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Microbiology should be part of everyone’s educational experience. European students deserve to know something about the influence of microscopic forms of life on their existence, as it is at least as important as the study of the Roman Empire or the Second World War. Knowledge of viruses should be as prominent in American high school curricula as the origin of the Declaration of Independence. This limited geographic compass reflects the fact that the science of microbiology is a triumph of Western civilization, but the educational significance of the field is a global concern. We cannot understand life without an elementary comprehension of microorganisms.

Appreciation of the microbial world might begin by looking at pond water and pinches of wet soil with a microscope. Precocious children could be encouraged in this fashion at a very early age. Deeper inquiry with science teachers would build a foundation of knowledge for teenagers, before the end of their formal education or the pursuit of a university degree in the humanities.

Earth has always been dominated by microorganisms. Most genetic diversity exists in the form of microbes and if animals and plants were extinguished by cosmic bombardment, biology would reboot from reservoirs of this bounty. The numbers of microbes are staggering. Tens of millions of bacteria live in a crumb of soil. A drop of seawater contains 500,000 bacteria and tens of millions of viruses. The air is filled with microscopic fungal spores, and a hundred trillion bacteria swarm inside the human gut. Every macroscopic organism and every inanimate surface is coated with microbes. They grow around volcanoes and hydrothermal vents. They live in blocks of sea ice, in the deepest oceans, and thrive in ancient sediment on the seafloor. Microbes act as decomposers, recycling the substance of dead organisms. Others are primary producers, turning carbon dioxide into sugars using sunlight or by tapping chemical energy from hydrogen sulfide, ferrous iron, ammonia, and methane.

Bacterial infections are caused by decomposers that survive in living tissues. Airborne bacteria cause diphtheria, pertussis, tuberculosis, and meningitis. Airborne viruses cause influenza, measles, mumps, rubella, chickenpox, and the common cold. Hemorrhagic fevers caused by Ebola viruses are spread by direct contact with infected patients. Diseases transmitted by animal bites include bacterial plague, as the presumed cause of the Black Death, which killed 200 million people in the 14^th century. Typhus spread by lice decimated populations of prisoners in concentration camps and refugees during the Second World War. Malaria, carried by mosquitos, massacres half a million people every year.

Contrary to the impression left by this list of infections, relatively few microbes are harmful and we depend on a lifelong cargo of single-celled organisms and viruses. The bacteria in our guts are essential for digesting the plant part of our diet and other bacteria and yeasts are normal occupants of healthy skin. The tightness of our relationship with microbes is illustrated by the finding that human DNA contains 100,000 fragments of genes that came from viruses. We are surprisingly microbial.

Missing the opportunity to learn something about microbiology is a mistake. The uninformed are likely to be left with a distorted view of biology in which they miscast themselves as the most important organisms. For example, “Sarah” is a significant manifestation of life from Sarah’s perspective, but her body is not the individual organism that she imagines, and nor, despite her talents, is she a major player in the ecology of the planet. Her interactions with microbes will include a healthy relationship with bacteria in her gut, bouts of influenza and other viral illnesses, and death in old age from an antibiotic-resistant infection. Sarah’s microbiology will continue after death with her decomposition by fungi. In happier times she will become an expert on Milton’s poetry, and delight students by reciting Lycidas through her tears, but she will never know a thing about microbiology. This is a pity. Learning about viruses that bloom in seawater and fungi that sustain rainforests would not have stopped her from falling in love with Milton.

Even brief consideration of microorganisms can be inspiring. A simple magnifying lens transforms the surface of rotting fruit into a hedgerow of glittering stalks topped with jet-black fungal spores. Microscopes take us deeper, to the slow revolution of the bright green globe of the alga Volvox as its beats its way through a drop of pond water. A greater number of microbes are quite dull things to look at and their appreciation requires greater imagination. Considering that our bodies are huge ecosystems supported by trillions of bacteria is a good place to start, and then we might realize that we fade from view against the grander galaxy of life on Earth. The science of microbiology is a marvel for our time.

Featured image credit: BglII-DNA complex By Gwilliams10. Public domain via Wikimedia Commons

The post Discovering microbiology appeared first on OUPblog.

        

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Every month OUP editor and author Jonathan Crowe answers your science questions in the monthly SciWhys column. Got a burning question about science that you’d like answered? Just email it to us, and Jonathan will answer what he can.

Today: how do organisms develop?

By Jonathan Crowe

Each of our bodies is a mass of cells of varying types — from the brain cells that give us the power of thought, to the cardiac cells that form our heart and keep our blood circulating; from the lung cells that take in oxygen from the air around us, to the skin cells that envelop the organs and tissues that lie within. Regardless of their ultimate function, however, each of these cells has come from a single source — the fertilised egg. But how can the complexity and intricacy of a fully-functioning organism stem from such humble beginnings?

