First multicellularity: claimed in a new bacteria (Evolution)

by David Turell , Wednesday, October 12, 2022, 17:14 (771 days ago) @ David Turell

This new bacterium has multicellular characteristics:

https://phys.org/news/2022-10-multicellular-bacteria-species.html

"The bacterium, HS-3, was isolated from a limestone cave wall that is intermittently submerged by an underground river. HS-3 has two distinct life phases; on a solid surface it self-organizes into a layer-structured colony with the properties of a liquid crystal. After maturation, the HS-3 colony forms a semi-closed sphere housing clusters of "daughter" coccobacillus (short rod-shaped) cells, which are released upon contact with water.

"'The emergence of multicellularity is one of the greatest mysteries of life on Earth," states corresponding author Kouhei Mizuno, a professor at the National Institute of Technology (KOSEN), Tokyo, Japan. "The point is that we already know the superior function and adaptability of multicellularity, but we know almost nothing about its origins. Established function and adaptability are not necessarily their own formative driving force. A curiosity of multicellularity is the conflict between the 'benefits of individuals' versus the 'benefit of the group' that must have existed in the early stage of the evolutionary transition. We don't have a good existing model to study multicellularity except theoretical models."

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"The team used microscopies to analyze the colony growth. The cells started to reproduce simply as coccobacilli, but the occurrence of cell elongation caused the colony to form a single-layered structure, orientated like a liquid crystal. Bulges form particularly at the colony edge, relieving internal pressure and granting HS-3 the unique ability to maintain this two-dimensional liquid arrangement for a prolonged period, which may be a prerequisite for HS-3 to establish multicellular behavior.

"Then, the colony then expanded to form additional layers. The internal filamentous cells buckled, generating vortex-structured domains. These domains and the liquid crystal-like arrangement explain the transparency observed in HS-3 colonies on agar. After two days, rapid cell reproduction occurred internally and the colony began to swell three-dimensionally, forming a semi-closed sphere housing the coccobacillus cells. After the fifth day, the internal cells were crowded-out of the colony, triggering a chain reaction of this event in adjacent colonies and thereby indicating some multicellular control.

"As the cave wall sampling site of HS-3 was regularly subject to flowing water in the cave, the team submerged the mature semi-sphere colonies in water. The internal coccobacilli were released into the water, leaving behind the filamentous cell architecture. By plating these daughter cells on fresh agar, they discovered that the cells were able to reproduce the original filamentous structure, showing that the two distinct phases of HS-3's life cycle are reversible, and may have arisen due to the changing conditions inside the cave.

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"'The first stage of HS-3's life cycle suggests that the liquid crystal-like organization is involved in the emergence of multicellularity, which has not been reported before. The existence of the second life stage implicates the involvement of dynamic water environment in the emergence of HS-3's multicellularity," says co-corresponding author Kazuya Morikawa, a professor in the Division of Biomedical Science, University of Tsukuba, Japan."

Comment: this is similar to other findings as in amoeba colonies. Still not an answer to the origin of multicellularity.