What is microbiology?
Rod Shaped bacteria
Microbiology is the study of microorganisms - bacteria, protozoal parasites, viruses and fungi. These organisms can only be seen under the microscope but despite their size these micro-organisms, or microbes for short, have a massive impact on our lives. It has been estimated that there are 5X1030 or 5 million trillion, trillion, microbial cells on Earth. The total amount of carbon in these cells is equivalent to that of all of the plants on the planet! They collectively constitute the largest mass of living material on earth and play a critical role in shaping the environment that we live in. Humans, plants and animals are intimately tied to the activities of microbes which recycle key nutrients and degrade organic matter. Some microbes, however, are pathogenic.
Microbiology and the Evolution of Life on Earth
Microbes have existed on Earth for billions of years and were here long before plant and animal life began. For the majority of its 4.5 billion year history, life on Earth was exclusively microbial. Microbial cells first appeared between 3.8 and 3.9 billion years ago. The fossilised remains of these early bacteria can be detected in stromatolites - rock-like build ups of microbial mats and trapped sediment. When the Earth first formed there was no oxygen present and only bacteria which could grow without oxygen could thrive. Eventually a group of bacteria called cyanobacteria evolved which were able to photosynthesise, thus generating oxygen. At this point the long process of oxygenating the world began, starting the slow, gradual process of the evolution of aerobic forms of life, including animals and plants.
Microbes as Guardians of the Earth
Microbes act as guardians of our planet ensuring that key minerals, such as carbon and nitrogen, are constantly recycled. Even though the Earth is now populated with green plants, microbes still play a crucial role in oxygenating the atmosphere and collectively they carry out more photosynthesis than plants. Microbes degrade dead organic matter, converting the organic carbon in their bodies back into carbon dioxide.
Compost heap
Microbes also play a key role in the nitrogen cycle. Bacteria in the soil convert atmospheric nitrogen into nitrates in the soil. Nitrates are an essential plant nutrient – they need the nitrogen for proteins - and the plants themselves provide food for live stock and other animals. The nitrogen locked in plant and animal proteins is then degraded into nitrates by microbes and eventually converted back into nitrogen by denitrifying bacteria. Compost heaps are a fantastic example of how effectively microbes breakdown organic matter. The mixture of garden weed, grass clippings and mouldy fruit and veg is decomposed rapidly by fungi and bacteria into carbon dioxide and plant compost containing nourishing nitrates and nitrites. Without the recycling power of microbes dead vegetation, carcasses and food waste would start piling up around us! In the UK 6.7 million tonnes of food waste is thrown away every year. Imagine what would happen to the Earth if this waste just sat there and wasn’t degraded…
The Birth of Microbiology
It wasn’t until the 17th century, when the microscope was invented by Robert Hooke, that the existence of microbes was even suspected. Hooke’s microscope, however, could only achieve magnifications of 20-30 times - not powerful enough to see bacteria. Around 1668 Antonie van Leeuwenhoek, an amateur microscope builder, improved microscope design so that he was able to make a microscope capable of magnifications of up to 200 times. Van Leeuwenhoek started examining things like pond water, tooth scrapings and then almost anything he could lay his hands on! In 1683 he described, in a letter to the Royal Society, that he had seen "an unbelievably great company of living animalcules, swimming more nimbly that I had ever seen up to this time” when he had used his microscope to look at the tooth scraping from an elderly man, who had never cleaned his teeth! The animacules were bacteria.
Microbes are everywhere
Microbiologists have discovered that microbes can be found just about anywhere. Microbes are an incredibly diverse group of organisms and can grow in extreme environments that no other living organisms can tolerate. Bacteria have been found to thrive in volcanic hot springs, where temperatures typically reach near boiling point. At the other extreme, living bacteria have also been discovered in Antarctic deserts, where temperatures range from -15 to -30°C. Bacteria can also thrive in salt flats, pools of saturated brine, where salt concentrations range from 120 to 230 grams per litre. Bacteria which live happily in these inhospitable environments have been termed ‘extremophiles’
Hot Springs teaming with swathes of bright, orangey-red thermophillic bacteria
In addition to being a biological curiosity bacteria which grow in these extreme conditions have proved a rich source of enzymes for the biotechnology industry. Fat-degrading and protein-degrading enzymes from bacteria isolated from hot springs have been used to make ‘biological washing powders’. Unlike equivalent enzymes from ‘ordinary’ bacteria these function efficiently at the high temperatures typically used for doing the laundry. Clearing up oil spills that have occurred in cold oceanic environments, the production of ice cream and artificial snow have also benefited from enzymes, produced by bacteria that thrive in near zero temperatures.
