All life is classified into three overarching domains: archaea, bacteria, and eukarya. We are all familiar with eukarya, seeing that humans fall under this domain, and bacteria, but archaea are often forgotten. They are defined as single-celled prokaryotes, meaning they exist as a cell without a defined nucleus. Archaea inhabit extreme environments, such as hydrothermal vents or salt lakes, and highly acidic or alkaline conditions. This is the main reason there is not as much information on archaea as there is on bacteria and eukarya. It is difficult to isolate these species from such environments and recreate the conditions in a lab setting.
But new findings in cell biology have put the single-cellularity of archaea into question. Normally, when under excessive pressure, cells will halt all cell division as a protective mechanism to ensure all cells have adequate volume and are without genetic defects. Recently, a species of archaea found in hypersaline environments, H. volcanni, was found to undergo a process closely resembling cellularization instead of regular cell division when under pressure. Cell division is the more common and orderly process, usually mitosis and cytokinesis, where a single cell replicates its DNA once and increases in size until it splits into two daughter cells. Cellularization, on the other hand, is when a single cell replicates its DNA until it has multiple nuclei, then splits into many smaller cells. Archaea do not have nuclei, but the process they underwent in the experiment strongly resembled that of eukaryotic cellularization.
In animals, cellularization is rare, primarily found in the early development of fruit fly embryos. In this case, the process forms tissues, which are the basis of multicellular organisms, defined as a group of cells that work together for a common function. The multicellular archaea can’t quite be defined as tissue, since they don’t have the connection and interaction that tissue does, but it is definitely an interesting new find. This also serves as evidence for the theory that multicellularity evolved before the teamwork seen in multicellular organisms.
H. volcanii also has certain traits that make this process favorable. They naturally contain multiple copies of their DNA spread throughout the cell, and their cell division is influenced by the pressure of their surroundings, which they recognize through their membrane tension. The cellularization also produces two types of cells, peripheral and central scutoid cells, each with distinct structural protein patterns. Further implications of this are unknown, but it will be exciting to watch this newfound trait of archaea unfold.
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