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van Niftrik, L.

Publications and source records attributed to van Niftrik, L..

2 recordsLinked to original sources
bioRxiv2019

On anammox activity at low temperature: effect of ladderane composition, process conditions and dominant anammox population

The application of partial nitritation-anammox (PN/A) under mainstream conditions can enable substantial cost savings at wastewater treatment plants (WWTPs), but how process conditions and cell physiology affect anammox performance at psychrophilic temperatures below 15 {degrees}C remains poorly understood. We tested 14 anammox communities, including 8 from globally-installed PN/A processes, for (i) specific activity at 10-30 {degrees}C (batch assays), (ii) composition of membrane lipids (U-HPLC-HRMS/MS), and (iii) microbial community structure (16S rRNA gene amplicon sequencing). Crucially, the key parameters impacting anammox activity were the membrane lipid composition and cultivation temperature. The size of ladderane lipids and the content of bacteriohopanoids were key physiological drivers of anammox performance at low temperatures. Higher contents of (i) short C18 [3]-ladderane alkyl and (ii) large phosphatidylcholine headgroup were determined in anammox more active at 15-30 {degrees}C and 10-15 {degrees}C, respectively. At below 15 {degrees}C, the activation energies of most mesophilic cultures severely increased while those of the psychrophilic cultures remained stable; this indicates that the adaptation of mesophilic cultures to psychrophilic regime necessitates months, but in some cases can take up to 5 years. Interestingly, biomass enriched in the marine genus "Candidatus Scalindua" displayed exceptionally highest activity at 10-20 {degrees}C (0.50 kg-N.kg-VSS-1.d-1 at 10 {degrees}C, Ea10-30 {degrees}C = 51{+/-}16 kJ.mol-1), indicating outstanding potential for nitrogen removal from cold streams. Collectively, our comprehensive study provides essential knowledge of cold adaptation mechanism, will enable more accurate modelling and suggests highly promising target anammox genera for inoculation and set-up of anammox reactors, in particular for mainstream WWTPs. HighlightsO_LILadderane size and cold exposure affected anammox activation energy (Ea). C_LIO_LIEa improved with more C18 [3]-ladderanes over C20 and larger polar headgroup. C_LIO_LILong-term cold exposure reduced Ea at 10-15 {degrees}C, not activity per se. C_LIO_LIMarine "Ca. Scalindua" was exceptionally suitable for cold streams. C_LIO_LIAnammox Ea at 15-30 {degrees}C was 79{+/-}18 kJ.mol-1. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=121 SRC="FIGDIR/small/873869v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@1c5c3aborg.highwire.dtl.DTLVardef@b11ed2org.highwire.dtl.DTLVardef@5e7ec9org.highwire.dtl.DTLVardef@1d5cba5_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗
bioRxiv2019

Extracellular electron transfer-dependent anaerobic oxidation of ammonium by anammox bacteria

Anaerobic ammonium oxidation (anammox) by anammox bacteria contributes significantly to the global nitrogen cycle, and plays a major role in sustainable wastewater treatment. Anammox bacteria convert ammonium (NH4+) to dinitrogen gas (N2) using nitrite (NO2-) or nitric oxide (NO) as the electron acceptor. In the absence of NO2- or NO, anammox bacteria can couple formate oxidation to the reduction of metal oxides such as Fe(III) or Mn(IV). Their genomes contain homologs of Geobacter and Shewanella cytochromes involved in extracellular electron transfer (EET). However, it is still unknown whether anammox bacteria have EET capability and can couple the oxidation of NH4+ with transfer of electrons to carbon-based insoluble extracellular electron acceptors. Here we show using complementary approaches that in the absence of NO2-, freshwater and marine anammox bacteria couple the oxidation of NH4+ with transfer of electrons to carbon-based insoluble extracellular electron acceptors such as graphene oxide (GO) or electrodes poised at a certain potential in microbial electrolysis cells (MECs). Metagenomics, fluorescence in-situ hybridization and electrochemical analyses coupled with MEC performance confirmed that anammox electrode biofilms were responsible for current generation through EET-dependent oxidation of NH4+. 15N-labelling experiments revealed the molecular mechanism of the EET-dependent anammox process. NH4+ was oxidized to N2 via hydroxylamine (NH2OH) as intermediate when electrode was the terminal electron acceptor. Comparative transcriptomics analysis supported isotope labelling experiments and revealed an alternative pathway for NH4+ oxidation coupled to EET when electrode is used as electron acceptor compared to NO2-as electron acceptor. To our knowledge, our results provide the first experimental evidence that marine and freshwater anammox bacteria can couple NH4+ oxidation with EET, which is a significant finding, and challenges our perception of a key player of anaerobic oxidation of NH4+ in natural environments and engineered systems.

microbiology↗