(614d) A Novel Phenotype of Haloalkaliphilic Methanotrophs Induced By Extreme Oxidative Stress

Methane (CH₄) is the second most abundant greenhouse gas (GHG), whose global warming potential is 72 times that of CO₂ within a 20-year period. At the same time, CH₄ is a low-cost, rich source for carbon and energy, and an essential component of the global carbon cycle. Because of its low volumetric energy density, it is desirable to convert CH₄ into other forms of liquid fuels, and microbial conversion of CH₄ at ambient temperature and pressure is an attractive alternative to the thermochemical gas-to-liquid conversion, particularly for small scale application ^[1].

Type I methanotrophs have drawn significant research interest in the last decade due to their potential for commercial methane bioconversion to value-added products such as fuels and chemicals. Haloalkaliphilic methanotrophs, such as Methylomicrobium buryatense 5GB1 and Methylomicrobium alcaliphilum 20Z, are especially promising biocatalysts due to their high growth rate and high resistance to contamination under the preferred high pH and high salt growth condition.

In our prior research, we found that for M. buryatense 5GB1, methane-limited phenotype yields higher organic compounds production than oxygen-limited phenotype. This is contrary to the common belief that oxygen-limited phenotype delivers increased production of organic compounds. In this work, we report a novel phenotype of haloalkaliphilic methanotrophs induced by extreme oxidative stress. By subjecting the cells to extremely high oxidative stress (80% or 90% O₂), we discovered that the methanotrophs produced significant amount of organic carbon compounds. For M. buryatense 5GB1, the average organic carbon yield was 32% with formate making up a majority, while optimal oxygen conditions measured an organic carbon yield of 1.1-1.5%. For M. alcaliphilum 20Z, the average organic carbon yield was 18% with formate making up the majority, while literature indicates a yield range of 1% for excreted organic carbon. These experiment further confirmed that higher O₂:CH₄ consumption ratio is correlated to higher organic compound (formate) production.

In this presentation, we report our efforts in characterizing this novel phenotype. Specifically, we cultured both M. buryatense 5GB1 and M. alcaliphilum 20Z under different oxygen conditions, and analyzed their growth, carbon yield distribution, excreted metabolites profiles (via analysis of supernatants) through targeted and untargeted metabolomics approach, and transcriptomic profiles of cells grown under different conditions. In addition, three different factors that showed significant effect on formate production were examined to gain better understanding on the new phenotype: feeding protocol, trace element media (NMS2 vs P), and nitrate limitation (different NO₃^- concentration).

References

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