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The study of microscopic organisms that exist as single cells or clusters is called microbiology. The microorganisms include bacteria, viruses, archaea, fungi, and protozoa. In the microbial world, microorganisms are everywhere. Almost every natural surface is colonised by microbes. Some microorganisms can live quite happily in boiling hot springs, whereas others form complex microbial communities in frozen sea ice.

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Obviously humans have had to deal with microbes even before recorded history. The first record of humans using microorganisms comes from ancient tablets from the Middle East.

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Microscope is an instrument used to magnify and see the enable microorganisms by humanbeeings.

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Microscope is an instrument used to magnify and see the enable microorganisms by human beings.

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Bacteria are very small, most being approximately 0.5 to 1.0 mm in diameter. The smallest bacteria are mycoplasmas, as small as 0.2 micrometers. But certain cyanobacteria are quite large; Oscillatoria cells are 7 micrometres in diameter, the size of red blood cells. And certain eukaryotes are very small, only 1 to 2 micrometres.

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Eukaryotic, spore-producing, achlorophyllous organisms with absorptive nutrition that generally reproduce both sexually and asexually and whose thallus is usually filamentous, branched somatic structures known as hyphae, typically surrounded with a cell wall.

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Algae are a large and diverse group of eukaryotic organisms that contain chlorophyll and carry out the oxygenic photosynthesis.

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Proto – first; Zoon – animal

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A virus can be defined as a genetic element containing either DNA or RNA that replicates in host cells and is characterized by having an extracellular state.

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The essential nutrients and their function in microbial cells

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Sterilization refers to the complete removal or elimination of microorganisms from an environment. Physical and chemical agents are available to remove the microorganisms from the environment. Heat, irradiation, and filtration are the three physical agents, and various chemicals are available for sterilization.

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Genetics is the study of heredity and variations of genes. How the genes carry information, expressed and replicated in subsequent generations of organisms.

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Industrial Microbiology is the discipline that uses micro organisms, usually grown on large scale, to produce commercial products or carry out important chemical transformations.

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The pathogenicity of an organism varies form mild attack to severe fatal attacks. The host has many mechanisms to resist or to avoid the pathogens apart from immune systems. One or few of these will be activated when the pathogen enters into the body. Following are some of the listed natural host defense mechanisms. Natural host resistance: The host has the natural ability to resist the pathogen. For example, the anthrax may cause mild pustules to man whereas cause fatal blood poisoning to cattles. Age, stress and diet: Very young and very old are susceptible whereas the adults are generally resistant against pathogens. Similarly the physical stress induces the susceptibility of the host against pathogens. Malnutrition is also allowed the pathogens to act very rapidly. Anatomical defenses: The body of host (man) has so many defense mechanisms to avoid the pathogens. Lysozyme of tears; rapid passage of air in nose; highly acidic pH of stomach (pH2); rapid change in pH of intestinal track; native microflora of large intestines; skin layers; mucous membrances of lungs; coughing; sneezing are some anatomical defenses of our body to resist the pathogens. Fever and inflammation: Redness, swelling, pain, heat and fever are some non-specific reactions carried out by host against pathogens. Immune system: The specific and non-specific immunity is the well-advanced resistance mechanism, which will be discussed in this chapter.

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The development of sophisticated procedures for the isolation, manipulation, and expression of genetic materials is a field called genetic engineering. Genetic engineering has applications in both basic and applied research. In basic research, genetic engineering techniques are used to study the mechanisms of gene replication and expression in prokaryotes, eukaryotes, and viruses. For applied research, genetic engineering is used for the development of microbial cultures capable of producing valuable products such as human insulins, growth hormones, interferons, vaccines, enzymes, etc. The commercial application of genetic sense, biotechnology refers to the use of living organisms to carry out defined chemical processes for industrial application.

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Microorganisms live as single cells in nature in association with other cells in an assemblage that we call a “population.”. Such populations are composed of groups of related cells generally derived by successive cell divisions from a single parent cell. The location in an environment where a population generally lives in association with other populations of cells is called “microbial communities.” Environmental microbiology deals with the study of these microbial communities in different habitats, naturally occurring on earth.

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It is used for sterilization of glassware, such as test tubes, pipettes, and petri dishes. Such dry sterilization is done only for glassware. Liquid substances, such as prepared media and saline solutions, cannot be sterilized in an oven, as they lose water due to evaporation. The glassware is sterilized at 180°C for 3 hours. An oven has a thermostat control, using which the required constant temperature can be obtained by trial and error. The thermostat dial reading is approximate, and the exact temperature is read by introducing a thermometer into the oven or on a built-in L-shaped thermometer. In a modern oven there is a digital temperature display and automatic temperature controller to set the desired temperature easily. Time is set by a digital timer. After loading the glassware, the door is closed and the oven is switched on.

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Sterilization:- It is defined as the process where all the living microorganisms, including bacterial spores are killed. Sterilization can be achieved by physical, chemical and physiochemical means. Chemicals used as sterilizing agents are called chemisterilants.

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Nutrient Agar is a general purpose, nutrient medium used for the cultivation of microbes supporting growth of a wide range of non-fastidious organisms. Nutrient agar is popular because it can grow a variety of types of bacteria and fungi, and contains many nutrients needed for the bacterial growth.

