Methanogens and Their Syntrophic Partners Dominate Zones of Enhanced Magnetic Susceptibility at a Petroleum Contaminated Site

Geophysical investigations documenting enhanced magnetic susceptibility (MS) within the water table fluctuation zone at hydrocarbon contaminated sites suggest that MS can be used as a proxy for investigating microbial mediated iron reduction during intrinsic bioremediation. Here, we investigated community composition over 5-year period hydrocarbon-contaminated site exhibited transient elevated responses. Our objective was to determine key populations in zones of MS. We retrieved sediment cores from petroleum-contaminated near Bemidji, MN, United States, and performed measurements on these cores. also characterized by high-throughput 16S rRNA gene amplicon sequencing samples collected along complete core length. spatial temporal analysis revealed generally stable throughout investigation. In addition, observed distinct vertical redox zonations extending upper vadose into saturated zone. These were concomitant with dominant metabolic processes follows: (1) dominated aerobic populations; (2) lower methanotrophic populations, reducers oxidizers; (3) smear reducers; (4) free product syntrophic methanogenic populations. Although common notion is high values are caused magnetite concentrations biotically formed through activities iron-reducing bacteria, here show highest susceptibilities measured free-phase petroleum zone, where predominant. This field study may contribute emerging knowledge methanogens switch their metabolism methanogenesis associated precipitation sediments. Thus, geophysical methods such help identify cycling/reduction occurring.