Selective enrichment of two different types of Nitrospira-like nitrite-oxidizing bacteria from a wastewater treatment plant. Microbes Environ

Nitrification is an important step in nitrogen removal in biological wastewater treatment processes. Recently, Nitrospira have been recognized as the numerically dominant nitrite-oxidizing bacterial genus primarily responsible for the second step of aerobic nitrification; however, Nitrospira usually resist cultivation under laboratory conditions and only one species enriched from activated sludge has been described. In this study, a novel enrichment method for Nitrospira was successfully developed using continuous feeding bioreactors. By controlling nitrite concentrations strictly in the bioreactor at low levels below 10 mg-N L−1, coexisting members of sublineages I and II of the genus Nitrospira were enriched selectively. The maximum ratios of sublineages I and II to total microbial cells achieved 88.3 % and 53.8%, respectively. This enrichment method is potentially applicable to other uncultured Nitrospira. Key words: continuous feeding bioreactor, nitrification, Nitrospira, uncultured bacteria Nitrite oxidation is an important step in nitrogen removal in biological wastewater treatment processes. The nitrite-oxidizing bacteria (NOB) previously identified as domi-nant in wastewater treatment plants belong to either the genus Nitrobacter or the genus Nitrospira. Traditionally, Nitrobacter were regarded as the key nitrite oxidizers becaus