Bacteria Use Simple Rules to Make Smarter Moves

close microscopic image of bacteria against white background

Biological Strategy

Bacteria

Mary Hoff

Image: Choksawatdikorn / Shutterstock / Some rights reserved

Navigate Through Liquid

Living systems that move in liquids must navigate around physical obstacles and find their way from place to place to locate resources or suitable climates. Many liquids are denser than air, which means it’s a thicker medium through which signals must pass. On the other hand, liquids tend to conduct some signals better than air or solids. Liquid dwellers must use strategies that enable them to detect and follow signals in this dense medium. For example, electricity transmits well in water and several organisms, such as Amazon electric eels, have organs that detect and use electric signals to navigate.

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Navigate Through Solids

Some living systems must find their way through solids, such as earthworms moving through soil or tapeworms moving through an animal body. Signals don’t transmit well through solids as through water or air, so navigation is likely based on information from short distances, such as signals detected through touch. For example, earthworms and moles are believed to follow tactile cues such as moisture, coolness, and vibrations to navigate within soil.

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Transduce/Convert Signals

Sometimes a signal, such as sound or vibration, reaches a living system and needs to be converted into a different, usable form. This requires converting from one type of energy form to another. For example, organisms with eyes have photoreceptors at the back of the eyes that convert light into electrical pulses. These pulses travel to the brain and allows it to register color, shape, and detail.

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Respond to Signals

To interact with its environment, a living system must not only sense a variety of signals, but also respond to them. To be energy- and material-efficient, those responses must be appropriate to the signal. This generally requires sensing thresholds to trigger an appropriate level of response (for example, hiding under a shrub versus running away to avoid a predator). Response strategies are tied to a specific signal and often have a response threshold, which determines how strong a signal must be to warrant expending energy to respond. One example is a plant that lives in arid regions in South Africa. Its seed capsules remain closed until rainfall triggers them to open to release the seeds. But the plant only responds to a second rainfall, thus protecting against releasing its seeds before there is enough sustained water for them to grow.

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Bacteria

Domain Bacteria (“small staff”): L. acidophilus, Staphylococcus

From inside of our own bodies to the deepest parts of the ocean, bacteria have adapted to almost every possible environment. All bacteria are unicellular, microscopic, and lack a membrane-bound nucleus and organelles, and come in three basic shapes: spherical (cocci), rod (bacilli), and spiral (spirilla). Some strains can be deadly, like Staphylococcus aureus (MRSA) while others, like Lactobacillus acidophilus, found in our intestinal microbiome, keep us healthy. Cyanobacteria, also known as blue green algae, caused the Great Oxidation Event 2.4 billion years ago, producing Earth’s first oxygenated atmosphere.

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Bacteria create swarms by making choices based on both their own and other bacteria’s choices

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Introduction

Have you ever stared at your GPS, wondering what is the most efficient path from where you are to where you’re going? Swarms of bacteria figure it out all the time without even a glance at a smartphone or other navigational aid. Their secret? An elaborate form of guess-and-check informed by feedback from neighbors that are making smart or not-so-smart choices themselves—combined with unusual adaptability in whether they follow the crowd or their own instincts.

The Strategy

Many birds, fish, and other animals travel in flocks or swarms, in which large groups of individuals gather information from each other and the environment allowing them to travel as a unified group rather than as individuals headed every which way. Often this works in their favor, leading them to food, providing protection from predators, or allowing them to minimize the energy expended in moving from one place to another. But if an individual misinterprets signals from the environment as to which direction is more favorable, it not only leads itself away from the optimal path, it can take others with it as well.

This first simulation illustrates how bacteria navigate to desirable conditions when they take into account only their own senses and the environment.

This simulation illustrates how bacteria navigate to desirable conditions when they take into account not only their own senses and the environment, but also the positions of other bacteria.

When more sophisticated organisms such as birds and fish move in groups, they use their brains to process large amounts of information related to the position of those around them and integrate that into the decision about how to move. Bacteria seem to be able to get around the problem of misinterpreting signals by following simpler rules than more complex organisms do regarding how to alter their direction based on signals from the environment and each other. Rather than always interpreting those signals similarly, they alter their responses based on whether the concentration of a chemical that attracts them is increasing in the direction they are currently moving. If it isn’t, they pay attention to the direction of the movement of other bacteria around them. But if it is indeed toward a more favorable setting, they pay less attention to their neighbors and follow their own instincts instead. Computer modeling has shown that this ability to alter “rules of movement” depending on the circumstances ultimately leads to a more beneficial outcome for the entire group of organisms—with a less complex algorithm to follow.

The strategies bacteria use could be applied to improving project management, workflows, and other activities that involve multiple steps and benefit from course correcting using information gathered along the way.

The Potential

The ability to use simple rules to efficiently find favorable conditions has boundless applications. It already is being used to help give robots protocols for movement that allow them to take into consideration environmental conditions as well as preprogrammed instructions for achieving a goal. And, although applications are most obvious related to physical movement, it’s possible that the sets of rules could be applied to other types of robotic “decisions” as well, such as when to deploy different kinds of tools and how to react to changes in weather, presence of living organisms, or other variable factors in the environment. In addition, the strategies bacteria use could be applied to improving project management, workflows, and other activities that involve multiple steps and benefit from course correcting using information gathered along the way.

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Bacteria Cooperate to Survive

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Pelotomaculum thermopropionicum bacteria gets its energy from alchohols in a reaction that normally requires an input of energy by forming communities with Methanothermobacter thermautotrophicus.

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Bacteria Use Chemical Signals to Communicate

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Colonies Self-organize

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Last Updated September 14, 2016

References

“Bacteria swarming behavior in colonies was explained by considering attractive and repulsive forces between colony parts, communication capabilities, physical interactions between cells, and forces from the environment. Bacteria navigate using chemotaxis, i.e., moving according to gradients in the chemical concentration. Bacteria are too small to detect the chemical gradients across their body receptors, and thus detect the concentration as they swim, and delay their tumble if the concentration increases. As a result, they make longer excursions towards areas of higher concentration. Each bacterium may only acquire local and partial cues from the environment, but as a group bacteria can navigate through challenging environments.” (Shklarsh et al. 2011:1–2)

Journal article

Smart Swarms of Bacteria-Inspired Agents with Performance Adaptable Interactions

PLOS Computational Biology | September 29, 2011 | Adi Shklarsh, Gil Ariel, Elad Schneidman, and Eshel Ben-Jacob

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Reference

“Many animal swarms, Shklarsh explains, can be harmed by “erroneous positive feedback,” a common side effect of navigating complex terrains. This occurs when a subgroup of the swarm, based on wrong information, leads the entire group in the wrong direction. But bacteria communicate differently, through molecular, chemical and mechanical means, and can avoid this pitfall.

Based on confidence in their own information and decisions, ‘bacteria can adjust their interactions with their peers,’ Prof. Ben-Jacob says. ‘When an individual bacterium finds a more beneficial path, it pays less attention to the signals from the other cells. But at other times, upon encountering challenging paths, the individual cell will increase its interaction with the other cells and learn from its peers. Since each of the cells adopts the same strategy, the group as a whole is able to find an optimal trajectory in an extremely complex terrain.’” (Hunka 2011:1)

Other

Smart swarms of bacteria inspire robotics researchers

EurekAlert! | November 17, 2011 | George Hunka

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