Vesicles of Mass Destruction

By: Amani El Khatib, Emma Lynch, and Khesveny Nyanaguru

Imagine a galaxy far far away, a planet called ‘Anti-Earth.’ On this planet lives an unusual species called the ‘Anti-living beings.’ They are an intelligent species but are known to have a sinister twist about them. The anti-living species have a peculiar look as each individual has an additional layer of protection covering their skin called the ‘outer-membrus’ which protects them from potential invaders. The outer-membrus has a lot of crucial functions such as sending and receiving signals from the community, other anti-living beings, and the environment. The outer-membrus is also crucial in the colonization and destruction of a newly found organism on a newly identified planet. On Anti-Earth the anti-living being scientists discover the Milky Way and within this new galaxy, planet Earth. With this new discovery they reveal the potential to harness energy by eating specific organisms that live on the planet. The “Anti-NASA” of Anti-Earth is an agency that manufactures an artifact to breakthrough Earth’s atmosphere in order to occupy the planet. However, Anti-NASA scientists and Anti-intelligence agencies think that this is not enough. They quickly get to work on the fabrication of chemical weapon cargos that will be able to hydrolyze the human species to make a delicious concoction of “human juice.”

Just as the anti-humans of Anti-Earth are able to use their additional protective layer, Myxococcus xanthus, a gram negative common soil bacterium, has an outer membrane just like the anti-human’s outer-membrus. M. xanthus displays a complex social behavior by being a micro-predatory bacterium while also being able to distinguish itself from other bacteria. With this behavior M. xanthus is able to hunt other bacteria as a community just as a wolf pack may hunt down their prey. This communal predatory behavior is made possible by a biofilm. The beneficial biofilm adheres the bacterium together as well as to a surface to support vegetative swarming motility.

Wolf Pack and Myxococcus xanthus Biofilm Devouring a Colony of Escherichia coli

Because M. xanthus targets many different types of prey, it has a very large genome. This enables it to produce a variety of secondary metabolites which facilitate a wide range of activities for the bacterium such as the production of antifungals, antibiotics, and anti-tumor. As the anti-humans prepare their attack on Earth they need to create a weapon carrying cargo. This is a model of the outer membrane vesicles (OMV) which also serve as vehicles to carry weapons such as hydrolytic enzymes, antibiotics, antifungals and anti-tumors. The environmental conditions, such as the change of nutrients around the bacterium, can also cause modifications of OMV activity. Because of the differentiation of functions the OMV has many different types of proteins. Specific proteins are used to target a specific prey.

Figure 1. OMV structures observed in situ and after purification. (A) Flow chart of experimental procedure with representative analytics (B–E). (B) Negative staining EM of an M. xanthus wild type DZ2 cell showing a mixture of extracellular structures associated with the cell including isolated vesicles and vesicle chains (Scale bar = 200 nm). After purification, these structures maintain their distinctive shape as (C) vesicles and (D) vesicle chains (Scale bars = 40 nm). (E) SDS-PAGE analysis showing consistency of protein profiles in OMV fractions used for protein MS: lane 1 standards, lane 2–4 OMV fractions from 3 independent cultures.

When the individuals from Anti-Earth sense danger, like starvation or realize that a battle cannot be won, they assemble a fruiting body to form a spore. Sporulation is their last chance to pass along their genes to prevent the destruction of their entire species. A thick layer over the dormant spore protects the genetic material needed to generate future populations.

A colony of Myxococcus xanthus forms fruiting bodies. Credit: Trance Gemini/Wikimedia

In the article, The Lethal Cargo of Myxococcus xanthus Outer Membrane Vesicles by Berleman et al., M. xanthus is introduced as a predatory bacterium containing special compartments called OMVs. OMVs facilitate M. xanthus in its attack of other bacterium. In order to identify the composition of the OMVs, secondary metabolites, proteins, and isolates, purified outer membrane (OM) and OMV fractions were analyzed by mass spectrometry. Berleman et al.’s study suggests that there is a protein cargo that is unique to the OMVs (Figure 2).

Figure 2. Cell fraction comparison and predicted function. (A) Conservative set of 548 (46 OMV only, 188 shared, 314 OM only) protein IDs from MS analysis of >10,000 peptides. Putative function binning of (B) 46 OMV-specific and (C) 188 OMV-enriched proteins.

Analysis of the vesicle proteins showed the abundance of chaperones as the OMV fractions suggested. This could deduce the possibility that OMV proteins may require proper protein folding after export into OMV structure. One of the main chaperones has been shown to be essential for fruiting body development and sporulation. Other chaperones play a significant role in antibiotic production and predation. The most abundant protein in the OMV is MepA metalloprotease which caught the interest of Berleman et al. Bacteria predation requires both extracellular lysis of prey as well as the acquisition of nutrients that are released. MepA protein was found to be likely involved in acquiring these nutrients from released extracellular proteins, but not in prey cell lysis. A diversity of secondary metabolites were also detected in OMVs, many of which are thought to have antibiotic properties. These may assist in killing prey bacteria and inhibiting the growth of competing microbes. The detection of several molecules with antibiotic properties lead to the idea that targeted delivery of antibiotics through OMVs mediates prey cell lysis on contact. Such a mechanism would be beneficial in order for expensive secondary metabolites not to be lost through diffusion. Furthermore, the packaging of several antibiotics and hydrolytic enzymes in a nano-scale package may provide a lethal cocktail that prevents the selection for single mutation resistance in the bacterial species that M. xanthus feeds on. If this holds true, then OMVs may be a powerful tool in the fight against multidrug resistant pathogenic bacteria. Perhaps, OMVs can be engineered to form a new generation of antibiotics—where susceptible cells are overwhelmed by a targeted cargo of multiple antibacterial molecules and hydrolytic enzymes. Further studies of the protein and small molecule contents in OMVs should improve our understanding of these organelles and their capacity to act as vehicles for intracellular delivery.

About the Authors:


Amani El Khatib '20
Amani is a Biology Major and French Minor. In her free time, she loves to ride horses.


Emma Lynch '18
Emma is a Biology Major with a Five College Coastal and Marine Science Certificate, and an Art Studio Minor. They love traveling, exploring, photography, food, jazz, and enjoying life with their wonderful fiancée.


Khesveny Nyanaguru '19
Khesveny is a Neuroscience Major and on the Pre-Veterinary track. She is from Malaysia and is obsessed with animals (as you can see in the picture above). This is her dog, Harry, who she is constantly hugging when she's home.