Tissue-scale microbiota of the Mediterranean mussel (Mytilus galloprovincialis) and its relationship with the environment

Abstract In this study, we characterize the structural variation of the microbiota of Mytilus galloprovincialis at the tissue scale, also exploring the connection with the microbial ecosystem of the surrounding water. Mussels were sampled within a farm located in the North-Western Adriatic Sea and microbiota composition was analyzed in gills, hemolymph, digestive glands, stomach and foot by Next Generation Sequencing marker gene approach. Mussels showed a distinctive microbiota structure, with specific declinations at the tissue level. Indeed, each tissue is characterized by a distinct pattern of dominant families, reflecting a peculiar adaptation to the respective tissue niche. For instance, the microbiota of the digestive gland is characterized by Ruminococcaceae and Lachnospiraceae, being shaped to ferment complex polysaccharides of dietary origin into short-chain fatty acids, well matching the general asset of the animal gut microbiota. Conversely, the gill and hemolymph ecosystems are dominated by marine microorganisms with aerobic oxidative metabolism, consistent with the role played by these tissues as an interface with the external environment. Our findings highlight the putative importance of mussel microbiota for different aspects of host physiology, with ultimate repercussions on mussel health and productivity

Molecular mechanisms controlling physiological plasticity in marine mussels under the influence of natural and anthropogenic stress factors

Marine mussels are exceptionally well-adapted to live in transitional habitats where they are exposed to fluctuating environmental parameters and elevated levels of natural and anthropogenic stressors throughout their lifecycle. However, there is a dearth of information about the molecular mechanisms that assist in dealing with environmental changes. This project aims to investigate the molecular mechanisms governing acclimatory and stress responses of the Mediterranean mussel (Mytilus galloprovincialis) by addressing relevant life stages and environmental stressors of emerging concern. The experimental approach consisted of two phases to explore (i) the physiological processes at early life history and the consequences of plastic pollution and (ii) the adult physiology processes under natural habitats. As the first phase, I employed a plastic leachate (styrene monomer), and polystyrene microplastics to understand the modulation of cytoprotective mechanisms during the early embryo stages. Results revealed the onset of transcriptional impairments of genes involved in MXR-related transporters and other physiological processes induced by styrene and PS-MPs. In the second phase, as a preliminary analysis, microbiota profile of adult mussels at the tissue scale and its surrounding water was explored to understand microbiota structures that may reflect peculiar adaptations to the respective tissue functions. The broader experiment has been implemented to understand the variability of transcriptional profiles in the mussel digestive glands in the natural setting. All the genes employed in this study have shown possibilities to use as molecular biomarker responses throughout the year for monitoring the physiology of mussels living in a particular environment and, in turn, more properly detecting changes in the environment. As a whole, my studies provide insights into the interactions between environmental parameters, and intrinsic characters, and physiology of marine bivalves, and it could help to interpretation of responses correctly under stress conditions and climate change scenarios

Styrene impairs normal embryo development in the Mediterranean mussel (Mytilus galloprovincialis)

This study analysed the effects of styrene, a main monomer in plastic manufacturing and acknowledged to be amongst the most common plastic leachates, on early embryo development of the Mediterranean mussel. Embryotoxicity tests showed that styrene impaired normal embryo development at concentrations (0.01 \u3bcg/L\u20131 mg/L) encompassing the environmental range. Occurrence of normal D-veligers was significantly reduced up to 40% of the total, and larval size was reduced of about 20%. D-veligers grown in the presence of styrene (0.1 and 10 \u3bcg/L) showed significant reduction of total Multixenobiotic resistance (MXR) efflux activity that was not apparently related to transcriptional expression of genes encoding P-glycoprotein (ABCB) and Mrp (ABCC), the two main ABC transporters of embryonal MXR system. Indeed, ABCB transcription was not affected by styrene, while ABCC was up-regulated. At these same concentrations, transcriptional profiles of 15 genes underlying key biological functions in embryo development and potential targets of adverse effects of styrene were analysed. Main transcriptional effects were observed for genes involved in shell biogenesis and lysosomal responses (down-regulation), and in neuroendocrine signaling and immune responses (up-regulation). On the whole, results indicate that styrene may affect mussel early development through dysregulation of gene transcription and suggest the possible conservation of styrene mode of action across bivalve life cycle and between bivalves and humans, as well as through unpredicted impacts on protective systems and on shell biogenesis

Glyphosate and its breakdown product AMPA elicit cytoprotective responses in haemocytes of the Mediterranean mussel (Mytilus galloprovincialis)

This study investigates the effects of glyphosate (GLY) and its metabolite AMPA on cytoprotective and detoxification mechanisms in haemocytes of Mytilus galloprovincialis. Cells were treated in vitro with 0.1 and 1.0 mu g/L GLY, 0.1 mu g/L, 0.1 and 1.0 mu g/L AMPA, or two mixtures GLY+AMPA (0.1 mu g/L GLY + 0.1 mu g/L AMPA, 1.0 mu g/L GLY + 1.0 mu g/L AMPA). GLY and AMPA increased MXR efflux activity and modulated expression of the ABCB transcript encoding a MXR related ABC transporter P-glycoprotein. The mixtures GLY+AMPA reduced efflux activity with ABCB down-regulation (at 1 mu g/L GLY/AMPA). Modulation of lysosomal and immune related transcripts generally agree with known effects of the chemicals on these physiological functions. Given their cumulative action as chemosensitizers of the MXR system, and their interactive effects on haemocyte parameters, glyphosate and AMPA at environmental concentrations should be addressed as a concern factor for the biological vulnerability of marine habitats