Following the growth of the global population and the subsequent rapid increase in urbanization and industrialization, the fisheries and aquaculture production has seen a massive increase driven mainly by the development of fishing technologies. Accordingly, a remarkable increase in the amount of fish waste has been produced around the world; it has been estimated that about two-thirds of the total amount of fish is discarded as waste, creating huge economic and environmental concerns. For this reason, the disposal and recycling of these wastes has become a key issue to be resolved. With the growing attention of the circular economy, the exploitation of underused or discarded marine material can represent a sustainable strategy for the realization of a circular bioeconomy, with the production of materials with high added value. In this study, we underline the enormous role that fish waste can have in the socio-economic sector. This review presents the different compounds with high commercial value obtained by fish byproducts, including collagen, enzymes, and bioactive peptides, and lists their possible applications in different fields.

The Arctic and Antarctic regions constitute 14% of the total biosphere. Although they differ in their physiographic characteristics, both are strongly affected by snow and ice cover changes, extreme photoperiods and low temperatures, and are still largely unexplored compared to more accessible sites. This review focuses on microalgae and bacteria from polar marine environments and, in particular, on their physiological and molecular responses to harsh environmental conditions. The data reported in this manuscript show that exposure to cold, increase in CO₂ concentration and salinity, high/low light, and/or combination of stressors induce variations in species abundance and distribution for both polar bacteria and microalgae, as well as changes in growth rate and increase in cryoprotective compounds. The use of -omics techniques also allowed to identify specific gene losses and gains which could have contributed to polar environmental adaptation, and metabolic shifts, especially related to lipid metabolism and defence systems, such as the up-regulation of ice binding proteins, chaperones and antioxidant enzymes. However, this review also provides evidence that -omics resources for polar species are still few and several sequences still have unknown functions, highlighting the need to further explore polar environments, the biology and ecology of the inhabiting bacteria and microalgae, and their interactions.

Enormous marine biodiversity offers an endless reservoir of chemicals for many applications. In this scenario, the extraction of seaweeds represents an interesting source of compounds displaying antimicrobial activity. In particular, among the different red algae, Gracilaria gracilis plays an important role due to the presence of important bioactives in its composition. In spite of these features, an efficient culture system is still absent. In the present study, a novel algal culture method was developed and compared to another more common cultural practice, widely reported in literature. A higher efficiency of the new method, both for daily growth rate and biomass, was assessed. Furthermore, the growth inhibitory activity of five extracts, obtained using ethanol, methanol, acetone, chloroform or diethyl ether as a solvent, from the cultured G. gracilis was tested against Gram-positive and Gram-negative pathogens. Algal extracts exhibited a considerable inhibitory activity against B. subtilis strains, while a slight inhibition was observed against V. fischeri. The different extracts showed significant differences in bacterial growth inhibition, with the highest activity that was recorded for the ethanol extract, followed by that of methanol. Based on the chemical characterization, these findings could be related to the antimicrobial activity played by the combination of total carbohydrates and polyphenols, which were determined at high levels in ethanol and methanol extracts, as well as by the highest number and levels of single polyphenols. Conversely, the lower growth inhibitory activities found in chloroform and diethyl ether extracts could be related to the isolation of minor lipid classes (e.g., neutral and medium polar lipids) composed by fatty acids, such as stearic, oleic and arachidonic acids, typically characterized by antimicrobial activity. In consideration of the results obtained, the present study has a double implication, involving both the field of cultural practices and the exploitation of natural sources for the isolation of antimicrobial agents useful both in pharmaceutical and food applications.

The marine bioprospecting could be considered as a new phenomenon, and already potentially more promising than terrestrial one in terms of possible discovery of new compounds. The secondary metabolites produced by associated-bacteria are actually studied for their remarkable role in several fields, including agricultural, industrial, medical, and bioremediation strategies against different contaminants. The use of such renewable sources could be helpful in the streamlining of the patenting process for natural compounds of good quality, produced with lower energy costs and less impact on the environment. Anyway, more improvements in the research and application of bioactive compounds as alternative to the synthetic counterparts have to be carried out for the costs reduction and the large-scale production upgrading. The use of marine invertebrates could help to overcome these difficulties, as hotspots of microbial diversity and favorable matrix for the development of conditions stimulating the production of substances with special activities. This review will deal with the current accepted definitions and recent advances concerning: (i) the marine symbiotic relationships in which microorganisms and invertebrates are involved; (ii) the principal taxa of marine invertebrates that establish interactions with microorganisms, the biodiversity of these latter, and their role in the symbiosis; (iii) we address the state of current literature and knowledge about the bacterial associated communities specialized in biosurfactants (BSs) and extracellular polymeric substances (EPSs) production; and, (iv) their potential biotechnological applications reported still now.

Background: The bacterial community responses to oil spill events are key elements to predict the fate of hydrocarbon pollution in receiving aquatic environments. In polar systems, cold temperatures and low irradiance levels can limit the effectiveness of contamination removal processes. In this study, the effects of a simulated acute oil spillage on bacterial communities from polar sediments were investigated, by assessing the role of hydrocarbon mixture, incubation time and source bacterial community in selecting oil-degrading bacterial phylotypes. Methods: The bacterial hydrocarbon degradation was evaluated by gas chromatography. Flow cytometric and fingerprinting profiles were used to assess the bacterial community dynamics over the experimental incubation time. Results: Direct responses to the simulated oil spill event were found from both Arctic and Antarctic settings, with recurrent bacterial community traits and diversity profiles, especially in crude oil enrichment. Along with the dominance of Pseudomonas spp., members of the well-known hydrocarbon degraders Granulosicoccus spp. and Cycloclasticus spp. were retrieved from both sediments. Conclusions: Our findings indicated that polar bacterial populations are able to respond to the detrimental effects of simulated hydrocarbon pollution, by developing into a more specialized active oil degrading community.

The ecological function of bacteria-invertebrate interactions in Polar areas remains poorly understood, despite increasing evidence that microbial metabolites may play pivotal roles in host-associated chemical defense and in shaping the symbiotic community structure. The metabolic and physiological changes that these organisms undergo in response to adapting to extreme conditions result in the production of structurally and functionally novel biologically active molecules. Deepening our knowledge on the interactions between bacteria and their invertebrate host would be highly helpful in providing the rationale for why (e.g., competition or cooperative purpose) and which (whether secondary metabolites, enzymes, or proteins) bioactive compounds are produced. To date, cold-adapted bacteria associated with marine invertebrates from the Arctic and Antarctica have not been given the attention they deserve and the versatility of their natural products remains virtually unexplored, even if they could represent a new attractive frontier in the search for novel natural compounds. This review is aimed at showcasing the diversity of cold-adapted bacteria associated with benthic invertebrates from Polar marine areas, highlighting the yet unexplored treasure they represent for biodiscovery.