**Preface to "Sulfur-Containing Marine Bioactives"**

This Special Issue, entitled "Sulfur-Containing Marine Bioactives", highlights the most recent findings related to the biological function of some marine sulfur metabolites and their effect on different cellular systems, with a focus on potential pharmacological properties.

Milito et al. show the involvement of ovothiols, which are histidine-derived thiols, in the light-dependent response of the diatom *Skeletonema marinoi*. Ovothiol biosynthesis is induced by high sinusoidal light mimicking natural conditions. Garcia-Jimenez et al. provide insights into the involvement of the sulfation and desulfation of galactan backbone in carrageenan synthesis in the red seaweed *Grateloupia imbricata* during thalli development and cystocarp maturation.

Parra-Riofrio et al. report that the microalga *Tetraselmis suecica* produces exopolysaccharides containing sulfate at higher yields when grown under heterotrophic conditions. These exopolysaccharides show antioxidant and cytotoxic effects on tumor cells, suggesting their possible use as nutraceuticals. Dorschmann et al. purify three sulfated fucans at different molecular weights from the brown alga *Laminaria hyperborea* and investigate their effects on cell viability, oxidative stress protection, and vascular endothelial growth factor secretion in ocular cells. The potential use of these compounds in the treatment of ocular diseases, such as age-related macular degeneration, is envisaged. Ma et al. investigate the effect of propylene glycol alginate sodium sulfate, obtained from the alginate polysaccharide of *Laminaria*, on FGF2-mediated angiogenesis and invasion in melanoma cells. Their results sugges<sup>t</sup> its involvement in the regulation of the tumor microenvironment. Khodamoradi et al. characterize two new thiopeptides, litoralimycins A and B, from a new actinomycetes bacterium, with one exhibiting strong cytotoxic activity.

Inspired by some marine sulfur compounds, Manzo et al. report that the immunological potency of a novel class of vaccine adjuvants, namely Sulfavants, is dependent on the supramolecular aggregation states. Vilas-Boas et al. synthesize coatings containing immobilized gallic acid persulfate that exhibit an anti-settlement effect against *Mytilus galloprovincialis* larvae.

> **Anna Palumbo** *Editor*

*Article*
