A Few Words about Microorganisms

Microorganisms are organisms that are not visible without aid of microscope, i.e., with size less than 70-100 µm [1]. Microorganisms play an important role in the natural or engineered protection of environment from chemical or biological pollution and they can restore polluted or degraded environment. Microorganisms or their products can be also used in the construction to improve the mechanical properties of the ground and building materials. At the same time, the engineers have to design the technologies against microorganisms causing diseases human, animals, and plants and preventing microbial induced deterioration or corrosion. Therefore, both civil and environmental engineering includes many engineering solutions that are based on the relevant knowledge of microbiology. However, this knowledge must be not a general biological science but has to be tightly connected with the engineering problems. Microorganisms are present in almost every location and environment on earth [2]. They are in the air, soil and water, on all plants and animals and in such extreme environments as Antarctic ice and rocks 3 km below the earth's surface where the temperature is 60 °C or more. Besides growing at extremes of temperature and pH, many bacteria survive and grow in the absence of oxygen; for these bacteria, described as anaerobes, oxygen is toxic. Microorganisms are present, too, in huge numbers and variety. The bacteria in the average human gut are estimated to comprise about 500 different species, and their total number, approximately 1014 (one hundred trillion), is about 10 times the number of human cells in the body and more than 10.000 times the human population of the earth. It is impossible to obtain precise data on the relative numbers of harmless and disease-causing (pathogenic) organisms for two main reasons: because new species are being identified all the time, and because of the difficulty of deciding what is harmless and what is not. Organisms that present no threat to a healthy individual might be pathogenic for a person with impaired immunity. Nevertheless, despite the extensive media attention on bioterrorism organisms and the so-called hospital ‘superbugs', the harmless bacteria, together with those that are actually beneficial, grossly outnumber the pathogens; one estimate is by a ratio of more than 200.000 to 1.