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

Abstract

Nitrospira spp. are chemolithoautotrophic nitrite-oxidizing bacteria (NOB), which are ubiquitous in natural and engineered environments. However, there exist few independent biokinetic studies on Nitrospira spp., likely because their isolation and selective enrichment from environmental consortia such as activated sludge can be challenging. Herein, planktonic Nitrospira spp. cultures closely related to Candidatus Nitrospira defluvii (Nitrospira lineage I) were successfully enriched from activated sludge in a sequencing batch reactor by maintaining sustained limiting extant nitrite and dissolved oxygen concentrations. Morphologically, the enrichment consisted largely of planktonic cells with an average characteristic diameter of 1.3 ± 0.6 μm. On the basis of respirometric assays, estimated maximum specific growth rate (μ), nitrite half saturation coefficient (K), oxygen half saturation coefficient (K), and biomass yield coefficient (Y) of the enriched cultures were 0.69 ± 0.10 d, 0.52 ± 0.14 mg-N/L, 0.33 ± 0.14 mg-O/L, and 0.14 ± 0.02 mg-COD/mg-N, respectively. These parameters collectively reflect not just higher affinities of this enrichment for nitrite and oxygen, respectively, but also a higher biomass yield and energy transfer efficiency relative to Nitrobacter spp. Used in combination, these kinetic and thermodynamic parameters can help toward the development and application of energy-efficient biological nutrient removal processes through effective Nitrospira out-selection.

Genome-Scale, Constraint-Based Modeling of Nitrogen Oxide Fluxes during Coculture of Nitrosomonas europaea and Nitrobacter winogradskyi

“…In addition, experimental corroboration of the energy models that inform the genome-scale models needs to occur. Recent work with Nitrospira enrichment cultures has begun to provide this important information for NOB (55). The integration of a genome-scale constraint-based model and abiotic reaction model presented in this work is a key step toward making meaningful predictions in complex systems.…”

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“…The nitrite half-saturation coefficient (KS) of pure cultures of Nitrobacter was 0.69-7.6 mg-N l -1 , while pure cultures of Nitrospira showed lower values of 0.13-0.38 mg-N l -1 [31]. The oxygen half-saturation coefficient (KO) of mixed cultures of Nitrobacter was 0.43-5.31 mg l -1 [3,33,34] while the value of KO of Nitrospira was 0.33-0.54 mg l -1 [33,35]. The difference of KS and KO between Nitrobacter and Nitrospira allows them to be dominant in distinct environments.…”

“…The analyzed Nitrospira sequences fell within Nitrospira lineage I and II. NOB genus Nitrobacter and Nitrospira are different in substrate affinities but were commonly found in wastewater treatment systems [29,30]. Nitrobacter has lower nitrite and oxygen affinities than Nitrospira [31,32].…”

“…Nitrobacter often dominates a substrate (nitrite and oxygen)concentrated environment, while Nitrospira often prefers a dilute, substrate-deficient environment [32,36,37]. In addition, differences in substrate affinity among some Nitrospira lineages, which have been often found in wastewater treatment systems [29] as lineage I and II, have been reported in a previous study [38]. Park and Noguera (2008) [38] found a partial shift toward Nitrospira lineage II along operating chemostat at high DO (8.5 mg l -1 ) while the low DO (< 0.24 mg l -1 ) chemostat was always dominated by Nitrospira lineage I.…”

Stimulating Nitrogen Biokinetics with the Addition of Hydrogen Peroxide to Secondary Effluent Biofiltration

“…The significant anoxic potential reflected from the relative abundance of functional genes can be explained by the denitrifying community capable of being active at the presence of oxygen (low half-saturation rate of oxygen inhibition, KOI = 0.1-0.2 mg/L) [43]. Moreover, favoring oxygen utilization for nitrification, with a C/N ratio similar to wastewater, can be explained by the selection of organisms that are more competitive and characterized with a low substrate half-saturation rate coefficient (KONitrospira = 0.1-0.2 mg/L, KOAOB = 0.26-0.15 mg/L), which is more typical to nitrifiers in comparison to heterotrophs [51,52]. Jiang et al (2013) also observed that the increase in oxygen availability in the upflow biofilter resulted in utilization by nitrifiers rather than heterotrophic biomass [19].…”