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

Abstract

The overall goal of this study was to develop an appropriate biological process for achieving autotrophic conversion of methane (CH(4)) to methanol (CH3OH). In this study, we employed ammonia-oxidizing bacteria (AOB) to selectively and partially oxidize CH(4) to CH(3)OH. In fed-batch reactors using mixed nitrifying enrichment cultures from a continuous bioreactor, up to 59.89 ± 1.12 mg COD/L of CH(3)OH was produced within an incubation time of 7 h, which is approximately ten times the yield obtained previously using pure cultures of Nitrosomonas europaea. The maximum specific rate of CH(4) to CH(3)OH conversion obtained during this study was 0.82 mg CH(3)OH COD/mg AOB biomass COD-d, which is 1.5 times the highest value reported with pure cultures. Notwithstanding these positive results, CH(4) oxidation to CH(3)OH by AOB was inhibited by NH(3) (the primary substrate for the oxidative enzyme, ammonia monooxygenase, AMO) as well as the product, CH(3)OH, itself. Further, oxidation of CH(4) to CH(3)OH by AOB was also limited by reducing equivalents supply, which could be overcome by externally supplying hydroxylamine (NH(2)OH) as an electron donor. Therefore, a potential optimum design for promoting CH(4) to CH(3)OH oxidation by AOB could involve supplying NH(3) (needed to maintain AMO activity) uncoupled from the supply of NH(2)OH and CH(4). Partial oxidation of CH(4)-containing gases to CH3OH by AOB represents an attractive platform for the conversion of a gaseous mixture to an aqueous compound, which could be used as a commodity chemical. Alternately, the nitrate and CH(3) OH thus produced could be channeled to a downstream anoxic zone in a biological nitrogen removal process to effect nitrate reduction to N(2), using an internally produced organic electron donor.

Anaerobic digestion and electromethanogenic microbial electrolysis cell integrated system: Increased stability and recovery of ammonia and methane

“…Methanol produced in the anode compartment due to the fermentation of organic compounds could migrate to the cathode compartment through the CEM. Methanol could be also produced at very low O 2 partial pressure, from methane by ammonia oxidising bacteria (AOB) which can partially oxidise CH 4 to methanol when using ammonia as an energy source [75]. The genera Nitrosomonas, a well known AOB, was present in the biocathode samples, although at low relative abundance (<0.01%).…”

A review on green liquid fuels for the transportation sector: a prospect of microbial solutions to climate change

“…Two groups of bacteria, methanotrophic and ammonia-oxidizing bacteria (AOB), can convert CH4 to methanol in aerobic conditions (Hanson and Hanson, 1996;Taher and Chandran, 2013). Methanotrophic bacteria can function to activate and oxidize the stable C-H bond of CH4 as a result of the action of the CH4 monooxygenase (MMO) enzyme, thus, facilitating the use of CH4 as a carbon (C) source.…”

Biocatalytic Conversion of Methane to Methanol as a Key Step for Development of Methane-Based Biorefineries

“…Using a fed-batch reactor, 59.9 mg methanol (expressed in COD)/l was produced for 7 h with a maximum specific rate of 0.82 mg methanol COD/mg biomass COD. Thus, partial oxidation of methane to methanol by AOB may be an alternative to methanotroph-mediated conversion [53].…”