I was recently approached about developing a children’s book to educate about bacteria in hopes of clarifying misconceptions many have about ‘nasty germs’. I must say how amazed and honored by the invitation I am. The company is small without a lot of capital to produce such a book at will. So, I was asked if I had contacts that would graciously sponsor the production of the book. This to me is bittersweet. I would love to be a part of something that would be so helpful for the public regarding the reality of microbes (they tend to get bad press in general). However, I’m not one to ask for money…ever.
This has sparked questions in my head about the state of educational media production. S.T.E.M. is all the rage these days and rightly so. As our society progresses, the need for a workforce trained for technical and scientific positions is essential. One example…billboard signs. Growing up, I used to get excited and amazed when I saw a person putting up a new billboard sign. Taking the old one off, applying the new one in its place. However, now these signs are replaced by digital billboards. Who is going to change the billboard advertisement? Someone trained to tear down the old and glue the new one on? Someone with a background in electrical engineering? If there is a problem with the billboard, who will fix it? A carpenter or an engineer? This is just one example.
The STEM push is necessary and welcome in my opinion. However, a quite fitting phrase comes to mind: show me the money. We are throwing money into public school systems that are fueled by bureaucracy and inefficiency. Yet we still have to cut out box tops to support local schools and have several fundraisers a year for a new gym floor. Anyone see the irony?
Put the money where it can be useful. Put it in projects that will encourage our children to pursue a career that will promote curiosity and critical thinking. This has been my soapbox, today sponsored by the letters S, T, E, and M.
Many do not place ‘bacteria’ and ‘memory’ in the same sentence. Normal human perception does not connect the two concepts. However, Mother Nature seems to have a more profound perception. The past 50 years or so of scientific investigation has shown how our uniqueness as humans is actually commonplace across all forms of life on Earth. Case in point, how closely associated molecular memory is between bacteria and human.
Bacteria use adaptation to signals as memory
Swimming bacteria do not move randomly in their environment. This behavior would be futile and counterproductive. Instead, bacteria are constantly monitoring their environment in search of food and poisons. Moving towards the former and away from the latter. This observation was first published in the late 19th century. Bacteria, like the famous and infamous E. coli, use molecular antennae to receive these important ‘signals’ as the basis in the decision of which direction to swim. What if the bacteria find a great place to reside with lots of food but still need to receive signals to ensure they remain there? The antennae have sections that can be modified easily and reversibly. These modifications, in the form of methylation, alter the sensitivity of the antenna protein to subsequent signals. Methylation allows these antennae not to receive the number of absolute signals but relative signals. In other words, the antenna protein through fine-tuned methylation detects changes in the number of signals now versus some time in the past. This is the basis of molecular memory.
These antennae are proteins called methyl-accepting chemotaxis proteins, or MCPs. MCPs accept methyl groups from the essential cofactor S-adenosylmethionine (aka SAM or AdoMet). AdoMet is essential to both prokaryotes and eukaryotes like humans. The methyl groups are added by a protein called CheR (pronounced ‘key R’) which transfers the methyl from AdoMet to very specific amino acid side groups of glutamate. The process, called O-methylation adds the methyl group to the single-bonded oxygen on the carboxyl.
The length of a bacterium’s molecular memory is very short in comparison to how we perceive memory at only a few seconds. But, to bacteria it is long enough to successfully navigate the environment with similar precision when concentrations of food or poison vary (up to several orders of magnitude, or ~1000x).
Does the basis of molecular memory in humans mimic bacteria?
Eukaryotes, including humans, use a very similar mechanism in signal transduction to bacteria. Phosphorylation (transferring a phosphate group from ATP or GTP to a protein amino acid) is the basis of all signal transduction and cell regulation. Bacteria use histidine kinases and response regulators, as do plants to some degree. However, the majority of regulation through signal transduction in eukaryotes is through two types of proteins, RAS proteins and the heterotrimeric G-proteins. G-proteins interact with membrane receptors that regulate their activity. What determines which surface receptors G-proteins interact with? Isoprenylcysteine methyltransferase, or ICMT, is one of two methyltransferases that regulate signal transduction activity. ICMT is a membrane protein that uses AdoMet to add methyl groups to isoprenylcysteine, a post-translationally modified cysteine residue on both heterotrimeric and RAS-related G proteins. Methylation regulates which receptors the G-proteins interact with, thus playing a major role in connecting the initial signal to downstream regulatory pathways. The carboxyl methylation essentially modulates G-protein signalling globally.
