Julie Starkey English

Bioreactors in Bacteria: the Bacterial Microcompartment

Breaking down the microbiology world one bite at a time

Bioreactors in Bacteria: the Bacterial Microcompartment

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Julie Starkey

“Mitochondria are the powerhouses of the cell”

If you learned anything in high school biology class, this was probably it. Our cells possess mitochondria that give us the energy we need to wake up in the morning, go to work, and live our lives. Only humans, along with plants and animals, possess these powerful organelles. Microbes, also known as prokaryotes, don’t have mitochondria. Most microbiologists will tell you that microorganisms don’t possess any organelles. However, some microbes actually do possess organelles that are, like mitochondria, critical for survival.

Many bacteria harbor specialized organelles called bacterial microcompartments (BMCs). The BMC is no mitochondrion, but it does function as a powerhouse in its own way.

A BMC is essentially a microscopic bioreactor: a unique protein shell that harbors specific chemical reactions (Figure 1). When expressed by the bacterium, the BMC proteins assemble around a cluster of chemicals and enzymes, keeping the resulting reactions contained within the shell (1). Compartmentalizing specific reactions in this way protects the cell from toxic byproducts and makes them more efficient. Not all bacteria are able to produce BMCs, but those that do often rely on the organelle to survive.

Figure 1. Generalized schematic of a bacterial microcompartment and it’s metabolic core. The microcompartment uses specific enzymes and molecules to turn available substrates into desired products. Image created with BioRender.

The first BMC discovered by researchers, known as the carboxysome, is found in photosynthetic bacteria. The carboxysome simply takes CO2 from the environment and transforms it into energy for the bacterium (1). It wasn’t long before more BMCs were identified, often with different functions. Some BMCs metabolize certain alcohols or sugars that are shuttled into pathways to make energy for the cells (2). Biologists have discovered that some bacteria use BMCs to thrive in harsh environments, and pathogens that possess these bioreactors are better able to attack their host and cause infections (1, 2). Many other BMCs have been identified using computational biology methods, but their functionality still remains a mystery (1, 2).

Why should anyone care about BMCs?

We can likely find BMCs in our own gut bacteria. Some of our normal microflora utilize specific BMCs to take nutrients commonly found in our gut and convert them into energy (1, 2). Intestinal pathogens in particular seem to depend on these BMCs for enhanced virulence and survival (2, 3). For instance, Salmonella enterica puts its BMC to work in order to better colonize our gut, cause inflammation, and replicate (3, Figure 2). While pathogens carry an arsenal of weapons to infect their host, BMCs give S. enterica and other pathogens the edge needed to survive otherwise lethal conditions.

Figure 2. Bacterial microcompartment function of (a) and coordinated invasion by (b) Salmonella enterica. Source: Jakobson et al. 2016.

There is still much to discover about the BMC and its roles in all types of bacterial lifestyles, and the inherent structure and function of BMCs give them great potential as valuable tools in biotechnology. Researchers learned to manipulate the structure of the BMC as well as change out the encapsulated enzymes and molecules (1, 4). This “plug-and-play” approach allows scientists to re-design BMCs for a number of purposes, from efficient biofuel production to cargo carriers for human health applications (1, 4).

The BMC may not be as advanced and sophisticated as the mitochondrion, but they still hold great power for both bacteria and humans.

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  1. Kerfeld, C., Aussignargues, C., Zarzycki, J. et al. Bacterial microcompartments. Nat Rev Microbiol 16, 277–290 (2018). https://doi.org/10.1038/nrmicro.2018.10
  2. Stewart, K. L., Stewart, A. M., Bobik, T. A. Prokaryotic organelles: Bacterial Microcompartments in E. coli and Salmonella. ASM EcoSal Plus 9(1) (2021). https://doi.org/10.1128/ecosalplus.ESP-0025-2019
  3. Jakobson CM, Tullman-Ercek D. Dumpster Diving in the Gut: Bacterial Microcompartments as Part of a Host-Associated Lifestyle. PLoS Pathog 12(5), e1005558 (2016). https://doi.org/10.1371/journal.ppat.1005558
  4. Frank, S., Lawrence, A. D., Prentice, M. B., Warren, M. J. Bacterial microcompartments moving into a synthetic biological world. Journ Biotech 163(2), 273-279 (2013). https://doi.org/10.1016/j.jbiotec.2012.09.002

Featured image: Created with BioRender