Magical little particles: extracellular vesicles
Where there are people, there are rivers and lakes. This also applies to microorganisms . Individual microorganisms cannot make waves, but when they work together, the team's ability to fight is impressive. Microorganisms form groups through complex interactions and perform functions collaboratively. How do microbial cells "talk" to each other in a real environment? What language do they have? In addition to the chemical communication role of star molecules - quorum sensing molecules, extracellular vesicles (EVs) have gradually become the dark horse among the many "diplomatic messengers" of cells, and have become the forefront of environmental microbiology research. EVs are nano-sized membrane vesicles secreted extracellularly by organisms. The phospholipid bilayer membrane structure gives EVs the talent to perform express delivery functions. It can carry, protect and deliver goods stably, specifically and efficiently like express packages in daily life. These cargoes include proteins, lipids , nucleic acids, etc. These "ghost" vesicles were first discovered in the prokaryotes , and later, their traces were also found in eukaryotes. Spanning the three realms of animals, plants, and microorganisms, this "ghost" is really crazy.
Figure 1 Extracellular vesicles derived from Gram-negative and Gram-positive bacteria. OMVs: outer-membrane vesicles; OIMVs: outer-inner membrane vesicles; EOMVs: explosive outer-membrane vesicles; CMV: cytoplasmic membrane vesicles. (Literature: Toyofuku et al. Nature Reviews Microbiology, 2019)
Extracellular vesicles are all around us
However, what is the status of these "messenger" EVs in real environmental media? In response to this challenging scientific issue, Institute of Urban Environment of the Chinese Academy of Sciences Academician Zhu Yongguan’s team and Huang Qiansheng’s research group conducted in-depth research. They published papers in Environmental Science Technology and the Journal of the International Association of Extracellular Vesicles (Journal of Extracellular Vesicles) , uncovering the tip of the iceberg of environmental extracellular vesicles. The
team first established a platform for the isolation, identification, and characterization of EVs in environmental samples by comprehensively using tangential flow filtration technology, density gradient centrifugation, transmission electron microscopy, and nanoflow cytometry. On this independent innovation platform, they then used typical microbial habitats, including human feces, wastewater, urban soil and indoor dust, to systematically reveal the widespread presence of EVs in the environment. These EVs have a typical membrane vesicle structure with an average particle size of approximately 70 nm, which is only one thousandth the diameter of a human hair. The number of EVs is huge, and the number of EVs per gram of indoor dust is even as high as 1011 particles, which is an order of magnitude more than the total population of the world. The abundance of EVs is significantly correlated with the abundance of bacteria and in their source samples.
Figure 2 Extracellular vesicles in environmental media
The team then based on the existing environmental resistance gene database data and combined with metagenomic sequencing technology to track the "shipper" of EVs in environmental samples, and found that EVs mainly come from bacteria, and some come from eukaryotes and archaea. Although the relative abundance of and in the sample is low, some microorganisms can produce EVs much higher than their own relative abundance, and thus may play a significant role. The relatively high abundance of Pseudomonas EVs in indoor dust is of particular concern.
Figure 3. Extracellular vesicles of microbial origin are widely found in water, soil, dust, and human feces media.
A preliminary study of the extracellular vesicle treasure box
Environmental sample EVs packages carry DNA from various microorganisms. Through data comparison, the team found that the glycoside hydrolase family GH25 gene was significantly enriched in EVs. Research has found that this family can move between microbial groups and serve as a "public resource", giving more microorganisms the ability to utilize sugar sources. The DNA cargo also includes functional genes such as bacterial resistance genes (ARGs) located on mobile genetic elements (MGEs), which may be a way of spreading environmental resistance genes, which has been rarely recognized in the past.
Figure 4 Extracellular vesicles in indoor dust carry drug resistance genes
Read the "language" of microorganisms' extracellular vesicles to protect population health
The above research allows us to realize the strong coverage of "diplomatic messengers" EVs in the real environment and the multiple functional genes "diplomatic materials" they package. However, this is only a small part of the cargo packaged by EVs. More cargoes and their functions in microbial groups deserve in-depth exploration to better reveal the complex interaction network between microorganisms, microorganisms, the environment, and the host, thereby providing theoretical understanding and technical development support for the development of pathogen prevention and control strategies.
Figure 5 Conceptual diagram of extracellular vesicles mediating the interaction between environmental microorganisms and the human body
The research was funded by the National Natural Science Foundation of China, the National Public Science Data Center for Basic Disciplines, Chinese Academy of Sciences Network Security and Informatization Special Application Demonstration Project, and Fujian Provincial Department of Science and Technology .
Source: Institute of Urban Environment, Chinese Academy of Sciences
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