G-protein carboxyl methylation is regulated by GPCR signaling and, as seen above, GPCR signaling is regulated by G-protein carboxyl methylation. This feedback/feed forward loop could be seen as a form of molecular memory stored in methylation patterns. Within the brain, ICMT activity is almost exclusively found in the region controlling coordination of movement. Thus, methylation could be used to modulate certain neuronal signaling pathways which result in learned patterns of sensory-motor skills.
The only other major methyltransferase is from a protein known as PPMT. PPMT interacts with a major enzyme in signal termination, the protein phosphatase PP2A. PPMT adds methyl groups to the backbone carboxyl of a specific leucine in PP2A. This carboxyl methylation helps determine which B subunit PP2A interacts with and where in the cell PP2A can be found. PPMT structurally resembles CheR in bacterial memory. Moreover, the enzyme that removes the methyl group from PP2A, PME, structurally resembles the bacterial enzyme that removes methyls from MCPs, CheB.
PP2A is one of the major regulators of pathway coordination to maintain synaptic plasticity in the brain. Interestingly, methylation defects and PP2A-PME complexes are suggested to play a role in the cause of Alzheimer’s Disease and memory loss. Methylation defects leading to defective phosphatase activity of PP2A leads to accumulation of a phosphorylated subunit of the structural protein microtubule. In this phosphorylated form, the filaments used to keep axons structurally sound collapse and lead to loss of normal synapses. Therefore, molecular memory in the form of methylation plays a vital role in promoting normal brain activity and its disruption can ultimately lead to dementia.
Chicken, meet egg. Egg, meet chicken.
So, from bacteria to human, carboxyl methylation is necessary for memory. Did these pathways evolve individually in parallel, or did the memory we have today originate in the predominant lifeforms found within us?
Li and Stock. (2009) Biol. Chem. 390: 1067-1096. DOI 10.1515/BC.2009.133
The science gap is huge. One of the biggest misconceptions hindering the advancement of scientific literacy in society is also one of the most crucial – the scientific method. And no wonder. Most people would look back at primary and secondary school and cringe when thinking about all the facts and concepts they had to memorize in science classes. I cringe when I think of the public concluding science is static and just the sum of all data gathered through the centuries.
The scientific method is dynamic and so is the collection of accepted scientific knowledge
Nothing in science is certain. In the words of the great Richard Feynman:
We absolutely must leave room for doubt or there is no progress and no learning. There is no learning without having to pose a question. And a question requires doubt. People search for certainty. But there is no certainty. People are terrified — how can you live and not know? It is not odd at all. You only think you know, as a matter of fact. And most of your actions are based on incomplete knowledge…
The idea that scientific knowledge is like a statue is a horrible, infectious disease in society. Consider this…
The scientific method is a bucket. This is not just any bucket; it holds all the scientific knowledge gathered throughout history. The bucket is just a utilitarian tool for collecting knowledge. Luckily, this bucket has a hole in the bottom. The scientific method is a two way street and is objective just like a bucket is just a bucket. At the beginning of it all, the bucket was filled with crystal clear water. Mother Nature had filled it for us but all its contents were a complete unknown. As human inquiry began, discoveries were like drops of color that allowed us to have a glimpse of the contents as it dispersed like food coloring in a glass of water. Each new discovery or observation adds a touch of color to the bucket. Nature’s true color will not be observed in our lifetime or possibly at all. Our curiosity and practice only adds to the hue within the bucket.
Sometimes we don’t know the hue of the water is wrong until new knowledge is obtained and added to the large bucket. With addition of the new color, drops of discolored water pour from the hole in the bucket. Soon the prevailing knowledge is uniform within the bucket. Science never sleeps so this constant increase in knowledge and data get us one step closer to the true color of the universe, or so we think until we find out the hue is all wrong as the hole opens and a novel color drops in.
This past Tuesday, something mysterious and amazing happened. My wife noticed a strange deposit into our bank account; a large deposit: $1,400. She asked when I was supposed to be paid for something I was working on and I told her not until later. This deposit piqued both our curiosities. What was it? Why was it in there? Who put it there? I started investigating; researching as much as I could. I was able to find out it was $1,400 cash, which bank branch and what time the money was put in. Paranoid it was some scam perpetrated to clean out our bank account, my wife wanted me to call the bank to inquire. So, Wednesday morning, I called. Long story short, my wife received a call Wednesday afternoon from a bank employee saying someone anonymously deposited money in our account because they thought we should have it. What? To say the least, we were humbled and astonished. The curiosity has not gone away. We are still trying to figure out who this saint(s) is.
