Biosensing systems for the detection and quantification of methane gas

Abstract

Climate change due to the continuous increase in the release of green-house gasses associated with anthropogenic activity has made a significant impact on the sustainability of life on our planet. Methane (CH₄) is a green-house gas whose concentrations in the atmosphere are on the rise. CH₄ measurement is important for both the environment and the safety at the industrial and household level. Methanotrophs are distinguished for their unique characteristic of using CH₄ as the sole source of carbon and energy, due to the presence of the methane monooxygenases that oxidize CH₄ under ambient temperature conditions. This has attracted interest in the use of methanotrophs in biotechnological applications as well as in the development of biosensing systems for CH₄ quantification and monitoring. Biosensing systems using methanotrophs rely on the use of whole microbial cells that oxidize CH₄ in presence of O₂, so that the CH₄ concentration is determined in an indirect manner by measuring the decrease of O₂ level in the system. Although several biological properties of methanotrophic microorganisms still need to be characterized, different studies have demonstrated the feasibility of the use of methanotrophs in CH₄ measurement. This review summarizes the contributions in methane biosensing systems and presents a prospective of the valid use of methanotrophs in this field. KEY POINTS: • Methanotroph environmental relevance in methane oxidation • Methanotroph biotechnological application in the field of biosensing • Methane monooxygenase as a feasible biorecognition element in biosensors.

Keywords: Biosensors; Methane biosensing; Methane monooxygenase; Methanotrophs.

Fig. 1

Structures of pMMO and sMMO components. X-ray crystal structures of (a) pMMO (PDB: 3RGB), (b) X-ray crystal structure of MMOH (PDB: 1MTY). NMR structures of (c) MMOB (PDB: 2MOB), (d) [2Fe-2S] domain of MMOR (PDB: 1JQ4), and (e) FAD and NADH binding domain of MMOR (PDB: 1TVC)

Fig. 2

Working principle of methane biosensing systems

Fig. 3

Schematic representation of CH₄ biosensing systems. (a) Sensing system based on the use of CH₄ oxidizing bacteria: 1, vacuum pump; 2, sample gas bag; 3, gas sample line; 4, cotton filter; 5, control reactor; 6, reactor containing M. flagellata; 7, O₂ electrode; 8, amplifier; 9, recorder; 10, vacuum pump; 11–17, glass stopcocks (Okada et al. ; Karube et al. 1982) (reprinted from (Karube et al. 1982) with permission from Elsevier). (b) Sensing system for CH₄ measurement in solution: 1, pump; 2, gas valve; 3, sample gas; 4, flow-meter; 5, thermostat magnetic stirrer; 6, magnetic bar; 7, oxygen sensor; 8, phosphate buffer solution; 9, bacterial beads; and 10, datalogger and computer (Wen et al. ; Zhao et al. 2009) (reprinted from (Wen et al. 2008) with permission from Elsevier). (c) Entire system (left) microsensor tip (right), composed of a gas and a media capillary. An internal O₂ electrode is present in the gas capillary which serves as the O₂ reservoir (Damgaard and Revsbech 1997) (reprinted from (Damgaard and Revsbech 1997) with permission from ACS)