Magnetic loofah sponge biochar facilitates microbial interspecies cooperation in surface and subsurface sediments for enhanced PAH biodegradation

Magnetic biochar had been used for the bioremediation of polycyclic aromatic hydrocarbon (PAH)-contaminated sediments. However, the long-term remediation pattern of vertical stratification driven by the application of magnetic biochar and the assembly of microbes had received little attention. In this study, magnetic loofah sponge biochar (MagLsBC), magnetic iron oxide (MagOx) and magnetic coconut shell activated carbon (MagCoAC) were applied for the 900-day remediation of contaminated sediments. Significant (p < 0.05) PAH biodegradation was observed in both the surface and subsurface sediments with MagLsBC addition. However, enhanced PAH biodegradation was observed only in the surface sediments with MagOx and MagCoAC treatments. Magnetotactic bacteria (Magnetococcus) was dominant genera in surface sediments and indigenous PAH degradation bacteria were more abundant in subsurface sediments of MagLsBC relative to other bacterial communities. The network interaction between microbes in surface and subsurface sediments with MagLsBC treatments was a less complex and tighter than those with MagCoAC, MagOx or Control treatments. Longdistance electron transfer rates could be enhanced through cooperation between magnetotactic bacteria and indigenous degradation bacteria, thus accelerating PAH degradation in sediment with MagLsBC treatment, especially in the underlying sediment.

Automated summary

Magnetic biochar was used for long-term bioremediation of PAH-contaminated sediments. The addition of magnetic biochar resulted in vertical stratification and microbial assembly patterns. Significant PAH biodegradation was observed in both surface and subsurface sediments with MagLsBC, while enhanced biodegradation was only observed in surface sediments with MagOx and MagCoAC treatments. The network interaction between microbes in MagLsBC-treated sediments was less complex and tighter compared to other treatments.