Host‐microbiota interactions shed light on mortality events in the striped venus clam Chamelea gallina

Abstract

Mass mortalities due to disease outbreaks have recently affected a number of major taxa in marine ecosystems. Climate‐ and pollution‐induced stress may compromise host immune defenses, increasing the risk of opportunistic diseases. Despite growing evidence that mass mortality events affecting marine species worldwide are strongly influenced by the interplay of numerous environmental factors, the reductionist approaches most frequently used to investigate these factors hindered the interpretation of these multifactorial pathologies. In this study, we propose a broader approach based on the combination of RNA‐sequencing and 16S microbiota analyses to decipher the factors underlying mass mortality in the striped venus clam, Chamelea gallina, along the Adriatic coast. On one hand, gene expression profiling and functional analyses of microbial communities showed the over‐expression of several genes and molecular pathways involved in xenobiotic metabolism, suggesting potential chemical contamination in mortality sites. On the other hand, the down‐regulation of several genes involved in immune and stress response, and the over‐representation of opportunistic pathogens such as Vibrio and Photobacterium spp. indicates that these microbial species may take advantage of compromised host immune pathways and defense mechanisms that are potentially affected by chemical exposure, resulting in periodic mortality events. We propose the application of our approach to interpret and anticipate the risks inherent in the combined effects of pollutants and microbes on marine animals in today's rapidly changing environment.

Mortality of marine mussels Mytilus edulis and M. galloprovincialis: systematic literature review of risk factors and recommendations for future research

“…This would facilitate the biological interpretation of the results and discard environmental DNA or traces that are not relevant to the mortality occurrence. First milestones in that direction have been laid by combining microbiome characterisation (16S rRNA HTS) and host gene expression profiles (RNA-Seq) to decipher the factors underlying mass mortality in the stripped venus clam, Chamelea gallina, which suggested potential chemical pollutant-pathogen interactions (Milan et al 2019).…”

“…First milestones in that direction have been laid by combining microbiome characterisation (16S rRNA HTS) and host gene expression profiles (RNA‐Seq) to decipher the factors underlying mass mortality in the stripped venus clam, Chamelea gallina , which suggested potential chemical pollutant–pathogen interactions (Milan et al . 2019).…”

Transcriptomic Analysis of the Reproductive Effects on Immunity in the Clam Meretrix Petechialis During the Breeding Season

“…For example, a review in oyster Crassostrea gigas summarized the omics approaches to investigate hostpathogen interactions in mass mortality outbreaks [20]. Besides, pathogene caused mass mortality were widely reported in scallop Chlamys farreri [21], clam Chamelea gallina [22] and abalone Haliotis gigante [23]. In our laboratory, we have investigated the immune response in the clam Meretrix petechialis to pathogenic bacteria associated with clam mass mortality in recent years [24,25].…”

Omics approaches for conservation biology research on the bivalve Chamelea gallina

“…In the Adriatic Sea, several mortality events due to sudden changes in the coastal environment (anoxia, river runoff, storm surges, pollution, and bacterial and/or viral infections) have strongly contributed to the decline of clam beds 12,26,27 from approximately 35,000-15,000 t in the last 2 decades (FAO FishStat).…”

“…To date, the molecular resources available for C. gallina are the transcriptome published by Coppe et al 28 and gene expression analyses obtained by Milan and colleagues 26,27 , which detected differences between organisms sampled from two close sites with different local periodic mortality rates in the Italian Adriatic region of Abruzzo. Moreover, very little is known regarding the genetic substructure of C. gallina 29 .…”