#FEMSmicroBlog: Archaeal buddies - membrane vesicles in the third domain of life

30-06-2021

Many living cells produce membrane vesicles or membrane nanotubes and use these vehicles to transport cell content. While membrane vehicles filled with nucleic acids are involved in genetic transfer, some microorganisms use them for cellular communication or biofilm formation. In Archaea, membrane vesicles mediate detoxification and biomineralisation while they can also transport DNA and thus influence genome evolution of the recipient cell, as recently outlined in the short review “Extracellular membrane vesicles and nanotubes in Archaea” in microLife. Corresponding author Patrick Forterre highlights for the #FEMSmicroBlog what is currently known about archaeal membrane vesicles and nanotubes and which questions remain to be answered. #FascinatingMicrobes

 

Many enveloped cells produce membrane vesicles

All living cells are separated from the outside world by a membrane and sometimes additional cell walls. Some cells can produce extensions called pseudopodes or microfilaments to move on surfaces. For example, white immune cells use this movement to hunt microbes.

Many cells from all corners of life can also excrete cellular content with so-called membrane vesicles. These are surrounded by lipid membranes, much like minicells, and carry material originating from the cytoplasm. Delivered material can include proteins, metabolites or nucleic acids; either DNA, RNA or both.

To deliver its content into the cytoplasm of a recipient cell, a membrane vesicle fuses with the membrane of another cell. Vesicle-mediated delivery is thus a powerful mechanism to exchange proteins but also genetic material.

Many living cells use membrane vesicles to exchange proteins or genetic material with each other.

In microorganisms, membrane vesicles and nanotubes play important roles in pathogenesis, for example in cell-to-cell communication, biofilm formation or horizontal gene transfer. Bacteria can also use membrane vesicles to protect themselves against viral infections, since viral particles can confuse membrane vesicles with bacterial cells.

 

Archaea might protect themselves with membrane vesicles

During the last 15 years, membrane vesicles and nanotubes have been observed and studied in Archaea, the third domain of life besides Bacteria and Eukarya. The short review “Extracellular membrane vesicles and nanotubes in Archaea” published in microLife outlines the current knowledge on archaeal membrane vesicles and nanotubes and their biological functions.

Many Archaea living in high-temperature environments, terrestrial or marine hot springs, or biotopes with high salt concentration, produce membrane vesicles. In these extremophiles, membrane vesicles promote several physiological processes such as detoxification, biomineralization and transport of biological molecules, including chromosomal, viral or plasmid DNA.

The role of membrane vesicles in the transfer of genetic material could be especially important for hyperthermophiles. In organisms with optimal growth temperature above 80°C, membrane vesicles can enclose and thus protect DNA against degradation at high temperatures.

In extremophilic Archaea, membrane vesicles can enclose DNA and thus protect it from degradation at high temperatures.

Some Archaea produce nanotubes and fill them with membrane vesicles. However, their biological functions remain mysterious. For example, do these nanotubes transport the enclosed vesicles? Are the vesicles involved in the formation of the nanotube? The latter might be true since some nanotubes have extruding vesicles at their extremities.

 

Archaea produce membrane vesicles similarly to Eukarya

A recent study by the first author of this review investigated the budding process of membrane vesicles in Sulfolobus. Here, the membrane vesicle formation depends on proteins that are evolutionarily related to eukaryotic proteins of the endosomal sorting complexes required for transport (ESCRT) complex.

In Eukarya, the ESCRT complex mediates the production of membrane vesicles and the transport of intracellular vesicles – so-called endosomes. Additionally, the complex is involved in the budding of viruses, such as HIV, from infected cells.

Interestingly, some Archaea, such as Thermococcus, lack this complex. Yet, they produce abundant membrane vesicles and nanotubes. This indicates that these Archaea use a completely unknown mechanism to produce membrane vesicles.

transmission electromicroscopic image of archaeal membrane vesicles
Transmission electron microscopy image of nanotubes produced by Thermococcales from Liu et al. (2021).

It seems that the budding of membrane vesicles from the archaeal cell membrane resembles the budding process in eukaryotes. Moreover, some scientists think that Archaea are our ancestors whereas some hypothesise that we share a common ancestor. Hence, investigating membrane vesicles and nanotubes in Archaea could bring us new insights on these important biological questions.

 

About the author of this blog

Portrait of Patrick ForterrePatrick Forterre is an emeritus professor at the University Paris-Saclay and an honorary professor at the Institut Pasteur. He has set up the first laboratory working on Archaea in France in 1989 and was head of the Microbiology Department at the Institut Pasteur from 2004 to 2010. He has been working on Thermococcus vesicles with Nicolas Soler and Aurore Gorlas, who are now research assistants in Nancy and Paris-Saclay, respectively. His European Research Council Advanced Grant supported the work of Jungfeng Liu and Viriginija Krupovic on Sulfolobus vesicles in the group of Mart Krupovic at the Institut Pasteur.

About this blog section

The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.

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