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Methane: A Bioresource for Fuel and Biomolecules

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Front. Microbiol. | doi: 10.3389/fmicb.2018.02239

Combined effects of carbon and nitrogen source to optimize growth of proteobacterial methanotrophs

 Catherine Tays1, 2,  Michael T. Guarnieri3, Dominic Sauvageau2 and  Lisa Y. Stein1, 2*
  • 1Biological Sciences Faculty of Science, University of Alberta, Canada
  • 2Chemical and Materials Engineering, University of Alberta, Canada
  • 3National Renewable Energy Laboratory (DOE), United States

Methane, a potent greenhouse gas, and methanol, commonly called wood alcohol, are common by-products of modern industrial processes. They can, however, be consumed as a feedstock by bacteria known as methanotrophs, which can serve as useful vectors for biotransformation and bioproduction. Successful implementation in industrial settings relies upon efficient growth and bioconversion, and the optimization of culturing conditions for these bacteria remains an ongoing effort, complicated by the wide variety of characteristics in methanotrophic isolates. Here we demonstrate the variable growth outcomes of five methanotrophic strains – Methylocystis sp. Rockwell, Methylocystis sp. WRRC1, Methylosinus trichosporium OB3b, Methylomicrobium album BG8, and Methylomonas denitrificans FJG1 – grown on either methane or methanol, at three different concentrations, with either ammonium or nitrate provided as nitrogen source. Maximum optical density, growth rate, and biomass yield were assessed for each condition. Further metabolite and FAMEs analyses were completed for Methylocystis sp. Rockwell and M. album BG8. The results indicate differential response to these growth conditions, with a general preference for ammonium-based growth over nitrate, except for M. denitrificans FJG1. Methane was also preferred by most strains, with methanol resulting in unreliable or inhibited growth in all but M. album BG8. Metabolite analysis points to monitoring of excreted formic acid as a potential indicator of adverse growth conditions, while the magnitude of FAMEs variation between conditions may point to strains with broader substrate tolerance. These findings suggest that methanotroph strains must be carefully evaluated before use in industry, both to identify optimal conditions and to ensure that strain selection is appropriate for the process of interest. This work is a step towards optimizing growth strategies for these promising microorganisms for their efficient and successful bioconversion of single-carbon substrates into value-added products.

Keywords: methanotrophic bacteria, Methane, Methanol, ammonium, nitrate, FAME, Growth optimization

Received: 25 Apr 2018; Accepted: 03 Sep 2018.

Edited by:

Obulisamy Parthiba Karthikeyan, University of Michigan, United States

Reviewed by:

Mariusz Cycoń, Medical University of Silesia, Poland
MUHAMMAD FARHAN UL HAQUE, University of East Anglia, United Kingdom  

Copyright: © 2018 Tays, Guarnieri, Sauvageau and Stein. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Lisa Y. Stein, University of Alberta, Biological Sciences Faculty of Science, CW 405 Bio Sci Centre, Edmonton, T6G 2E9, Canada, lisa.stein@ualberta.ca