Biological complexity: bacterial colonies cooperation (Introduction)

by David Turell , Wednesday, November 02, 2022, 15:04 (752 days ago) @ David Turell

In recent Vibrio studies:

https://www.quantamagazine.org/ocean-bacteria-reveal-an-unexpected-multicellular-form-2...

"The growth curve for her Vibrio cultures, however, didn’t show the usual smoothly rising line but rather a bumpy squiggle like the track of a roller coaster. No matter how many times she repeated the process, the bacteria didn’t produce the expected cloudiness in the broth.

"To check what was going on, Schwartzman deposited a droplet of the culture solution on a glass microscope slide and peered through the lens at 40 times magnification. What she and Ebrahimi saw were not swarms of individual Vibrio but rather beautiful, layered orbs consisting of hundreds or thousands of bacteria living together

"Further work showed that the hollow spheres were Vibrio’s solution to the complicated challenge of eating at sea. An individual bacterium can produce only so much enzyme; breaking down alginate goes much more quickly when Vibrio can cluster together. It’s a winning strategy, Schwartzman says — up to a point. If there are too many Vibrio, the number of bacteria outstrips the available alginate.

"The bacteria resolved the conundrum by developing a more complex life cycle. The bacteria live in three distinct phases. At first, an individual cell divides repeatedly and the daughter cells huddle in growing clumps. In the second phase, the clumped cells rearrange themselves into a hollow sphere. The outermost cells glue themselves together, forming something rather like a microscopic snow globe. The cells inside become more mobile, swimming about as they consume the trapped alginate. In the third phase, the brittle outer layer ruptures, releasing the well-fed inner cells to start the cycle anew.

"In effect, Vibrio become a heterogeneous mixture of cells, with the bacteria using different genes to control their behavior in each phase. As the cells interact with their neighbors in the structure, what emerges is “a surprising amount of complexity,” said Schwartzman, who is launching her own lab at the University of Southern California in January. “The bacteria are constantly taking in information from their environment, and sometimes they respond in ways that change the environment.”

"This complexity pays off for Vibrio in several ways. By altering their life cycle to include a multicellular stage, the bacteria can digest the alginate efficiently: Their numbers increase, and the hollow shell helps to concentrate the enzymes. Meanwhile, the structure of the community prevents too many cells from being born. The cells in the shell lose the opportunity to reproduce, but their DNA lives on in the next generation anyway, since all the cells in the orb are clones.

***

"James Shapiro, a retired microbiologist from the University of Chicago, has little doubt that she’ll find it.

"Beginning in the 1980s, Shapiro and other microbiology luminaries such as Bonnie Bassler at Princeton University showed that the single-celled lifestyle of well-studied bacteria was often an artifact of the artificial flask environments in which they were grown. In a 1998 article in the Annual Review of Microbiology, Shapiro argued that bacteria aren’t unicellular loners. “I came to the conclusion that basically all bacteria are multicellular organisms,” he said.

"Over his four-decade career, Shapiro saw his hypothesis transform from nearly heretical to incontrovertible. “At first, I got just bemused attention, but now it’s become conventional wisdom,” he said. “Multicellularity is an inherent property of bacteria.'”

Comment: this work shows that bacteria contain the beginnings of multicellularity. Our old friend Shapiro is supported in his work.