Microbial Nutrition and Cultivation

In Chapter 2 we introduced the major groups of macromolecules found in living cells the raw materials from which these are synthesised are ultimately derived from the organism's environment in the form of nutrients (Table 4.1). These can be conveniently divided into those required in large quantities* (macronutrients) and those which are needed only in trace amounts (micronutrients or trace elements). You will recall that carbon forms the central component of proteins, carbohydrates, nucleic...

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...

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...

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...

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...

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...

Chemical bonds

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...

Carcinogenicity testing the Ames test

The great majority of carcinogenic substances, that is, substances that cause cancer in humans and animals, are also mutagenic in bacteria. This fact has been used to develop an initial screening procedure for carcinogens instead of the expensive and time-consuming process of exposing laboratory animals not to mention the moral issues involved , a substance can be tested on bacteria to see if it induces mutations. The Ames Test assesses the ability of a substance to cause reverse mutations in...