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...
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...
Estimation of microbial numbers
Several methods exist for the measurement of bacterial numbers, most of which are also applicable to the enumeration of other unicellular forms such as yeasts. Such methods fall into two main categories those that count total cell numbers, and those that count viable cells only. Total cell counts are generally done by direct microscopic examination. A specialised glass slide is employed, which carries an etched grid of known area Figure 5.1 . The depth of the liquid sample is also known, so by...
