How Environmental Factors Affect the Production of Guanidine Alkaloids by the Mediterranean Sponge Crambe crambe

Abstract

Most marine sponges are known to produce a large array of low molecular-weight metabolites which have applications in the pharmaceutical industry. The production of so-called specialized metabolites may be closely related to environmental factors. In this context, assessing the contribution of factors like temperature, nutrients or light to the metabolomes of sponges provides relevant insights into their chemical ecology as well as the supply issue of natural sponge products. The sponge Crambe crambe was chosen as a model due to its high content of specialized metabolites belonging to polycyclic guanidine alkaloids (PGA). First results were obtained with field data of both wild and farmed specimens collected in two seasons and geographic areas of the North-Western Mediterranean. Then, further insights into factors responsible for changes in the metabolism were gained with sponges cultivated under controlled conditions in an aquarium. Comparative metabolomics showed a clear influence of the seasons and to a lesser extent of the geography while no effect of depth or farming was observed. Interestingly, sponge farming did not limit the production of PGA, while ex situ experiments did not show significant effects of several abiotic factors on the specialized metabolome at a one-month time scale. Some hypotheses were finally proposed to explain the very limited variations of PGA in C. crambe placed under different environmental conditions.

Keywords: abiotic factors; metabolomics; specialized metabolome; sponge; sponge farming.

Figure 1

Collection sites of Crambe crambe in the Ligurian Sea (A) (a Punta del Faro, b Punta Pedale); and Sardinia Sea (B) (c Capo Caccia).

Figure 2

PCA plot obtained from the metabolomics study on wild (Wi) and farmed (Fa, Tile or Mesh protocols) samples harvested at different locations (Sar = Sardinia, Lig = Ligurian) in both autumn (Aut) and spring (Sp). The table lists the five most important ions contributing to the distribution of samples in the PCA plot.

Figure 3

Concentrations of crambescidins and crambescins in C. crambe in µmol·g⁻¹ sp obtained from the targeted metabolomics study for (A) wild and farmed specimens, (B) Temperature and Light experiment, and (C) Nutrient experiment (*** p < 5 × 10⁻⁴; ** p < 0.005; * p < 0.05, one-way ANOVA).

Figure 4

PCA plot obtained from an untargeted metabolomics study of the temperature/light experiment. C = control, D = Dark, L = Light, 14 °C = Temperature 14 °C and 20 °C = Temperature 20 °C. The table shows the five most important peaks that contribute to the distribution of samples on the PCA plot, along with their retention time.

Figure 5

PCA plot obtained from an untargeted metabolomics study of the nutrients. C = control and N = nutrient-treated samples and triplicates of biological samples are represented by a colored point. The table shows the five most important ions contributing to explain the sample distribution on the PCA plot along with their retention time and their expected [M + H]⁺.

Figure 5

PCA plot obtained from an untargeted metabolomics study of the nutrients. C = control and N = nutrient-treated samples and triplicates of biological samples are represented by a colored point. The table shows the five most important ions contributing to explain the sample distribution on the PCA plot along with their retention time and their expected [M + H]⁺.

Figure 6

Proposition of a biosynthetic intermediate for crambescin A1.