The potential of methane‐oxidizing bacteria for applications in environmental biotechnology

Abstract

Methanotrophic bacteria possess a unique set of enzymes enabling them to oxidize, degrade and transform organic molecules and synthesize new compounds. Therefore, they have great potential in environmental biotechnology. The application of these unique properties was demonstrated in three case studies: (i) Methane escaping from leaky gas pipes may lead to massive mortality of trees in urban areas. Lack of oxygen within the soil surrounding tree roots caused by methanotrophic activity was identified as one of the reasons for this phenomenon. The similarity between metabolic reactions performed by the key enzymes of methanotrophs (methane monooxygenase) and ammonium oxidizers (ammonium monooxygenase) might offer a solution to this problem by applying commercially available nitrification and urease inhibitors. (ii) Methanotrophs are able to co‐metabolically degrade contaminants such as low‐molecular‐weight‐chlorinated hydrocarbons in soil and water in the presence of methane. Batch and continuous trichloroethylene degradation experiments in laboratory‐scale reactors using Methylocystis sp. GB 14 were performed, partly with cells entrapped in a polymer matrix. (iii) Using a short, two‐stage pilot‐scale process, the intracellular polymer accumulation of poly‐β‐hydroxybutyrate (PHB) in methanotrophs reached a maximum of 52%. Interestingly, an ultra‐high‐molecular‐weight PHB of 3.1 MDa was accumulated under potassium deficiency. Under strictly controlled conditions (temperature, pH and methane supply) this process can be nonsterile because of the establishment of a stable microbial community (dominant species Methylocystis sp. GB 25 ≥86% by biomass). The possibility to substitute methane with biogas from renewable sources facilitates the development of a methane‐based PHB production process that yields a high‐quality biopolymer at competitive costs.

Techno-economic assessment of poly-3-hydroxybutyrate (PHB) production from methane—The case for thermophilic bioprocessing

“…Mixed methanotrophic cultures have been found to self-regulate, giving stable populations under non-sterile conditions (15), thereby offering significant savings in capital and operating cost. The bioreactors for both growth and accumulation were assumed to operate under an elevated pressure of 5 bar in the head space to improve gas-liquid mass transfer efficiency (15). Operating temperature was set at 38 o C. Due to high volumetric gas requirements air-lift bioreactors with a concentric internal draft tube were selected to reduce mixing costs (26).…”

“…The remaining yields were calculated using elemental balances. Methane conversion was fixed to achieve a safe flue gas composition of 2% (v/v), below the explosive limit of 5% (15). Methane was assumed to be available off the grid at 5 bar pressure.…”

“…In contrast, methane is a cheap, abundant and widely available carbon source. Also, the robust, self-regulating nature of mixed methanotrophic cultures (15) offers the opportunity to operate under non-sterile conditions, thereby reducing operating costs on an industrial scale.…”

Competition between Metals for Binding to Methanobactin Enables Expression of Soluble Methane Monooxygenase in the Presence of Copper

“…T he increased availability of methane through industrial practices such as hydraulic fracturing has enhanced interest in using methanotrophs, prokaryotes that thrive on methane as their sole source of carbon and energy, to convert methane to more valuable products, e.g., liquid biofuels, plastics, and protein to supplement animal feed (1)(2)(3)(4)(5)(6)(7). Methanotrophs have also received increasing attention given that methane is a very potent greenhouse gas, with a global warming potential 28 to 34 times that of carbon dioxide over a 100-year period (8), and methanotrophs are estimated to remove up to 90% of the methane produced in anaerobic soils (9).…”

Highly efficient methane biocatalysis revealed in a methanotrophic bacterium

“…Interest in new technologies for effective conversion of flared/waste sources of methane into chemical compounds, including next-generation fuels, continues to increase [4][5][6] . The use of microbial cells and enzymes as catalysts for methane conversion represents an appealing approach in this context [7][8][9][10][11] .…”