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A high-power or compound microscope achieves higher levels of magnification than a stereo or low-power microscope. It is used to view smaller specimens, such as cell structures, which cannot be seen at lower levels of magnification. Essentially, a compound microscope consists of structural and optical components. However, within these two basic systems, there are some essential components that every microscopist should know and understand. These key microscope parts are illustrated and explained below.

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Microorganisms govern most of the soil fertility processes. Viable counts, or biomass, in soil are generally correlated with the fertility level of soil and more so with the organic matter content. Hence, viable counts serve as an index of soil productivity. This procedure counts only a small portion of the total population but is useful for studying the relative abundance of soil bacteria and changes in density of that population that develops on the medium. The method involves the dispersion of the soil in the medium to such an extent that an individual cell, spore, or mycelial fragment has reasonable opportunity, when exposed to suitable conditions, to develop into a discrete and macroscopically visible colony. The necessary degree of dispersion is usually achieved by making successive dilutions of the given soil sample. Various factors that determine the accuracy of the plating method are: The use of an appropriate medium. It is particularly important that the agar medium be low in readily available energy materials such as sugar or proteins, in order that a few fast growing bacteria do not dominate growth on the plate and inhibit the development of a much larger number of slow growing species. Carefully controlled temperature of incubation Length of incubation. Error in sampling and in sample preparations. The manner in which the colonies are counted.

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Fungi constitute an important part of micro flora of normal soil. In soils fungal propagules vary from 2 x 104 to 1 x 106 per gram soil. The propagule being considered as fungal hyphae, spore, and hyphal fragments which is capable of giving colony on the plate. Most soil forms have a filamentous organisation and are capable for reproduction by means of spores. Soil fungi has significant role in organic matter decomposition, as a plant pathogens and in the interaction with other soil microorganisms. They are first to attack the straw added in soil. Agar plate count method is commonly used as a measure of fungal population in soil, although there are few limitations of this method. The method fails to distinguish Fungi constitute an important part of the microflora of normal soil. In soils, fungal propagules vary from 2 × 104 to 1 × 106 per gram of soil. The propagule being considered is fungal hyphae, spores, and hyphal fragments, which are capable of giving colonies on the plate. Most soil forms have a filamentous organization and are capable of reproduction by means of spores. Soil fungi have a significant role in organic matter decomposition, as plant pathogens, and in the interaction with other soil microorganisms. They are first to attack the straw added in soil. The agar plate count method is commonly used as a measure of fungal population in soil, although there are a few limitations to this method. distinguish between spores and hyphae as a source of colonies. The method is biased strongly toward organisms that grow rapidly and sporulate rapidly. The mere act of shaking often introduces an error into the population estimates; the agitation tends to rupture the mycelium and sporulating body into an indeterminate number of fragments each of which may produce a single colony. So this always gives more count than actually found in soil.

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The actinomycetes, sometimes called ray fungi, are intermediate in morphology between the bacteria and the true fungi. They possess a very fine vegetative mycelium that does not fragment into bacillary or coccoid forms, and therefore their colonies on agar are commonly cohesive or though in consistency. In many soils, the actinomycetes account for from 10 to 25% of the total count on agar plates and in soils for more than 50%. Their number is higher in soils of low moisture content than in wet soils. They are responsible for degrading more resistant carbon material in soil like humus. They are also important flora of manure heaps.

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Selection of a medium to grow any particular type of microbe is extremely important since the microbes vary in their nutritional requirements. Certain nutrients are needed by almost all the microbes and are called basal medium. Each genus has some specific nutritional requirements. Thus, different media are used for different groups of microbes. The following are the main types of media that will be used in this course: General purpose media (Nutrient agar) Selective media (N-free medium for free living N2-fixers) Differential media

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Rhizobium is heterotrophic soil bacteria that can fix appreciable amount of atmospheric nitrogen, in association with the compatible host legume. This type of association where both the partners (Symbiont) are benefited is termed as symbiosis. A group of host plants infected by a single species of Rhizobium is called inoculation group. There are about 20 cross inoculation groups of legumes but only seven are important.

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The fixation of atmospheric nitrogen by free-living microorganisms without another host system is known as non-symbiotic nitrogen fixation. It is restricted to certain microorganisms, mostly bacterial and blue-green algae. The bacteria that have the ability to fix molecular nitrogen come under the genera Azotobacter, Azomonas, Beijerinckia, Derixa, Mycobacteria, Azospirillum, Bacillus, Enterobacter, Klebsiella, and Clostridium. Different strains of Azotobacter are able to fix 2–15 mg

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Soil inhabits many photosynthetic microorganisms. Of these prokaryotic bluegreen algae, which contain phycocyanin pigment are also known as cyanobacteria. Cyanobacteria mostly prefer moist conditions, abundance of sunlight, mesophilic temperature and neutral to alkaline conditions. These organisms synthesize protoplasm and fix N2 and can enhance the soil fertility. The contribution of soil algae (cyanobacteria, BGA) to agriculture has been established in rice (Oryza sativa L) fields.

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Azolla is a small water fern and is found floating on water in ponds and shallow ditches. Anabaena azollae has been found to fix dinitrogen in cavities of its upper lobes. Azolla has about 3% N content on dry weight basis and has long been used as green manure in rice growing countries.