Academic journal article Proceedings of the American Philosophical Society

Cell to Cell Communication1

Academic journal article Proceedings of the American Philosophical Society

Cell to Cell Communication1

Article excerpt

I'M ABSOLUTELY DELIGHTED to be here and to tell you about how bacteria talk to each other. I appreciate being invited and I'm glad to get my turn to contribute to today's different topics. I have only one goal in today's seminar, and that is to try to convince you that bacteria can indeed talk to each other. If I can convince you of that, my secondary goal is to try to show you that bacteria are multhingual.

We've known about bacteria for almost 400 years. I think that you probably all know that bacteria are considered the most primitive organisms on earth. They are single cells, and the way that they grow is that they consume nutrients from the environment. They double their size, they cut themselves in half, and they make two from one. For 390 of the 400 years that we've known about bacteria they've always been considered to live asocial, reclusive lives. They divide in half and each sibling goes out and does its own thing and doesn't "know" anything about his brother or sister.

Of course you have read about bacteria in the newspaper, but sadly that's a rather one-sided view. In the news, bacteria get a bad rap for doing a variety of terrible things that make us sick. But what they do not get nearly as much press for is all of the miraculous activities they carry out that keep us alive and healthy. Furthermore, even though they are invisible, they make up about half of the earth's biomass, they occupy extremely diverse niches, and they are the most effective and diverse organisms on the planet. Whether you are thinking about all the harmful things bacteria do or all the beneficial things bacteria do, the question is, how can bacteria manage to do anything at all? They are itty bitty little critters living in an enormous world. If it is true that they act as asocial individuals, how can bacteria accomplish all of the tasks that we know they do?

What we've learned is that bacteria do not live as recluses. Rather, they have evolved language, and the language is made of chemicals. As bacteria grow and divide, they release into their surroundings small molecules that you can think of as you would hormones. As the bacterial population is increasing in number, since all the members are participating in releasing these hormones into the extracellular environment, the more cells there are, the more of the hormone molecules there are. When the hormone molecules accumulate to a particular level, the bacteria detect that the molecules are there with receptors that are located on their cell surfaces. All the bacteria respond in unison to the build-up of these molecules. They simultaneously alter their gene expression, which results in synchronous alterations in behavior.

What the bacteria are doing with this chemical language is counting one another, recognizing when they have a proper number of neighbors present, so that if they all act together, they will be able to accomplish tasks they could never accomplish if they simply acted as individuals.

Using this chemical mechanism, bacteria are acting as a collective; in essence, the actions of these groups of cells are similar to the way groups of cells act together in multicellular organisms. Because bacteria have been here for billions of years, we now know that the ability to carry out collective behaviors is ancient. Thus, bacteria invented multicellularity long ago. Furthermore, the principles bacteria evolved to robustly organize group traits are conserved in the multicellular processes occurring in the human body.

I thought I would give you a historical view of how we came to this idea of bacteria that talk with chemical languages and carry out tasks as groups. The field began with two beautiful but obscure bacteria called Vibrio harveyi and Vibrio fischeri. These harmless marine bacteria have the unique property that they produce bioluminescence. So they make light, in much the same way that fireflies make light.

Woody Hastings from Harvard initially focused on V. …

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