Quantification of Nitrosomonas oligotropha-like ammonia-oxidizing bacteria and Nitrospira spp. from full-scale wastewater treatment plants by competitive PCR

HEBE M. DIONISI; ALICE C. LAYTON; GERDA HARMS; IGRID GREGORY; KEVIN ROBINSON; GARY S. SAYLER

APPLIED AND ENVIRONMENTAL MICROBIOLOGY

ASM Press

Año: 2002 vol. 68 p. 245 - 253

0099-2240

Utilizing the principle of competitive PCR, two assays were developed for the enumeration of Nitrosomonas oligotropha-like ammonia-oxidizing bacteria and nitrite-oxidizing bacteria of the genus Nitrospira. The specificity of two primer sets, designed for target regions amoA gene and Nitrospira 16S rDNA, was verified by DNA sequencing. Both assays were optimized and applied to full-scale, activated sludge wastewater treatment plant (WWTP) samples. Assuming an average of 3.6 copies of 16S rDNA per cell in the total population and 2 copies of amoA gene per ammonia oxidizing bacterial cell, these nitrifiers represented 0.0033 ± 0.0022% of the total bacterial population density in the municipal WWTP. N. oligotropha-like AOB were not detected in the industrial WWTP. Assuming one copy of the 16S rDNA gene per nitrite oxidizing bacteria, Nitrospira spp. represented 0.39 ± 0.28% of the biosludge population in the municipal WWTP, and 0.37 ± 0.23% of the population in the industrial WWTP. The number of Nitrospira spp. in the municipal wastewater treatment plant exceeded the N. oligotropha-like population by a factor greater than 62, based upon competitive PCR analysis. The results of this study extended our knowledge on the comparative composition of nitrifying bacterial population in wastewater treatment. Importantly, they demonstrate the ability to quantify these populations, which is ultimately required for accurate prediction of process performance and stability in the cost effective design and operation of WWTPs.