Thinking Microbes
Cognition is a term frequently used in several loosely related ways to refer to a faculty for the human-like processing of information. Signal transduction networks certainly fit that bill, as the mediate adaptive changes in gene expression to specific sensory inputs. Melinda Baker and Jeffry Stock, in the recent issue of Current Biology, elaborate on modalities of such cognition in bacteria: Networks and integrated circuits in bacterial cognition.
Of course, they’re not quite circuits in the electrical engineering sense either. Think chemical networking, where each biomolecule in a signaling network can interact with a variety of other molecules, with varying interaction kinetics, and where each interaction has the potential to impact additional outcomes. Coupled with the selection of functions in the micro-environmental milieu, cellular networks ended up organized in efficient ways to control motility, metabolism, growth, and eventually higher processes.
But just suppose for a moment that a cell, even a bacterium, didn’t merely process inputs from the micro-environment. Some people suggest that the information processing, regulatory feedback loops, and adaptive response to stimuli, constitute something else:
Bacteria–and by extension unicellular eukarotes–have long been considered too simple, too reactive and too determined to be a member of the cognitive gang. However, Pamela Lyon argues that this exclusion is unwarranted. She suggests that bacteria are sensitive, communicative and decisive organisms and bacterial responses are more flexible, complex and adaptable than generally believed. In terms of re-defining cognition, Lyon argues that behaviour at the microbial level is precisely what must be understood in order to comprehend how more complex and specialized forms evolved and now function. Lyon claims that cognition is part of basic biological function, like respiration.
Jeff Stock’s work at Princeton on principles of molecular logic that underlie signal transduction and information processing in biological systems sound similar to Pamela Lyon’s. He’s done pioneering work on the control of motor behavior in bacteria via what he calls the “nanobrain”: a bundle of several thousand receptor proteins located at one pole of each bacterium.
Cells don’t actually have brains, however - Many think that these terms carry too much teleological baggage, including myself. But for the person trying to comprehend the microbe’s world, describing information processing as something akin to consciousness has its value.
- Baker MD, Stock JB. Signal Transduction: Networks and Integrated Circuits in Bacterial Cognition. Curr Biol., 2007 Dec 4;17(23):R1021-4. DOI:10.1016/j.cub.2007.10.011
About the Author
Dan Rhoads
Dan is an American working in industry in a small Mediterranean country. He has a BSc in Molecular Biology and a PhD in Cancer Pharmacology and Biochemistry.
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