Immune and biochemical responses in hemolymph and gills of the Patagonian freshwater mussel Diplodon chilensis, against two microbiological challenges: Saccharomyces cerevisiae and Escherichia coli

Freshwater mussel conservation: A global horizon scan of emerging threats and opportunities

We identified 14 emerging and poorly understood threats and opportunities for addressing the global conservation of freshwater mussels over the next decade. A panel of 17 researchers and stakeholders from six continents submitted a total of 56 topics that were ranked and prioritized using a consensus-building Delphi technique. Our 14 priority topics fell into five broad themes (autecology, population dynamics, global stressors, global diversity, and ecosystem services) and included understanding diets throughout mussel life history; identifying the drivers of population declines; defining metrics for quantifying mussel health; assessing the role of predators, parasites, and disease; informed guidance on the risks and opportunities for captive breeding and translocations; the loss of mussel-fish co-evolutionary relationships; assessing the effects of increasing surface water changes; understanding the effects of sand and aggregate mining; understanding the effects of drug pollution and other emerging contaminants such as nanomaterials; appreciating the threats and opportunities arising from river restoration; conserving understudied hotspots by building local capacity through the principles of decolonization; identifying appropriate taxonomic units for conservation; improved quantification of the ecosystem services provided by mussels; and understanding how many mussels are enough to provide these services. Solutions for addressing the topics ranged from ecological studies to technological advances and socio-political engagement. Prioritization of our topics can help to drive a proactive approach to the conservation of this declining group which provides a multitude of important ecosystem services.

Response of Sabella spallanzanii to multiple stressors. The combined effect of infection and copper sulphate

The aim of this work is to study the immune responses of the polychaete Sabella spallanzanii after exposure to copper sulphate, an immunomodulating agent in marine organisms, and the multiple stresses caused by Escherichia coli infection, to validate the species as a model organism in marine-coastal biomonitoring programmes. Polychaetes were housed in laboratory and divided into five experimental groups: 1. Control (no microinjected), 2. filtered seawater + TBS injection (control of point 3), 3. filtered seawater + E. coli injection (control of point 4), 4. CuSO₄ + TBS injection (control of point 5), and 5. CuSO₄ + E. coli injection. The immune variables, esterase and alkaline phosphatase activity, cytotoxicity and detoxifying/antioxidant enzymes such as glutathione peroxidase were evaluated in total body extracts of the animals. Moreover, toll-like receptor, allograft inflammatory factor-1, lysozyme and haemagglutinating activity were investigated to highlight possible interactions. Indeed, the results of this work demonstrate the immunomodulating effect of copper sulphate on S. spallanzanii total body extracts related to oxidative stress and inflammatory markers.

Effects of Dietary Copper and Escherichia coli Challenge on the Immune Response and Gill Oxidative Balance in the Freshwater Mussel Diplodon chilensis

Copper is a water and sediment pollutant that can be biomagnified by phytoplankton, and it often co-occurs with fecal bacteria. We addressed the combined effects of copper and Escherichia coli on the immune response and gill oxidative balance of the freshwater mussel Diplodon chilensis. Bivalves were sorted into four groups fed with 1) control algae, 2) bacteria (E. coli), 3) copper-enriched algae (Cu²⁺ ) algae, and 4) copper-enriched algae followed by bacteria (Cu²⁺  + E. coli). Cellular and humoral immune and cytotoxic variables were analyzed in hemolymph, and detoxifying/antioxidant enzyme activities (glutathione S-transferase [GST] and catalase [CAT]) and lipid peroxidation (thiobarbituric acid reactive substances [TBARS]) were studied in gill tissue. The total hemocyte number increased after Cu²⁺ exposure, independently of the E. coli challenge. The proportion of hyalinocytes significantly diminished in the E. coli and Cu²⁺ groups but not in Cu²⁺  + E. coli groups; granulocytes significantly increased with E. coli but not with Cu²⁺  + E. coli treatments. Phagocytic activity was higher in all treatments than in control mussels. Acid phosphatase activity was increased by E. coli and inhibited by Cu²⁺ and Cu²⁺  + E. coli. Both E. coli and Cu²⁺ but not Cu²⁺  + E. coli augmented alkaline phosphatase activity. The Cu²⁺ and Cu²⁺  + E. coli treatments reduced the lysosomal membrane stability and cell viability. Humoral bacteriolytic and phenol oxidase activities were not affected by any treatment. The Cu²⁺ treatment induced gill CAT and GST activities and increased TBARS levels. The Cu²⁺  + E. coli treatment reversed this CAT and GST stimulation and increased the Cu²⁺ effect on TBARS. Dietary Cu²⁺ affects bivalves' immunological and oxidative status and impairs defensive responses against bacteria. In turn, E. coli potentiates the gill oxidative effects of Cu²⁺ . Environ Toxicol Chem 2023;42:154-165. © 2022 SETAC.

