Bioconversion of Methane to Lactate by an Obligate Methanotrophic Bacterium

Calvin A. Henard, Holly Smith, Nancy Dowe, Marina G. Kalyuzhnaya, Philip T. Pienkos, Michael T. Guarnieri

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114 Scopus Citations

Abstract

Methane is the second most abundant greenhouse gas (GHG), with nearly 60% of emissions derived from anthropogenic sources. Microbial conversion of methane to fuels and value-added chemicals offers a means to reduce GHG emissions, while also valorizing this otherwise squandered high-volume, highenergy gas. However, to date, advances in methane biocatalysis have been constrained by the lowproductivity and limited genetic tractability of natural methane-consuming microbes. Here, leveraging recent identification of a novel, tractable methanotrophic bacterium, Methylomicrobium buryatense, we demonstrate microbial biocatalysis of methane to lactate, an industrial platform chemical. Heterologous overexpression of a Lactobacillus helveticus L-lactate dehydrogenase in M. buryatense resulted in an initial titer of 0.06 g lactate/L from methane. Cultivation in a 5 L continuously stirred tank bioreactor enabled production of 0.8 g lactate/L, representing a 13-fold improvement compared to the initial titer. The yields (0.05 g lactate/g methane) and productivity (0.008 g lactate/L/h) indicate the need and opportunity for future strain improvement. Additionally, real-time analysis of methane utilization implicated gas-to-liquid transfer and/or microbial methane consumption as process limitations. This work opens the door to develop an array of methanotrophic bacterial strain-engineering strategies currently employed for biocatalytic sugar upgrading to "green" chemicals and fuels.

Original languageAmerican English
Article number21585
Number of pages9
JournalScientific Reports
Volume6
DOIs
StatePublished - 23 Feb 2016

NREL Publication Number

  • NREL/JA-5100-65849

Keywords

  • greenhouse gas (GHG)
  • lactate
  • methane
  • microbial biocatalysis

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