Environmental DNA sequencing of chimney rock collected at the Lost City hydrothermal vent field on the Mid-Atlantic Ridge. The vent field is fueled by chemical reactions between the ultramafic rock under the chimneys and ambient seawater. These serpentinization reactions provide reducing power (as hydrogen gas) and organic compounds that can serve as microbial food the most abundant of these being methane and formate. Our results indicate that carbon metabolism in these Lost City chimney biofilms might depend on the utilization of formate by low-abundance Chloroflexi and Sulfurouvum species.