The rules of biology are different from the inorganic world in that the emergent properties(such as cells, multicellular properties, ect.) are based on natural selection, not just physical parameters. Multicellularity is an emergent property that changes a lot, such as making life more affected by gravity and allowing cell specialization. Just like defining life is hard to define due to viruses, defining multicellularity is also somewhat hard as the difference between a colony of single-celled organisms and multicellular organisms is not clear. Cell-cell communication, adhesion(the cells sticking together), and coordinated activity are considered the defining factors in multicellularity. Even though bacteria aren’t traditionally considered multicellular, the multicellular bacteria(or colonies of single cells depending on who you ask) are a good model for understanding multicellularity. Multicellular bacteria are simple and growing them in a lab can help understand the forces that lead to multicellularity and how multicellularity evolves.One form of multicellularity in bacteria is filamentous bacteria where they the cells all connect and sometimes share a cytoplasm or periplasm, they are usually clonal(all cells are the same), and they can sometimes be branched or linear. Filamentous bacteria are estimated to be the first multicellular organisms to evolve. Another type of multicellularity in bacteria is aggregates which usually have a biofilm around the cells and have cell differentiation(specialization). A third type is multicellular magnetotactic prokaryotes which appear to be completely coordinated in motion with the flagellar, and the cells do not appear to ever exist alone. Instead, they reproduce by the entire structure splitting in two. They appear to be connected similar to the connection in animal epithelial tissue and will die if separated from the rest of the cells.Advantages of multicellularity include resistance to physical, chemical, and biological conditions, improved ability to collect nutrients, and the possibility of cell specialization. The coordinated releasing of the extracellular matrix is important for resisting stress. When bacteria hunt, they can come together to form a “net” to catch prey. Bacteria that get eaten by other organisms benefit from multicellularity in that it is harder to engulf multicellular organisms and this effect can also be observed in algae suggesting that resisting prey may be an original function of multicellularity. Cell specialization allows some cells to perform different functions than others when one cell can’t perform all the needed functions, such as allowing some cells to fix nitrogen while others do photosynthesis in Cyanobacteria, and the dead cells can provide nutrients to the live cells.Most of the evidence suggests that multicellularity evolved independently in different types of bacteria in convergent evolution(when the same feature evolves twice independently). Extracellular matrixes are composed of many different chemical makeups across different species. Some evidence for this is that kin discrimination(the process in mostly limiting interactions to genetically similar organisms) is done differently in different multicellular species. There is however evidence that some genes that are in most bacteria increase the potential of multicellularity. They have gotten certain single-celled organisms such as yeast to become multicellular in labs by giving conditions favorable to that, and they have become fairly advanced.
