About This Project

The biological conversion of methane into liquid fuel is a promising way to capitalize on the increased levels of methane in the atmosphere. While much attention has focused on the aerobic oxidation of methane, the anaerobic oxidation of methane was long ignored. In our project we will explore whether a recently cultured thermophilic microbe is capable of anaerobically converting methane into the potential biofuel methanol.

Ask the Scientists

Motivating Factor

Methane is the 2^nd highest contributor to global warming and has a 28 times higher greenhouse warming potential than carbon dioxide over a one-hundred year span. Atmospheric methane levels are the highest in at least the last 800,000 years and methane has contributed approximately 30% (0.5 ºC) in warming to the atmosphere since the dawn of the industrial revolution (1). Microorganisms, lifeforms that cannot be observed with the naked eye, are the key producers and consumers of methane in both natural (virtually all anoxic habitats) and anthropogenic ecosystems (landfills, rice paddies, ruminant livestock, wastewater) (2). Microbes are the most efficient catalysts known by science and likely hold the solution to mitigating methane emissions (3). Much work has been dedicated to reducing methane levels using aerobic methane oxidizing bacteria. However, their inability to grow at elevated methanol levels currently limits their wide-spread application.

Specific Bottleneck

One largely unexplored potential solution to mitigating methane is the use of anaerobic (oxygen-independent) microorganisms (4). Several reasons currently limit their application: first, all yet discovered anaerobic methanotrophs oxidize methane all the way to carbon dioxide, meaning one greenhouse gas is simply replaced by another (although less harmful one). Also, the very few anaerobic methanotrophic cultures that exist are obligate syntrophic assemblies of methanotrophic archaea and sulfate-reducing bacteria that depend on each other to achieve methane oxidation. In these interspecies associations, the oxidation of methane and reduction of a terminal electron transfer occurs in two different cells. Slight disturbances to this relationship might have devastating consequences for methane removal. This sensitivity to physicochemical changes might help explain why a long-term stable culture capable of anaerobic oxidation of methane has never been achieved.

Actionable Goals

The few cultures in existence have been obtained from deep-sea cold seeps, sites on the ocean floor where methane bubbles into the water column from sub-seafloor clathrates. These cultures grow at 4-8 ºC, which reduces enzyme kinetics and gas transfer rates (4, 5, 6). Cultures capable of anaerobic oxidation of methane (AOM) at high temperatures must be developed. Ideally, they would not oxidize methane all the way to carbon dioxide but stop at an intermediate step at which cells gain enough energy for growth but excrete an easy to harvest metabolic product. Methods that would enable this include:

- Cultivation of high temperature adapted microbes capable of AOM.

- Modification of their enzymes to allow conversion of methane to a soluble product that can be used as fuel precursor.

- Carbon- and energy-efficient oxidation of methane.