Distribution of Toxigenic Halomicronema spp. in Adjacent Environments on the Island of Ischia: Comparison of Strains from Thermal Waters and Free Living in Posidonia Oceanica Meadows

Symbiotic relationship between filamentous algae (Halomicronema sp.) and extracellular polymeric substance-producing algae (Chlamydomonas sp.) through biomimetic simulation of natural algal mats

To lower the cost of biomass harvesting, the growth of natural biofilm is considered to be an optimal alternative to microalgae aggregation. This study investigated algal mats that naturally agglomerate into a lump and float on water surfaces. Halomicronema sp., a filamentous cyanobacterium with high cell aggregation and adhesion to substrates, and Chlamydomonas sp., which grows rapidly and produces high extracellular polymeric substances (EPS) in certain environments, are the main microalgae that make up selected mats through next-generation sequencing analysis. These two species play a major role in the formation of solid mats, and showed a symbiotic relationship as the medium and nutritional source, particularly owing to the large amount of EPS formed by the reaction between EPS and calcium ions through zeta potential and Fourier-transform infrared spectroscopy analysis. This led to the formation of an ecological biomimetic algal mat (BAM) that mimics the natural algal mat system, and this is a way to reduce costs in the biomass production process as there is no separate treatment process for harvesting.

Ecological and Biotechnological Relevance of Mediterranean Hydrothermal Vent Systems

Marine hydrothermal systems are a special kind of extreme environments associated with submarine volcanic activity and characterized by harsh chemo-physical conditions, in terms of hot temperature, high concentrations of CO2 and H2S, and low pH. Such conditions strongly impact the living organisms, which have to develop adaptation strategies to survive. Hydrothermal systems have attracted the interest of researchers due to their enormous ecological and biotechnological relevance. From ecological perspective, these acidified habitats are useful natural laboratories to predict the effects of global environmental changes, such as ocean acidification at ecosystem level, through the observation of the marine organism responses to environmental extremes. In addition, hydrothermal vents are known as optimal sources for isolation of thermophilic and hyperthermophilic microbes, with biotechnological potential. This double aspect is the focus of this review, which aims at providing a picture of the ecological features of the main Mediterranean hydrothermal vents. The physiological responses, abundance, and distribution of biotic components are elucidated, by focusing on the necto-benthic fauna and prokaryotic communities recognized to possess pivotal role in the marine ecosystem dynamics and as indicator species. The scientific interest in hydrothermal vents will be also reviewed by pointing out their relevance as source of bioactive molecules.

Symbioses of Cyanobacteria in Marine Environments: Ecological Insights and Biotechnological Perspectives

Cyanobacteria are a diversified phylum of nitrogen-fixing, photo-oxygenic bacteria able to colonize a wide array of environments. In addition to their fundamental role as diazotrophs, they produce a plethora of bioactive molecules, often as secondary metabolites, exhibiting various biological and ecological functions to be further investigated. Among all the identified species, cyanobacteria are capable to embrace symbiotic relationships in marine environments with organisms such as protozoans, macroalgae, seagrasses, and sponges, up to ascidians and other invertebrates. These symbioses have been demonstrated to dramatically change the cyanobacteria physiology, inducing the production of usually unexpressed bioactive molecules. Indeed, metabolic changes in cyanobacteria engaged in a symbiotic relationship are triggered by an exchange of infochemicals and activate silenced pathways. Drug discovery studies demonstrated that those molecules have interesting biotechnological perspectives. In this review, we explore the cyanobacterial symbioses in marine environments, considering them not only as diazotrophs but taking into consideration exchanges of infochemicals as well and emphasizing both the chemical ecology of relationship and the candidate biotechnological value for pharmaceutical and nutraceutical applications.

The Marine Sponge Petrosia ficiformis Harbors Different Cyanobacteria Strains with Potential Biotechnological Application

Marine cyanobacteria are a source of bioactive natural compounds, with a wide range of biotechnological applications. However, information on sponge-associated cyanobacteria are relatively scarce to date. In this paper, we carried out the morphological and molecular characterization of eight cyanobacterial strains, previously isolated from the Mediterranean sponge Petrosia ficiformis, and evaluated their biological activities on epithelial- and neuron-like cultured cells of human and murine origin. The new analysis allowed maintaining the assignment of three strains (Cyanobium sp., Leptolyngbya ectocarpi, and Synechococcus sp.), while two strains previously identified as Synechococcus sp. and Leptolyngbya sp. were assigned to Pseudanabaena spp. One strain, i.e., ITAC104, and the ITAC101 strain corresponding to Halomicronema metazoicum, shared extremely high sequence identity, practically representing two clones of the same species. Finally, for only one strain, i.e., ITAC105, assignment to a specific genus was not possible. Concerning bioactivity analyses, incubation of cyanobacterial aqueous cell supernatants induced variable responses in cultured cells, depending on cell type, with some of them showing toxic activity on human epithelial-like cells and no toxic effects on human and rat neuron-like cells. Future investigations will allow to better define the bioactive properties of these cyanobacteria strains and to understand if they can be useful for (a) therapeutic purpose(s).

Growth and toxicity of Halomicronema metazoicum (Cyanoprokaryota, Cyanophyta) at different conditions of light, salinity and temperature

Cyanobacteria may live in the water column and in the benthos of aquatic environments, or be symbionts of other organisms, as in the case of Phormidium-like cyanobacteria, known to influence the ecology of freshwater and marine ecosystems. A strain of Phormidium-like cyanobacteria has been recently isolated as a free-living epiphyte of leaves of Posidonia oceanica (L.) Delile in the Mediterranean sea and its biology and ecology are herein investigated. It was identified as Halomicronema metazoicum, previously known uniquely as a symbiont of marine sponges. We cultivated it in a range of light irradiances, temperatures and salinities, to establish the most suitable conditions for the production of allelopathic and toxic compounds. The bioactivity of its spent culture medium was measured by means of standard toxicity tests performed on two model organisms. Our results indicate that at least two bioactive compounds are produced, at low and high irradiance levels and at two temperatures. The main compounds influencing the survival of model organisms are produced at the highest temperature and high or intermediate irradiance levels. The present research contributes to the understanding of critical toxigenic relationships among cyanobacteria and invertebrates, possibly influencing the ecology of such a complex environment as P. oceanica Future isolation, identification and production of bioactive compounds will permit their exploitation for biotechnologies in the field of ecological conservation and medical applications.

Emerging Marine Biotoxins

The emergence of marine biotoxins in geographical areas where they have never been reported before is a concern of considerable impact on seafood contamination, and consequently, on public health [...].