Effects of Different Types of Microplastics on Cold Seep Microbial Diversity and Function

The massive production and widespread use of plastics have resulted in a growing marine plastic pollution problem. Cold seep ecosystems are maintained by microorganisms related to nitrogen and carbon cycling that occur in deep-sea areas, where cold hydrocarbon-rich water seeps from the ocean floor. Little is known about plastic pollution in this ecosystem. To fill this knowledge gap, we collected sediment and seawater samples from the Haima cold seep and conducted laboratory cultivation experiments, simulating in situ environmental conditions. Environmental factors and microbial genetics were analyzed at different stages over a 2-month cultivation period. Our main conclusions are as follows: (1) When microplastics (MPs) were added to sediment and seawater environments, the microbial communities most closely resembled those of the original habitat. The changes in the plastisphere communities were mainly associated with the culture time. (2) The co-occurrence network of the plastisphere was more fragile than that of environments. (3) Multiple environmental factors determined the community composition, whereas a small number of environmental variables drove the community function. MPs affected nitrogen cycling and methane metabolism and might aggregate pathogenic species. This work provides a better perspective of the effect of MPs on the community structure and function in cold seeps.