Microbial associations with animals

Termites are insects belonging to the order Isoptera that are found particularly in tropical regions. Their famous ability to destroy trees and wooden structures such as buildings and furniture is due to a resident population of flagellated protozoans in their hindgut, which are able to break down cellulose. Termites lack the enzymes necessary to do Symbiosis is sometimes taken to mean a relationship between different organisms from which both participants derive benefit. We use the term in its...

Box 82 Ergot

Members of the genus Claviceps may infect a variety of grains, particularly rye, when they come into flower, giving rise to the condition called ergot. No great damage is caused to the crop, but as the fungus develops in the maturing grain, powerful hallucinatory compounds are produced, which cause ergotism in those who consume bread made from the affected grain. This was relatively common in the Middle Ages, when it was known as St Anthony's Fire. The hallucinatory effects of ergotism have...

Microorganisms in the production of biochemicals

Many products of microbial metabolism find an application in the food and other industries. These include amino acids, steroids, enzymes and antibiotics (Table 17.4). Microbial growth conditions are adjusted so that production of the metabolite in question takes place at an optimal rate. Often an unnaturally high rate of production is achieved by the use of a mutated or genetically engineered strain of microorganism, or by manipulating culture conditions to favour excess metabolite production....

Microorganisms as food

As we have seen in the previous section, a number of microorganisms are involved in the production of food products. Others, however, are foodstuffs Perhaps the most obvious of these are mushrooms, the stalked fruiting bodies of certain species of basidiomycete (see Chapter 8), notably Agaricus bisporus. These are grown in the dark at favourable temperatures, in order to stimulate the production of fruiting bodies. Another fungus, Fusarium forms the basis of QuornTM, a processed mycoprotein...

Nutritional categories

Microorganisms can be categorised according to how they obtain their carbon and energy. As we have seen, carbon is the most abundant component of the microbial cell, and most microorganisms obtain their carbon in the form of organic molecules, derived directly or indirectly from other organisms. This mode of nutrition is the one that is familiar to us as humans (and all other animals) all the food we eat is derived as complex organic molecules from plants and other animals (and even some...

Cell wall

As we have just noted, not all eucaryotes possess a cell wall among those that do are fungi, algae and plants. Whilst the function, like that of procaryotes, is to give strength to the cell, the chemical composition is very different, generally being a good deal simpler. The cell walls of plants, algae and lower members of the fungi are based on cellulose (Figure 3.17a), a repeating chain of glucose molecules joined by f-1,4 linkages, and may also include pectin and hemicellulose, both also...

Fungi and disease

A limited number of fungi are pathogenic to humans (Table 8.1). Mycoses (sing mycosis) in humans may be cutaneous, or systemic in the latter, spores generally enter the body by inhalation, but subsequently spread to other organ systems via the blood, causing serious, even fatal disease. Cutaneous mycoses are the most common fungal infections found in humans, and are caused by fungi known as dermatophytes, which are able to utilise the keratin of skin, hair or nails by secreting the enzyme...

Products derived from genetically engineered microorganisms

Bioreactor Design

In Chapter 12 we saw how recombinant DNA technology can be used to genetically modify microorganisms so that they produce commercially important proteins such as human insulin. This is done by incorporating the gene for the desired protein into an PRODUCTS DERIVED FROM GENETICALLY ENGINEERED MICROORGANISMS 419 PRODUCTS DERIVED FROM GENETICALLY ENGINEERED MICROORGANISMS 419 Figure 17.7 A continuous flow stirred tank reactor. Parameters such as pH and concentrations of specific metabolites are...

Basidiomycota

This large group of some 25 000 species contains the true mushrooms and toadstools as well as other familiar fungi such as puffballs and bracket fungi. In fact the great majority of the fungi that we see in fields and woodlands belong to the Basidiomycota. They are of great economic importance in the breakdown of wood and other plant material (Chapter 16). The group derives its common name of the club fungi from the way that the spore-bearing hyphae involved in reproduction are swollen at the...

Airborne transmission influenza

Tied And Penetrated

Influenza is a disease of the respiratory tract caused by members of the Orthomyx-oviridae. Transmission occurs as a result of inhaling airborne respiratory droplets from an infected individual. Infection by the influenza virus results in the destruction of epithelial cells of the respiratory tract, leaving the host open to secondary infections from bacteria such as Haemophilus influenzae and Staphylococcus aureus. It is these secondary infections that are responsible for the great majority of...

Expression vectors

Sometimes, the aim of a cloning experiment is not just to obtain large amounts of a specific gene, but for the gene to be expressed. This involves using the host cell as a sort of 'factory', to manufacture the specific protein encoded by the cloned gene. One of the earliest applications of genetic engineering was the production of human insulin in E. coli (Figure 12.10). Insulin is needed in considerable quantities for the treatment of diabetics for years it was obtained from the pancreas of...

Phylum Chlamydiae

Formerly grouped with the Rickettsia (see above), these non-motile obligate parasites of birds and mammals are now assigned a separate phylum comprising only five genera, of which Chlamydia is the most important. Like the Rickettsia, members of the Chlamydiae have extremely small cells, and very limited metabolic capacities, and depend on the host cell for energy generation. Unlike that group, however, they are not dependent on an arthropod vector for transmission from host to host. Chlamydia...

Glossary

Acid-fast stain a procedure for assessing the ability of an organism to retain hot carbol fuchsin stain when rinsed with acidic alcohol. Acidophilic 'acid-loving' a term applied to organisms that show optimal growth in acid conditions pH lt 5.5 . Activated sludge treatment a method of wastewater treatment involving aeration in tanks that have been seeded with a mixed microbial sludge. Activation energy the energy required to initiate a chemical reaction. Active site the part of an enzyme...

