Testing the Toughness of Microbial Cell Walls

September 10, 2019

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Cells of the Gram-positive bacteria (a) and fungal enrichment culture (b) after cell disruption with an ultra-sonication bath for 10 minutes. With identical treatment, no intact cells were found in the Gram-negative bacterial enrichment culture (c).
Cells of the Gram-positive bacteria (a) and fungal enrichment culture (b) after cell disruption with an ultra-sonication bath for 10 minutes. With identical treatment, no intact cells were found in the Gram-negative bacterial enrichment culture (c).
(2019) 9:5618 | https://doi.org/10.1038/s41598-019-42188-9 CC License

The Science

Microbial cells contain biological material that can be important for research or industrial use, such as DNA or proteins. Yet, reaching this cellular material can be a challenge. Different methods to disrupt cells have a wide range of effects on microbial communities and their environments. Researchers compared different cell disruption techniques. They found that fungal and gram-positive bacteria cells (which have a thicker cell wall and do not have an outer membrane) resisted common cell disruption techniques. In contrast, the same techniques destroyed gram-negative bacterial cells (which have a thin cell wall and an outer membrane).

The Impact

This work measured differences between microbial populations’ resistance to cell disruption. In particular, it increases what we know about how long microbial cells persist in the soil. Microbial residues—what is left of microbes when they die—create soil organic matter. They are believed to persist in soil for decades. The susceptibility of microbes’ cell walls to breaking down as a result of natural cycles (i.e. freeze-thaw and wet-dry cycles) influences how much residues build up. How soil microbial populations differ in their resistance to cell disruption could affect long-term soil carbon storage. Differences in soil carbon storage may influence soil structure, fertility, and water holding capacity. These differences could also influence which microbes research and development efforts detect.

Summary

Previous research showed some bacterial and fungal resistance to cell disruption, but did not quantify differences in the efficiencies and yields of cell disruption techniques. This led to uncertainty in the potential magnitude of differences in cell disruption among soil microbial communities. Scientists compared how different types of microbes responded to common cell disruption methods. Researchers studied the effects of bead-beating (shaking the sample in a combined solution with glass beads) and ultra-sonication (applying high-frequency sound energy to the sample) to demonstrate differential resistance of cell disruption. Fungal and gram-positive bacterial cells remained almost intact after ultra-sonication, indicating a strong resistance to some forms of cell disruption. After bead-beating and ultra-sonication, fungi produced lower DNA yields than expected, supporting the idea of fungal resistance to cell disruption. The team did not find any intact cells in the gram-negative bacterial enrichment culture. Implications of these findings could include increased extraction of biomolecules from microbes with less rigid cell walls and underrepresentation of resistant microbes—particularly fungi—in ecological studies.  Next, researchers aim to understand how differences in resistance to cell disruption may influence the turnover of microbial populations in soil and their contribution to the generation and persistence of soil organic matter.

Contact

Contacts (BER PM)

Pablo Rabinowicz
Pablo.Rabinowicz@science.doe.gov
(301) 903-0379

(PI Contact)

Kirsten Hofmockel
Environmental Molecular Sciences Laboratory/Iowa State University
kirsten.hofmockel@pnnl.gov

Funding

The research was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research program under Early Career Research program award number FWP 68292. The research was performed using EMSL (grid.436923.9), a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research

Publications

R. Starke, N. Jehmlich, T. Alfaro, A. Dohnalkova, P. Capek, S.L. Bell, and K.S. Hofmockel, "Incomplete cell disruption of resistant microbes.Scientific Reports 9, 5618 (2019). [DOI: 10.1038/s41598-019-42188-9].