Colonization and Biodegradation Potential of Fungal Communities on Immersed Polystyrene vs. Biodegradable Plastics: A Time Series Study in a Marina Environment.

Plastic pollution of the ocean is a major environmental threat. In this context, a better understanding of the microorganisms able to colonize and potentially degrade these pollutants is of interest. This study explores the colonization and biodegradation potential of fungal communities on foamed polystyrene and alternatives biodegradable plastics immersed in a marina environment over time, using the Brest marina (France) as a model site. The methodology involved a combination of high-throughput 18S rRNA gene amplicon sequencing to investigate fungal taxa associated with plastics compared to the surrounding seawater, and a culture-dependent approach to isolate environmentally relevant fungi to further assess their capabilities to utilize polymers as carbon sources. Metabarcoding results highlighted the significant diversity of fungal communities associated with both foamed polystyrene and biodegradable plastics, revealing a dynamic colonization process influenced by the type of polymer and immersion time. Notably, the research suggests a potential for certain fungal species to utilize polymers as a carbon source, emphasizing the need for further exploration of fungal biodegradation potential and mechanisms.

Highlighting the Biotechnological Potential of Deep Oceanic Crust Fungi through the Prism of Their Antimicrobial Activity.

Among the different tools to address the antibiotic resistance crisis, bioprospecting in complex uncharted habitats to detect novel microorganisms putatively producing original antimicrobial compounds can definitely increase the current therapeutic arsenal of antibiotics. Fungi from numerous habitats have been widely screened for their ability to express specific biosynthetic gene clusters (BGCs) involved in the synthesis of antimicrobial compounds. Here, a collection of unique 75 deep oceanic crust fungi was screened to evaluate their biotechnological potential through the prism of their antimicrobial activity using a polyphasic approach. After a first genetic screening to detect specific BGCs, a second step consisted of an antimicrobial screening that tested the most promising isolates against 11 microbial targets. Here, 12 fungal isolates showed at least one antibacterial and/or antifungal activity (static or lytic) against human pathogens. This analysis also revealed that Staphylococcus aureus ATCC 25923 and Enterococcus faecalis CIP A 186 were the most impacted, followed by Pseudomonas aeruginosa ATCC 27853. A specific focus on three fungal isolates allowed us to detect interesting activity of crude extracts against multidrug-resistant Staphylococcus aureus. Finally, complementary mass spectrometry (MS)-based molecular networking analyses were performed to putatively assign the fungal metabolites and raise hypotheses to link them to the observed antimicrobial activities.

Antifouling Activity of Halogenated Compounds Derived from the Red Alga Sphaerococcus coronopifolius: Potential for the Development of Environmentally Friendly Solutions.

Nowadays, biofouling is responsible for enormous economic losses in the maritime sector, and its treatment with conventional antifouling paints is causing significant problems to the environment. Biomimetism and green chemistry approaches are very promising research strategies for the discovery of new antifouling compounds. This study focused on the red alga Sphaerococcus coronopifolius, which is known as a producer of bioactive secondary metabolites. Fifteen compounds, including bromosphaerol (1), were tested against key marine biofoulers (five marine bacteria and three microalgae) and two enzymes associated with the adhesion process in macroalgae and invertebrates. Each metabolite presented antifouling activity against at least one organism/enzyme. This investigation also revealed that two compounds, sphaerococcinol A (4) and 14R-hydroxy-13,14-dihydro-sphaerococcinol A (5), were the most potent compounds without toxicity towards oyster larvae used as non-target organisms. These compounds are of high potential as they are active towards key biofoulers and could be produced by a cultivable alga, a fact that is important from the green chemistry point of view.

Meta-omics highlights the diversity, activity and adaptations of fungi in deep oceanic crust.

The lithified oceanic crust, lower crust gabbros in particular, has remained largely unexplored by microbiologists. Recently, evidence for heterogeneously distributed viable and transcriptionally active autotrophic and heterotrophic microbial populations within low-biomass communities was found down to 750 m below the seafloor at the Atlantis Bank Gabbro Massif, Indian Ocean. Here, we report on the diversity, activity and adaptations of fungal communities in the deep oceanic crust from ~10 to 780 mbsf by combining metabarcoding analyses with mid/high-throughput culturing approaches. Metabarcoding along with culturing indicate a low diversity of viable fungi, mostly affiliated to ubiquitous (terrestrial and aquatic environments) taxa. Ecophysiological analyses coupled with metatranscriptomics point to viable and transcriptionally active fungal populations engaged in cell division, translation, protein modifications and other vital cellular processes. Transcript data suggest possible adaptations for surviving in the nutrient-poor, lithified deep biosphere that include the recycling of organic matter. These active communities appear strongly influenced by the presence of cracks and veins in the rocks where fluids and resulting rock alteration create micro-niches.

Recycling and metabolic flexibility dictate life in the lower oceanic crust.

The lithified lower oceanic crust is one of Earth's last biological frontiers as it is difficult to access. It is challenging for microbiota that live in marine subsurface sediments or igneous basement to obtain sufficient carbon resources and energy to support growth1-3 or to meet basal power requirements4 during periods of resource scarcity. Here we show how limited and unpredictable sources of carbon and energy dictate survival strategies used by low-biomass microbial communities that live 10-750 m below the seafloor at Atlantis Bank, Indian Ocean, where Earth's lower crust is exposed at the seafloor. Assays of enzyme activities, lipid biomarkers, marker genes and microscopy indicate heterogeneously distributed and viable biomass with ultralow cell densities (fewer than 2,000 cells per cm3). Expression of genes involved in unexpected heterotrophic processes includes those with a role in the degradation of polyaromatic hydrocarbons, use of polyhydroxyalkanoates as carbon-storage molecules and recycling of amino acids to produce compounds that can participate in redox reactions and energy production. Our study provides insights into how microorganisms in the plutonic crust are able to survive within fractures or porous substrates by coupling sources of energy to organic and inorganic carbon resources that are probably delivered through the circulation of subseafloor fluids or seawater.