Nitrifying niche differentiation in biofilms from full-scale monochloraminated drinking water distribution system under tropical weather

CRUZ, MERCEDES CECILIA; WOO, YISSUE; FLEMING HANS-CURT; WUERTZ, STEFAN

Singapore

Congreso; IUMS Congresses 2017 Singapore; 2017

International Union of Microbiological Societies

Nitrifying niche differentiation in biofilms from full-scale monochloraminated drinking water distribution system under tropical weatherObjectives: This study shows the results from the largest survey ever performed on actual biofilms from full-scale monochloraminated drinking water distribution systems (DWDS) using next generation sequencing techniques. We characterized the microbial community with emphasis on nitrifiers bacteria and archaea to understand their implications for the provision of safe and biological stable water.Methods: The monitoring campaign consisted of sampling biofilms from 21 in-service pipes. The multi-parametric approachinvolved cultivation-independent molecular methods and cultivation-based techniques such as: 16S amplicon sequencing, real time PCR and potential N-activity with the most probable number technique. Representative bulk water samples were collected at each sampling site. Multivariate statistical analyses were used to describe the microbial community and its relationships withenvironmental data (physicochemical water quality) and the pipe characteristics.Results: Pipes sampled had diverse sizes (100 to 700 mm diameter) and age of service (from six to 60 years), and made of four different material types.Microbial community analysis showed high variability of richness among the samples, from 392 to 1529 OTUs. The α-diversity indices varied from 2.2 to 55.5, indicating the presence of strong dominant operational taxonomic units (OTUs) in some samples. Taxonomic classification revealed that 63.9% of OTUs were associated with phylum Proteobacteria, followed by Actinobacteria (11.3%) and Nitrospira (9.4%). Microbial community ordination analysis by means of Hierarchical Clustering and nMDS plots showed that samples group in two clusters, characterized by their low (Cluster LD) and high (Cluster HD) α-diversity. Cluster LD had high dominance of Nitrosomonas (relative abundance 24.9 to 68.8%). Meanwhile, in Cluster HD genus Nitrospira (9.8 ? 32.5%), Parvularcula (2.4 ? 15.2%), Thaumarchaeota (1.4 ? 10.9%), Bradyrizhobium (0.5 - 11.5%), and Rhodospirillacea (0.6 ? 12.4%) were the most abundant OTUs and were identified by SIMPER analysis as the drivers of the community structure. Nitrospira negatively correlated with Nitrosomonas (r = -0.6) and positively with Thaumarchaeota (r = 0.87). Nitrosomonas, an ammonia oxidising bacterium (AOB), occurred in Cluster LD and Nitrospira, a nitrite oxidising bacteria (NOB) and Thaumarchaeota, a chemolitholigotrophic ammonia oxidising archaea (AOA), in cluster HD. The two clusters harbour microorganisms related to nitrification, providing evidence that N-related processes occur in the DWDS. These processes were corroborated with activity tests analysis performed with fresh biofilm samples.DistLM-dbRDA analysis showed that monochloramine (MCA) concentration in the water phase is one of the best predictors to explain variability in the microbial community assemblages. Cluster LD is correlated with a high concentration of MCA. Most likely, the disinfectant selects for the most resistant microorganisms (Nitrosomonas) causing the high unevenness of this cluster. MCA is negatively correlated with nitrite (r = -0.599). Nitrite chemical reactions increased MCA demand, releasing ammonia and allowing other non-resistant bacteria to grow, like AOA and NOB in cluster HD.Conlusion: Nitrifiers were present in all samples. The two clusters indicate two distinctive biofilm niches performing two stages of the nitrification process. A MCA residual gradient along the DWDS drives and shapes the microbial community and diversity.