This mystery made me think; it is eerily like the field of science. The path to discovery in any science discipline begins with something very simple, an observation. My wife observed a strange deposit into our bank account. Observations lead to curiosity and ultimately yield questions. What was this deposit? Why was it there? Who put it there? Explanations or answers to the questions are developed.These explanations, or hypotheses, have their validity tested through experiment or some action. My wife’s initial explanation was that someone deposited it to somehow gain access to our account to clean it out. My action of calling the bank to report the deposit as not originating from the wife or myself was partly to make sure the deposit was legitimate and not some clever scam. Through experiment or action, facts are gathered to support the explanations or rule them out. The fact a bank employee called to let us know the deposit was from an anonymous ‘Good Samaritan’ ruled out the hypothesis of the scam. Scientific discovery ultimately leads to more observations, curiosity, questions, and hypotheses.
For my wife and I, the discovery that someone thought so highly of us to give us any amount of money has only fueled the mystery. The main question now is, who did it? Unlike any good mystery, or science for that matter, we may never find out.
This post is dedicated to my family’s ‘Good Samaritan’. Thank you…
Recap: The restaurant is the bacterial cell, the employees are the proteins/enzymes that serve the patrons which are the compounds/metabolites.
Who are the bosses that determine which, and how many, employees are needed for each type of patron?
The restaurant managers have a very important job to perform. They have to make sure the right number of employees are available to help their respective patron. If the balance between employees and patrons is not well maintained, it could cause disaster for the restaurant itself. In a past post, I tried to describe how bacteria made decisions. One of the predominant ways was the use of two-component systems. For this story, think of the restaurant managers as actually two people who need to work well together. One identifies its respective patrons and the other makes changes to the number of employees for those patrons. It is this balancing act that helps the entire restaurant to work smoothly.
A successful restaurant will open up new locations. The same can be said for bacteria. If conditions are right, the cell will divide into two cells. As with a cell, restaurants have to make sure certain activities are undertaken to ensure the new restaurant will be exactly like the successful one it is copying. The success of this restaurant is based upon the ability to keep the employees happy (by having patrons to serve and not sitting around bored) and keeping the patrons coming in. To duplicate this success, the new restaurant should have a building exactly like the current one so the patrons will easily continue to enter and leave. The new restaurant will also need the exact employee list for the managers to call upon when needed. The employee list is the genome of the cell that encodes the proteins needed for survival. That would make the copy machine that duplicates the employee list the DNA replication machinery. This special restaurant building is state of the art. It can expand until it is roughly double its original size then place a dividing wall down the middle of the large building until the building becomes actually two buildings. Now the restaurant can serve twice the number of patrons with the same efficiency as before. Each new building has the same employee list and rough the same number of employees to start off with. Then the managers start their work identifying the patrons in the restaurant to make sure the employees are there to serve them.
The two buildings shake hands and go their merry way…ready to serve.
In Part III, I will talk about the intercom system that allows major changes to happen to the kind of employees needed for economic downturns.
Many say storytelling in science is a great way to describe complex material in an understandable way for the masses. In this post, I will try to use an analogy to illustrate the complexity of a typical motile bacterial cell.
Microbial Physiology through Storytelling
If there is anything Americans know, it’s food. We are a nation obsessed with food and frequent restaurants on a regular basis.
Imagine your favorite restaurant as one huge bacterial cell.
When I travel to another city, I can’t rely on habit to guide me to a restaurant for dinner. I have to search for it while driving down the road. In order to know when I have found the restaurant I am searching for, I must rely on signs telling everyone what the restaurant is. The sign is a way to recognize and identify the building as i) a restaurant and ii) the specific type of restaurant. Bacteria do the same. They have ‘signs’ (proteins and other molecules) attached to the outside of the cell that lets other cells around identify what the cell is. I go into the restaurant through a door that allows patrons to move in and out of the building like bacteria have gates or channels that allow molecules to move in and out of the cell. Almost always, patrons are different leaving than they were when entering the restaurant; filled with yummy food they consumed and perhaps stopping to make a deposit in the waste room before leaving. Many molecules that leave a cell are different than those that enter. The workers of the restaurant have to keep track of the number of patrons entering and leaving the building to efficiently serve the patrons. Each employee has a specific job to do for very specific patrons. The employees have to identify their patrons and serve them as described by the bosses. Bacteria have an array of workers (proteins and protein complexes) that have very specific job descriptions depending on the patrons (substrates and product molecules) present in the cell. The restaurant survives by serving as many patrons as possible efficiently and correctly just as a cell must survive by responding correctly and quickly to everything in its environment.