Microbial carriers promote and guide pyrene migration in sediments

Microbial carriers may co-transport polycyclic aromatic hydrocarbons (PAHs), but lack substantial experimental evidence. Cable bacteria use gliding or twitching motility to access sulfide; hence, they could be important microbial carriers in co-transporting PAHs from the sediment-water interface into suboxic zones. In this study, the effect of cable bacteria on pyrene migration was investigated by connecting or blocking the paths of cable bacteria to the suboxic zones. The results showed that downward migration of pyrene in the connecting groups were significantly higher (17.3-49.2%, p < 0.01) than those in the control groups. Meanwhile, significant downward migration of microbial communities in the connecting groups were also observed, including abundant filamentous-motile microorganisms, especially cable bacteria. The adsorption of surrounding particles by cable bacteria were morphologically evidenced. The biomechanical model based on the Peclet number indicated that filamentous-motile microorganisms demonstrated stronger adsorption ability for pyrene than other microorganisms. Supposedly, the downward migration of microbial communities, especially cable bacteria, significantly enhanced pyrene migration, thus influencing the distribution and ecological risk of pyrene in sediments. This study provides new insights into the important roles of motile microorganisms in the migration of PAHs in sediments, shedding lights on guidance for ecological risk assessment of PAHs.