Nowadays, the development of new drugs only relies on a small number of molecules and 50% of all existent drugs are extracted or synthetically obtained. This work intends to evaluate the antibacterial potential of the ethanolic and polysaccharide extracts obtained from Grateloupia turuturu and to characterize the composition of the alga’s polysaccharides by FTIR-ATR. We used sequential extraction to obtain the extracts that were tested against S. aureus and E. coli. The ethanolic extracts in E. coli, at the highest concentration used (15 mg mL⁻¹) showed 45.7% (Tetrasporophyte extract) and 55.1% (Carposporophyte extract) of growth reduction and in S. aureus 56.2% (T extract) and 51.8% (C extract). Polysaccharide extracts started showing significant reduction effect on E. coli and S. aureus growth at 7.5 mg mL⁻¹ with a reduction of 54.9% and 39.5%, respectively. At 15 mg mL⁻¹ the reduction observed was 88.5% and 85.4%. The FTIR-ATR allowed to characterize G. turuturu’s polysaccharides concluding that it is composed by a hybrid kappa/iota carrageenan with traces of agar, in both phases of the life cycle. This work allows us to conclude about the antibacterial properties of this alga and the compounds that might be behind this activity, showing that there’s a lot more than a small number of molecules that can be used as natural drugs.

The genus Ulva is globally distributed and has been thoroughly studied because of its functional biochemical composition, rapid growth rates and opportunistic features, and interest in Ulva cultivation is growing worldwide. In Europe, mostly near- and on-shore flow-through cultivation systems are used and land-based recirculating aquaculture systems (RAS) using fresh water or artificial seawater have not been developed for Ulva. While RAS provides quality control and can be located inland, maintenance costs are high. Using selected strains adapted to low-salinity could reduce seawater production costs and improve the economic feasibility. Therefore, our study assessed how salinity can be used as a tool for strain selection and optimization of functional traits. Growth rates and antioxidant activity of three species (four strains) of tubular and foliose Ulva from the NE-Atlantic and Mediterranean (foliose: Ulva lacinulata – two geographical strains, tubular: Ulva linza and Ulva flexuosa) were followed for three weeks at salinities ranging from 10 to 30 PSU. The tubular strains achieved optimal growth at a lower salinity than U. lacinulata. However, growth rates of both foliose strains were higher than of tubular strains, even at sub-optimal salinity. Therefore, U. lacinulata is a good candidate for RAS with artificial seawater, and the cost of salt can be reduced by up to 33.3% (20 PSU) without significantly reducing the growth rate of U. lacinulata. Higher antioxidant activity was achieved by reducing the salinity to 10 PSU for 10 days, suggesting that the functional traits of cultivated Ulva lacinulata can be optimized prior to harvest.

The genus Ulva, described as a good source of antioxidants known for its antibacterial properties and associated with the capacity to adapt to different environments and high growth rates, has justified the increasing interest in its large-scale production. While extensive research has been done on optimizing the extraction of Ulva’s bioactive compounds, few studies were conducted on increasing or optimizing antioxidant activity (AA) of Ulva spp. during cultivation. Our study aimed to investigate an optimization method of Ulva lacinulata by testing the impact of light dose and irradiance on its AA. Two geographically different strains (NE-Atlantic and Mediterranean) were observed for 5 days under two irradiances (70 or 185 µmol photons m⁻² s⁻¹) with the same light dose (4 mol photons m⁻² d⁻¹). Samples were collected at different times (0, 3, 24, 48 and 120 h) to evaluate their antioxidant activity (with 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) radical decolorization assay) and photosynthetic performance (with Pulse Amplitude Modulated fluorometer). A strain-dependent response was observed in the NE-Atlantic strain which had significantly higher AA after 5 days (89 %) under the photosynthetic saturating irradiance, while the Mediterranean strain was not impacted, suggesting that light dose may significantly affect AA in certain Ulva spp.

Interest in Ulva cultivation grows worldwide, but associated bottlenecks exist, including ineffective seeding methods, spontaneous reproduction or biomass loss, and high cultivation costs. Spontaneous biomass degradation causes significant losses, and the underlying biological process is still poorly understood. During a spontaneous degradation event in Ulva lacinulata and a reproduction event in Ulva compressa , production of natural protoplasts was observed. U. lacinulata produced high protoplast yields and parts of the original biomass regenerated. In U. compressa , protoplasts were found in fertile thalli, but the original biomass was lost. Protoplast germination rates were low (2.01 ± 0.48 % in U. lacinulata , 4.14 ± 3.31 % in U. compressa ), and resulted in three morphologies: unattached germlings, unattached discs, and cell masses. Discs and cell masses became fertile early and released gametes. Our results provide the first evidence of natural production of protoplasts in Ulva spp. We estimate that higher seeding yields can potentially be obtained by natural protoplast production (5.95 ± 4.50 × 10 ¹⁰ individuals g ⁻¹ ) than by gametogenesis (2.03 ± 1.15 × 10 ⁹ individuals g ⁻¹ ), thus closing an important knowledge gap in the life cycle of Ulva species. These results provide important insights into the reproductive cycle of Ulva spp. relevant for large-scale cultivation.