This study investigated the interaction of the macrophyte Acorus calamus and sediment microbial fuel cells (SMFC) during the degradation of high molecular weight-polycyclic aromatic hydrocarbons (HMW-PAHs) in sediments. Over 367-days, the combination of macrophyte and SMFC led to an increase in pyrene and benzo[a]pyrene degradation rates by at least 70% compared to SMFC or macrophyte alone. While either the macrophyte or SMFC increased redox potential in sediments, redox potentials near the anode (approximately 6 cm depth) in the macrophyte-SMFC combination were markedly lower than that in the only macrophyte treatment. Moreover, rhizospheric bacterial communities in macrophyte-SMFC and macrophyte treatments were distinctly different. Aerobic genera (Vogesella, Pseudomonas, Flavobacterium and Rhizobium) and anaerobic genera (Longilinea, Bellilinea, Desulfobacca and Anaeromyxobacter) became dominant in the rhizosphere in macrophyte and macrophyte-SMFC treatments, respectively. In addition, the macrophyte-SMFC combination improved the numbers of not only aerobic but anaerobic PAHs degraders in sediments. So, the SMFC employment facilitated the formation of anoxic zones in sediments with oxygen loss and exudates from the roots. As a result, cooperation of anaerobic/aerobic microbial metabolism for accelerating HMW-PAHs removal occurred within sediments after combining macrophytes with SMFC.

A pyrene-degrading strain Hydrogenophaga sp. PYR1 was isolated from PAH-contaminated river sediments and found to be able to degrade high molecular weight-polycyclic aromatic hydrocarbons under both aerobic and anaerobic conditions. The strain was Gram-negative, rod-shaped, pale yellow and motile flagellum with rounded ends. Under aerobic conditions, 94% pyrene could be degraded by the strain PYR1 within 15 d at 28 °C, while the degradation of benzo[a]pyrene was not obvious. However, this strain could significantly degrade pyrene and even benzo[a]pyrene under iron-reducing anaerobic conditions. Through Fourier transform infrared spectroscopy and amino acids analysis, it was found that ferric citrate as the sole electron acceptor stimulated lipopeptide biosurfactant production by the strain during PAH degradation. The presence of lipopeptide biosurfactant facilitated benzo[a]pyrene degradation possibly through improving the bioavailability of benzo[a]pyrene. Furthermore, six intermediates formed under iron-reducing conditions were identified, and then a pathway for anaerobic benzo[a]pyrene degradation by this strain was proposed. It seemed that this bacterial isolate has great potential in the bioremediation of PAH-contaminated sediments.