Fatty Acid Profile and Sterol Composition of the Marine Sponge Petrosia testudinaria

Abstract

The interest of chemists, biochemists, and biotechnologists in lipids and fatty acids from marine sponges has been stimulated because among aquatic animals, sponges possess the greatest diversity of fatty acids, sterols, etc. Various applications of lipids, phospholipids, and saturated and unsaturated fatty acids in pharmaceutical formulations have been reported [1, 2]. Some unusual FAs of sponges exhibit biological activity. Petrosia testudinaria (Lamarck) is a barrel marine sponge widely distributed in the Bay of Bengal of the Odisha coast [3]. Sponges of the genus Petrosia have yielded various types of secondary metabolites, viz. isoquinoline antibiotic alkaloids, bisquinolizidine alkaloids, polyacetylenes, and steroids [3–8]. A novel steroid, 23-ethyl-24-methyl-27-norcholesta-5,25-diene-3 -23-diol, is isolated from the sponge P. testudinaria [9]. The methanol and dichloromethane extract of this species have shown broad-spectrum larvicidal and insecticidal activity [10]. The present paper deals with the study of the FA profile and sterol of the lipid composition of P. testudinaria, collected from the Bay of Bengal region of the Odisha coast. The study of the FA and sterols of the lipophilic extract of P. testudinaria was carried out mainly to search for new FA structures, to evaluate a new source of major polyunsaturated fatty acids (PUFAs) of biological interest, and to get valuable information on its chemotaxonomy. Analysis of Fatty Acids. Twenty-three fatty acids were identified in the mixture of total lipids of P. testudinaria by GC-MS analysis (Table 1). Peak identification was carried out by comparison of the mass spectra with those available in the NIST and WILEY libraries and also confirmed by comparison of their chromatographic retention times as well as mass fragmentations with those of authentic standards C4–C24 (Supelco standard FAME mixtures). Among the identified FAs, linear saturated FAs constituted 45.26% of the total FA content. Generally among linear saturated FAs, 16:0 and 18:0 dominated in most of the marine sponges. In the present analysis, 19:0 (17.13%) was the major one among the linear FAs. Fatty acids 18:0 (9.76%) and 16:0 (7.44%) were also present in good amount. Branched saturated FAs constituted 15.26% of the total FA content, and 13-methyl-14:0 (7.42%) was the major one. The position of the methyl branch was confirmed by analysis of their pyrrolidide derivatives and further confirmed by comparing their key mass fragments with those already reported for similar fatty acids. In the mass spectrum of 13-methyl-14:0 (iso), there was a gap of 28 amu between two peaks at m/z 252 and 280 due to the loss of carbon 13 with its methyl group. Similarly in the mass spectrum of 12-methyl-14:0 (anteiso), two peaks m/z 238 and 266 occurred at a gap of 28 amu due to the loss of carbon 12 and its methyl group. In the mass spectrum of 10-methyl-15:0, there was a gap of 28 amu between two peaks at m/z 210 and 238 due to loss of carbon 10 with its methyl group. A gap of 28 amu between two peaks at m/z 196 and 224 in the mass spectrum of 9-methyl-16:0 is due to the loss of carbon 9 with its methyl group, and the structure is confirmed. In the mass spectrum of 6-methyl-18:0 there was a gap of 28 amu between two key mass fragments m/z 154 and 182 due to the loss of carbon 6 with its methyl group, whereas in 18-methyl-20:0, two peaks m/z 322 and 350 occurred at a gap of 28 amu due to the loss of carbon 18 and its methyl group. It is considered that saturated iso and anteiso C15–C20 acids have a bacterial origin [11]. Thus, in the sponge P. testudinaria, the content of iso and anteiso may be due to symbiotic bacteria.