CONICET | Buscador de Institutos y Recursos Humanos

Nitrification is a common occurrence in drinking water distribution systems (DWDS) employing chloramination for secondary disinfection, where nitrifiers like ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) are regularly detected during nitrification episodes. Ammonia-oxidizing archaea (AOA) are usually only found when ammonia and/or residual chloramine concentrations are very low and little is known about their abundance and function in this environment. The cultivation of AOA is more challenging than that of AOB, with various strategies such as filtration and antibiotic treatment having been developed to selectively cultivate AOA over AOB. Such methods had been met with limited success, often times sterilizing the culture or reducing the growth rate of the AOA. In this study, a method was developed to help AOA outcompete AOB during enrichment, by means of chemical inhibition of AOB respiration through the use of dimethylthiourea and pyruvate, while stimulating the growth of AOA. Defined mixtures of AOA and AOB were cultivated in the presence of both dimethylthiourea and pyruvate or pyruvate only, or in the absence of either compound. The proportion of AOA increased to over 99% of ammonia oxidizers after cultivation with both compounds, up from an initial 30% AOA and 70% AOB. Heterotrophic bacteria were also present. In contrast, cultivation with only pyruvate produced cultures with an AOA content of less than 3% compared to 1% after cultivation without added compounds. This new enrichment strategy will facilitate the study of interactions between AOA and monochloramine, by selectively enriching AOA over AOB without sacrificing the growth rate to obtain a purified AOA enrichment. Future studies on the relationship between AOA and monochloramine can inform on its regrowth pattern in chloraminated DWDS.