Response and resilience of anammox consortia to nutrient starvation

Abstract

Background: It is of critical importance to understand how anammox consortia respond to disturbance events and fluctuations in the wastewater treatment reactors. Although the responses of anammox consortia to operational parameters (e.g., temperature, dissolved oxygen, nutrient concentrations) have frequently been reported in previous studies, less is known about their responses and resilience when they suffer from nutrient interruption.

Results: Here, we investigated the anammox community states and transcriptional patterns before and after a short-term nutrient starvation (3 days) to determine how anammox consortia respond to and recover from such stress. The results demonstrated that the remarkable changes in transcriptional patterns, rather than the community compositions were associated with the nutritional stress. The divergent expression of genes involved in anammox reactions, especially the hydrazine synthase complex (HZS), and nutrient transportation might function as part of a starvation response mechanism in anammox bacteria. In addition, effective energy conservation and substrate supply strategies (ATP accumulation, upregulated amino acid biosynthesis, and enhanced protein degradation) and synergistic interactions between anammox bacteria and heterotrophs might benefit their survival during starvation and the ensuing recovery of the anammox process. Compared with abundant heterotrophs in the anammox system, the overall transcription pattern of the core autotrophic producers (i.e., anammox bacteria) was highly resilient and quickly returned to its pre-starvation state, further contributing to the prompt recovery when the feeding was resumed.

Conclusions: These findings provide important insights into nutritional stress-induced changes in transcriptional activities in the anammox consortia and would be beneficial for the understanding of the capacity of anammox consortia in response to stress and process stability in the engineered ecosystems. Video Abstract.

Keywords: Anammox consortia; Nutrient starvation; Recovery; Resilience; Response; Transcriptional pattern.

Fig. 1

UASB reactor performance. a Nitrogen loading rate (green line) and removal rate during the long-term operation. S1–S4, indicated in red, represent the samples collected on Day 680, Day 693, Day 702, and Day 824, respectively. S2 indicates the time point at which the influent was interrupted. b Nitrogen concentrations in the influent and the effluent

Fig. 2

Relative abundance and gene expression profiles of recovered MAGs. a The proportion of the top 10 most abundant MAGs and other recovered MAGs in the whole community calculated based on the relative abundance of individual MAGs. b The proportion of gene expression of the top 10 most abundant MAGs and other recovered MAGs in the whole community calculated based on the expression of individual MAGs. c The relative abundance (normalized by the genome size) of the top 10 most abundant MAGs at different time points. d Gene expression of the top 10 most abundant MAGs at different time points. See Methods section for calculation details

Fig. 3

Expression profiles of genes involved in the anammox process. a Venn diagram indicating the genes encoded by AMX1 were significantly upregulated (GFOLD value > 1) at S2 compared with the other three time points. b Venn diagram indicating the genes encoded by AMX1 were significantly downregulated (GFOLD value < -1) at S2 compared with the other three time points. c The relative gene expression of key genes possibly involved in anammox reactions. Asterisks indicate the genes that were differentially expressed between S2 and the other three time points (except hzsA S2 vs. S3). d The relative gene expression (indicated by bubble diameter) of ammonium transporters, nitrite transporters and nitrate transporters at different time points

Fig. 4

Transcriptional activity of KEGG modules across the top 10 most abundant MAGs. The relative gene expression of KEGG modules were calculated; see the Methods section for calculation details. Gray box indicates module absence

Fig. 5

Transcriptional activity of predicted peptidases, amino acid, and peptide transporters among the top 10 most abundant MAGs at different time points. a The relative gene expression of peptidases across the MAGs. The peptidases in these recovered MAGs were identified by searching against the MEROPS database, and the locations of peptidases were predicted by PSORTb. b The relative gene expression of amino acid transporters predicted across the MAGs. c The relative gene expression of peptide transporters across the MAGs. Transporters encoded by the recovered MAGs were annotated against TransportDB 2.0 using the automated annotation pipeline TransAAP

Fig. 6

Transcriptional patterns and proposed metabolic interactions of the top 10 most abundant MAGs at different time points. a Principal coordinates analysis (PCoA) (based on Bray-Curtis distance) based on the expression profiles of KEGG modules illustrating the transcriptional pattern of each MAG. The dashed line highlights the time point of the influent interruption. b The proposed metabolic interactions among the core autotrophic producers (AMX1), secondary producers (CHL1 and CHL2), and other abundant heterotrophs