Evaluation of the global protein synthesis in Mytilus galloprovincialis in marine pollution monitoring: Seasonal variability and correlations with other biomarkers

Protein synthesis down-regulation is a life-saving mechanism for many organisms exposed to xenobiotics that threaten normal life. The present study was designed to assess the spatial and seasonal variability of global protein synthesis, determined in the microsomal fraction of digestive glands from caged Mytilus galloprovincialis mussels exposed for 30 days in a relatively clean region and two unevenly polluted areas (Stations 1 and 2) along the Gulf of Patras (Greece). The in vivo activity of translating ribosomes was evaluated by analyzing the translating ribosomes, polysome content, which may serve as an indicator of the efficiency of the protein-synthesizing machinery. To correlate with classical biomonitoring strategies, various biomarkers were measured in digestive glands, including metallothionein content, heavy-metal content, and lysosomal membrane stability. In parallel, gill cells were examined for micronucleus frequency. Metal ion concentrations were also estimated in the surrounding waters as a measure of metal exposure. Substantially lower polysome content was recorded in caged mussels collected from Station 1, in particular during the winter and spring sampling. As verified by chemical analysis of the seawater and measurement of other biomarkers, Station 1 was more contaminated than Station 2. Polysome content was found negatively correlated with metallothionein levels, micronucleus frequency and cytosolic Cu and Hg in all seasons. In addition, negative correlations were obtained between polysome content and lysosomal membrane stability in winter and spring. A progressive increase in polysomes was observed from winter to autumn, in particular in samples from Station 1. A non-uniform trend was detected in 80S ribosomal monosomes, whereas the seasonal changes in ribosomal subunits were opposite to those found in polysome content. Comparisons between seasonal and local site-specific influences on polysome content provides evidence that winter and spring are the most appropriate sampling seasons for application of translation activity as a possible biomarker in biomonitoring studies.