Caulerpa racemosa (Forsskål) J. Agardh, 1873
|Common Names:||Sea Grapes|
This is the most variable Caulerpa species, but is typically characterized by possessing short erect branches bearing crowded determinate ramuli with short stalks and oval or spherical tips. The arrangement and shape of the ramuli differ in the various varieties.
Read more about the Bryopsidales order.
Read more about the Caulerpaceae family.
Widely distributed in tropical waters; common in Southeast Asia and recorded in Myanmar, Thailand, Indonesia, Vietnam, Malaysia, Singapore, the Philippines and Papua New Guinea.
Caulerpa racemosa that grows on sandy substrate in calm and turbid waters tend to have long erect branches while those growing on rocky wave-exposed waters have strong short erect branches.
The fronds are consumed fresh as a salad or eaten mixed with spices. In the Philippines it is used as a fish feed and in traditional medicine to lower blood pressure and to treat rheumatism.
Prud’homme van Reine, W. F. & G. C. Trona Jr. (eds.) (2002). Plant resources of South-East Asia No. 15(1). Cryptogams: A;gae. Prosea Foundation, Borgor, Indonesia. 318 pp.
Teo, L. W. & Y. C. Wee, 1983. Seaweeds of Singapore. Singapore University Press. 123 pp.
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Marine organisms are rich sources of structurally novel and biologically active metabolites, exhibiting numerous interesting biological effects and thus constituting valuable opportunities for drug discovery. Recently, several studies on the growing problem of non-indigenous species have proven that the knowledge of marine bioactive compounds may indicate the capacity of non-indigenous species to invade new systems [1,2,3,4,5,6,7,8,9]. In a recent review, Mollo et al.  showed that the commercial use of the natural products obtainable from marine bioinvaders might also be considered as an effective option for reducing their impact on marine ecosystems.
In coastal habitats, macroalgae are abundant and represent a source of bioactive metabolites exhibiting numerous promising and remarkable biological activities capable of influencing the abundance, distribution, and survival of marine organisms [11,12]. Seaweeds are known for their richness in polysaccharides, minerals, and certain vitamins . Marine algae have been also recognized as potential source of antioxidants [14,15] and traditionally consumed as a readily available whole food, especially among coastal communities [16,17,18]. Fatty acids and enzymatic and non-enzymatic antioxidant properties of have been investigated in Caulerpa species [19,20,21,22]. Macroalgae also contain bioactive substances like polysaccharides, proteins, lipids, and polyphenols, with antibacterial, antiviral, and antifungal properties .
Seaweeds have been prescribed for several diseases in different Asian traditional medical systems . In recent years, pathogenic bacteria resistant to multiple drugs have become a worldwide emergency. The discovery of new antibacterial compounds, as suitable substitutes to conventional antibiotics, might be a possible solution to this problem. Seaweeds could represent a potential source of new antimicrobial compounds . Ballesteros and Uriz  have screened several marine macrophytes from the Central Mediterranean to evaluate the production of antibacterial, antifungal, compounds, founding, among the Chlorophyta, with the maximum level of activity found in the order Bryopsidales. In particular, species belonging to the genus Caulerpa show interesting antibacterial activity compared to other groups of algae . A study conducted on the aqueous extract of Caulerpa racemosa collected in India (Gulf of Mannar) showed a pronounced antibacterial activity against different pathogenic organisms . Moreover, the methanol extract of C. racemosa was found to exhibit significant activity against the test pathogens Staphylococcus aureus, Escherichia coli, and Enterobacter aerogenes .
In the present study, we focused on the Mediterranean non indigenous seaweed Caulerpa cilindracea (Sonder) , previously known as C. racemosa var. cylindracea (Sonder) Verlaque, Huisman and Boudouresque . The vector of introduction in the Mediterranean Sea is unknown. It was initially hypothesized to be a Lessepssian immigrant, or a hybrid between C. racemosa var. turbinata and an unknown tropical variety  until molecular analyses identified a possible source population around the Australian-Pacific area [30,31,32]. It can invade different habitats, grow rapidly, and spread though fragmentation and propagation [33,34], leading to profound structural and functional alterations of native benthic assemblages and fish metabolism [9,35,36]. In the Mediterranean, the production of secondary metabolites by the alga changes seasonally and the highest levels have been observed during the period of vegetative algal growth (summer and autumn) . Moreover Blažina et al.  observed that in C. racemosa from sheltered sites generally small variations in total lipids were found.
Here the chemical characterization of C. cylindracea lipidic extract was carried out by means of the advanced analytical technique of multinuclear and multidimensional NMR spectroscopy. In addition, the presence of secondary metabolites in the seaweed extract including bioactive compounds with antimicrobial and antioxidant activities was assessed. Since eradication has been recently suggested as a powerful action to protect areas highly impacted by invasive species, the secondary metabolites were investigated with the perspective of using C. cylindracea in eradication programs to support biotechnology and recycling options.
2.1. NMR Spectoscopy
The 1D 1H (Figure 1) spectrum in spectrum in CDCl3 of the algal lipid fractions shows the characteristic signals of fatty acids (FAs), such as saturated (SAFAs) and unsaturated (UFAs) fatty acids, as well as caulerpin and other metabolites. At low frequencies the singlet at 0.66 ppm, which in the 1H–13C HSQC shows cross peak correlation with the carbon at 11.8 ppm, was attributed to a methyl group of sterols.
