Response of the Ambient Marine Microbial Community to a Mixture of Pollutants in the Coastal Ecosystem

Microorganisms can be important indicators of environmental change due to their diverse sensitivity, rapid responses to environmental changes and ubiquitous presence. Marine microorganisms are exposed to complex mixtures of different pollutants in their natural environment, which often do not exceed concentration limits prescribed by legislation, nevertheless might have a negative impact on microbiota, larger organisms and even human health. The response of the ambient marine microbial community to different concentrations of the mixed pollutants was studied in the controlled laboratory experiments. To assess the effect of season, experiments were performed using ambient seawater microbial community samples in summer and spring. The addition of low and 10-times higher concentrations of hazardous compounds resulted in an increase production of proteins by bacterial cells (based on the incorporation of 3H-Leucin into newly synthesized proteins). At the same time, the total number of bacterial cells decreased in the experimental flasks. The analyses of bacterial community showed that the mixture of pollutants promoted growth of bacteria affiliated with Alteromonadaceae family, while members of Rhodobacteraceae family showed higher sensitivity to added mixture, as reflected in the decrease of their relative abundance. Additional tests performed on bacterial isolates have shown that a mixture of pollutants effected different bacterial groups differently. Our preliminary results emphasize the potential of microbiological analyses for detecting and understanding changes induced by pollutants in marine ecosystems, even when present in low concentrations, and highlighted the need for perform additional toxicity studies regarding the combined effects on pollutants on functioning of marine ecosystems.