Chemotaxis-selective colonization of mangrove rhizosphere microbes on nine different microplastics

Microplastics pollution poses a new threat to the environment of intertidal zone. The sea forest, mangrove, has been polluted by a large number of plastic debris worldwide. To fill the gaps in knowledge of mangrove rhizosphere microbes connected with the 'plasticsphere', a semi-controlled in situ exposure experiment for nine different types of microplastics were conducted in mangrove ecosystem. A sign of biodegrading was observed on polyethylene, polyamide 6 and polyvinyl chloride microplastics surface after 3 months exposure. We discovered that the metabolic activities of the dominant bacteria on certain microplastics were related to the specific groups on polymers molecule. The selective colonization may be driven by the chemotaxis of bacteria. Specially, microplastics biofilms of polyethylene, polyamide 6, polyvinyl chloride and expanded polystyrene possess distinctive dominant bacteria assemblages which have great significance in ecosystem processes involving carbon cycle or sulfur cycle. Community of mangrove soil microorganism and microplastic biofilm varies as the seasons changes. As a new niche, microplastics has higher inclusivity to bacteria than surrounding soil. Additionally, pathogens for human beings (Vibrio parahaemolyticus and Escherichia-Shigella) were detected both in microplastics and soil. We stress that the interaction between microplastics and rhizosphere microorganisms may affect the growth and health of mangrove plants. Besides, we point out that mangrove rhizosphere microorganism can be an ideal candidate for plastics-degradation.