Microbes and Food
Microorganisms also provide us with pleasure! They play a hugely important role in producing a whole variety of delicious foods. Who knew that microbes were involved in making chocolate? Cocoa pods are split open and their contents – 20 to 30 bitter seeds in a sweet sticky pulp - are heaped together and covered with banana skins and naturally fermented for 7 days. Over 30 different types of bacteria are involved in this process, along with yeasts and moulds. While in this heap, the sticky pulp becomes a turbid chocolate-coloured broth which gives the cacao seeds both their characteristic chocolate flavour and colour. Microbes play a key role in making wine and beer and foods such as bread, cheese and yoghurt. Salt-loving bacteria, like those found in salt flats, play a key role in the production of Thai fish sauce and Japanese soy sauce. Chinese cooking also depends heavily on microbes which are essential in the production of black bean and yellow bean sauces. Salt-loving bacteria are also important in the production of cured meats and sausages such as salami. Without microbes our culinary repertoire would be smaller and our diets extremely bland.
Colonies of fungi growing on bread. Image courtesy of Matt Wharton
As we all know to our cost, the interaction between microbes and food is not always beneficial. Mouldy bread and rotten fruit caused by microbial degradation is not very appetising. Pizzas and pies which have passed their sell by date may not be obviously full of bacteria, but sell by dates are based on the amount of time it takes for the numbers of bacteria to reach a level where the chances of food poisoning are high. Microbial spoilage makes food unappetising and perhaps foul tasting, but rotten food won’t automatically make you sick – but contamination of food with microbial pathogens will.
The bacterium Campylobacter jejunii is the commonest cause of food poisoning in the UK. In 2010 the Food Standards Agency estimated that 65% of all fresh chickens sold in the UK were contaminated with C. jejunii. Although cooking will kill this bacterium it is still responsible for approximately 300,000 cases of food poisoning in England and Wales each year. For most healthy people, food poisoning, although very unpleasant, is not life-threatening. However for both babies and elderly people food poisoning can be extremely serious as it can cause severe dehydration and kidney failure. Learning how to handle raw meat and to cook poultry and meat properly is therefore essential, particularly during the barbecue season when the incidence of food poisoning, due to poorly cooked food, soars.
Microbes and Disease
Influenza virus
The study of infectious disease is another important branch of microbiology. At the beginning of the 20th century infectious diseases, caused by microbial pathogens, were the major cause of death. Large numbers of children and the elderly succumbed to diseases such as tuberculosis, diphtheria and pneumonia. At this time microbiologists had little idea about how diseases were spread, or how they could be controlled, so epidemics flourished. The "Spanish" influenza pandemic of 1918–1919, caused ˜50 million deaths worldwide - more than the total number of deaths recorded in World War One. Diarrhoeal disease was also common since people regularly ate contaminated food and drank contaminated water.
Microbiology research has, therefore, been concerned with developing antibiotics and vaccines to protect the population from infectious disease. The discovery of penicillin by Alexander Flemming has saved the lives of many millions of people. The development of vaccines which protect against, diphtheria and pneumonia dramatically reduced the number of childhood deaths caused by these diseases. Children in developed countries are also routinely vaccinated against common viral infections such as measles, mumps, rubella and polio. As a direct result of the efforts of microbiologists, smallpox, once a dreadful scourge, is now officially extinct on the planet. However a vaccine against HIV, which in 2009 was reported to infect approximately 33.3 million people around the world, still eludes us.
Friendly bacteria
Babies are colonised by bacteria immediately after birth. It has been estimated that the average person is colonised by 200 trillion bacteria, comprising at least 1,000 different species. This doesn’t mean that we are teaming with potentially pathogenic bacteria, quite the opposite! The bacteria that call the human body home are often essential for our health and well being. Our intestines contain about 100 trillion bacteria and collectively they make up 60% of the dry weight of faeces. These intestinal bacteria play an essential role in helping us to digest food, they provide us with essential vitamins such as vitamin K and biotin and they help to prevent the growth of harmful pathogenic bacteria. The surface of our skin is also home to millions of friendly bacteria which crowd out potential pathogens and prevent them from growing. One bacterium which is abundant on the skin is Staphylococcus epidermidis which produces chemicals called bacteriocins that kill pathogenic bacteria. Friendly bacteria can also be found in our noses but many of these bacteria also carry a health warning. Neisseria meningnitidis which causes meningitis, lives in the noses of millions of people without causing disease, but if the immune system becomes weakened through ill-health then this bacteria can, almost by accident, cause disease which may result in the death of the human that has become its home.
Although microbiology is a relatively young science it has had an enormous impact on our health and well being. Without vaccines and antibiotics we would still be struggling to contend with epidemics of infectious disease and would be vulnerable to relatively minor infections. The microbes that make us sick are however vastly out numbered by microbes that are essential for our existence and allow the Earth to remain habitable. For better or for worse, a world with microbes is unthinkable.
Edited by Tashenka Ninel