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Testing the Toughness of Microbial Cell Walls
Published: April 04, 2019
Posted: April 02, 2020

Some cells stand firm against techniques to extract the biological material inside, while others dot not stand a chance.

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 is known 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 that research and development efforts detect.

Summary
Previous research showed some bacterial and fungal resistance to cell disruption, but it 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 ultrasonication (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 ultrasonication, indicating a strong resistance to some forms of cell disruption. After bead-beating and ultrasonication, 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.

Contacts
BER Program Manager
Pablo Rabinowicz
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Biological Systems Science Division (SC-23.2)
Foundational Genomics Research and Biosystems Design
pablo.rabinowicz@science.doe.gov

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

Funding
The research was supported by the Early Career Research program (award number FWP 68292) of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science. The research was performed using the Environmental Molecular Sciences Laboratory (EMSL; grid.436923.9), a DOE BER Office of Science user facility.

Publications
Starke, R., 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].

Topic Areas:

  • Research Area: Carbon Cycle, Nutrient Cycling
  • Research Area: DOE Environmental Molecular Sciences Laboratory (EMSL)
  • Research Area: Genomic Analysis and Systems Biology
  • Research Area: Microbes and Communities
  • Cross-Cutting: Early Career

Division: SC-33.2 Biological Systems Science Division, BER

 

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