Mechanisms of Anammox Adaptation to High Temperatures: Increased Cyclization of Ladderane Lipids and Proteomic Insights

![Graphical abstract][1] Graphical abstract Although anammox-based processes have been widely applied in mesophilic conditions of reject water and recently in mainstream conditions, the potential of their implementation in high-temperature wastewaters remains largely unexplored. Therefore, this study investigated the operation parameters for the successful adaptation of anammox bacteria and the mechanisms involved on the proteomic and cellular level including unique ladderane lipids. For this purpose, the enrichment of ‘ Candidatus Brocadia’ was cultivated in two fed-batch reactors (FBRs) at a lab scale. The temperature of one FBR was gradually increased from 30 to 40 °C while the other FBR was maintained at 30 °C with four consecutive replicates of this experiment. For this adaptation to be successful, the original loading rate had to be at least halved, or ideally maintained below half the value of the specific anammox activity at the time. The most notable adaptation mechanisms included: (1) upregulation of chaperones and (2) doubled ladderane cyclization via the replacement of non-ladderane fatty acid by a ladderane fatty acid in ladderane lipids (p-value 0.005). To our best knowledge, this is the first study to describe the novel mechanism of ladderane cyclization which together with other adaptation strategies presents crucial indicators in anammox adaptation to high-temperature wastewaters. ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes