U.S. Department of Energy

Pacific Northwest National Laboratory

Getting from Greenhouse Gas to Microbial Biomass

In this microscopy image of the co-culture, green represents the methane-oxidizing bacteria and red represents a fluorescence specific to the cyanobacterium Synechococcus 7002.

The Science

Microbial biomass is a clean, renewable energy source with the potential to significantly diversify and sustain future energy and transportation fuel requirements. A new paper by researchers at the Pacific Northwest National Laboratory (PNNL) describes a process that captures methane from natural gas and biogas and uses photosynthesis to convert it into biomass feedstock. In this way, energy-rich carbon is not dispersed into the atmosphere as a greenhouse gas and instead is converted to useful products. 

The Impact

The new process is scalable and flexible, and presents a proof-of-concept that obtains exceptional biomass productivity compared to future targets for algal biomass production.At the heart of the process is a new way to cultivate engineered microbial consortia that self-regulate members’ growth. It does this by harnessing a natural metabolic coupling between two organisms: photosynthetic cyanobacteria and methane-oxidizing bacteria. The resulting scheme is more stable and reliable than conventional methods of producing energy-viable biomass via photosynthesis and methane oxidation alone. This new benchmark technology for co-cultivation converts anthropogenic methane (CH4) and carbon dioxide (CO2) into beneficial microbial feedstocks in a way that positively impacts the environment. Presently, these two gases are the largest manmade contributors of greenhouse gases to the atmosphere. That’s because a large fraction of natural gas and biogas – significant sources of manmade CH4and CO– are flared or vented into the air. Losses of the natural gas co-produced with oil recovery, for instance, are equivalent to wasting 5 quadrillion BTUs of energy a year.

Summary

Greenhouse gases such as COand CHare emitted into our atmosphere as waste products of current energy production activities. But imagine turning this waste carbon into a reliable, economical, and safe source of feedstocks for biofuels and other bioproducts. In a paper by lead author Eric Hill, four PNNL researchers propose a robust, integrated, self-regulating co-cultivation platform of well-known microbes that accomplishes that beneficial conversion. One derives energy from the sun (a photoautotrophic cyanobacteria) and the other from the oxidation of methane (a methanotroph).

Many state-of-the-artbiotechnologiesalready in development are trying to capitalizeontheproductivityandstabilityderived from co-cultivating microbialconsortia. But this PNNL study, led by corresponding author Hans Bernstein, presents a new benchmark in co-culture technology – a scalable platformforengineering custom bioprocesses. It’s safer, more flexible, and more stable than previously presented methods for generating microbial biomass or bioproducts from CO2and CH4.

At the heart of the new method is acyanobacteria-methanotrophbinaryculture basedona robustand natural metaboliccouplingbetweenenergy from the sun (oxygenicphotosynthesis)andenergy from a common carbon compound (methaneoxidation). The cultureis amenabletometabolicengineering, which makes theplatformflexibleand scalablefortheproduction ofdifferent bioproductsbased oncost-effective,renewableCOand CH4 feedstocks.

Microbial biomass is a promising intermediate feedstock for synthesizing biofuels and bioproducts. It can be processed by using modern thermochemical conversion technologies, including hydrothermal liquefaction and pyrolysis methods that produce biocrudes that are much like petroleum crude oils. The ability of multi-species microbial consortia to capture and convert CHand CO2represent a tremendous future research opportunity for biotechnologists and engineers. 

Funding

The Linus Pauling Distinguished Postdoctoral Fellowship Program, a Laboratory Directed Research and Development Program of Pacific Northwest National Laboratory. Capabilities investments by the Genomic Science Program, Office of Biological and Environmental Research. The Biofuels Scientific Focus Area at PNNL. Additional acknowledgement is given to the DOE Energy Efficiency & Renewable Energy’s Lab-Corps program that provided specialized training related to the future impact and commercialization of this technology.

Publications

Eric A. Hill, et al., “A flexible microbial co-culture platform for simultaneous utilization of methane and carbon dioxide from gas feed stocks.”Bioresource Technology, 228, 250-256 (2017) [doi.org/10.1016/j.biortech.2016.12.111]

Date: 
March 2017
| Pacific Northwest National Laboratory