High-Rate, High-Yield Production of Methanol by Ammonia-Oxidizing Bacteria

The overall goal of this study was to develop an appropriate biological process for achieving autotrophic conversion of methane (CH₄) to methanol (CH₃OH). In this study, we employed ammonia-oxidizing bacteria (AOB) to selectively and partially oxidize CH₄ to CH₃OH. In fed-batch reactors using mixed nitrifying enrichment cultures from a continuous bioreactor, up to 59.89 ± 1.12 mg COD/L of CH₃OH was produced within an incubation time of 7 h, which is approximately ten times the yield obtained previously using pure cultures of <i>Nitrosomonas europaea</i>. The maximum specific rate of CH₄ to CH₃OH conversion obtained during this study was 0.82 mg CH₃OH COD/mg AOB biomass COD-d, which is 1.5 times the highest value reported with pure cultures. Notwithstanding these positive results, CH₄ oxidation to CH₃OH by AOB was inhibited by NH₃ (the primary substrate for the oxidative enzyme, ammonia monooxygenase, AMO) as well as the product, CH₃OH, itself. Further, oxidation of CH₄ to CH₃OH by AOB was also limited by reducing equivalents supply, which could be overcome by externally supplying hydroxylamine (NH₂OH) as an electron donor. Therefore, a potential optimum design for promoting CH₄ to CH₃OH oxidation by AOB could involve supplying NH₃ (needed to maintain AMO activity) uncoupled from the supply of NH₂OH and CH₄. Partial oxidation of CH₄-containing gases to CH₃OH by AOB represents an attractive platform for the conversion of a <i>gaseous</i> mixture to an <i>aqueous</i> compound, which could be used as a commodity chemical. Alternately, the nitrate and CH₃ OH thus produced could be channeled to a downstream anoxic zone in a biological nitrogen removal process to effect nitrate reduction to N₂, using an <i>internally</i> produced organic electron donor

Biodegradation and Cometabolic Modeling of Selected Beta Blockers during Ammonia Oxidation

Accurate prediction of pharmaceutical concentrations in wastewater effluents requires that the specific biochemical processes responsible for pharmaceutical biodegradation be elucidated and integrated within any modeling framework. The fate of three selected beta blockersatenolol, metoprolol, and sotalolwas examined during nitrification using batch experiments to develop and evaluate a new cometabolic process-based (CPB) model. CPB model parameters describe biotransformation during and after ammonia oxidation for specific biomass populations and are designed to be integrated within the Activated Sludge Models framework. Metoprolol and sotalol were not biodegraded by the nitrification enrichment culture employed herein. Biodegradation of atenolol was observed and linked to the activity of ammonia-oxidizing bacteria (AOB) and heterotrophs but not nitrite-oxidizing bacteria. Results suggest that the role of AOB in atenolol degradation may be disproportionately more significant than is otherwise suggested by their lower relative abundance in typical biological treatment processes. Atenolol was observed to competitively inhibit AOB growth in our experiments, though model simulations suggest inhibition is most relevant at atenolol concentrations greater than approximately 200 ng·L^–1. CPB model parameters were found to be relatively insensitive to biokinetic parameter selection suggesting the model approach may hold utility for describing pharmaceutical biodegradation during biological wastewater treatment

Impact of Cu(II) exposure on relative sOUR values, normalized to control values in stationary and exponential phase <i>N. europaea</i> cultures.

<p>Error bars depict standard deviation based on duplicate oxygen uptake rate measurements and cell counts from ten replicate counting chamber wells.</p

Impact of Cu(II) exposure on gene expression in stationary and exponential phase <i>N. europaea</i> cultures.

<p>Impact of Cu(II) exposure on gene expression in stationary and exponential phase <i>N. europaea</i> cultures.</p

Impact of Cu(II) exposure on membrane integrity in stationary and exponential phase <i>N. europaea</i> cultures.

<p>Error bars depict cell counts from ten replicate fluorescence images.</p

Elemental profiles in exponential phase <i>N. europaea</i> cultures exposed to different Cu(II) doses.

<p>*: done without replication.</p

Comparison of elemental profiles in exponential and stationary phase cultures of <i>N. europaea</i> with stationary phase cultures of <i>P. fluorescens</i>[<b>5</b>].

<p>Error bars depict standard deviation of 5–9 replicates in this study and 5 replicates in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0021255#pone.0021255-Kemner1" target="_blank">[5]</a>. * represents the elements for which the molar fractions in <i>N. europaea</i> were statistically higher (α = 0.05). ** represents the elements for which the molar fractions in <i>N. europaea</i> were statistically lower (α = 0.05). The molar fractions of remaining elements were statistically not dissimilar (α = 0.05).</p

Elemental profiles in stationary phase <i>N. europaea</i> cultures exposed to different Cu(II) doses.

<p>Elemental profiles in stationary phase <i>N. europaea</i> cultures exposed to different Cu(II) doses.</p

Spatial profiles of several elements in two <i>N. europaea</i> cells in close proximity at stationary phase and not exposed to Cu(II), quantified using MAPS software [<b>33</b>].

<p>Dark colors represent lower concentrations and lighter colors represent higher concentrations.</p

Comammox Functionality Identified in Diverse Engineered Biological Wastewater Treatment Systems

Complete ammonia oxidation (comammox) to nitrate by certain <i>Nitrospira</i>-lineage bacteria (CMX) could contribute to overall nitrogen cycling in engineered biological nitrogen removal (BNR) processes in addition to the more well-documented nitrogen transformations by ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and anaerobic ammonia-oxidizing (anammox) bacteria (AMX). A metagenomic survey was conducted to quantify the presence and elucidate the potential functionality of CMX in 16 full-scale BNR configurations treating mainstream or sidestream wastewater. CMX proposed to date were combined with previously published AOB, NOB, and AMX genomes to create an expanded database for alignment of metagenomic reads. CMX-assigned metagenomic reads accounted for between 0.28 and 0.64% of total coding DNA sequences in all BNR configurations. Phylogenetic analysis of key nitrification functional genes <i>amoA</i>, encoding the α-subunit of ammonia monooxygenase, <i>haoB</i>, encoding the β-subunit of hydroxylamine oxidoreductase, and <i>nxrB</i>, encoding the β-subunit of nitrite oxidoreductase, confirmed that each BNR system contained coding regions for production of these enzymes by CMX specifically. Ultimately, the ubiquitous presence of CMX bacteria and metabolic functionality in such diverse system configurations emphasizes the need to translate novel bacterial transformations to engineered biological process interrogation, operation, and design