At heart, the growth of any organism relies on the repeated growth and division of cells. A cell grows, then splits into two. Each of those cells grows, then splits into two… and so the cycle continues. Before long, we’ve gone from having one cell to two, from two to four, and then to eight, to sixteen, etc. In fact, after ten ‘cycles’ we already have over 1000 cells. (We still have some way to go to generate the millions of cells that form an embryo, but you get the idea.)

Initially, the egg divides to from a hollow ball of cells. However, living creatures aren’t hollow. Instead, they have a clear inside and outside, with the inside usually comprising some kind of gut, which passes the length of the body, from mouth to anus. So how do we go from a hollow ball to something with a clear internal structure? Well, imagine holding a sponge ball between the fingers of two hands, and then pushing in the bottom of the ball with your thumbs. The bottom of the ball folds up and in, almost forming a ‘tunnel’ into the ball. Our hollow ball of cells does the same thing: the cells at the bottom of the hollow ball move up and inside to form a tunnel. These cells will go on to form the digestive tract, which (as our experience tells us) runs right through the inside of our bodies.

Shortly after, a strip of cells along the back of the ball of cells roll up to form a furrow. The cells forming this furrow will go on to form the nervous system, with the furrow itself becoming our spinal cord. And, again, this fits with our experience: our spinal cord does indeed run up and along our back.

The previous paragraphs reveal an important feature of the development of a living organism. It’s not just a question of having lots of cells: to have a fully-functioning organism, we need different cells to do different things – to have different functions. After all, our bodies would be quite useless (not to mention odd-looking) if we were composed entirely of lung cells. Instead, as a population of cells grows, it also clusters into groups with common functions, forming different tissues and different organs.

So how does a cell know what kind of cell it should become? At the simplest level, it depends on the cell’s location – its position in the embryo. But how can cells tell where they are? Do they have some kind of cellular GPS system? Actually, in a way they do. Just as the GPS feature of a mobile phone can tell us our location by picking up a signal from a satellite, cells can also receive signals from their surroundings, which vary according to their location. And, because cells at different positions in the embryo — top or bottom, front or back, left or right — receive different signals, they behave in different ways.

Our everyday experience tells us that our behaviour is modified by signals in the world around us – the most obvious example being the traffic lights that tell us when to stop or go when driving. In a cellular world,

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This is the second post in our latest regular OUPblog column: SciWhys. Every month OUP editor and author Jonathan Crowe will be answering your science questions. Got a burning question about science that you’d like answered? Just email it to us, and Jonathan will answer what he can. Today: What are genes and genomes?

By Jonathan Crowe

I described in my last blog post how DNA acts as a store of biological information – information that serves as a set of instructions that direct our growth and function. Indeed, we could consider DNA to be the biological equivalent of a library – another repository of information with which we’re all probably much more familiar. The information we find in a library isn’t present in one huge tome, however. Rather, it is divided into discrete packages of information – namely books. And so it is with DNA: the biological information it stores isn’t captured in a single, huge molecule, but is divided into separate entities called chromosomes – the biological equivalent of individual books in a library.

I commented previously that DNA is composed of a long chain of four building blocks, A, C, G, and T. Rather than existing as an extended chain (like a stretched out length of rope), the DNA in a chromosome is tightly packaged. In fact, if stretched out (like our piece of rope), the DNA in a single chromosome would be around 2-8 cm long. Yet a typical chromosome is just 0.00002–0.002 cm long: that’s between 1000 and 100,000 times shorter than the unpackaged DNA would be. This packaging is quite the feat of space-saving efficiency.

Let’s return to our imaginary library of books. The information in a book isn’t presented as one long uninterrupted sequence of words. Rather, the information is divided into chapters. When we want to find out something from a book – to extract some specific information from it – we don’t read the whole thing cover-to-cover. Instead, we may just read a single chapter. In a fortuitous extension of our analogy, the same is true of information retrieval from chromosomes. The information captured in a single chromosome is stored in discrete ‘chunks’ (just as a book is divided into chapters), and these chunks can be read separately from one another. These ‘chunks’ – these discrete units of information – are what we call ‘genes’. In essence, one gene contains one snippet of biological information.

I’ve just likened chromosomes to books in a library. But is there a biological equivalent of the library itself? Well, yes, there is. Virtually every cell in the human body (with specific exceptions) contains 46 chromosomes – 23 from each of its parents. All of the genes found in this ‘library’ of chromosomes are collectively termed the ‘genome’. Put another way, a genome is a collection of all the genes found in a particular organism.

Different organisms have different-sized genomes. For example, the human genome comprises around 20,000-25,000 genes; the mouse genome, with 40 chromosomes, comprises a similar number of individual genes. However, the bacterium H. influenzae has just a single chromosome, containing around 1700 genes.

It is not just the number of genes (and chromosomes) in the genome that varies between organisms: the long stretches of DNA making up the genomes of different organisms have different sequences (and so store different information). These differences make sense, particularly if we imagine the genome of an organism to represent the ‘recipe’ for that organism: a human is quite a different organism from a mouse, so we would expect the instructions that direct the growth and function of the two organisms to differ.

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