15 N ‐ and 2 H proteomic stable isotope probing links nitrogen flow to archaeal heterotrophic activity

Summary Understanding how individual species contribute to nutrient transformations in a microbial community is critical to prediction of overall ecosystem function. We conducted microcosm experiments in which floating acid mine drainage ( AMD ) microbial biofilms were submerged – recapitulating the final stage in a natural biofilm life cycle. Biofilms were amended with either 15 NH 4 + or deuterium oxide ( 2 H 2 O ) and proteomic stable isotope probing ( SIP ) was used to track the extent to which different members of the community used these molecules in protein synthesis across anaerobic iron‐reducing, aerobic iron‐reducing and aerobic iron‐oxidizing environments. S ulfobacillus spp. synthesized 15 N ‐enriched protein almost exclusively under iron‐reducing conditions whereas the L eptospirillum spp. synthesized 15 N ‐enriched protein in all conditions. There were relatively few 15 N ‐enriched archaeal proteins, and all showed low atom% enrichment, consistent with A rchaea synthesizing protein using the predominantly 14 N biomass derived from recycled biomolecules. In parallel experiments using 2 H 2 O , extensive archaeal protein synthesis was detected in all conditions. In contrast, the bacterial species showed little protein synthesis using 2 H 2 O . The nearly exclusive ability of A rchaea to synthesize proteins using 2 H 2 O may be due to archaeal heterotrophy, whereby A rchaea offset deleterious effects of 2 H by accessing 1 H generated by respiration of organic compounds.