Bivalve Haemocyte Subpopulations: A Review

Bivalve molluscs stand out for their ecological success and their key role in the functioning of aquatic ecosystems, while also constituting a very valuable commercial resource. Both ecological success and production of bivalves depend on their effective immune defence function, in which haemocytes play a central role acting as both the undertaker of the cellular immunity and supplier of the humoral immunity. Bivalves have different types of haemocytes, which perform different functions. Hence, identification of cell subpopulations and their functional characterisation in immune responses is essential to fully understand the immune system in bivalves. Nowadays, there is not a unified nomenclature that applies to all bivalves. Characterisation of bivalve haemocyte subpopulations is often combined with 1) other multiple parameter assays to determine differences between cell types in immune-related physiological activities, such as phagocytosis, oxidative stress and apoptosis; and 2) immune response to different stressors such as pathogens, temperature, acidification and pollution. This review summarises the major and most recent findings in classification and functional characterisation of the main haemocyte types of bivalve molluscs.

Histopathology, antioxidant responses, transcriptome and gene expression analysis in triangle sail mussel Hyriopsis cumingii after bacterial infection

Bacterial disease outbreaks in filter feeder bivalve Hyriopsis cumingii as water contamination become more frequent in the water ecosystem, especially in intensive aquaculture habitats. To characterize host-pathogen interactions between H. cumingii and bacterial infection, we investigated the effects of Stenotrophomonas maltophilia HOP3 and Aeromonas veronii GL1 on the antioxidant response, tissue invasion and transcriptome expression of H. cumingii by infectivity trials. We showed that bacterial infections resulted in tubular necrosis of the hepatopancreas and induced the acute immune response in H. cumingii. The transcriptomic study identified a total of 5957 differentially expressed genes (DEGs) after A. veronii challenge. These DEGs were implicated in 302 KEGG pathways, notably in Apoptosis, Phagosome and Lysosome. The results showed that the relative expressions of all six immune-related DEGs were effectively stimulated with A. veronii, accompanied by tissue differences. Overall, these findings will contribute to an analysis of the immune response of H. cumingii to bacterial infection at the transcriptomic level and its genomic resource for research.

Effects of high stocking density on the galectin gene expression in noble scallop Chalmys nobilis under bacterial infection

High stocking densities have been shown to have adverse effects on the physiology of bivalves. The noble scallop Chlamys nobilis is one of the most important cultured shellfish in Southern China. However, the effects of scallop stocking density on its immunity is not well understood. In this context, this study was conducted to assess the effect of high stocking density on the galectin (an important protein in innate immunity) gene expression of C. nobilis during bacterial infection. A full-length galectin (CnGal) gene was cloned. The ORF of the CnGal cDNA encodes a predicted protein containing 549 aa with four CRDs and no signal peptide. Our results reveal that high stocking density in the scallop not only led to high mortality and slow growth, but also changed tissue distribution of the CnGal expression. The individuals from the high stocking density group exhibited more differences among tissues than those from the control group, but the highest expression were both recorded in hemolymph. After the Vibrio parahaeomlyticus challenge, the gene's expression levels were all significantly up-regulated in the hemolymph and gill, but the time up to peak was different between the two tissues. The findings of this study could fill a gap in knowledge about how high stocking density affect scallop immunity at the molecular level.