1 Supplementary Material Relative abundance and diversity of bacterial methanotrophs at the oxic-anoxic interface of the Congo deep-sea fan. Sandrine BESSETTE, Yann MOALIC, Sébastien GAUTEY, Françoise LESONGEUR, Anne GODFROY, and Laurent TOFFIN* *Correspondance: Corresponding Author: Laurent.Toffin@ifremer.fr 1 Supplementary Data 1.1 Geochemical analyses Pore-water analyses were performed on replicate sediment push-cores using Rhizon samplers and methane (CH 4 ) concentrations were measured as described in (Vigneron et al., 2013). CH 4 fluxes at sediment-water interface were determined in situ by using a Calmar benthic incubation chamber (Caprais et al., 2010) deployed on almost every investigated habitats by the ROV Victor 6000 as described in (Khripounoff et al., 2015). Diffusive oxygen (O 2 ) uptake and oxygen penetration depth (OPD) in the bottom water and in the sediment were measured in situ and analyzed as described in (Rabouille et al., 2009).