The signals at 0.85 ppm were assigned to the methyl groups of all FAs except ω3, which give a triplet at 0.95 ppm. The large signal at 1.21 and 1.50 ppm was attributed to alkyl chain and methylene group in β position to C=O of all fatty acids. The large signals between 1.94 and 2.12 ppm and the signals at 5.35 ppm were attributed to methylene groups in α position with respect to vinyl groups and vinyl groups of all UFAs, respectively. The methylene groups in α to C=O of all FAs resonate at 2.29 ppm. The bisallylic protons, characteristic of fatty acids with two or more double bonds, give signals at 2.78 ppm.
In addition, the characteristic spin system of poly-β-hydroxybutyrate (PHB) was identified in extract by 2D 1H COSY spectra (two signals at 2.45 and 2.58 ppm, attributed to the methylene group, coupled with the methyl group at 1.26 ppm and the methine at 5.23 ppm). By 1D 1H and 2D 1H COSY spectra of all fractions different pattern signals for esterified glycerols were observed. The coupling system connecting the multiplet at 5.25 ppm and the doublet of doublet at 4.27 and 4.12 ppm was assigned to the CH sn2 and the two CH2sn1 and sn3 of triacylglycerol. However, by 1D 13C-NMR a higher intensity of signals at 179 ppm, attributed to carbonyl groups (C=O) of free fatty acids (FFAs) with respect to the signals in the range 173–174 ppm assigned to carbonyl groups of esterified fatty acids (EFAs) was observed.
In the 1D 1H NMR spectrum at high frequencies the aromatic signals of caulerpin were observed. The doublets at 7.41 and 7.28 ppm and the multiplets at 7.16 and 7.07 ppm were assigned to the bis-indolic ring of caulerpin, whereas the singlets at 9.22, 8.04, and 3.88 ppm were assigned to NH of bis-indole, =CH- of central ring and ester methyl groups, respectively. The signals in the high frequencies region between 11.2 and 8.5 ppm were attributed to methine bridge protons of chlorophyll and pheophytins. These signals were confirmed by the presence at negative value of chemical shift (−1.5 to −2.00 ppm) of peaks corresponding to the N-H protons of the tetrapyrrole ring. The signals in the range 6.00 to 6.70 ppm were assigned to conjugated double bonds of carotenoids. Isomers that are all trans are prevalent in fresh matter and the quantities of cis isomers increase after thermal processing.
2.2. Antioxidant Activity
The antioxidant activity of the lipidic extract from C. cylindracea assayed by TEAC and ORAC assays is reported in Table 1. Antioxidant capacity of the seaweed extract measured by the ORAC assay was eight times higher than the activity measured by the TEAC assay.
2.3. Antimicrobial Activity
The results of antimicrobial activity of Caulerpa cylindracea lipidic extract towards the utilized microbial strains are shown in Table 2. Yeasts were not affected in their growth by C. cylindracea lipidic extract. Moreover, the extract did not show antibacterial activity against Enterococcus sp., Escherichia coli, Staphylococcus sp., and Streptococcus sp. By contrast, the degree of inhibition produced by the lipidic extract on some Vibrio species was quantified. In particular, using discs with 100 μL of algal extract, V. fischeri, V. inusitatus, and V. litoralis were the most inhibited (diameter of growth inhibition = 0.9 cm). A lower percentage of inhibition was measured on V. aestuarinus (0.85 cm), V. mediterranei (0.8 cm), and V. vulnificus (0.8 cm).
In the present study, the lipidic extract of the Mediterranean invasive alga C. cylindracea was analyzed by multinuclear and multidimensional NMR spectroscopy and its antioxidant, antibacterial, and antifungal activities have been evaluated.
Some important issues can be inferred from the obtained results:
By the NMR analysis the 1H NMR spectrum in CDCl3 of C. cylindracea algal lipid fraction interestingly, for the first time, showed the presence of polyhydroxybutyrate (PHB), a natural, linear biodegradable, and biocompatible polymer belonging to the polyesters group of bioplastics. PHB is synthesized by microorganisms as a form of energy-storage granules and utilized when the other energy sources are not available . PHB has been already evidenced in the red algae Plocamium cartilagineum (Linnaeus) Dixon , Gracilariopsis longissima , and Cladophora rupestris . Due to the rapid degradation and the non-toxicity of the final products, PHB represents an important ingredient for the production of polymers used in various biotechnological applications such as in the production of several medical devices and compostable plastic [41,42]. As crude oil reserves decrease throughout the world, petroleum based plastics are becoming less economical. Moreover, petroleum based plastics cannot be considered environmentally friendly due to their resistance to natural or biological decomposition. In this framework, Caulerpa cylindracea could represent one of the alternatives for the production of bioplastics because it is an excellent renewable resource due to its high bioinvasion potential and high growth rate. The technology development for seaweeds-based bioplastics are still in the research phase. The challenge is to have significant advancements in the bioplastics industries to make seaweed bioplastics a concrete alternative in the future as already underlined in a recent review by Noreen et al. .
The NMR analysis besides other metabolites also showed the characteristic signals of SAFAs, UFAs, FFAs, and EFAs. NMR has indeed the desirable property of providing a global profiling tool for monitoring rapidly the molecular components of marine organisms . Fatty acids are compounds usually bound to other molecules including glycerol, sugars, or phosphate groups thus constituting the lipids. As already reported for other algal lipid extracts [39,45], the presence of monogalactosyl diacylglycerol (MGDG) was recognized in C. cylindracea by NMR spectroscopy. Our results are in accordance with other studies on C racemosa and other seaweeds confirming their nutritional value . In particular, seaweeds are low in calories, have high content of dietary fiber, are a good source of polyunsaturated fatty acids DHA and EPA, and may contain proteins with an amino acid profile of interest . Apart from the importance of fatty acids for diet, their ability to interfere with bacterial growth and survival has been established in several organisms including seaweeds [40,47