Julius Adler

doi:10.19080/APBIJ.2023.07.555705

Review Article

Mechanism of Behavior

Julius Adler*

Department of Biochemistry and Department of Genetics, University of Wisconsin-Madison, USA

Submission: September 15, 2023; Published: October 16, 2023

*Corresponding author: Julius Adler, Department of Biochemistry and Department of Genetics, University of Wisconsin-Madison, USA

How to cite this article: Julius A.Mechanism of Behavior. Anatomy Physiol Biochem Int J: 2023; 7(1): 555705. DOI: 10.19080/APBIJ.2023.07.555705.

Abstract

Behavior of bacteria. Behavior of fruit flies. Decision-making.

Keywords: Organisms; Eukaryote Drosophila; Bacteria; Chemotaxis in Bacteria; Biology; Metabolism; Genetics; Neurobiology; Psychology; Biochemistry; Neuroscience

Behavior of Bacteria

History

Anton van Leeuwenhoek, in Holland. improved the microscope and then discovered bacteria and their motility, 1976. His life: October 24, 1632-August 26, 1723.

The German botanist Theodor Engelmann in Utrecht, Holland, and later at the University of Berlin, discovered in 1881 that bacteria are attracted to oxygen, and he discovered that bacteria are attracted to light. He used this bacterial oxygen response to demonstrate that green plants, including algae, give off oxygen during photosynthesis. For details see Engelmann [1], Gerhart Drews [2] & Howard Berg [3] part 1 (Figure 1).

Wilhelm Pfeffer, in (Figure 2) Tuebingen, Germany, discovered in [4] that bacteria are attracted and repelled by various chemicals, this was named “chemotaxis” by him. He studied this in 1884, [5,6] by placing into a suspension of motile bacteria a tube containing complex attractant (the leg of a fly or a piece of meat or meat extract or potato sap or tryptone or peptone) or repellent (inorganic acids or inorganic salts or alcohol). With attractants he observed that the bacteria accumulated around the mouth of the tube and after a while also inside, and with repellents he observed that the bacteria moved away. Chemotaxis was studied by Pfeffer in a mainly qualitative and subjective way since rather few defined chemicals were known by then. This is reviewed by Jacqes Loeb [7], in “Forced Movements, Tropisms, and Animal Conduct”. Roderick Clayton at Cal Tech studied phototaxis in photosynthetic bacteria from [8].

Our studies on the behavior of bacteria

In order for us to identify stimuli in E. coli, it was first necessary to determine the conditions needed for optimal motility and the conditions needed for chemotaxis. The behavior of bacteria was now studied in the following way, see Adler, “A method for measuring chemotaxis and use of the method to determine optimum conditions for chemotaxis”, [9]. This paper describes an objective method for measuring chemotaxis in bacteria. The procedure was made quantitative by measuring how many bacteria accumulate inside a capillary tube containing the stimulus by plating the contents of the capillary tube and then counting colonies the next day. At the start of this work (1960) I got E. coli from Hatch Echols upstairs. It just happened to be a strain that required L-methionine for growth. That’s how I discovered that methionine plays a central role in bacterial chemotaxis! (Otherwise, it might have taken many years to find out that methionine is needed for bacterial chemotaxis.) (Figures 3-10).

Figure 11 shows the key figure from the very first summary of the mechanism of bacterial chemotaxis [10]. It formed the basis for all the subsequent reports by many other scientists who study the behavior of bacteria.

The biochemical mechanism for chemotaxis in bacteria is presented here (Figure 12):

As indicated in that Figure, bacteria sense attractants and repellents by means of sensory chemotaxis proteins, called methyl-accepting chemotaxis proteins (MCP). These send the sensed information onward by means of excitation, which then informs the flagella to respond. Then MCP by its methylation brings about adaptation to stop the excitation process (Figure 13).

MCP can be methylated or demethylated to effect adaptation or deadaptation. This involves use of L-methionine (as S-adenosyl-L-methionine) for methylation, or production of methanol for demethylation (Figures 14 & 15).

Of the various stimuli, some are attractive, and others are repulsive. What the organism does depends on the intensity of each stimulus. When there is more attractant than repellent, the organism will be attracted and when there is more repellent than attractant, the organism will be repelled. We were interested in learning the mechanism that an organism uses to decide what to do.

