptunea heros

“…The taxonomic source specificity that individual sterol structures can provide was expanded through the analysis of compound-specific carbon isotopic analysis (CSIA) of major sterols in N. heros to investigate if isotopic values allow insight into the balance of direct incorporation versus metabolic synthesis or modification of these structural lipids (e.g. Gergs et al 2015). Sterols and other lipids have shown their value for seasonal examination of diet trends in other mollusks such as scallops (Lavaud et al 2018), but here, foot muscle tissues of whelks from juveniles to gravid adults were characterized to determine if lipid composition reflected long-term diet trends.…”