Molecular and Kinetic Characterization of Planktonic Nitrospira spp. Selectively Enriched from Activated Sludge

Nitrospiraspp. are chemolithoautotrophic nitrite-oxidizing bacteria (NOB), which are ubiquitous in natural and engineered environments. However, there exist few independent biokinetic studies on Nitrospiraspp., likely because their isolation and selective enrichment from environmental consortia such as activated sludgecan be challenging. Herein, planktonic Nitrospiraspp. cultures closely related to Candidatus Nitrospiradefluvii ( Nitrospiralineage I) were successfully enriched from activated sludgein a sequencing batch reactorby maintaining sustained limiting extant nitriteand dissolved oxygen concentrations. Morphologically, the enrichment consisted largely of planktoniccells with an average characteristic diameter of 1.3 ± 0.6 μm. On the basis of respirometric assays, estimated maximum specific growth rate (μmax), nitritehalf saturation coefficient (KS), oxygen half saturation coefficient (KO), and biomass yield coefficient (Y) of the enriched cultureswere 0.69 ± 0.10 d–1, 0.52 ± 0.14 mg-N/L,...