A powerful way to study behavior is to isolate and describe mutants that don’t have normal behavior owing to defects in genes that control behavior. This is neurogenetics, also called behavioral genetics, see a review by Maxwell Cowan, Donald Harte & Eric Kandel [11]. That approach was first used in fruit flies (Margaret Bastock, Seymour Benzer, William Bak, Martin Heisenberg, and David Suzuki). It has been carried out in bacteria (Julius Adler, Sandy Parkinson, Gerald Hazelbauer, Joseph Falke, Mel Simon, Ann Stock, Jeff Stock and others), in nematodes (Sydney Brenner and others), in zebra fish (John Kuwada and others), and in mice (Richard Sidman, Pasko Ragik, Jacqueline Crawly and others). E. coli bacteria are attracted and repelled by a variety of different stimuli and for many of them mutants have been obtained. The response to stimuli takes place in the flagellar mechanism (Figure 16). The complex structure at the base of the flagella of E. coli was first described by Melvin DePamphilis & Adler [12]. Since 1971 other scientists have successfully produced a very much more complicated view of the bacterial flagellum as demonstrated in a figure by Fabienne Chevance and Kelly Hughes, 2008. See that figure on page 56 of Adler “My Life with Nature” [13]. Also see figures by Shin-Ichi Aizawa et al. [14] & David Blair [15].

Videos about the behavior of bacteria

Videos of the behavior of bacteria have been described by Adler with music by David Adler: go to “Google, The Behavior of Bacteria – You Tube, 7.5 minutes of behavior”, to see and hear them. Here is a summary of a few of those videos (Figure 17). For an excellent review of behavior of bacteria see Howard Berg’s “Marvels of Bacterial Behavior” in Proceedings of the American Philosophical Society 2006.

Behavior of Fruit Flies

Next is described the behavior of Drosophila, the fruit fly, which is a eukaryote (bacteria are prokaryotes).

The assay used here to study the behavior of fruit flies

The behavior of Drosophila fruit flies was studied here by use of the following method (Figure 18).

The mechanism of behavior of fruit flies

Fruit flies are attracted by many stimuli and repelled by many stimuli. Next, as an example, is the use of this assay to show flies attracted to light. Mutants that fail to be attracted to light have been obtained and the result for one of these is shown here (Figure 19).

Decision Making

“Decision-making has all the secrets of everything: who we are, what we do, how we navigate the world.” “How do I decide? The brain with David Eagleman” [16].

Decision making in bacteria

What will a motile bacterium do if confronted simultaneously with a gradient of attractant and a gradient of repellent? In this “conflict” situation a bacterium must “decide” whether to pursue the attractant or flee from the repellent. Already in [5,6] reported that the relative strength of the two gradients determines whether attraction or repulsion will occur. He determined this microscopically by observing the entrance of bacteria into a tube containing both attractant (meat extract) and repellent (inorganic acids) at various concentrations.

We have confirmed and extended Pfeffer’s report. First, Escherichia coli were exposed to a capillary tube containing only attractant or only repellent, and then after an hour the number of bacteria that had entered the capillary tube was determined by plating its contents. For attractant we used L-aspartate, a chemical that is beneficial because it can be readily metabolized, and for repellent we used L-valine, a chemical that harms by inhibiting the growth of E. coli. Then after that, attractant and repellent were used together. At a low concentration (10-6M) of L-aspartate, bacteria fail to be attracted to L-aspartate when there is a high concentration (10-1M) of L-valine (Figure 20) [17-25].

The conclusion of this: motile bacteria presented simultaneously with both attractant and repellent respond to whichever is present in the more effective concentration. Apparently, bacteria have a processing mechanism that compares opposing signals from the chemoreceptors, sums these signals up, and then communicates this to the flagella [26-39].

Decision-Making and its mutants in fruit flies

Here is a report on decisions made by fruit flies. Mutants of this are then studied for getting at the mechanism involved in decision-making. Fruit flies were placed at one end of a tube and attractant (light) plus overpowering repellent (eugenol) were placed at the other end. The result is described here (Figure 21). That Figure shows that the parent flies stay put because they are repelled by more repellent than attractant coming at them. But mutants in decision-making can’t tell this, so the mutants move randomly over the whole tube. In this way decision-making mutants were obtained.

Another way for measuring flies making a decision: At right, attractant light plus attractant temperature, at left flies start out with repulsive chemical (benzaldehyde) and repulsive high temperature; the flies move to the attractive end. But mutants in decision-making can’t tell this, so the mutants move randomly over the whole tube. In this way additional decision-making mutants were obtained (Figure 22). This mutant 2 is missing RNA splicing and RNA helicase, so those activities would be a part of this mechanism (Figure 23).

Acknowledgement

I am highly thankful to the National Institutes of Health for support of the research carried out in my laboratory over many years. I am most grateful to The Camille and Henry Dreyfus Foundation for six years of grants in support of my undergraduate research program on Drosophila fruit flies. Lar Vang has been an associate research specialist here. I am sorry to report his death, due to pancreatic cancer, I am most sad. Robert Kreber, a research specialist in Barry Ganetzky’s laboratory, has helped us greatly in studies of the genetics of our mutants. I thank Barry Ganetzky for teaching me about fruit flies. I am very thankful to Laura Vanderploeg for the beautiful artwork.