The research paper by Kohei Oba, Toshikazu Suenaga, Shohei Yasuda, Megumi Kuroiwa, Tomoyuki Hori, Susanne Lackner, and Akihiko Terada

titled “Quest for Nitrous Oxide-reducing Bacteria Present in an Anammox Biofilm Fed with Nitrous Oxide (2024) 39: ME23106“

wins The Most Valuable Paper of The Year 2024 in Microbes and Environments.

This study focuses on the anammox process, a nitrogen removal pathway mediated by microorganisms that remains largely unexplored. The aim is to identify N₂O-reducing bacteria within an anammox reactor, characterize their genetic features, and clarify their functional activity. Based on the hypothesis that N₂O is a limiting factor, a biofilm reactor equipped with a gas-permeable membrane was employed to supply N₂O without bubble formation, and various datasets were collected. By integrating multiple analytical techniques—including ¹⁵N tracer experiments, quantitative PCR, 16S rRNA amplicon sequencing, and shotgun metagenomic analysis—it was revealed that members of the Anaerolineae and Ignavibacteria lineages, which possess Clade II nosZ-type N₂O reductase genes, play a significant role in N₂O uptake. In addition, it was demonstrated that Dehalococcoidia and Clostridia, which exhibit a high metabolic capacity for vitamin B₁₂, also contribute to N₂O reduction. This study has been highly regarded for its comprehensive analytical approach in identifying the key bacterial taxa involved in N₂O reduction and elucidating the supporting microbial community structure, based on 1,200 days of anammox reactor operation. Furthermore, its novel focus on electron acceptors to explore microbial symbiosis is a distinguishing feature. These contributions were highly praised by the review committee and led to the selection of this work as the award-winning paper.