Microbiology

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.
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.