Systematic Carbon and Growth Analysis of a Promising Methanotroph Strain

Systematic carbon and growth analysis of a promising methanotroph strain

Kyle Stone, Q. Peter He, and Jin Wang

Department of Chemical Engineering, Auburn University, Auburn, AL, 36849, USA

Methanotrophs are widespread bacteria that use methane as their sole carbon and energy source¹. In doing so the organisms, are not only able to reduce the global warming potential of natural gas leaks or effluent from coal ventilation, but also fulfill the role of a steady biocatalyst utilizing the 376-490 trillion Btu worth of biogas made in the US². Due to recent developments in genetic studies, metabolic modeling, and downstream processing, these cells have been studied for commercial applications, including the production of single cell protein (SCP), lipids (for biodiesel), methanol, poly-β-hydroxybutyrate (PHB), as well as waste treatment or bioremediation³. One strain in particular, Methylomicrobium buryatense 5GB1, has been identified as a promising biocatalyst because it is a fast growing organisms with the ability to generate a variety of products including lipids for biodiesel, organic acids, and ectoine. Since the organism is haloalkaliphilic the high pH and salt concentrations are inhibitory to many overpowering contaminants, as well ^3-6.

In this work we provide a systematic approach in analyzing the carbon use and growth patterns of 5GB1 with an in house gas mixing system that safely creates a variety of headspace conditions with methane, oxygen, and nitrogen. Of particular interest are the yields of methane to biomass, to carbon dioxide, and to organic liquid products in batch cultures with balanced, methane limited, or oxygen limited headspaces. The approaches used accurately measure carbon products with an overall balance of 95%-102%, taking into account CO₂ that becomes far more soluble in alkaliphilic conditions. This solubility studied, illustrated the requirement of an effective Henry’s constant to properly characterize the gas-liquid equilibrium of CO₂ and to have an accurate carbon balance.

The growth patterns observed thus far with the systematic comparison suggest that oxygen concentration amongst different oxygen:methane ratios plays a significant role on the optimal growth rate of this organism. Specifically, an excess of oxygen leads to a general decrease of growth rates in the cultures tested. Additionally, gas uptake rates are evaluated to further gauge when substrate limitation occurs and to use as an indicator of possible metabolic pathway changes. Overall the study contributes to the much needed knowledge base for successful methane fermentation strategies with this promising methanotroph.

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