Approved Abstracts

Comparative transcriptomic analysis reveals pollution-related genes in oysters Crassostrea rhyzophorae from contaminated sites as potential biomarkers of exposure



Author(s): Zacchi, F.L.; Fonseca, G.C.; Toledo-Silva, G.; Gomes, C.H.A.M.; Melo, C.M.R.; Henning, F.; Soares, R.; Gerber, A.; Brustolini, O.J.B.; Solé-Cava, A.; Bainy, A.C.D.; Vasconcelos, A.T.R.;
Presenter: Afonso Celso Dias Bainy

Brazilian estuaries are constantly exposed to organic and inorganic pollutants discharged into their waters as a consequence of anthropogenic and industrial activities. Organisms inhabiting these environments, such as the native mangrove oyster Crassostrea rhizophorae, possess biological mechanisms of adaptation to tolerate these pressures. C. rhizophorae can be found along the Brazilian coast and has been evaluated as an alternative organism either for oyster farming aquaculture or as a sentinel species for environmental monitoring programs. Understanding the biochemical and molecular mechanisms by which these organisms respond to environmental changes is necessary for its use in aquaculture, ecology and ecotoxicology. In order to identify possible metabolic pathways affected in C. rhizophorae exposed chronically to sanitary sewage discharges in the environment, oysters (n=30) were collected in March 2019 at two sites in Florianópolis: a polluted and a reference site, and the differential transcriptional profile was evaluated in gills by Paired-end strand-specific RNA-seq analysis. For each oyster, the species was confirmed by PCR-RFLP. Total mRNA was individually extracted and then clustered into six pools with five animals each. The de novo assembly of the RNA-seq reads was performed using Trinity. The assembled transcripts were annotated by Blast against the genome of C. virginica. Only transcripts with more than 80% query and subject coverage were kept to downstream analysis. Bowtie2 was used to map the reads and the statistical analysis was performed by DESeq2 and GOstats. Comparing oysters collected from the polluted site against the reference site, 186 upregulated and 132 downregulated genes were obtained (log2 Fold Change > |1| and adjusted p-value < 0.05). Upregulated annotated genes found are involved in oxidation-reduction, superoxide metabolic, reactive oxygen species metabolic and growth processes. Among these are the following genes such as Extracellular Superoxide Dismutase-like (10.5-log2 Fold Change), Complement C1q-like (8.4-log2 Fold Change) and Carnosyne synthase 1-like (4.5-log2 Fold Change), which may respectively be involved in: processes of antioxidant and immune defense systems; biotransformation of xenobiotics; and maintenance of anaerobic metabolism during the necessity of keeping shells closed. Some monoxygenase-related genes are among the main downregulated genes, such as dimethylaniline monooxygenase (-3.7-log2 Fold Change) and cytochrome P450 1A5-like (-3.0-log2 Fold Change). In addition, there are genes related to innate immune responses against pathogenic microbial invasion, such as Fucolectin-like (-3.4-log2 Fold Change). It is important to mention that there are several unidentified genes both in the up and down regulated genes list. In order to correlate molecular responses to the presence and concentration of chemicals in collection sites, chemical analysis will be carried out in sediment samples from both sites.

Keywords: RNA-Seq; Biomarker; Crassostrea rhyzophorae

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