05/23/2017

Modifications to the Bacterial Cell Envelope Increase Lipid Production

A new strategy significantly increases the production and secretion of microbial lipids in bacteria that can be grown at industrial scale.

The Science

High-yield microbial production of lipids presents a significant challenge, often falling short of what can be theoretically obtained. This study characterized high-lipid (HL) mutant variants of Rhodobacter sphaeroides and showed that alterations to the bacterial cell envelope can result in increased accumulation of lipids relative to the parent strain.

The Impact

Knowledge of the mechanisms that limit microbial lipid production can reveal new strategies to increase lipid yield and the economic viability of alternatives to fuels or chemicals currently derived from petroleum.

Summary

Microbial lipids are potential replacements for petroleum-based fuels and chemicals; however, their production often falls short of theoretical yield, and improvement strategies are needed. Researchers from the Department of Energy’s (DOE) Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, and Environmental Molecular Sciences Laboratory (EMSL; a DOE Office of Science user facility) advanced their research on microbial lipid production by examining a new class of Rhodobacter sphaeroides mutants that exhibited enhanced lipid accumulation relative to the parent strain. The researchers used EMSL’s FEI Tecnai T-12 cryo-transmission electron microscope and structured illumination super resolution fluorescence microscope, in which chemical sensitivity profiles indicated HL mutants were sensitive to drugs that target the cell envelope. Changes in cell shape were also observed, suggesting that previously undescribed alterations in the bacterial cell envelope could be used to increase bacterial lipid production. Importantly, a subset of the HL mutants were able to secrete lipids, two of which accumulated approximately 60 percent of their total lipids extracellularly, potentially enabling easy product recovery from a bioreactor. When one of the highest lipid-secreting strains was grown in a fed-batch bioreactor, its lipid content was comparable to oleaginous microbes, defined as those accumulating 20 percent or more of their dry cell weight as lipid. Knowledge of the biological mechanisms that limit lipid production can inform new genetic engineering and growth strategies and enable this important class of molecules to be adopted as fuels or chemicals on a larger scale.

Principal Investigator(s)

Timothy J. Donohue
University of Wisconsin-Madison
tdonohue@bact.wisc.edu

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Funding

This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory and Great Lakes Bioenergy Research Center.

References

Lemmer, K. C., W. Zhang, S. J. Langer, A. C. Dohnalkova, D. Hu, R. A. Lemke, J. S. Piotrowski, G. Orr, D. R. Noguera, and T. J. Donohue. 2017. “Mutations That Alter the Bacterial Cell Envelope Increase Lipid Production,” mBio 8(3), e00513-17. DOI: 10.1128/mbio.00513-17.