Overproduction of microbial extracellular polymeric substances in subtropical intertidal sediments in response to endocrine disrupting chemicals

Abstract

Microorganisms and their extracellular polymeric substances (EPS) in sediments are important in sediment stabilization and the fate of pollutants. However, how toxic organic pollutants affect bacteria and EPS in sediments, particularly in subtropical intertidal zones is poorly known. The present study aims to investigate the bacterial abundance and related EPS in simulated intertidal sandflat and mangrove sediments under the stress of endocrine disrupting chemicals (EDCs). Results showed that the temporal changes of the bacterial number in both sandflat and mangrove sediments were similar, increased from days 0 to 56 then became steady during the 84-days incubation. Bacteria exhibited an important role in the production of high molecular weight (HMW) EPS protein and the degradation of the low molecular weight (LMW) EPS protein. During incubation, the EPS polysaccharides changed from a colloidal-LMW fraction at the beginning to a more complex-HMW fraction at the end of the experiment. The increases in the concentration of HMW polysaccharides might contribute to sediment stabilization. Among different spiked EDCs, nonylphenol (NP) and 17α-ethinylestradiol (EE2) tended to accumulate in both sandflat and mangrove sediments and posed stresses to bacterial growth, especially the latter sediment. The persistent EDCs promoted a higher production of EPS polysaccharides and proteins in both sediments when compared to the respective control, but the EPS in the sandflat sediment was mainly in the colloidal fraction while the bound fraction was more abundant in the mangrove sediment. The present results enhance our understanding of the effects of EDCs on sediment biofilms in intertidal systems. This study also demonstrates the significance of EPS polysaccharides and proteins in sediment stabilization and provides a fundamental basis for future microbiology studies.