Bacterial natural products (NPs) are still a major source of new drug leads. Polyketides (PKs) and non-ribosomal peptides (NRP) are two pharmaceutically important families of NPs and recent studies have revealed Antarctica to harbor endemic polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) genes, likely to be involved in the production of novel metabolites. Despite this, the diversity of secondary metabolites genes in Antarctica is still poorly explored. In this study, a computational bioprospection approach was employed to study the diversity and identity of PKS and NRPS genes to one of the most biodiverse areas in maritime Antarctica—Maxwell Bay. Amplicon sequencing of soil samples targeting ketosynthase (KS) and adenylation (AD) domains of PKS and NRPS genes, respectively, revealed abundant and unexplored chemical diversity in this peninsula. About 20% of AD domain sequences were only distantly related to characterized biosynthetic genes. Several PKS and NRPS genes were found to be closely associated to recently described metabolites including those from uncultured and candidate phyla. The combination of new approaches in computational biology and new culture-dependent and -independent strategies is thus critical for the recovery of the potential novel chemistry encoded in Antarctica microorganisms.

Mercury is a hazardous pollutant of global concern. While advances have been made in identifying the detrimental effects caused by Hg species in phytoplankton, knowledge gaps remain regarding the metabolomic perturbations induced by inorganic mercury (Hg(II)) and monomethylmercury (MeHg) in these organisms. Diatoms represent a major phytoplankton group essential in various global biogeochemical cycles. The current study combined targeted metabolomics, bioaccumulation, and physiological response assays to investigate metabolic perturbations in diatom Cyclotella meneghiniana exposed for 2 h to nanomolar concentrations of Hg(II) and MeHg. Our findings highlight that such exposures induce reprogramming of the metabolism of amino acids, nucleotides, fatty acids, carboxylic acids and antioxidants. These alterations were primarily mercury-species dependent. MeHg exposure induced more pronounced reprogramming of the metabolism of diatoms than Hg(II), which led to less pronounced effects on ROS generation, membrane permeability and chlorophyll concentrations. Hg(II) treatments presented distinct physiological responses, with more robust metabolic perturbations at higher exposures. The present study provides first-time insights into the main metabolic alterations in diatom C. meneghiniana during short-term exposure to Hg species, deepening our understanding of the molecular basis of these perturbations.

Silver nanoparticles (AgNPs) are increasingly used in various consumer products and industrial applications, raising concerns about their environmental impact on aquatic ecosystems. This study investigated the physicochemical stability, trophic transfer, and toxic effects of citrate-coated AgNPs in a freshwater food chain including the diatom Cyclotella meneghiniana and the gastropod Lymnaea stagnalis. AgNPs remained stable in the exposure medium, with a minimal dissolution ( 1, indicating efficient uptake and retention. Foodborne exposure exhibited a biomagnification factor (BMF) > 1, despite efficient elimination. Combined exposure had the highest depuration rate, with BCF > 1 and BMF < 1, reflecting reduced trophic transfer potential. Oxidative stress in L. stagnalis was highest during combined exposure, with increased ROS in hemolymph during uptake. Foodborne exposure caused prolonged immune stress, evidenced by elevated total antioxidant capacity (TAC) and protein levels. In the hepatopancreas, foodborne exposure during depuration led to increased lipid peroxidation and TAC, indicating oxidative and metabolic challenges specific to dietary exposure. These results highlighted the complex interactions of AgNPs with primary producers and consumers in freshwater ecosystems, emphasizing the need for multi-route assessments in nanoparticle risk evaluations.

Environmental context: Understanding mercury transformations in the aquatic environment is of utmost importance for the improvement of mercury biogeochemical modelling and sound environmental risk assessment. In such a context, we discuss critically the advancement in the knowledge on the role of the phytoplankton (algae and cyanobacteria) in mercury cycling and transformations in the aquatic environment. Important research advances revealed that different microalgal species and cyanobacteria contribute: to biotic reduction of inorganic mercury to elemental mercury; to demethylation of methylmercury and transformation of inorganic mercury into metacinnabar; and to production of different biomolecules which can contribute to abiotic mercury reduction. Phytoplankton may directly influence biogeochemical cycling and transformations of mercury (Hg) through biotic transformations of the accumulated metal via methylation/demethylation and reduction/oxidation, and indirectly, through the excretion of low and high molecular weight ligands, likely triggering or influencing different abiotic transformation pathways as well as the transformations carried out by bacteria. However, unlike the extensive work already done on the role of bacteria in Hg transformations, the current knowledge about the influence of phytoplankton (algae and cyanobacteria) on such processes is still limited. Critical evaluation of the existing advances in the research topic revealed that different microalgal species and cyanobacteria contribute to the biotic reduction of inorganic mercury (iHg or HgII) into elemental Hg (Hg0), monomethylmercury (MeHg) demethylation and transformation of iHg into metacinnabar. The low and high molecular weight biomolecules released by phytoplankton can complex Hg species and contribute to abiotic mercury reduction. Despite these advances, the underlying mechanisms and their importance in the aquatic environment are to be explored and detailed. The development of novel molecular, stable isotope-based and multi-omics approaches would provide further impetus for the understanding of the key interactions between Hg species and phytoplankton. Such understanding will be of utmost importance for the improvement of Hg biogeochemical modelling, mitigation strategies and rational environmental risk assessment in the changing aquatic environment.