Acids bases and pH

Only a minute proportion of water molecules, something like one in every 5 x 108, is present in its dissociated form, but as we have already seen, the H and OH- ions play an important part in cellular reactions. A solution becomes acid or alkaline if there is an imbalance in the amount of these ions present. If there is an excess of H , the solution becomes acid, whilst if OH- predominates, it becomes alkaline. The pH of a solution is an expression of the molar concentration of hydrogen ions In...

Airborne transmission strep throat

Streptococcal pharyngitis, commonly known as strep throat, is one of the commonest bacterial diseases of humans, being particularly common in children of school age. The primary means of transmission is by the inhalation from coughs and sneezes of respiratory droplets containing Streptococcus pyogenes p-haemolytic type A streptococci , although other routes kissing, infected handkerchiefs are possible. The primary symptoms are a red and raw throat and or tonsils , accompanied by headaches and...

Box 11 Kochs postulates

1 The microorganism must be present in every instance of the disease and absent from healthy individuals. 2 The microorganism must be capable of being isolated and grown in pure culture. 3 When the microorganism is inoculated into a healthy host, the same disease condition must result. 4 The same microorganism must be re-isolated from the experimentally infected host. Despite their value, it is now realised that Koch's postulates do have certain limitations. It is known for example that certain...

Ascomycota

Life Cycle Ascomycota

The Ascomycota are characterised by the production of haploid ascospores through the meiosis of a diploid nucleus in a small sac called an ascus. For this reason they are sometimes called the sac fungi or cap fungi. Many of the fungi that cause serious plant diseases such as Dutch elm disease and powdery mildew belong to this group. They include some 30 000 species, among them yeasts, food spoilage moulds, brown fruit rotting fungi and truffles. Note that the latter, often regarded as the most...

Beyond the cell wall

Peritrichous

A number of structural features are to be found on the outer surface of the cell wall these are mainly involved either with locomotion of the cell or its attachment to a suitable surface. Perhaps the most obvious extracellular structures are flagella sing flagellum , thin hair-like structures often much longer than the cell itself, and used for locomotion in many bacteria. There may be a single flagellum, one at each end, or many, depending on the bacteria concerned Figure 3.10 . Each flagellum...

Chlorophyta

Asexual Reproduction Chlorophyta

The green algae have always attracted a lot of interest because, as a group, they share a good deal in common with the higher plants in terms of ultrastructure, metabolism and photosynthetic pigments, pointing to the likelihood of a common ancestor. They possess both chlorophyll a and b and certain carotenoids, store carbohydrate in the form of starch, and generally have a rigid cell wall containing cellulose. The starch is stored in structures called pyrenoids, which are found within...

Zygomycota

Mucor Gametangia

The Zygomycota is a relatively small phylum, comprising less than a thousand species. Its members are typically found in soil, or on decaying organic matter, including animal droppings. Some members of the group are of great importance in the formation of a mutualistic association with plant roots known as a mycorrhiza. This will be discussed in more detail in Chapter 15. Members of the Zygomycota are characterised by the formation of a dormant form, the zygospore, which is resistant to...

Phylum Firmicutes The low GC Grampositive bacteria

The low GC Gram-positive bacteria form volume 3 of the second edition of Bergey. The spore-forming Gram-positive bacteria include two large genera, Clostridium and Bacillus. Although not particularly close in phylogenetic terms, they are both capable of propagation by endospores. Clostridium species are obligate anaerobes, and common inhabitants of soil. Sugars are fermented to various end-products such as butyric acid, acetone or butanol. Lacking an electron transport system, they obtain all...

Chemical bonds

Carbon Dioxide Ionic Bond

The force that causes two or more atoms to join together is known as a chemical bond, and several types are found in biological systems. The interaction between sodium and chloride ions shown in Figure 2.4 is an example of ionic bonding, where the transfer of an electron from one party to another means that both achieve a complete outer electron shell. There is an attractive force between positively and negatively charged ions, called an ionic bond. Certain elements form ions with more than a...

Box 52 The most probable number MPN method

Most Probable Number Table

In the example below, three sets of five tubes of broth were inoculated with 10 ml, 1 ml and 0.1 ml of a water sample. The tubes were incubated to allow any bacteria present to multiply in number, and were scored as 'growth' dark shading or 'no growth' no shading . The cell density statistically most likely to give rise to the result obtained 5-3-1 is then looked up on a set of MPN tables. The table only part shown indicates that there is a 95 probability that the sample fell within the range...

Temperature

Temperature For Microbial Growth Images

Microorganisms as a group are able to grow over a wide range of temperatures, from around freezing to above boiling point. For any organism, the minimum and maximum growth temperatures define the range over which growth is possible this is typically about 25-30 C. Growth is slower at low temperatures because enzymes work less efficiently and also because lipids tend to harden and there is a loss of membrane fluidity. Growth rates increase with temperature until the optimum temperature is...

How do we know Microbiology in perspective to the golden age and beyond

Leeuwen Hoeks Microscope

We have learnt an astonishing amount about the invisible world of microorganisms, particularly over the last century and a half. How has this happened The penetrating insights of brilliant individuals are rightly celebrated, but a great many 'breakthroughs' or 'discoveries' have only been made possible thanks to some frequently unsung development in microbiological methodology. For example, on the basis that 'seeing is believing', it was only when we had the means to see microorganisms under a...