Mitigating the detrimental effects of salt stress on anammox process: A comparison between glycine betaine and mannitol

Potential Role of the Anammoxosome in the Adaptation of Anammox Bacteria to Salinity Stress

The underlying adaptative mechanisms of anammox bacteria to salt stress are still unclear. The potential role of the anammoxosome in modulating material and energy metabolism in response to salinity stress was investigated in this study. The results showed that anammox bacteria increased membrane fluidity and decreased mechanical properties by shortening the ladderane fatty acid chain length of anammoxosome in response to salinity shock, which led to the breakdown of the proton motive force driving ATP synthesis and retarded energy metabolism activity. Afterward, the fatty acid chain length and membrane properties were recovered to enhance the energy metabolic activity. The relative transmission electron microscopy (TEM) area proportion of anammoxosome decreased from 55.9 to 38.9% under salinity stress. The 3D imaging of the anammox bacteria based on Synchrotron soft X-ray tomography showed that the reduction in the relative volume proportion of the anammoxosome and the concave surfaces was induced by salinity stress, which led to the lower energy expenditure of the material transportation and provided more binding sites for enzymes. Therefore, anammox bacteria can modulate nitrogen and energy metabolism by changing the membrane properties and morphology of the anammoxosome in response to salinity stress. This study broadens the response mechanism of anammox bacteria to salinity stress.

Microbial response and recovery strategy of the anammox process under ciprofloxacin stress from pure strain and consortia perspectives

Ciprofloxacin (CIP) poses a high risk of resistance development in water environments. Therefore, comprehensive effects and recovery strategies of CIP in anaerobic ammonia oxidation (anammox) process were systematically elucidated from consortia and pure strains perspectives. The anammox consortia was not significantly affected by the stress of 10 mg L-1 CIP, while the higher concentration (20 mg L-1) of CIP caused a dramatic reduction in the nitrogen removal performance of anammox system. Simultaneously, the abundances of dominant functional bacteria and corresponding genes also significantly decreased. Such inhibition could not be mitigated by the recovery strategy of adding hydrazine and hydroxylamine. Reducing nitrogen load rate from 5.1 to 1.4 kg N m-3 d-1 promoted the restoration of three reactors. In addition, the robustness and recovery of anammox systems was evaluated using starvation and shock strategies. Simultaneously, antibiotic resistance genes and key metabolic pathways of anammox consortia were upregulated, such as carbohydrate and energy metabolisms. In addition, 11 pure stains were isolated from the anammox system and identified through phylogenetic analysis, 40 % of which showed multidrug resistance, especially Pseudomonas. These findings provide deep insights into the responding mechanism of anammox consortia to CIP stress and promote the application of anammox process for treating wastewater containing antibiotics.

Deciphering performance and microbial characterization of marine anammox bacteria-based consortia treating nitrogen-laden hypersaline wastewater: Inhibiting threshold of salinity

Hypersaline wastewater posed a challenge to microbial nitrogen removal processes. Herein, halophilic marine anammox bacteria (MAB) were applied to treat nitrogen-rich wastewater with 35-90 g/L salts for the first time. It was found that MAB, with low relative abundance (2.3-6.9 %), still exhibited good nitrogen removal efficiency (>90 %) under 35-70 g/L salts. The specific anammox activity peaked at 180.16 mg N/(g·VSS·d) at 65 g/L salts. MAB secreted more extracellular polymeric substances to resist the adverse effects of hypersaline stress. Nevertheless, the nitrogen removal deteriorated at 75 g/L salts, and further collapsed as the salinity increased. At 90 g/L salts, total nitrogen removal rate decreased by 74 % compared with that of 35 g/L salts. Besides, SBR1031 increased from 12.0 % (35 g/L salts) to 17.4 % (90 g/L salts) and became the dominant bacterial genus in the reactor. This work shed light on the treatment of hypersaline wastewater through MAB.

Improved regression model for anaerobic ammonium oxidation by repeated and prolonged batch assay under stressful salinity and pH conditions

The aim of this study was to propose repeated and prolonged batch (RPB) assay as a promising specific anammox activity (SAA) methodology assessing the anammox activity under stressed salinity and pH conditions. Response surface analysis (RSA) was used as a regression tool to evaluate statistical significance. The feasibility of RPB was investigated at 0 to 15 g-NaCl/L of salinity and pH 6 to 8 with reflecting the results of preliminary SAA. As a result, conventional SAA was statistically insignificant. In addition, the RSA results obtained from repeated batch did not meet the statistical significance despite ten times iterative reaction. Interestingly, the RPB assay (i.e., applied both repeated and prolonged reaction) was effective to obtain the reliable results. Candidadus Brocadia and Candidadus Jettenia were functional anammox microbiome during RPB. Outcomes of this study suggest that RPB assay can be applied to accurately determine the anammox activity under various stressful conditions.