U.S. Department of Energy

Pacific Northwest National Laboratory

Testing the Toughness of Microbial Cell Walls

Figure 1.TEM images of representative cells of the Gram-positive bacteria (a) and the fungal enrichment culture (b) derived from KBS switchgrass soil 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).

The Science                      

A microbial cell contains important biological material for research or industrial use, such as DNA or proteins. Yet, reaching this cellular material can be a challenge. Different methods of natural or mechanical lysis, cell disruption, can have wide-ranging effects on microbial communities and their environments. To better understand the extent of lysis resistance of various microbial cell walls, different cell disruption techniques were compared. Researchers found that cells from fungal and gram-positive bacterial enrichment cultures resisted common cell disruption techniques, while cells were destroyed in gram-negative bacterial enrichment cultures.

The Impact

This work provided quantitative evidence for differences between microbial populations in their resistance to cell disruption. These differences could influence the types of microbes that are detected in research and development efforts. This study advances understanding of how long microbial cells persist in the soil. Microbial residues—what is left of microbes when they die—create soil organic matter and are believed to persist in soil for decades. An important aspect of microbial residue accumulation is susceptibility to natural cell disruption methods (i.e. freeze-thaw and wet-dry cycles) and subsequent breakdown of the cell wall. Differences between soil microbial populations in their resistance to cell disruption could affect long-term soil carbon storage, which would have implications for soil structure, fertility, and water holding capacity.

Summary

Previous research showed some bacterial and fungal resistance to cell disruption, but differences in the efficiencies and yields of cell disruption techniques were not quantified. This led to uncertainty in the potential magnitude of differences in cell disruption among soil microbial communities. 

Scientists from EMSL, the Environmental Molecular Sciences Laboratory, a U.S. Department of Energy Office of Science user facility, Iowa State University, the Institute of Microbiology of the CAS in the Czech Republic, and UFZ in Germany, collaborated to compare 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 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.

(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, and Office of Biological and Environmental Research program under 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. 

Publication

R. Starke, N. Jehmlich, T. Alfaro, A. Dohnalkova, P. Capek, S.L. Bell, and K.S. Hofmockel, “Incomplete cell disruption of resistant microbes.”Scientific Reports9:5618 (2019). [https://doi.org/10.1038/s41598-019-42188-9].

Date: 
May 2019
| Pacific Northwest National Laboratory