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Appl Environ Microbiol. 2017 May 17;83(11). pii: e00289-17. doi: 10.1128/AEM.00289-17. Print 2017 Jun 1.

Evolution of a Biomass-Fermenting Bacterium To Resist Lignin Phenolics.

Cerisy T1,2,3,4, Souterre T1,2,3,4, Torres-Romero I1,2,3,4, Boutard M1,2, Dubois I1,2, Patrouix J1,2, Labadie K1,2, Berrabah W1,2, Salanoubat M1,2,3,4, Doring V1,2,3,4, Tolonen AC5,2,3,4.

Author information

1
CEA, Genoscope, Évry, France.
2
CNRS-UMR8030, Évry, France.
3
Université Paris-Saclay, Évry, France.
4
Université d'Évry, Évry, France.
5
CEA, Genoscope, Évry, France atolonen@genoscope.cns.fr.

Abstract

Increasing the resistance of plant-fermenting bacteria to lignocellulosic inhibitors is useful to understand microbial adaptation and to develop candidate strains for consolidated bioprocessing. Here, we study and improve inhibitor resistance in Clostridium phytofermentans (also called Lachnoclostridium phytofermentans), a model anaerobe that ferments lignocellulosic biomass. We survey the resistance of this bacterium to a panel of biomass inhibitors and then evolve strains that grow in increasing concentrations of the lignin phenolic, ferulic acid, by automated, long-term growth selection in an anaerobic GM3 automat. Ultimately, strains resist multiple inhibitors and grow robustly at the solubility limit of ferulate while retaining the ability to ferment cellulose. We analyze genome-wide transcription patterns during ferulate stress and genomic variants that arose along the ferulate growth selection, revealing how cells adapt to inhibitors through changes in gene dosage and regulation, membrane fatty acid structure, and the surface layer. Collectively, this study demonstrates an automated framework for in vivo directed evolution of anaerobes and gives insight into the genetic mechanisms by which bacteria survive exposure to chemical inhibitors.IMPORTANCE Fermentation of plant biomass is a key part of carbon cycling in diverse ecosystems. Further, industrial biomass fermentation may provide a renewable alternative to fossil fuels. Plants are primarily composed of lignocellulose, a matrix of polysaccharides and polyphenolic lignin. Thus, when microorganisms degrade lignocellulose to access sugars, they also release phenolic and acidic inhibitors. Here, we study how the plant-fermenting bacterium Clostridium phytofermentans resists plant inhibitors using the lignin phenolic, ferulic acid. We examine how the cell responds to abrupt ferulate stress by measuring changes in gene expression. We evolve increasingly resistant strains by automated, long-term cultivation at progressively higher ferulate concentrations and sequence their genomes to identify mutations associated with acquired ferulate resistance. Our study develops an inhibitor-resistant bacterium that ferments cellulose and provides insights into genomic evolution to resist chemical inhibitors.

KEYWORDS:

clostridia; evolution; genomics

PMID:
28363966
PMCID:
PMC5440714
DOI:
10.1128/AEM.00289-17
[Indexed for MEDLINE]
Free PMC Article

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